SeZdoonl    d  Cotzpanzzy's _ Yext-ooks.
FRENCH AND GERMAN.
PROF. KEETELS' TNEW FRENCH SERIEIS.
The Ori'al Method  with  the  Fri elch.  By Prof. J 3EAN
GUSTAVE KEETELS, Author of " Keetels' New Method with the
French."  In three parts, 12mro, cloth, each 75 cents.
[The student is saved the expense of a large bookl in commencing
the study.]
The Oral Method of Teaching living languages is buperior to all others in
many respects.
It teaches the pupil to speak the language he is learning, and he begins to do
so from the first lesson.
Hie never becomes tired of the book, because he feels that, with moderate
efforts, he is making constant and rapid progress.
The lessons are arranged so as to bring in one difficulty at a time. They are
adapted to class purposes, and suitable for large or small classes, and for
scholars of all ages.
The teacher, with this book in his hand, is never at a loss to profitably
entertain his aupils, without rendering their task irksome.
In fine, the Oral Method works charmingly in a class. Teachers and pupils
are equally pleased with it; the latter all learn-the qluck and the dull-each in
proportion to his ability and application. It is our opinion that before long
the Oral Method will find its way into every school where French is taught.
"I find that pupils understand and improve more rapidly under the Oral
Method of Keetels' instruction than any other heretofore used."-A. TAYLO,
Elmwood Seminary, Glenn's Falls, NX. Y.
A New Miethod of Learning the French Langnuage.
BY JEAN GUSTAVE KEETELS, Professor of French and German
in the Brooklyn Polytechnic Institute.  12mo.  Price $1.75.
Al Key to the above. By J. G. KEETETS.  Price 60 cents.
This work contains a clear and methodical expose of the principles of the
language, on a plan entirely new. The arrangement is admirable, The lessons are of a suitable length, and within the comprehension of.i classes of
students. The exercises are various, and well adapted to the purpose for
which they are intended, of reading, writing, and speaking the language. The
Grammar part is complete, and accompanied by questions and exercises on
every subject. The book possesses many attractions for the teacher and student, and is destined to become a popular school-book. It has already been
introduced into many of the principal schools and colleges in the country.
FEISSNER S HERMAN FRAMMAPK
A ComparatGive Englyish-Gernman, Grammlar., based on
the affinity of tule two languages.  By Prof. ELIAS PEIssERt.
late of the University of Munich, and of Union College, Sche-^nectady.  New edition, revised.  316 pages.  Price $1.75.
















0 OOK ER'S
NEW PHYSIOLOGY,
DESIGNED AS
A TEXT-BOOK
FOR
INSTITUTIONS OF LEARNING.
BY
WORTHINGTON HOOKER, M.D.,
PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE IN YALE COLLEGE.
AUTHOR OF "PHYSICIAN AND PATIENT."
REVISED BY
J. A. SEWALL, M.D.,
PROFESSOR OF NATURAL SCIENCES IN ILLINOIS STATE NORMAL UNIVERSITY.
AUTHOR OF "CONDENSED BOTANY."
WITH QUESTIONS.
ILLUSTRATED BY NEARLY TWO HUNDRED ENGRAVINGS.
NEW YORK:
SHELDON ANDC COMPANY,
No. 677 BROADWAY.
1874.




FOR USE IN HIGH SCHOOLS AND COLLEGES.
Olney's Complete School    ebra,  -    -    -             1.50
K" Key to          "                    -    -   -    1.50
University,Algebra,    -   -    -    -   2.00
Key to  "        "                              2.00
Test Exalmples in,,lVebra, -            -.75
Geometry and Tridonownetry (Scll. Ed.),   2.50
Geomnetry and,  Trijonooxmetry (Univ. Ed.), 3.00
Ele7ments of Geomnetry (Separate), -   -    1.50
Trifonomnetry (Separate), -    1.50
General Geolntetry and Ccalculues,   -    2.50
Entered according to Act of Congress, in the year 1874, by
SHELDON  & CO.,
In the Office of the Librarian of Congress, at Washington.
Electrotyped by SMITH & MCDouGAL, 82 Beekman St., N. Y.




CONTENTS.
CHAPTER I.
PAGE
ORGANIZED AND UNORGANIZED SUBSTANCES..................  1
CHAPTER II.
THE DISTINCTION BETWEEN ANIMALS AND PLANTS............  9
CHAPTER III.
MAN IN HIS RELATIONS TO THE THREE KINGDOMS OF
NATURE................................................. 13
CHAPTER IV.
THE BONES.......................................... 17
CHAPTER V.
THE MUSCLES............................................... 50
CHAPTER VI.
THE LANGUAGE OF THE MUSCLES............................   74




iv                            CONTENTS.
CHAPTER VII.
PAGE
DIGESTION.................................................   81
CHAPTER VIII.
CIRCULATION OF THE BLOOD................................. 105
CHAPTER IX.
RESPIRATION................................................ 127
CHAPTER X.
FORMATION AND REPAIR.....................................     155
CHAPTER XI.
CELL-LFE.................................................. 165
CHAPTER XII.
THE:  NERVOUS SYSTEM..................................... 178
CHAPTER XIII.
THE VOICE............................................. 205
CHAPTER XIV.
THE EAR............................................. 219




CONTENTS.                            V
CHAPTER XV.
PAGE
THE EYE..............................................  228
CHAPTER XVI.
HYGIENE................................. 249
PART II.
CHAPTER XVII.
CONNECTION OF THE MIND WITH TEIz BODY................. 274
CHAPTER XVIII.
DIFFERENCES BETWEEN MAN AND THE INFERIOR ANIMALS... 292
CHAPTER XIX.
VARIETIES OF THE HUMAN RACE........................... 310
CHAPTER XX.
LIFE AND DEATH...........................         325
QUE STIONS........................................     336
GLOSSARY.............................................  365
INDEX..........................................   374
~~~~~ ~~ ~~  r~ ~ ~     ~    ~    37








PREFACE.
I HAVE aimed so to write this book, that it shall be fitted both for
general reading, and for instruction. It is designed for the family
as well as for the school. It seeimed desirable that these two objects
should be accomplished at the same time, and I have not found them
to be at all incompatible. The instruction needed by the family on
this subject does not differ from that which is required in the schoolroom, either in regard to the facts to be communicated, or the manner
in which it should be done. No one will question the truth of this,
so far as the facts are concerned. But it is true even as to the mode
of communicating them. In both cases there need to be clearness in
statement, and fullness of illustration.  Actual instruction is to be
given in both cases, and to minds that are very nearly in the same
attitude. I could not, therefore, see the necessity of writing a book on
this subject for the people which should differ from one written for the
school. Besides, it has seemed to me desirable that there should be a
greater community of interest between the school and the family than
as yet exists; and this object, books equally interesting to both will
tend to promote.
I have avoided technical terms so far as possible. Whenever they
are used they are sufficiently explained at the time, so that no glossary
is needed. Some points commonly considered hard to be understood
are treated of, but I have endeavored to simplify them, by full illustration, and by a presentation of the truth uncomplicated with speculations and hypotheses. And these points are so introduced, that the
mind is prepared by the previous investigation to understand them.
I have aimed so to arrange the topics, as to have a preparation constantly going on in the mind of the student, fitting him for the proper
understanding of what is to follow. By this natural gradation in the
development of the whole subject some of the deep things in Physiology can be made clear, which it would otherwise be impossible for
the student to understand.
Although Physiology is becoming a prominent study in the schools
and colleges in some parts of our country, its importance is no where
as yet appreciated as it should be. It should be made a regular branch
in our Educational System. This has been already done in France.
"A  competent knowledge," says Carpenter, "of Animal Physiology
and Zoology is there required fronm every candidate for University




'Vill                      PREFACE.
honors; and men of the highest scientific reputation do not think it
beneath them to write elementary books, for the instruction of the
beginner."
The importance of Physiology as a study, will appear from various
considerations.
Many of the subjects comprised in Physiology have, in the case of
most students, been already studied in a different phase, or mode, in
other branches. Thus, if the student has attended to the Mechanical
Powers in his Natural Philosophy, he finds in the human body the
principles of the pulley and the lever illustrated in great variety and
perfection. The principles in relation to strength in the form and arrangement of structure he sees exemplified in the framework of the
body in the most admirable manner. If he has studied Hydraulics, he
sees in the body the most perfect, and at the same time the most complicated hydraulic machinery, working incessantly throughout life in
the circulation of the blood. The principles of Pneumatics he finds
applied in the respiration-those of Optics in the eye-those of Acoustics in the ear-and those of Musical Sounds in the apparatus of the
voice. And then, his chemical knowledge meets with new applications
in his observation of the changes and the processes going on in the body.
The relations, then, of Physiology to some of the common branches
taught in the higher classes in schools, are of the most intimate character. Physiology, in part, merely extends these branches into a new
and interesting field; and the student who has once entered this field
recurs to these same branches with a renewed interest. Hydraulics,
Pneumatics, Optics, &c., have now a new attraction for him, from this,
to him novel, application of their principles. The interest thus awakened in his mind is worth much in itself, aside from the mere addition
made to his knowledge. And the interest is enhanced by the consideration, that in the human body he sees the applications of these
principles to mechanism that exhibits the skill of perfect wisdom and
almighty power.
But there are relations of Physiology to still other studies which
should be noticed.
The analogies that exist between the human body and all other
living things, in relation to structure and growth, are numerous and
striking. Though life is so diverse in its processes and in the forms
which we see it evolve in the whole range of animated nature, it in
some important respects displays a great similarity, which it is interesting to trace throughout its diversified manifestations. Growth, or
nutrition, as you will see in the following pages, is essentially the same
in the Plant as it is in the Animal. Botany, therefore, taught as it
should be, has quite an intimate relation to Animal Physiology. The
Science of Life is, in many respects, one Science; and if, in studying
any of its subdivisions, we fail to take this broad view of it, and to trace




PREFACE.                          ix
out the analogies referred to, we lose a large part of the interest of the
study. Human Physiology, the subject of study in this book, is but a
part of. a science which offers to the student wide fields of observation
exceedingly diversified and full of interest. This being so, I could not
avoid in the following pages making occasional references to the analogies existing between the phenomena of life as exhibited in the human
system, and those which we see in the living world around us; and as
the student proceeds with the study, he will find himself interested in
these in whatever form they are presented.
This leads me to say that this study of nature, in its broad common
relations and its beautiful and extensive analogies, should be made very
prominent in our systems of education. It is the application of the
principles of abstract science to the forms, and especially the living
forms of nature all about us, that gives interest to these principles, and
makes us to understand and appreciate them. It is here that we find
a very serious defect in the prevalent mode of education, even at the
present time, notwithstanding all our improvements. We live in the
midst of a material world, animate and inanimate, and have daily converse, so to speak, with material forms of every variety, presenting phenomena of the highest interest and of endless diversity. And yet,
through almost all the period of childhood, and perhaps we may say
youth also, this book of nature is in the school-room very nearly a
sealed book. The very process of education shuts in the pupil from
this broad contemplation of the world in which he lives. He is drilled
through spelling, reading, grammar, &c., but he is left in total ignorance of the beautiful flowers, and the majestic trees outside of the
school-room. How very few even of thoroughly educated adults, know
the processes by which a plant or a tree grows! And the same can be
said of other phenomena of nature.
The defect which I have pointed out runs through the whole of education. We can see it even in the prevalent mode of teaching the
natural sciences themselves. One would suppose that here the facts,
the phenomena, would command the chief attention of the teacher and
the student. But it is very commonly not so. The mere technicalities
and the classification are made much too prominent. Botany, really one
of the most interesting of all branches of natural science, is thus
ordinarily made one of the driest of studies. To teach this aright, the
phenomena of vegetation, so varied dnd so beautiful, should constitute the
chief material of instruction, and the mere classification should be considered, although necessary, as wholly a secondary thing.
The great facts of the world, both of mind and matter, should
furnish really the material for education, amd those branches that are
ordinarily pursued with such assiduity should be considered as merely
subsidiary to the teaching of these facts. The whole order of education
must be reversed. Instead of beginning the child's education with




X                       PREFACE.
learning to spell and read, the object should be to make him an observer of nature, and the spelling and reading should be done in connection with this, and as subsidiary to it. Things and not words, or
mere signs, should from the first, constitute the substantial part of instruction. The child should be made, at home, in the school, and everywhere, a naturalist in the largest sense of that word. We should aim
to impart to him a spirit in consonance with the following precept of
Hugh Miller, the famous self-taught geologist: "Learn to make a
right use of your eyes; the commonest things are worth looking ateven stones and weeds, and the most familiar animals."
As it is now, no one becomes a naturalist early in life, except in
spite of the tendencies of his education. The study of nature is not
only not encouraged, but is absolutely discouraged in our educational
system. If any one, like Hugh Miller, by the force of a taste that can
not be repressed by the training of the school-room, undertakes to
make a "right use of his eyes," and curiously examines "stones and
weeds," he is regarded by the world of spellers and readers and grammarians and cipherers, as a strange genius. But he is pursuing, from an
irresistible internal force, the very course that I would have every
student, even from his childhood, encouraged to pursue, in a measure
at least, by the external circumstances of his education. The tendencies of his training should be decidedly in this direction.
If the general mode of education were changed in the manner indicated, education would have much less of the character of-mere drudgery than it now has. Not that there would be any the less labor; but
the labor would be made lighter by the interest imparted to it-the
interest which always results from the study of facts and phenomena,
and never from the learning of mere words and technicalities and
classification. I would gladly dwell on this subject, and show by
varied illustrations how the mode of instruction referred to, should be
pursued, and especially with younger scholars; but the limits of a
preface will not allow me to enter so large a field.
The change which I have pointed out can not be effected at once.
It will require time. Confirmed traditional customs are to be done
away, the habits of teachers are to be altered, and the proper books are
to a great extent to be yet written, especially such as are fitted for the
first years of education.
If the study of nature should be thus made prominent in education,
human physiology would be considered altogether its most interesting
and important branch, and for several reasons. First: there is nowhere to be found so curious a collection of mechanisms, or so interesting and wonderful a series'of processes, as in the human body. In
nothing else in the wide world are the principles of so many departuents of science so extensively and perfectly exemplified. Life works
here its most complicated set of machinery. Secondly: the singular




PREFACE.                           xi
and mysterious connection of the immaterial and immortal soul with
the material and perishable body, gives intense interest to this study.
In Physiology we do not study matter alone, or spirit alone, but both
matter and spirit united, and often acting together. This circumstance distinguishes this from all other studies. Thirdly: it is our own
frames, moved by the spirit within us, that we study. The subject has
a personal interest for us that is not presented by most studies, and
by none in so large a degree as in this. And, fourthly: the study is
of great importance, because a judicious and efficient Hygiene must
be based upon a knowledge of the laws of physiology. We can
not know how to keep our functions in the condition of health, without understanding the laws that regulate them. I have said but
little in this book in regard to hygiene, and that only incidentally,
because that subject would require of itself a whole volume to elucidate it properly.
I have not thought it proper to indulge to any great extent in those
reflections which the contemplation of so perfect and diversified a
congeries of mechanisms as are presented in man would naturally
suggest, in regard to the skill of the great Builder of the universe.
Such reflections would extend the book to too great length. Besides,
they are so readily suggested to the mind of both teacher and scholar,
that it is entirely unnecessary for the author to dwell on them.
I have treated of some subjects on which, from the difficulty of
understanding them, there has been a disposition in many minds to go
beyond what we know, and indulge in unwarranted speculation. On
these points I have taken pains to draw the line very distinctly between what is known, and what is supposed. I deem it important to
prevent the minds of the young from being led away from the simple
truths of science by ingenious speculations and plausible reasonings.
Let me not be understood to decry all hypothesis. I object only to the
mingling of facts and suppositions together in one indiscriminate mass,
as is often done. The disposition to do this, which is more common
than is generally supposed, exerts so injurious an influence upon the
habits of the mind, and so confuses its views of truth, that we ought
to look upon it as one of the most serious evils to be guarded against
in education. It is really one of the most prominent obstacles to the
progress of truth on all subjects, both in individual minds, and in the
minds of the community at large. This disposition, so apt to be fostered in the enthusiastic mind of youth, by ingenious but dreamy
speculations, should be corrected at the outset, and the mind should,
in its forming stage, be habituated to the discrimination between the
proved, the true, and that which rests on presumptive, perhaps merely
plausible evidence. This discrimination should therefore be exemplified in books designed for instruction, and this I have attempted in the
present volume.




SUGGESTIONS TO TEACHERS.
IN order to be able to teach from this book properly, the teacher
should himself study all of it thoroughly before he begins his instruction. If he merely keep a little in advance of his class, he will fail in
his conceptions of the general scope and plan of the book. If the
interest of the subject awaken in him and in his pupils a spirit of inquiry, there will be a continual looking forward to points which are
explained and illustrated further on in the book.
Now if the teacher has made himself master of all the subjects
treated of, instead of turning off the inquiry of a scholar without an
answer, or even the promise of an answer in the future, or endeavoring to clear up the points about which inquiry is made, which of
course he can do, under the circumstances, in an imperfect manner at
the best, he can satisfy the scholar by informing him that these points
will be found explained in their proper place at a future stage of the
investigation.
I have aimed to have every topic treated of in its right place in the
development of the general subject, and, the teacher should be thoroughly master of the whole book at the outset, in order that he may
fully carry out my plan in the mode of developing the topics to the
minds of his pupils.
It must be obvious to any teacher that he can teach the minutime of
the subject with more of interest, to say nothing of thoroughness, if,
while doing it, he takes in the general views presented, and has in
mind the relations of the particular topics in hand to other branches
of the subject.  Indeed it will be profitable occasionally for the
teacher to afford the scholar some glimpses of the interesting fields to
be explored further on, taking care, however, not to anticipate so
much as to mar the natural method and order of developing the
whole subject, which I have taken such especial care to observe in the
preparation of the work.
The teacher should read the book through in course. If, instead of
doing this, he opens to some chapter in the middle or latter part of the
book, he may get the impression that too high matters are treated of,
and that the minds of his pupils are not competent to understand
them. They cannot be understood unless there be a preparation of
mind for them; and just this preparation is aimed at in the first part
of the book. And besides, it is quite important that the subjects
treated of should be developed to the mind of the teacher in the
same order in which they are to be developed to the minds of his pupils.




SUGGESTIONS TO TEACHERS.                   Xiii
In the engravings, clearness has been aimed at rather than beauty.
Yet I should not do the engraver justice if I did not say, that in beauty
they are generally quite equal to those which we find in our standard
professional works on physiology. It is to be borne in mind that
wood.cuts cannot represent correctly the beauty and delicacy of living
structures. These can be realized only by seeing the structures them.
selves. Another thing to be kept in mind is, that parts which are represented in engravings with definite lines for the sake of distinctness,
are ordinarily not thus distinct in the structures. To make them so,
the dissecting knife must separate them, and take off the cellular substance, which, as the general packing material of the body, everywhere
connects adjacent parts together.
The teacher can be aided very much in giving his scholars a correct
idea of different organs, by presenting to them organs taken from the
bodies of animals. Thus, in giving them an idea of the lungs, the
lungs of a calf or a sheep can be used. A pipe may be fastened into
the windpipe; and by blowing into this, you can show how the lungs
are inflated. An idea of the appearance of the human brain can be
given by means of the brain of a calf, or any other animal of sufficient size. An ox's heart may be used in showing the structure and
arrangement of the valves and other parts of that organ, for they are
essentially the same as in man. A very good idea of the arrangement
of the cartilages that make up the larynx, can be obtained from the
larynx of an ox or a cow. The general shape and arrangement are
the same as in man.
It is some trouble to clear the parts of muscular substance, but the
teacher can get some physician or medical student to do it for him.
When the preparation is once made, it can be dried for permanent use.
I have one which I made twenty-five years ago. In drying, it will be
necessary to keep the wings of the thyroid cartilage apart by a wedge,
and the supple epiglottis must be placed in such a position as not to
interfere with a view of the interior of the larynx. The large eye of
the ox can be made use of to show the various parts of that organ,
and also to show the formation of the images of objects on the retina.
One great advantage of thus using parts from different animals is,
that a taste is given for the examination of the phenomena of life,
with its wonderful mechanisms, wherever they may be seen. All
living nature thus becomes full of suggestive interest to the young
student.
There are some things of which plates can give no correct idea.
Such, for example, is the cellular membrane. The attempt to represent it is made in most books on physiology, but it is an entire failure.
I have a plate representing its cells as seen in a dried preparation
under the microscope; but to give the scholar an idea of it as it appears to the naked eye in its natural condition, I refer him to it as
seen in any common piece of meat between the muscles and between




xiv              SUGGESTIONS TO TEACHERS.
the fibres of each muscle. The teacher can use a piece of meat for
this purpose. The difference between muscles, tendons, and ligaments
can be shown in the same way.
Those figures which are mere diagrams it will be well for the
scholar to draw on the blackboard, and his skill in description and remark may be exercised for his own benefit and for that of the class.
He should be trained in this exercise in such a way that he will acquire the power of giving well-proportioned and well-arranged descriptions, without the aid of prompting by minute questions from the
teacher.
It will be proper to say something of the use which should be made
of the questions that I have prepared. I have two reasons for not
placing them at the foot of the page. One reason is, that the book
is designed for general reading as well as for instruction. But the
chief reason is, that I wish to prevent a too free use of questions on
the part of both teacher and scholar. The marking with the pencil
of parts which contain the answers to the questions, so often done in
our schools, should never be permitted by the teacher, for reasons that
I need not stop to notice.
The scholar should read the text at first without reference to the
questions; and then the questions can be made use of, perhaps witlh
profit, to fix definitely in the mind the principal points that are
brought out. It will be a useful exercise for the scholar, after reading
a page or two, to think over the main points, and then see by the aid
of the questions whether any important point has escaped his recollection, or failed to make the proper impression on his mind.
The questions that I have constructed will, I think, be found to be
fitted to the great majority of scholars. But of course the teacher
will vary them to suit the different capacities and mental attitudes
which he finds in his class.
It is best not to have an uniform mode of asking questions, even
with the same scholar. Variety should be given to the mode of hearing the recitation. Sometimes the questions should be minute, and at
other times the mind of the scholar should be left to go on with as
little leading as possible.
The scholar should be encouraged occasionally to give the substance
of a whole paragraph, or even of more than this. In doing so, any
failure in arrangement or proportion can be noticed by the teacher,
for the benefit not only of the scholar that is reciting, but also of
the whole class. The general scope of an argument may also be
given in the same way, and the manner of doing it be made the subject of criticism.
The numbers attached to the questions refer to the pages, this being
more convenient to the scholar than a numbering by paragraphs would
be, though of course it cannot be quite so definite in all cases.




PHYSIOLOGY AND HYGIENE.
CHAPTER I.
ORGANIZED AND UNORGANIZED SUBSTANCES.
1. The Crystal and the Plant are both wonderful
growths. The crystal was once a minute nucleus, and the
plant was once a little germ.
In one respect they are alike in their growth-both have
increased from particles taken from things around them.
But the processes by which this is done are different in the
two cases. The crystal has increased or grown by layer
after layer of particles. Any part of it, when once formed,
is not altered. It can receive additions upon the outside
alone. - The plant enlarges by particles which are introduced into passages and interstices. It grows by absorption
or by intussusception.
2. Organs.-This absorption is effected by certain vessels or organs, constructed in the root of the plant for this
purpose. These absorb or take up fluid matter from the
earth. Other organs circulate this fluid through all the
plant; and still others use it for the purpose of growth or
formation. There are no such organs in the crystal, for it
has no inner growth. The plant is therefore said to be an
organized substance or being, and the crystal an unorganized substance.
~3. Mechanical Principles.-These organs. which
thus absorb, and circulate, and construct, do not act simply
on mechanical principles. They are active agents, and they




h2           PHYSIOLOGY AND HYGIENE.
perform their duty with a force, and after a manner, for
which no mechanical principles can account. No mechanical powers could alone supply the leaves of the mighty
tree of the forest with sap from its deep roots; much less
could they form those leaves.
4. Chemical Principles.-Neither do these organs
act simply on chemical principles. While man, through the
agency of chemistry, can form some of the crystals which
are' found in nature, he can not by any arrangement of
constituents make a plant, a flower, or a leaf. And the
plant, left alone to the action of chemical principles, wilts;
and at length ceases to be a plant, and becomes common
unorganized matter.
5. Vital Principles. — Mechanical and chemical
principles, it is true, are both exhibited to some extent in
the growth of plants; but they are under the control of
other principles, which we term vital. So the plant is not
only an organized substance, but a living being.
6. Animals.-What has been said of plants, in distinction from minerals, may also be said of animals. They
are also Qrganized living beings, and they have, generally, a
more complex organization than plants.
The whole material world, then, that we see around us,
we divide into two parts —the unorganized and lifeless, and
the organized and living. The distinctions thus pointed
out between organized and unorganized matter are essential
and fundamental. But let us look at some other distinctions, which either arise from these or accompany them.
7. Other Distinctions between the Organic
and Inorganic.-All the parts of the mineral are independent of each other, while it is otherwise with the plant
or the animal. Acoordingly, we do not examine the properties of plants and animals as we examine those of minerals.
The chemist can ascertaiwn all the properties of a crystal
or a rock if you give him but a small piece of it.
But the botanist can not ascertain all the properties of a
plant by looking at some one part of it. If he examine the
flower, this gives him no knowledge of the root. In order




ORGANIZED AND UNORGANIZED SUBSTANCES.               3
to know all about the plant, he must examine every part by
itself, and then look at it in its relations to the other parts.
The same may be said of the physiologist, in his investigation of the properties of animals.
8. Assimilation in Organized Substances.As the crystal is forming by layer after layer of particles, no
change is effected in these particles as they are becoming
arranged in the layers. But in the case of the living organized being, a change is produced in the particles which are
taken up by the absorbents.  And the change, ordinarily, is
both a gradual and a complex one. In the plant, a change
is produced in the particles in the very act of absorption;
but this change is only the beginning of a process which is
afterwards perfected. The sap is not thoroughly fitted for
nutrition when it first begins to circulate. It is carried up
through the vessels of the trunk or stalk to the leaves.
There the last step of the process is taken, and the sap is
now ready to be used in the growth of the plant or tree.
So, also, in the animal, the nutritious part of the food,
taken up by the absorbents in the digestive organs, is first
acted upon by certain little glands, through which it passes,
is then poured into the circulation, to be mingled with the
blood, and is carried with the blood to the lungs, to be exposed to the air; and thus it is fitted for the nutrition or
growth of the body
This process, which is thus carried on in the plant and in
the animal, is very properly called assimilation. For the
particles that are taken up by the absorbents in the root of
the plant are, by this process, made like to the plant; and
the particles taken up by the absorbents in the stomach*
* The word stomach requires some little explanation, as it is used in
physiology in two senses-in a limited sense, and also in an extended
one. It is used in its limited sense, as referring to the cavity at the
beginning of the alimentary canal, as it is termed; this latter term
being applied to the series of cavities, the stomach and the small and
large intestines, which are found in the digestive apparatus in the
higher orders of animals. In comparisons, however, between these
animals and those which have a more simple digestive apparatus, the
word stomach is used in a more extended sense, as being synonymous




4             PHYSIOLOGY AND HYGIENE.
are made like the animal. So obvious is this, in the case of
the animal, that some French physiologist speaks of the
blood as chair coulante, or running flesh.
9. Perrnanency.-Another prominent distinction between organized and unorganized substances is in relation
to permanency. Constant change appears in all organized
bodies; while permanency is written upon all substances
which are unorganized. In organized beings, continual
change is going on at every point. It is a condition of their
being.
This is true, not only of the decline of a plant or animal,
but even of its growth. For, in its growth, as the parts enlarge internally as well as externally, they change not only
the arrangement of the particles, but, to a great extent, they
change the particles themselves. It is true, as well of the
towering tree as of the tiny plant, that these changes have
been going on during all its growth; so that, at its maturity, it is, both in relation to the arrangement of its particles and in relation to the particles themselves, a very
different thing from what it was when it pushed its germ
up through the ground, or even when it was but a small
tree. So, in all animals, the same internal changes are
going on, and to a much greater extent; because, from the
activity of their nature, there is wear and tear, and, therefore, refuse matter to be disposed of. As you will see in
another part of this book, the human body undergoes these
changes very largely.
The crystal, as fast as it is formed, becomes permanent.
No changes occur within it. In itself, it is unchangeable.
It can not change its own particles, as the plant or the
animal does. It can be changed only by external addition,
or by external diminution, through the influence of agents
acting upon its surface.
10. Reproduction. — With the constant changes
going on in organic nature, there is constant succession.
with the term alimentary canal. It is used in this sense, also, when,
as in the present case, it is referred to in a comparison between animals
and vegetables.




ORGANIZED ATNID UNORGANlZED SUBSTA'NCES.    5
Plants and animals produce other plants and animals, and
themselves die, making room for their successors. But the
crystal does not form other crystals, and then crumble into
dust. In itself, it is both unchangeable and unproductive.
11. Observations  of Change and Perinanency. —This distinction between organized and unorganized substances, in relation to change and succession,
meets the eye everywhere. The mountains, the rocks, and
even the stones under our feet, remain the same year after
year, while all vegetable and animal life is ever changing
its forms and manifestations. There are the changes of
growth, and the changes of decay and death, all around and
within us; and they are strangely mingled together.
There is death even in the changes of life, as the waste
particles are taken away, and are replaced by the new; and
life springs out of the very bosom of death, as from decayed
nature new forms of vigor and beauty arise. The mountains stand as they have stood, as the passing generations
have looked upon them, while the continual changes of
vegetation have been going on upon and around them.
The seasons crown their battlements with the emblems of
their ever-returning mutations of life, decay, and death,
and even the mighty trees, that have shed their leaves from
year to year, in obedience to the great law of change, but
have themselves stood, at length bow their heads to the
same law, and give place to other lords of the forest.
From  the "everlasting  hills," which thus remain the
same, though change is ever about and upon them, man gets
the unchangeable and imperishable rock to construct his
habitation, while he himself is changeable and perishable —
the creature of a day, whose life is as a vapor. He wears
the precious stones, and traffics in the golden ores, which
have existed from the creation of the world, through all the
changing and dying generations, and passes away, leaving
them to others as changeable and perishable as himself.
12. Forms.-Another distinction between organized
and unorganized substances relates to the forms which they
assume. There is regularity in both, but it is different in




6             P'HYSIOLOGY AND HYGIENE.
each. Unorganized matter is disposed to arrange its particles in straight lines, and with angles mathematically exact.
The tendency is to regularity; and irregularity is the
result of interfering circumstances. A similar disposition
to regularity is manifest in organized substances, but in a
different manner. They are disposed to curved, rather than
straight lines, and seldom make lines or angles with mathematical exactness. We see this law of regularity exemplified both in animal and vegetable life. The leaf, for example, has the same general shape, that is, the same general
arrangement of particles, when it attains its full size, that
it had when it was small; and the same can be said of the
arm of the man, compared with his arm when a child.
13. Regqularity. —This regularity is more wonderful
in organized substances than in the unorganized, because
it rules in them in the midst of constant change. In the
case of the crystal, as there are no internal changes in it,
and as each layer of it, when formed, is permanent, regularity is comparatively, so to speak, easily secured. But in
the case of the leaf, as it is growing to its full size, and of
the arm, as it grows from infancy to be the stalwart arm of
manhood, continual change is going on at every point; and
regularity here is obviously a more difficult achievement.
This regularity appears still more wonderful, when we
look at the infinite variety of forms in organized matter, in
both the vegetable and the animal world. In all these forms,
each part of every animal and of every plant maintains its
own peculiar plan and contour. Take, for example, the leaf
in its endless varieties. HIow definitely does each variety
preserve its individual character, and how easily is it distinguished from every other variety!, The same can be said
of every part of every organized being.
14. Persistencjy of Form.-Another circumstance
still must be mentioned, as adding- to the wonderfulness of
this regularity. It has been scrupulously maintained,
through all the changes of the world from its creation,
when God pronounced the works of his hands to be "very
good."  The leaf of every tree, for example, is like the leaf




ORGANIZED AND UNORlGANIZEI) SUBSTANCES.
Of its ancestral trees back to that time; and so it will be in
all its successors to the end of the world. " The trees of the
garden," which delighted the eyes of our first parents, and
refreshed them with their shade in their innocence, and
amid which after their sin they hid themselves from the
presence of their Maker, undoubtedly had the same characteristic shapes, and the same leaves and flowers which their
successors present to our eyes.
15. Vatriety of Eornm.-Again, it is interesting to
notice that, in the midst of this regularity, so strictly maintained in each specific form from age to age, there is a
measure of irregularity allowed. While each kind Df tree,
for example, has specific characteristics in the arrangements
of branches and other parts, and in the shapes of its leaves,
no two trees of the same kind are exactly alike, and there is
always much variety in the leaves of the same kind. While
the face of man is so entirely different from the face of
every other animal, at the same time, among the hundreds
of millions of the human family, how uncommon it is to
find two faces that are very nearly alike.
16. Symmn etry of Halves.-In the animal world, we
see remarkable examples of the preservation of regularity of
form in the exact correspondence which exists so commonly
between the two halves of the body.
The brain has two halves, which are precisely alike, and
the same is true of the nerves which are distributed from it.
And so of other parts. But, mingled with this symmetrical arrangement of parts, there are other parts which are irregular in their shape. This is the case with the stomach,
the heart, the liver, &c.  There are some animals which
are altogether destitute of this arrangement of two similar
halves of the body. The oyster is a familiar example. The
shell of this animal is strikingly in contrast, in this respect,
with the shells of some other of the bivalve tribe, as, for
instance, the common clam.
17. Size. —There is a distinction between organized and
unorganized substances, in regard to size. The size of unorganized bodies has no fixed limit. A crystal or a rock




8            PHYslOL,:( Y ANDxxT HYGIENE.
may grow to any imaginable size, if the particles forming it
are sufficiently abundant. But organized bodies have limits
fixed to their growth. There is, it is true, more or less latitude to these limits; but they are so well defined in the case
of most vegetables and animals, that when growth reaches
much beyond or below the limit, it is recognized as a remarkable fact.
18. Structure and Elements.-The last distinction, between organized and unorganized substances, which
will be mentioned, relates to their structure. While unorganized substances are made of one form of matter, either
solid or liquid, or gaseous, organized bodies are made of a
mixture of fluids and solids. They are therefore more or
less soft and flexible; while the solid, unorganized substances are hard and brittle.
There is a still further difference in structure. Organized
substances are much more compound than the unorganized.
Most of the unorganized substances are composed of only
two or three elements. Thus, air is composed of oxygen and
nitrogen, water of oxygen and hydrogen; and most of the
mineral salts are composed of three elements-as, for example, carbonate of lime, or chalk, which is composed of
oxygen, carbon, and calcium, the mineral base of lime.
But organized substances are composed of at least three or
four elements and sometimes more. The four principal elements in the composition of organized bodies are, oxygen,
nitrogen, hydrogen, and carbon. But there are other elements introduced for special purposes. Thus, carbonate of
lime (a combination of calcium with two of the common
elements, carbon and oxygen,) is diffused very generally
throughout the textures of plants, giving them firmness
and strength. In animals of the higher orders, phosphate
and carbonate of lime compose in part the framework of
the body.
We find iron, too, in the blood. Of the sixty-four elementary substances discovered in mineral bodies, only eighteen or nineteen have been found in plants and animals,
and some of these in very small amounts. The essential




THE DISTI1NCTION/S BETWlEI'EN ANIMALS AND PLAN'TS.!)
components of living substances are the four non-metallic
elements mentioned above-oxygen, hydrogen, nitrogen,
and carbon; while the bulk of the inorganic world is composed of the metals and their compounds, viz., the alkalies and
the earths. And it is interesting to observe that, of the
four elements which compose the bulk of the animal and
vegetable world, both the fluids and the solids, three are
gaseous, while bat one, carbon, is a solid substance.
CHAPT ER I I.
THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS.
HAvING pointed out the distinctions between organized
and unorganized substances, we will now consider the distinctions between the two classes of organized beingsanimals and vegetables; first noticing those differences which
are obvious; and second, pointing out those which are
essential.
19. Locomnotion.-One of the most obvious distinctions is in relation to locomotion. The plant remains in one
place; while the animal moves about, in the air, or in the
water, or upon the surface of the earth. And the structures
of the animal and the plant of course differ, so as to accommodate these two very different modes of existence.
As the animal moves from place to place, it must, for
this reason, if for no other, have an apparatus of nourishment and growth different from that of the plant. The
plant, by means of its absorbents in the roots, takes up
from the earth, in the form of sap, its nutrition, or food, as
it may very properly be called. The moving about of the
animal would in itself forbid its deriving its food directly
from  the earth, even if the earth contained the proper
materials for its nourishment.




10            PHYSIOLOGY ANI) HYGIENE.
So a cavity is provided in its body, called a stomach,
into which nutritious substances can be introduced. And
this cavity is lined with absorbents, which there do for the
animal what the absorbents in the roots of the plant do for
the plant.
20. Central Oryans.-Besides the stomach, there
are other great central organs which are peculiar to most
animals, in distinction from vegetables-as the heart, the
liver, the lungs, etc. Branches and roots may be cut off
extensively, and even a large portion of the stem or trunk
may be destroyed; and yet what remains of the plant may
still live. Even a small portion of it may be made to take
root and live by itself. It is not so with most animals.
Mutilation can not be carried far without injuring some
large organ which is essential to the life of the whole; and
no part taken from its extremities can be made in any way
to live by itself.
21. Sensation and Volunntary AMotion. — Another
obvious distinction is this: The higher order of animals
are sentient and spontaneously-noving beings, while vegetables are not. The animal feels the action of agents upon
it, and this it can not do without consciousness and thought.
The evidences of the existence of consciousness and thought,
and the consequent spontaneous motion, are very slight
in some animals. We see these evidences plainly in the
great majority of animals; and we infer the existence of
sensation and thought in those exceptional cases, where the
evidences are doubtful or absent, as we find in them other
marks of animal, in distinction from vegetable life.
22. Exceptions. —The distinction in regard to locomotion, if we look at the animal as a whole, has its exceptions.
There are some animals, as the coral animal and the sponge,
that are entirely confined to one spot during all their existence. But, while some animals are thus confined, they
have the power of spontaneous motion in some of their
parts, which is exercised for the purpose of obtaining food,
and, in some cases, for the avoidance of danger.
This power is not possessed by any plant. Some few




THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 1 
plants, as the sensitive plant and the Venus's fly-trap,
(Dionaea muscipula,) exhibit a property which resembles it,
but it is essentially a different thing. In these cases, the
influence of the stimulus that excites the motion is communicated from particle to particle, from the point where
the stimulus is applied; and the motion is only in one
direction, and not in various directions, as is the case with
spontaneous animal motions.
23. lllustration.-This can be very readily seen, if
we compare the motion of the sensitive plant or the flytrap with those of the little fresh-water polyp called the
Hydra. This animal, of which an enlarged representation
is here given, and also a representation of its natural size,
is found in ponds. It attaches itself to any floating object
-a stick or straw, as seen in the Figure-by a kind of
sucker. Thus supporting itself, it stretches out its long
arms, to take for its food any
minute worm  or insect which              FIG. 1
may float within their reach.
When it catches one, it directs
it to the mouth, a, which opens
into  the  stomach  or general
cavity. Now, in doing all this,  a
there is a variety, a compound
character in the motion, which
is in plain contrast with the
simple motion of the leaves of
the fly-trap and those of the
sensitive plant.
24. Nervous  System. —Accordingly, we find a peculiar
structure in animals devoted to
these functions, and others con-          HYDRA.
nected with them. This structure is the nervous system. No trace of such a structure
has ever been discovered in any plant. If there were any
true analogy between animal motion and the motions of the
sensitive plant and the fly-trap, we should be able to find in




12)          PHYSIOLOGY AND HYGIEN-E.
them traces of nervous structure; for the structure of
these plants is so plainly developed, that its constituent
parts are easily distinguished. It is true, also, that in some
of the lower animals no trace of a nervous system is found.
25. Not Esseiltial to Nuttrition.-The nervous
system is evidently not essential to nutrition, for this is as
well effected in the plant as in the animal. This is accomplished in both in substantially the same way. The means
by which it is done, and its arrangements, are modified, in
the two cases, to suit the differing circumstances.
26. Functions of Organic Life and of Animal Life.-The nervous system is, for particular purposes, superadded in the animal to what is common both to
the animal and the plant, and so constitutes the essential
difference between them. And so, all the functions relating to nutrition, which are common to plants and animals,
are called functions of organic life. But the functions
which are performed by the system superadded in the animal, the chief of which are sensation and spontaneous
motion, are termed functions of animal life. These are
sometimes also called functions of relation, from the especial connection which they form between the animal and
all that is around him.
2M. Thought and Will.-These animal functions,
sensation and spontaneous motion, imply thought and will.
The order of action is this: sensation-thought in regard
to it -action of the will in consequence of thought —
then, from this action, an impression carried through
nerves to organs termed muscles-motion in them from
their contraction.
This order, however, is not always observed. The first
link, sensation, may be absent. Thought, without any preceding sensation, may prompt the will, and spontaneous
motion results. The action of the will, too, may be left
out, or may be in opposition. Thus, emotions may produce
action of the muscles, the will not concurring, and perhaps
opposing; as when we laugh at what is ridiculous, or weep at
what is sad, in spite of restraining efforts dictated by the wilL




MAN IN HIS RELATIONS TO- NATURE.         1
28. Chemtical Constituents.-One more important
distinction between animals and plants remains to be noticed. Organized substances are composed mostly of four
elements-oxygen, hydrogen, nitrogen and carbon. Plants
differ from  animals, in having but little nitrogen in their
composition. It was formerly supposed that they contained
none of this element. It is found only in particular parts
of plants, as the seeds. We may regard carbon as the most
characteristic constituent of vegetables, and nitrogen of
animals. And in this connection it is interesting to observe
that, while carbon is largely thrown off from the lungs of
animals, in the shape of carbonic-acid gas, it is as largely
absorbed by the leaves of plants. Of this fact more particular notice will be taken when the subject of respiration
is reached.
CHAPTER III.
MAN  IN  HIS RELATIONS TO THE THREE KINGDOMS
OF NATURE:29. Peculiart Endowments of ]Man.-Man is
commonly spoken of as being at the head of the animal
kingdom, and in the book of the naturalist is made an
order of the class termed Mammalia. As the basis of the
whole classification is mere material organization, and has
no reference at all to mental or spiritual endowments, the
classification, in regard to man, is in its principle correct.
At the same time, it must be admitted, that it fails to
recognize altogether the essential distinctions between mall
and other animals. These distinctions, making, as they do,
a wide gap-" an impassable chasm," as Professor Guyot
expresses it-between man and the inferior animals, are to
be found in certain peculiar spiritual endowments which
man possesses.




14            PHYSIOLOGY AN) HYGIENE.
30. Abstract Reasoning.-One of these endowments is the power of abstract reasoning. Otheranimals,
in a certain sense, reason, that is, they make inferences; but
they never arrive at any general or abstract truths.
31. Conscience.-Another endowment is a moral one,
linking man in his spiritual nature to the Deity: this is
conscience, or the knowledge and sense of what is right, in
distinction from what is wrong. Other animals, in obedience
to the passions of fear and love, sometimes appear to the
superficial observer to have an idea of what is right, as
such; but there is not the slightest evidence that they
really have any such knowledge.
32. Immo rtality.-The force of this view of the
subject is enhanced, if we take into consideration the great
fact, revealed to us by God in his Word, that man is destined to immortality. It may be objected that, as this fact
is learned only by revelation, and not by observation, it is
not to be regarded as a scientific fact.
But, granting that there is truth in the objection, it certainly is allowable to allude to the revelations of Scripture,
as confirming or enforcing views developed by scientific observation. The view here presented is based upon endowments that are recognized by the scientific observer, without the aid of revelation; and we can appeal to the revealed
fact of man's immortality, as adding force to this view, and
not as being at all necessary to the establishment of its
truth.
33. Real Relation to the Animal Kingdom.The grand essential distinction between animals and plants
lies, as you have seen in the last chapter, in the fact that
animals have a nervous system. Now, with this system, as
you have also seen, appear certain mental manifestations.
These differ widely in different animals, and are most
prominent in those in which this system is most prominent
and complicated. As we trace upward these complications,
when we come to man, we find certain mental manifestations, which separate him by " an impassable chasm" from
all other animals.




M.AN IN HIIS RELATIONS TO NATURE.        1 i
Till we arrive at him, the difference is, for the most part,
one of degree. But in his case it is a difference of kind,
and a very wide one. Of such a difference the naturalist
should certainly take very distinct cognizance; and, if it be
not consistent for him to do so in his classification, great
force and prominence should be given to these views in his
instructions on this subject. As the superadding of the
nervous system separates the animal from the plant, so,
also, as Professor Guyot very justly maintains, the superadding of such endowments as we find in man separates
him, by a chasm quite as "impassable," from other animals.
34. The Hand of,Man.-The distinction commonly
received as the ground of classification for man, is a trivial,
perhaps a questionable one. He is said to have two hands,
and so makes the order Bimana; while apes and monkeys
are said to have four hands, and are, therefore, considered
as making the order Quadrumana.
Now, if we observe carefully and fully the wonderful endowments of the human hand, we shall hardly be willing to
allow that the monkey has four such members. With a full
view of the capabilities of the human hand, that of the
monkey can not be considered as a hand, but as a member
possessing some of the properties of both hand and foot.
Hands are given to these animals to enable them to climb
with facility, and to grasp their food; but they have none
of that great variety of motion, which is so striking a peculiarity of the hand of intelligent man. The ground upon
which they are said to have four hands is that which is thus
stated by Cuvier.  "That which constitutes the hand,
properly so called, is the faculty of opposing the thumb to
the other fingers, so as to seize upon the most minute objects." No animal besides man has this arrangement, except the Quadrumana. It is claimed, therefore, that they
have hands, although they are very imperfect when compared with the hand of man. The imperfection is indeed
so great, as to make us at least reluctant to admit the claim
set up by the naturalist.




16           PHYSIOLOGY AND HYGIENE.
35. Views of Dr. Carpenter. —" While," says Carpenter, "the thumb in -the human hand can be brought
into exact opposition to the extremities of all the fingers,
whether singly or in combination, in those Quadrumana
which most nearly approach man, the thumb is so short,
and the fingers so much elongated, that their tips can
scarcely be brought into opposition, and the thumb and fingers are so weak, that they can never be opposed to each
other with any degree of force. Hence, although admirably
adapted for clinging round bodies of a certain size, such as
the small branches of trees, &c., the extremities of the Quadrumana can never seize any minute object with such precision, nor support large ones with such firmness, as are
essential to the dextrous performance of operations for
which the hand is admirably adapted."
36. Chin, Erect Posture, Man's Weeping andl
Laughing. — Man's structure differs in many respects front
that of the inferior animals. It would make this chapter too
long to point out all the differences. As an example of the
latter, no animal but man has a chin. Every other animal
has its lower jaw retreating from the teeth, instead of projecting forward below, as in man.
One of the most important and striking peculiarities of
man's structure is that general arrangement which enables
him to be in the erect posture. No other animal naturally
assumes this posture, or is able to maintain it for any length
of time; and most animals assume one which is entirely the
opposite of this. Even the monkey, when taught by man
to stand and walk, is by no means erect, but his lower limbs
are crooked, and the moment that he escapes the necessity
of being an imitator, he is on all fours.
There is a distinction of an interesting character, which
concerns both the nervous and muscular systems. It is this,
that no animal but man can shed tears, or perform those
muscular motions which are necessary to the acts of weeping and laughing. In view of this marked distinction, man
has sometimes been designated as " a laughing and crying
animal."




THE BOXES.                   1
37. The Essential Distitnctions.-But the great
essential distinctions, to which all the rest are really
tributary, are, as has been stated, of a mental or spiritual
character. And these should always be made peculiarly
prominent, whenever the distinctions between man and the
inferior animals are treated of by the naturalist. This
should be done, not only because they are essential, but also
because all other distinctions are subordinate and tributary
to them. It is the mental peculiarities of man, for the most
part at least, that render necessary those peculiarities which
distinguish his organization from that of other animals.
CHAPTER IV.
BONES,
38. Structure  of Bones.-From  the osseous or
bony tissue, the solid part of the framework of the body is
made. Bone is composed in part of animal matter, and in
part of mineral. The mineral part is mostly phosphate of
lime. These two parts of bone are in different proportions
to each other in the different periods of life.
39.   lineral Matter.-The mineral part in the
child is about one half of the bone; in the adult, fourfifths; and in the old, seven-eighths. Bones are, therefore,
very brittle in old age, while they are somewhat yielding in
childhood. The mineral and the animal portions of bone
can be separated from each other. If a bone be put into
diluted muriatic acid, the mineral part will, after a time
become united with the acid, and the animal part will be
left, having the perfect shape of the bone. Thus separated
from the mineral part, it is so flexible, that it can be tied
into a knot. On the other hand, by subjecting a bone for
some time to the action of heat, the animal part can be removed, and the mineral part be left by itself.




18            PHYSIOLOGY AND HYGIENE.
40. Aninal Matter.-The- animal part of bone is
cartilage, or gristle. This part is formed first, constituting
a sort of mold, in which the bone is to be formed. The
mineral matter is gradually deposited in the cells of the
cartilage. In the very young child, you can see that this
process is not completed, especially if you observe the bones
of the head. The bones are not united together, as they
are in the adult, and there is so little of mineral matter
near their edges, that they can be bent with a very slight pressure. The proportion of mineral matter which is deposited
in the cartilaginous bones varies much in different animals.
In many fishes, there is almost none of this deposit, the
skeleton retaining its cartilaginous character throughout
life.
41. Cartilages.-Besides the cartilaginous portion of
bones, there are cartilages which are destined to remain so,
instead of having mineral deposits made in their cells.
The ends of the bones are tipped with them. They are
placed between the bones of the spinal column. They also
form the connecting links between the breast-bone and the
ribs. Cartilage constitutes the body of the outer ear, of
the eyelids, and of the lower part of the nose. The transparent part of the eye is formed of cartilage. This substance is placed wherever firmness and tenacity are required
without hardness.
42. Iunction of Bones.-The bones furnish the
points of support and attachment for the muscles which
move the different parts of the body. They are, therefore,
the passive instruments of locomotion. They are united
together by ligaments of various degrees of strength, according to the necessity of the case.
The bones, forming the framework of the body, not only
furnish points of support and attachment to the muscles,
but in many cases serve to defend important organs from
injury. Thus, the soft brain is thoroughly secured from
harm by being inclosed in the skull; and the lungs are surrounded by walls of bone so arranged that, while they
defend the lungs from external violence, they secure a




THE BONES.                   19
wide range of motion for the necessary expansion of these
organs.
43. Structure of Bones.-There are some points
of interest in relation to the structure of bone and its
growth. It has been stated that bone is generally formed
in cartilage, the cartilage being formed first as a mold for
the bone. Bone is deposited in two forms, solid and cellular. In the flat bones, as in the skull, the cellular structure lies between two plates of solid bone. In the long
bones the cellular part is at the two ends, and is covered
with a thin plate of solid bone, while the shaft is a hollow
tube with the bone very much condensed. This arrangement is seen in Fig. 2, representing
the thigh-bone and the bone of the       EIG. 2.
arm.
44.  Hollow   Cylinders. -
Certain well known mechanical principles are observed in this arrangement. The bone would be unnecessarily heavy if it were solid throughout. Lightness in a moving limb is
of considerable importance. At the
same time strength is to be carefully
provided for in a bone which is to
sustain the weight of the body, and
to which the large muscles of the'
thigh are attached. By having the
bone hollow, both of these objects,
lightness and firmness, are secured.
The principles involved are recognized by the architect in the construction of pillars, and we see them
exemplified in the hollow stalks of
plants. The hollow pillar has more,,,
strength than the same quantity of
matter would have if in one compact;
mass; and the stalk which supports
the full clusters of grain, would break under its load as it




2.0           PHYSIOLOGY AND' HYGIENE.
moves back and forth in the wind, if it were solid instead of
being hollow.
But the round cavity of the shaft of the bone does not
extend to the ends. These are necessarily large, in order to
present broad surfaces for articulation with the neighboring
bones; and strength and lightness are secured in this case
by a cellular arrangement of the body matter, the outer
plate of solid bone being conparatively thin. There is
obviously more firmness in the resistance to shocks or pressure, secured in this way, than there would be if the bony
matter were all consolidated into a shell containing a cavity.
The round canal in the shaft and the cellular structure
at the ends are filled with an oily substance called marrow.
This, like all other fatty substances, is contained in fat-cells.
The marrow is also present in the cellular structure between the plates of the fiat bones. The cavities and the
cells in bones have blood-vessels, branches of arteries
and veins that enter the body of the bone at some particular points, in the long ones, near the middle of the shaft.
45. Cov'ering of the.Bones.-It is from these bloodvessels, together with those that come from the membrane
investing the bone, called periosteum, that the bone is nourished. But, although an artery runs through the body of
the bone, to branch out upon the walls of its cavity, none
of its branches enter the very substance of the bone.
46. Growth of Bone. —The manner in which material is carried to every point of the solid bone has been
developed by the aid of the microscope. If we cut across
the solid portion of bone, and examine it with a microscope, we see here and there orifices of certain minute
canals that run lengthwise of the bone.
These canals are found to communicate with the cavity
of the bone and receive therefore blood, or some of the constituents of the blood, from the blood-vessels which are
situated there. These orifices, as seen under the microscope,
are represented in Fig. 3.  Around these orifices a a, you
see little dark spots arranged in rings, with lines running
to them from the orifices. By magnifying the section of




THE BONES.                   21
bone still more, we see what these spots and lines are. The
dark spots are small cavities, and the lines are minute tubes
running to them. In Fig. 4 is a representation of this arrangement as seen in a little portion of the section of bone,
more highly magnified than it is in Fig. 3. The tubes pass
FIG. 3.
FIG. 4.
SECTION OF BONE.
out from the canals to the rows of cavities which are around
the canals, and thus a circulation is kept up at every point
of the solid bone. It is supposed that the blood itself does
not circulate in these little channels and cavities in the
solid bone, but a fluid containing the constituents of bone.
For these channels are too small even to admit the cells
which the microscope shows us swimming in the blood.
The fluid that circulates in them is selected from the blood,.which is contained in the blood-vessels in the cavity of the
bone, and in the periosfeum that envelopes it.
47. Bones not Sensitive.-It is a very common
popular notion, that the bones are endowed with great sensibility, and especially the central part, the marrow. But
they have in their healthy state no perceptible sensibility,
and the sawing of the bone in amputation occasions no
suffering. When, however, a bone becomes inflamed, severe
pain is one of the symptoms. If it were not so, disease




22              FRONT VIEW OF THE SKELETON.
FIG. 5.
The Skeleton  consists of
201 bones.  In this enumeration  the  teeth, the  hyoid
bone, and the bones of the                              --
ear are not included. Certain                    f-.
bones in the sutures of the
head, and  in some of the
joints, which, though  generally present, are not regarded  as  essential parts           z-'
of the framework, are also
omitted.
NAMES AND CLASSIFICATION OF
THE BONES.                                    -]
a The frontal bone,.. 1           1b The parietal bones,.. 2   ~
e Occipital bone, (Fig. 6) 1 [
c The temporal bones,. 2  o
t The sphenoid bone,. 1        r
t The ethmoid bone,. 1
t The nasal bones,.. 2
t The lachrymal bones,. 2
f The upper maxillary                        
bones.             2.  o  
g The malar bones,.. 2 
t The palatine bones,. 2..
t The  lower  spongy
bones,.             2 
t The vomer,.           1 1
h The lower maxillary                                     w
bone,...... J
The bones whose names are
marked t cannot be shown                        SKELETON
in the figs.




BACK VIEW OF THE SKELETON.                             23
FIG. 6.
f  The vertebrae,.24
o The sternum,. 3  -
o' The ribs,...24 
Fig. 5. m The ossa innominata,. 2
j/ The sacrum,   1 
—'-""";;f  /ck The coccyx,. 1J
i The scapula,   2
g The clavicle     2
| FigZ.. i' The humerus,. 2.j'; %    1      y The ulna,.. 2 
a, n~~~~~.~-a    z Theradius, 
e'  The carpal
3,  c viW kbones,..  10
b' The metacarpal   |
bones,...10
c' The phalanges, 28 
d' The femur,.. 2
e' The tibia,.. 2
f' The fibula,.. 2
Pt The patella,.. 2
g' The tarsalbones, 14
h' The metatarsal
i' The phalanges, 28  T
SKELETON.




'24           PHYSIOLOGY AND HYGIENE.
might go onl to produce disastrous results in a part so
covered up by others, without any warning of the danger
of the case.
48, Shape an(I Place of Bones.-The bones are of
every variety of shape, to suit the various offices which they
are to fulfill. You will see this to be true, as you cast your
eye over the skeleton as represented in Fig. 5. You first
observe the somewhat round box of bones, which contains
the brain, and at the same time furnishes sockets for the
eyes, extended irregular surfaces for the apparatus of smelling, and for that of the taste, a place for the organs of hearing, and at its lower part, in connection with the lower jaw,
a mill for grinding the food. Then you observe the many
bones of the thorax or chest, containing and protecting the
heart and the lungs.
49. Spinal Coltuntn.-The spiall column, f, composed of twenty-four bones, you see as a firm but movable
pillar, extending the whole length of the body, and having
its base firmly planted upon that stout thick bone, the
sacruin, which is wedged in so tightly like the key-stone of
an arch, between the broad spreading bones on either-side.
To this pillar are strongly fastened the walls of the chest;
and from the chest thus supported by the spine hang the
lax front and lateral walls of the abdomen.
50. Pelvis.-Then below you see the pelvis, as it is
called,-a set of large bones so arranged in a bowl-form, as
to offer a broad surface of support to the contents of the
abdomen. The bone called the iliuim, m and 1, on either
side, with its flaring upper surface, is especially. serviceable
in this way. The pelvis also furnishes a socket for the
round head of the thigh bone s, and points of attachment
for the large muscles that move the lower extremity.
51. Bonnes of the Lowter Extremity.-Observe
the large bones of the thigh and leg, intended to give firmness to the lower extremity, and the lighter bones of the
arm and forearm, fitted for extent and quickness of motion.
Finally notice the numerous bones which enter into the
structure of the hand and the foot. These bones, together




THE BONES.                     25
with the intervening cartilages, give them great elasticity
and variety of motion.
We notice with some particularity some of the bones, of
which has been given a general description, as they are
united together to form the whole skeleton. We can not
notice them all, nor dwell upon every point of interest, for
this would require much more space than can be devoted
to the subject. We therefore select those points which can
be made most clear and interesting.
52. Sktltl.-Your attention is first called to the bones
of the head, as you see them in Fig. 6. There are twentytwo bones in the whole head. Fourteen of these belong to
the face, while eight belong to the cranium; that is, that
part of the skull which incloses the brain. Of these, notice particularly the large bone in front called the frontal
bone, a, making the forehead, and below forming the upper
portion of the orbits of the eyes; the parietal bone, b, the
FIG. 6.
BONES OF THE EEAD.
upper lateral part of the dome of the skull; and c the temporal bone on which the parietal bone rests. There is a large
bone in the. rear forming the back of the cranium as the
frontal bone does the front. There are also two bones in
2




26            PHYSIOLOGY AND HYGIENE.
the base of the cranium which are out of sight in this view
of the skull. You may, perhaps, be disposed to inquire why
this box for holding the brain, should be made of so many
bones.
One reason is, that the enlargement of the skull from
infancy to adult age is effected more easily and better than
it would be if the cranium were one bone. Another reason
is, that even in the adult, in whom these bones are at length
so tightly united, violence is less apt to produce injury,
from the giving, as it is expressed, of the bones upon each
other, than it would be if one bone made the whole structure. And this is especially true of the child, in whom the
bones are very imperfectly united. Hence it is that the
frequent falls of children upon their heads so seldom do
any injury.
53. Structure and -Union of the Skull Bones.
-The principal bones of the head are composed of two
solid plates, while the bony matter between these plates is
arranged in a cellular or sponge-like form. The outer table
or plate (for both of these terms are used in relation to it) is
rather rough, and in some parts has ridges for the attachment of muscles. But the inner plate is very smooth
on account of the soft delicate organ that is contained in
the cranium. It is so brittle that it has been called the
vitreous table, from its resemblance to glass in this respect.
The modes of the joining of the bones differ in the two
tables. In the outer table the joining is by a minute dovetailing, called a suture. Numerous little projections from
one bone fit accurately into corresponding spaces in the
edge of the other. This is very well represented in Fig. 7,
in which you see the sutures on the top of the skull; b being the suture which is formed between the two parietal
bones; a, a, that between the parietal and the frontal bone in
front; and c c, that between the parietal and the bone which
forms the back of the cranium. A better joining for bones
of such a shape as these have, can not be conceived of. But
the inner table is joined differently. It is so brittle that
the small projections of the dovetailing mode of joining




THE BONES.                     27
would not answer here, for they would break very easily.
The joining accordingly is in this case by smooth accurately
fitted edges, somewhat beveled, so that one slightly overlaps
the other.
The upper part of the cranium is in the shape of a dome,
and is constructed upon the same principles as such strucFIG. 7.
STRUCTURES IN THE SKULL.
tures are as regards resistance to pressure or violence. As
in domes that are built by man, so in this dome of the
cranium, great strength is secured around the lower part, so
as to resist outward lateral pressure. In the dome of St.
Paul's there is a double iron chain around its base for this
purpose, of course concealed from view. In the head of man
the dome may be considered as composed of the frontal bone
in front, the parietal bones at the side, and the occipital bone
in the rear. In front, the base of the dome is strongly fortified, in the heavy arches that form the upper part of the
sockets of the eyes, and on the jutting edges of which are
the eyebrows. In the rear the base of the occipital bone is
very thick, and is fortified with ridges which furnish attachment to the large muscles in the back of the neck.




28            PHYSIOLOGY AND HYGIENE.
But the most marked and interesting contrivance for the
strengthening of the base of this dome is at the side. It is
where the parietal bone b, as seen in Fig. 6, is joined by the
temporal, c. The joining here is not by suture, for that
would afford no resistance to lateral pressure, either outward or inward. To secure this object, the lower bone,
the temporal, laps over the upper, the parietal, with a beveled edge. It abuts upon or against it. It has the relation
to the parietal of a buttress to an arch.
When great pressure is made on the top of the head, as
when a heavy load is carried there, there must be a tendency to outward lateral pressure at the base of the dome
of the cranium. This pressure is effectually resisted by the
temporal bones acting as buttresses. The same thing is
true, also, when a blow is inflicted on the top of the head.
And if a blow be received at the side of the head, on the
temporal bone, it is evident that the bones will not be so
apt to be fractured and pressed inward upon the brain, as
they would be, if they were united by suture.
54. Protection to the Brain. —You are now prepared to see, to what extent the brain is guarded against
the effects of violence inflicted upon the head. These
effects come either from fracture of the bones, or from
concussion without fracture. In either case the vibration
of the parts concerned is the cause of these effects. The
guards of the brain defend it from injury,by lessening or
diffusing this vibration. And it is to be observed, that
when vibration passes from one texture to another, it loses
some of its force in the change.
No two substances vibrate just alike; and when a vibration in one is communicated to another, it is modified, and
is therefore lessened. Some substances modify and lessen
vibrations communicated to them more than others do. If
you apply these principles to the effects of violence on the
head, you at once see that the brain would be much more
apt to receive a dangerous shock from the vibration occasioned by a blow, if its coverings were condensed into one firm
and thick layer of substance, than it is now. So also, if the




THE BONES.                    29
bones of the head were in one solid layer, instead of having
two layers, or plates, with the spongy structure between,
and the integuments were all consolidated into one thick
substance, there would be much more liability to fracture
than there is with the present arrangement.
Observe now how many, and how various are the textures,
through which the vibration of a blow must pass, before it
reaches the brain. Outside of the bone there is first the
hair; next comes the skill; then there is the cellular membrane containing some fat; then a muscular coat; and
lastly, the lining membrane over the surface of the bone.
These various textures must deaden very much the force of
a blow, and especially the outer cushion of hair, and those
inner cushions, as we may call them, of fatty cellular membrane and of muscle. Then, when the vibration reaches
the bone, it is lessened by the two plates with the intervening cells, and there is diffused largely among the many
bones that unite with the one on which the force comes.
Then as the shock goes into the brain, it is still farther
lessened by the membranes which cover that organ. These
greatly diminish the vibration, precisely as a coating of
leather on the inside of a bell would deaden its vibration
when produced by a blow upon the outside. With all these
provisions the result is, that comparatively few of the blows
received by the head do harm.
55. P)rotection  (ft Particular Points.-There
are some especial guards at particular points in the cranium,
where there is much liability to exposure to violence.
Thus, as the lower part of the frontal bone, where the eyebrows are, is especially exposed, the distance from the surface to the brain is made considerable by an intervening
chamber in the bone, called the frontal sinus. This sinus,
which varies much in size in different individuals, is lined
with a membrane, and communicates with the nose. You
can see that this arrangement is a great protection to the
bone at that point. The outer plate could be broken, and
the inner remain uninjured.
But the protection which this arrangement affords, is not




30            PHYSIOLOGY AIND HYGIENE.
confined to that single point; it serves also to deaden the
-vibration of a blow received by any part of the forehead, or
by the forehead as a whole. The side of the head, too, is
peculiarly exposed to blows. And, therefore, the skull is
peculiarly guarded at this point. Beside the overlapping
of the temporal bone upon the parietal, to which allusion
has been made, the parietal bone is made thicker at its
lower part, where it is most liable to be struck, than it is in
most of the other parts of it.
Then, too, the place of joining of the temporal and parietal bones is covered over by a thick muscle, the contractions
of which you can feel if you press your fingers upon the
temple while moving the lower jaw as in eating. This
cushion of muscle is of great use in breaking the force of a
blow received in that quarter.
56. P'otectionl, of Organs. —The cranium not only
contains and protects the brain, but it at the same time
serves various other purposes, and protects other important
organs. The tender and delicate eye has there a bony socket
with jutting prominences all around it, to guard it against
violence. The exceedingly minute and complicated apparat-as of the hearing is also carefully protected by the skull,
and the most important part of it is furnished with winding and intricate apartments, halls of audience, in that part
of the temporal bone which is so hard, that it is called the
petrous or rock-like bone. To the bones of the cranium
are attached in various ways, the fourteen bones of the
face. All these, with the exception of the lower jaw, are
immovable. The two principal of them are the upper jaw
bone, and the cheek bone. The former makes with its
mate of the other side the forward portion of the roof of
the mouth, the palate bones making its rear portion; and
it furnishes the sockets for the teeth. It also at its upper
part makes nearly the whole of the floor of the orbit of
the eye.
The cheek-bone forms the outer lateral part of the
socket of the eye, and sending back a process or projection
to unite with one from the temporal bone, c, Fig. 6, forms




THE BONES.                     31
the zygorlc or arch, inside of which the temporal muscle
passes down to be fastened to the lower jaw. The bones of
the nose make quite a complicated series of cavities, for the
purpose of presenting, in the mucous membrane, which
lines them, a large surface, over which the nerve of smell
is expanded.
A representation of these cavities is given in Fig. 8; i"
which a is the mouth; b, the
opening into the nostril; d, a          FIG. 8.
part of the base of the skull; c,   m   g  i
the communication of the nostril with the back of the throat;
e, the curtain of the palate; 1,
the frontal sinus; m, another
large sinus; g, i, h, spongy
bones projecting into the cavity,.-...
of the nostril. There is a large
sinus, that is not seen in this      i
figure, which lies over the teeth              a
in the jaw-bone. The different   INNER BONES OF THE NOSE.
sinuses are lined with the mucous membrane extending into them from the nose.
These, with the spongy bones, make a very large extent of
surface in the cavities devoted to the sense of smell. The
branches of the nerves of smell enter these cavities, to be
distributed over thin walls, through many small openings
in a bone in the roof of the nose, giving it a sieve-like
appearance.
The lower jaw is a bone shaped something like a horseshoe, with its ends turned considerably upward.  It has
two smooth projecting surfaces which articulate with two
corresponding shallow cavities in the temporal bone. Its
prominence at the lower part in front, the chin, is peculiar
to man, there being no such prominence in any other animal. The lower jaw has sockets for the teeth, and it is so
constructed, and is so provided with muscles, that these
teeth can be brought to bear against the teeth of the upper
jaw in cutting and grinding motions.




32            PHYSIOLOGY AND HYGIENE.
57. ThVe Teeth.-The teeth are very nearly like the
other bones in their structure, but differ from them in some
particulars. Every tooth has in it three distinct structures,
which differ in hardness, for reasons which will appear clear
to you as we proceed. The dentine or ivory constitutes the
body both of the tooth and of its fangs. In the body of the
tooth there is a coating of that very hard substance, the
enamel, over the whole surface of the ivory.  This is
thickest over the top of the tooth, and grows thinner on the
sides till it is entirely gone where the gum begins. The
ivory in the fangs has a coating of a very different character,
called the cementum. It is not hard like the enamel. This
arrangement is represented in Fig. 9. This is a tooth with
two fangs or roots; 1, is the enamel; 3, the dentine or
ivory; 2 and 7, the cementum; 4, an unnatural enlargement of the cementum, making an
FIG. 9.      excrescence; 5, the cavity of the tooth
supplied with blood-vessels and nerves
which come through  the channels
that you sej running up the middle
of each fang.
This cavity is analogous to that
which is found in the slfafts of the
long bones as seen in Fig. 2.  The
i;ory and the cementum are seen by
the microscope to be very different
t-extures. The ivory is traversed by
imnuumerable branching tubes run-'3^~  f ning from within outward towards the
cementum, as represented in Fig. 10.
Vertical      This is a section of a small portion of
SECTION OF A TOOTH.  the dentine and cernentum  in the
fang of a tooth, very much magnified,
a, a, being the dentine, and c, c, the cementum, evidently a
different structure.
58. Difference between Bones and Teeth. —A
tooth differs from a common bone in one important particular-when once formed it is never altered in its size. A




TEE BONES.                   33
bone grows with the growth of the other parts of the body;
but a tooth, when it first protrudes through the gum, is as
large as it ever will be. The reason of this is, that so hard
FIG. 10.
a substance as enamel can not be made changeable as bone
is. Its hardness is inconsistent with anything like circulation in it, and without circulation there can be no change.
If the enamel were not needed, and the teeth could be
composed only of dentine, they could grow as other bones
do. And if they could grow, one set of teeth might be
made to answer the purpose. As it is, the second set are
needed, because as the jaws grow, the first set are neither
large enough in proportion to the size of the jaws, nor
numerous enough to fill up the whole space. If the first
set were to be the only set, when the jaws became of their
full size, the teeth would be altogether too small, and would
be quite separated from each other. Twenty small teeth (the
number of the first set) in the jaws of an adult, in place of
the thirty-two large teeth of the second set, would present
a very odd appearance, besides being incapable of doing the
service required of them.
59. Bones not 7belongingq to the Xatural Skeletoi,. —Under the lower jaw is a little bone, called from its
resemblance to the Greek letter v, the hyoid or u-like bone.
Its round end is towards the root of the tongue, and its




34            PHYSIOLOGY AND HYGIENE.
two free ends reach backward towards the spine. The
larynx is suspended from it as from a frame, and the muscles that draw up this bone, draw up the larynx with it.
It is one of the few bones in the body not directly connected
with any other bone. The patella, or kneepan, is one of
these bones. Also the four little bones in the ear, are not
connected with any other bone.
60. The Spinie comlsildePed as a Singlae Piece.
-Pass now to the bones of the trunk of the body. Let us
first consider the spinal column, or the backbone, as it is
called in common language, as if it were all one bone. In
some respects it does act as one, although it is made
up of twenty-four distinct bones. It is the great pillar of
the body. As such, it has the head resting on its top, and
it furnishes support for the walls of the chest, and for the
muscles which make up the most of the walls of the abdomen. To it also are fastened the mass of intestines in the
abdomen, and indeed to some extent all the viscera both of
the abdomen and the thorax. Sustaining, therefore, so
much weight in so many ways, it stands firmly planted on
its great pedestal, the strong broad bone of the pelvis, the
sacrum.
And this pedestal is supported, as before said, after the
manner of a keystone, between the lighter spreading bones
of the pelvis on either side. But while the spinal column
acts as a strong and firmly supported pillar, it is necessary
that it should be flexible for the different motions of the
body. It is therefore composed of twenty-four bones called
the vertebrla, so that, as in any considerable motion of the
column as a whole, there is but little motion between any
two of them, the motion does not interfere with its office
as a firm pillar. It is most free in its uppermost part,
the neck; considerably so in its lower part, the small of
the back; and it is least free in that part to which the
ribs are joined.
You readily see the reasons for this difference in motion
in different parts of the column. For the varied motions
of the head there is need of a free movement of the verte



THE BONES.                     35
brae. Then for the twisting and turning motions of the
body, you have the free movement at the lower part of the
column, which is easily provided for there, because there
are attached to that portion of it nothing but parts that
are pliable. It is not so with that portion of it that forms
the supporting pillar of the framework of the chest. There
is little motion here of the vertebrae, because the joining of
the ribs to the column forbids it.
But besides serving as a firm pillar, and as a flexible
chain, the spinal column also forms a canal or tube in which
the spinal marrow, one of the most delicate and important
organs in the body, is securely lodged. This canal extends
through its whole length, and from the spinal marrow included in this canal, nerves pass out to all parts of the
body.
(61. Vertebrwe and their) Union.-In Fig. 11, you
see a representation of one of the vertebrae; a, being the
FIG. 11.
FIG. 12.
A BIDE VIEW OF A VERTEBRA.
A VERTEBRA.
body of the bone; b, the hole which forms this vertebra's
part of the canal for the spinal marrow; and c, the spinous
process. It is these spinous processes that make the row
of projecting points seen down the length of the back.
There are six other processes, only four of which you can
see'in the figure. Four of these processes serve to' lock the




36            PHYSIOLOGY AND HYGIENE.
vertebra with its two adjoining ones above and below, which
they do so strongly, that there can be no dislocation of
them  without a fracture. Fig. 12 gives a side view of a
vertebra.
Strong ligaments bind these bones together, and there are
very numerous muscles attached to the
FIG. 13.  processes, so that this jagged column  of
bones is very thoroughly enveloped in
softer substances.
62Es. Spinal Cod. —In Fig. 13, you
see the whole spinal column with the
sacrum on which it stands. It is laid open
by a vertical section dividing it into two
halves, so as to show the manner in which
the bones form the tube that contains the
spinal marrow. The darkly shaded strip
through the length of the figure represents this tube. It extends, you see, down
beyond the limits of the column itself
through the sacrum.  It is bounded in
front by the bodies of the vertebrae represented as sawed through from front to rear,
and by the spinous processes behind also
sawed in the same way. In this canal you
/:~,~.   see there is a row of little openings, arranged just behind the bodies of the vertebroe. Through these openings, each of
which is between two of the vertebrae, the
nerves go out from the spinal marrow. The
arrangement is such, that the nerves are
very securely guarded against the hazard
of pressure in the movements of the vertebrme upon each other.
SPINAL COLUMN.
63. IJnter;ertebral Cartilages.You see also that there are spaces between the bodies of all
the vertebre. These are filled with cartilages, which vary
in thickness in different parts of the column, from onequarter to three-quarters of an inch, being thickest in.the




THE BONES.                    37
lower part of the back, where the backward and forward
motion of the vertebroa upon each other is the greatest.
Each cartilage is firmly fastened to the two vertebrae,
between which it is situated, by the rough surface of the
body of the bone which you see represented in Fig. 11.
This arrangement of cartilages is an important provision
for the motion of the spinal column. It contributes greatly to
its flexibility. When you stoop forward, all the cartilages
are compressed, and when you rise up they return to their
usual size by their elasticity. And besides this, they serve
to diminish any shock which might otherwise be transmitted through the column of bones to the head with too
great force. There is another guard against the injurious
transmission of shocks to the brain, in the slhape of the
spinal column, the twenty-four bones being arranged, not in
a straight line, but in a double curve.
The vibration, communicated upward through the spinal
column, is thus not only lessened by the elasticity of the
cartilages, but is also distributed in different directions by
the curved arrangement of the. bones. If the column had
been made straight, the head would be subject to frequent
jars in the movements of the body, which would be disagreeable and often injurious.
64. Diffeirent Objects inf the Arrangement of
the Spinal Golumn. —You have thus seen how three
different objects, apparently incompatible with each other,
are accomplished in the arrangement of the spinal column.
To p)ut twenty-four bones together in such a way, that they
shall form a strong firm pillar for the whole frame, and yet
they shall make a column or chain flexible enough for the
various motions of the trunk of the body, and at the same
time provide, in this column,a secure canal for the rod of
nervous matter which moves all the muscles of the body, is
to produce a piece of mechanism which far transcends any
thing that has ever been contrived by the ingenuity of man.
6,. ArraJn.geimeit of the F'irst and  Seco(d,
rVertebrwc.-Th ere remains to be noticed one especial
contrivance in the spinal column. It is at its summit,.and




PHYSIOLOGY AND HYGIENE.
is for the purpose of providing for the free motions of the
head in various directions. and at the same time securing the
spinal marrow at that part,from all hazard of pressure from
these motions.
These two objects are accomplished in this way. The
head in moving backward and forward rocks on two smooth
surfaces on the first vertebra.  But when the head moves to
the right and left, this first vertebra moves along with the
head on the second vertebra. And there is a tooth-like process that projects up from  the second vertebra inside of
the first, around which this rotary motion is performed.
In Fig. 14 is represented the first vertebra. J, J, are the
two surfaces on which the head rests, and rocks backward
and forward. A is the opening for the spinal marrow. L
is the strong ligament which confines the tooth-like process
that projects upward from the second vertebra.  In Fig. 15
is the second vertebra. P is the tooth-like process, around
which the first vertebra rotates, carrying the skull with it.
You see it is smaller at its root than at its top. This
smaller part is bound firmly by the ligament in the first
vertebra. It is shaped thus to prevent its slipping out from
the ligament. J, J, are the two surfaces on which the first
vertebra moves as it rotates around the tooth-like process.
Fig. 16 shows the two bones together, the tooth-like process being confined in the ring of the upper bone. Special
pains are taken to make this arrangement secure, that the
process may not be in danger of pressing upon the spinal
marrow at this important point. It is thus that the lateral
rotary motion of the head and the forward and backward
motion are secured by two joints, just as is done in the
mounting of a telescope. The difference between the two
cases is, that in the mounting of the telescope there are no
difficulties to overcome, while in arranging the mounting of
the head, as we may term it, a peculiar contrivance and a
nice adjustment are needed to prevent injury of a very important organ. It is a wonderful contrivance, by which so
much and so varied motion can be effected in the very walls
that contain the soft and delicate spinal marrow, without




THE BONES.                    39
injuring it. You will fully appreciate this, if you observe
the extent and variety of the motions of the head and neck
executed chiefly with the two bones previously described.
FIG. 14
A
FIP.T VERfEBRR.
FIG. 15
VERTEBRU TOGETHER.
SECOND VERTEBRA.
66. Vertebrce of the Bird. —In the neck of birds
there is a contrivance of a different character, for the arrangement which answers for the motions required by man,
obviously could not secure the very free motions which the
bird executes with its neck. As the bird bends its neck at
such abrupt angles in all directions, a peculiar arrangement




40            Y'PHYSIOLOGY,AND HYGIENE.
of the vertebrae is necessary, to prevent the spinal marrow
from being pressed upon.
The arrangement is a simple, but effectual
FIG. 17.   one. This can be made plain to you by the
c       rough diagram in Fig. 17. A, A, are two
of the vertebra of the neck laid open. B is
the spinal canal, and C is the spinal n-arrow.
You observe that each vertebra is larger at
its ends than in the middle, allowing (at the
A   joinings of the bones, where the motion is,
a considerable space between the bone and
the spinal cord.
SPINAL COLUMN    Now if each of these bones was of equal
in Bird,  size throughout, and the spinal marrow
filled up the canal, you can readily see that
when any two of these were much bent upon each other, there
would be pressure upon the spinal cord; and pressure would
produce palsy, and often destroy life. But with the simple
arrangement above described, free motion, almost to a rightangle in some directions, can be executed without pressing
on the cord. And besides this, you can see that the cord by
this arrangement will not be bent at an angle, as the vertebrae are, but in a curve, for the spaces in the spinal canal
at the joinings allow of a lateral movement of the spinal
marrow at these points.
6. Vertebrtec of Qutadtru1pe1ds.-In quadrupeds, as
they have their heads suspended, instead of being supported,
as in man, upon a column of bones, the spinous processes in
the neck are very large, and project much, for the attachment of c trong muscles which hold up the head and move it.
There is also attached to these processes, a very stout fibrous
ligament, commonly called the paxy-waxy, to assist in sustaining the head.
68. Vertebwue of iFshes.-Inh fishes the spinal column
is so arranged as to give it great flexibility. In Fig. 18 is represented one of the vertebra- of a fish. If you compare it with a
human vertebra, as seen in Fig. 11, you will see that it differs
very widely from it. It has no transverse or side processes.




THE BONES.                      41
While the human vertebra has one spuinous process that
projects behind, this has two, f,f, one in front and one in
the rear, or rather, according to the usual position of the fish, one above and one below.  The    FIG 18
body of the vertebra has a cup-like cavity on
each side towards its neighboring vertebra.
Whllen, therefore, two of these vertebrae are
joined together, their two cup-like cavities
make one cavity of the shape of a double cone,
as seen in Fig. 19.
This is a representation of a section of a portion of the spine of a fish.  The division is
made so as to cut the vertebrae into two halves,   VERTEBRA
and thus show these cavities. Each one of these   of n Fish.
contains a sac which is filled with a gelatinous fluid.  This
arrangement, which secures very
great flexibility  of  the  spinal         FIG.19.
column, you can examine at any
time when you have fish on the
table.  The  long  spinous processes make the broad,framework
of the animal, to which its muscles
are attached.
69. Jeertebrce of Reptiles.
-In reptiles there is still greater
flexibility of the spine than  in  SPINAL COLUMN OF A FISH.
fishes.  This is secured in  two
ways, by the great number of the vertebrae, and by a peculiar arrangement of them. There are three hundred and
four vertebra in the boa-constrictor, over three hundred in
the common ringed-snake, and over two hundred in the rattlesnake. The articulations of the vertebrae in reptiles are with
a ball-and-socket arrangement.  The forward part of each
vertebra has a deep cup-like depression, in which plays a
round smooth ball from the back part of the next vertebra.
And as these joints are firmly bound together by ligaments,
the spinal column is very strong as well as flexible. In the




42)           PHYSIOLOGY AND HYGIENE.
gracefully flexible neck of the giraffe we have the same
ball-and-socket articulations of the vertebrae.'T. Bontes of the Thorax,-The breastbone, which
is flat and of simple form in man, is much larger and less simple in its form in some animals. In flying birds it is not only
broader, but it has a keel-shaped projection for the attachment of the large muscles used in flight. The clavicl7, g,
Fig. 5 (so called from its resemblance to a key, and coummnonly called the collar-bone), is attached at one end to the
top of the breastbone, and at the other unites with a process of the scapula, or shoulder-blade at the top of the
shoulder-joint. It is a prop to the shoulder, pressing it outward; and accordingly it is large in those animals the
movements of whose superior extremities tend to bring the
shoulders toward each other, while it is very slender, or
absent even, in those the tendency of whose movements is to
keep the shoulders apart. Thus in birds the drawing down
of the wings by the strong muscles would bring the shoulders
toward  each  other, were this not prevented  by stout
clavicles. Sometimes a second bone is added for the same
purpose.
But in the horse and other similar animals, the pressure
of the body downwards between the shoulders tends to
separate them, and here we find the clavicle deficient because it is not needed. The scapula, or shoulder-blade, is a
thin bone with a stout raised spine or ridge running across
it, and forming by its end the top of the shoulder-joint. It
is situated differently from any other bone in the body. It
is imbedded in muscles and has a very free motion. The
design of this attachment is to give freedom of motion
to the arm. The scapula is directly connected with. the
skeleton only by its union with the clavicle.
In Fig. 20 you see the arrangement of the clavicle, scapula,
and breastbone. C, C, are the scapula  or shoulder-blades.
A, is the upper part of the breastbone. B, B, are the clavicles
fastened to the breastbone at one end, and to the shoulderblade at the other end at E, which is a process of the
shoulder-blade, making the projecting top of the shoulder



THE BONES.                     43
FIG. 20
THE COLLAR-BONES AND SHOULDER BLADES.
FIG. 21.




'44           PHYSIOLOGY AND HYGIENE.
joint. D, is another process of the shoulder which serves
for the attachment of muscles and ligaments. It is called
the coracoid process, from its resemblance to the beak of a
crow.
T1. Bones of the  Upper Extreniities.-The
upper extremity is divided into three parts, the arm, the
forearm, and the hand. The arm has but one long bone,
the hukmerus, i, Fig. 5. This has a round head which moves
in a shallow cup formed by the shoulder-blade. The shallowness of the socket is the cause of the frequency of dislocations of the shoulder. But if there were a deep socket like
that which receives the head of the thigh-bone, the arm
could not have anything like its present freedom of motion.
Such an arrangement would involve too much of a sacrifice
of necessary uses for the sake of security. At its lower part
the humerus makes a hinge-joint with the forearm.
The forearm  has two bones, the radius, b, Fig. 21, and
the bnia, a. The peculiar arrangement of these two bones
is worthy of notice. The hinge-like motion of the forearm
upon the arm is performed by the ulna alone. This bone has a
beak-like process, which works over a smooth round surface
at the end of the humerus. It is the outside of this process which you feel at the point of the elbow. The other
bone, the zradius, has nothing to do with this motion. This
only rolls on the ulna in the rotary motions of the forearm.
But at the other end of these bones, at the wrist, the arrangement is reversed. Here, it is the radius on which the
hand moves in a hinge-like manner, while the ulna at c rolls
on the radius, as the radius does on the ulna at the elbow.
You can readily see that as the radius rolls on the ulna
at the elbow, and the ulna on the radius at the wrist, a very
free rotary motion of the forearm  is provided for. The
combination of this motion with the motions at the wrist,
the elbow, and the shoulder, secures that almost endless
variety of movement, which is so striking a peculiarity of
the upper extremity, as compared with the lower.
The hand is divided into three parts, the carpus, p, Fig. 5,
composed of eight small bones, the metacarp us, q, composed




THE BONES.                    45
of bones which are like the bones of the fingers, r. The
eight bones of the carpus are firmly packed together, but
they have a slight motion upon each other, and this, together with the motion of the metacarpal bones, makes the
hand a more easy, light, and springy instrument than it
would be, if these bones were all consolidated into one.
The metacarpal bones are the framework of the flat part of
the hand, and to them are joined the first row of the bones
of the fingers. The metacarpal bone of the thumb has a
very free motion upon the carpus, differing in this respect
altogether from the metacarpal bones in the body of the
hand. The bones in the wrist and hand are bound together
by very strong ligaments. Those which are seen in the
palm of the hand are represented in Fig. 22. Those which
you see at a, b, and c bind the small bones of the wrist toFIG. 22.
gether, and also tie them strongly to the bones of the forearm, the ends of which you see in the Figure.




46            PHYSIOLOGY  AND HYGIENE.
The bone at b, to which so many of these ligaments are
attached, is the prominent bone which you feel at the beginning of the palm of the hand on the side towards the
body. The ligament g connects this bone with the metacarpal bone of the little finger. At d, d, are ligaments which
running across the hand bind the metacarpal bones together at their beginning. At e, e, are similar ligaments,
where the bones of the fingers join them. The bones of the
fingers and thumb are strongly held together by lateral ligaments, as seen at f, f. The various
FIG. 23.     ligaments of the wrist and hand pera         mit a slight motion between the bones;
and thus the hand has freedom and
ease in its motions while it is also a
very strong and firm instrument.
fo'72. Bones of the Lotwer Extremities. —The  lower extremities
have some resemblance to the upper
in their structure and arrangement,
but differ from them in some import-'ant respects. Here firmness is the
chief object, while freedom of motion
is the great thing to be secured in
the upper extremities. The lower extremities are chiefly for locomotion,
but the upper are fitted for a variety
of purposes.  The body is supported
upon the lower extremities, and therefore, the thigh-bones have sockets in
the broad flaring bones of the pelvis m
and 1, Fig. 5.  In Fig. 23, is represented a rear view of the thigh-bone.
Its head, a, is round, and fits into a
i-;ly     ~  deep socket in the pelvis.
At b is a depression in which one end
h  o  ji      of a stout short ligament is fastened,
its other end being attached to the
bottom  of the socket. At c is the neck of the bone; at d




THE BONES.                    47
and e are two projections to which are attached large
muscles to move the limb. Along the shaft of the bone, g,
there is a rough ridge, h, to which muscles are fastened; i
and k are two smooth surfaces for articulation with the leg
below. At t, Fig. 5, is the bone called the patella or kneepan, which answers as a defence to the joint, and at the
same time affords a mechanical advantage to the muscles
which throw the leg forward.
These muscles are fastened to the upper part of the patella,
and then a connection is formed by a strong tendon between
its lower part and the large bone of the leg. You see at
once that the leg can be thrown forward with more force by
this arrangement, than it could be if the tendon of the
muscles passed over the front of the joint without any
patella.
This will be referred to again in the Chapter on the Muscles. The leg has two bones, v and'I, Fig. 5; but unlike
those of the forearm they are constructed and arranged for
strength, and not for freedom of motion. The foot, like
the hand, is divided into three parts. The tarsuls, a, Fig. 24,
is that part of the foot which extendS from the heel to the
middle of the foot. It is composed of seven bones, the
largest of which makes the body of the heel. The metatarsus, b, has five long bones reaching from the tarsus to the
FIG. 24
toes. The toes, c, have fourteen bones. The object of having so many bones in the body of the foot is to give a certain springiness to it, which guards against shocks, and
facilitates motion. Its arched form also tends to secure the




48            PHYSIOLOGY AND HYGIENE.
same object. In every movement of the foot there is a slight
motion between all these bones.
Thus in walking, when the foot first touches the ground,
it does so at the heel, as represented in Fig. 24. Then as
the body moves forward, the fore-part of the foot is brought
down, the weight of the body at length pressing upon the
ground at the ball of the foot, b. In executing this movement, elasticity is given to the tread of the foot by the
very slight motion which occurs between these many bones.
If the body of the foot were all one bone it would manifestly be a very stiff and awkward affair, and ease and grace
in walking would be an impossibility. With such a foot we
should not walk much better than one does with a wooden
leg.
M3. Synovial liembrane.-Before leaving the subject of the bones, your attention is called to the provision
which is made for the easy movement of
FIG. 25.    their joints. The ends of the bones are
tipped with cartilage, so as to afford a firm
but smooth surface for the motion of the
one bone upon the other. Besides this provision, the ends of every two bones that
move upon each other are lined with a
membrane, so arranged as to make a blind
(    0~fl3~  ~~~This is illustrated in Fig. 25, in which a
and b are the ends of two bones, the sac, c,
lying between them represented here as detached from  the bone, in order that the
arrangement may be clear to you. It is as
DIAGRAM    if a small bladder were introduced between
showing the lining of a the two ends of the bones, and were fastened all over the surfaces that press together.
The inside of this sac is kept lubricated with a bland fluid
resembling the white of egg, so that the joint may work
easily. This fluid is secreted by the membrane itself, and
the moving machinery of the human system may therefore
be said to oil its own joints.




SKELETON-BONES, JOINTS, LIGAMENTS,
COMPOSITION.                3 EARTHY MATTER.
ANIMAL MATTER,
( COLOR.
HARDNESS,
POROSITY.
r/j              CHARACTERISTICS.             FORM.
Y  | WERIGHT.        J~oints,    Ball and Socket.
o  STRENGTH,.                   With slight movement.
BONES.                                   FORM.
BON         USES.                        LEVERS.
H  PROTECTION.
CYLINDRICAL,
CLASSES AS TO FORM.   FLAT.                                  Flat or Band.
IRREGULAR.           Ligament. Capsular.
Round.
H   Cranium, 8.
NUMBER, PLACE, AND FHEAD.               1 Facei   8.
NAMES.                     TRUNK, 155.
UPPER EXTREMITIES, 64.
|  LOWER EXTREMITIES, 60.




50            PHYSIOLOGY AND HYGIENE.
In the knee-joint, the broad surfaces of-which are subjected to so much pressure, there are two flat pieces of carti.
lage loose in the joint, which operate like friction-wheels in
lessening the friction. There is a similar provision in the
articulation of the lower jaw. This member does so much
work in talking, and such heavy work in mastication, that
each of its joints has a movable cartilage for the diminution of friction. Sometimes when the lubricating fluid is
deficient, or becomes too thick. a disagreeable crackling
noise is produced by these cartilages in the motions of the
jaw.
CH APTER V.
THE MUSCLES.
74. Structure of Muscles.-Muscular substance is
what is commonly called the lean mneat. It is of various
colors in different animals, or in the same animal at different periods of life.
All motion in animals is produced by muscles. They
act by contracting or shortening the fibrils of which they
are composed. Commonly there are tendons united with
the muscles. These tendons are composed of strong white
fibres, and have no power of contraction themselves. They
serve merely as the cords by which the contracting muscles
move the bones and other parts.
75. Each Fibril of a 2Muscle Sulpplied with a
Nerve. —Each fibril of which the muscle is composed, is a
chain of cells, and it is the shortening of all these chains of
cells in a muscle that produces its contraction. The action
of a muscle is dependent upon the nerves. Each fibril has
a nervous fibril or tubulus, by which its connection with
the brain or spinal marrow is established. And each fibril
is in this respect probably wholly separate from every other




THE MUSCLES.                  51
fibril.  When, therefore, the mind wills that a certain
motion shall be performed, an impression is sent to each
fibril of every muscle engaged in that motion, through the
tubulus devoted to that fibril. When the action is a very
complex one, calling into operation many muscles, a multitude of these impressions are communicated through a multitude of distinct channels or tubuli. The individual is not
at all conscious of the compound nature of muscular action,
and he knows nothing of the muscles which produce any
particular movement, unless he has studied anatomy and
physiology. He wills the movement to take place, and at
once the requisite impressions are sent along the appropriate
channels or tubuli to their destination.
These impressions must differ in degree or intensity in
producing different amounts of motion; and they must
differ in some cases in different parts of the same muscle, as
some fibres are put in motion while others are not, or as
some act with more force than others.
76. _Tendons.-Muscles commonly end in tendons,
which, as they are white and shining, are quite in contrast
with the red muscular fibres. The tendons have in themselves no power of contraction, but are mere passive cords.
They have the same relation to the muscles that ropes have
to the men that pull them. They are of various shapes, according to circumstances. Long and slender tendons may
be seen on the back of the hand in thin persons, the muscles
that pull them being in the full arm above.
The tendons are not bounded by a distinct line where they
join the muscles, but tendinous and muscular fibres intertwine, so that they appear to run insensibly into each other.
Tendinous fibres also mingle in the same way with the
fibres of bone, making so strong an union, that a great force
exerted in pulling on the tendon will sooner effect a rupture
of the tendon or the bone, than a separation of the connection between them.
77. Strength and Size of Tendons.-The tendons are very strong, being made of very condensed fibrous
substance.  The tendon of a muscle is, therefore, much




52           PHYSIOLOGY AND HYGIENE.
smaller than the muscle itself. This is a circumstance of
much importance in the arrangement of the moving apparatus of our frames. The bulky muscles and the slender
tendons are so arranged, for example, in the limbs, as to
give them both freedom of motion and beauty of form. The
muscles that move the fingers help to make up the full part
of the arm, while their slender tendons occupy but little
space as they play over the bones of the wrist. If there were
no tendons, and the muscles were extended to the i arts
which they move, the hand would be a large cumbrous mass,
instead of the light and agile thing that it is now.
78. Action of l1uscles.- In  the action of the
muscles upon the bones, we have examples of the three
kinds of levers treated of in natural philosophy.
79. First Kind of Lever.-The first kind of lever
has the fulcrum between the weight and the power, as represented in Fig. 26. F is the fulcrum, W the weight, and
FIG. 26.
FIRST KIND OF LEVER.
P the power. You have examples of this lever, in the common pump-handle, the beam of a pair of scales, the crowbar,
as commonly used, scissors, &c. You have an example of
this form of lever in the human body, in the action of the
muscles in moving the head back and forth on the top of
the spinal column.
In this case, when the head is moved forward, the top of
the spine is the fulcrum, the weight to be moved is the back
of the head, and the power is the contraction of the muscles
that bow the head forward. When the head is bent backward, the power is the contraction of the muscles behind,
and the weight is the front part of the head. The muscles
that move the head backward are stronger than those that




THE MUSCLES.                   53
move it forward. It is necessary that this should be so, for
there is more of the head in front of the point of support
or fulcrum than there is behind it. Hence, when sleep relaxes the muscles, if we are sitting up the head falls forward.
80. Second Kind of Lever. —In the second kind
of lever the weight is between the fulcrum and the power,
as represented in Fig. 27. The common wheelbarrow is an
example of this form of lever. You have an example of it
in the body in the raising of the heel from the ground
FIG. 27.
SECOND KIND OF LEVER.
in walking. In doing this, the weight to be raised is the
whole body, the foot being the lever, and the forward part
of the foot being the fulcrum. This will be made clear by
Fig. 28. W  is the large bone of the leg sustaining the
FIG. 28.
F
weight of the body; F, is the fulcrum, the forward part of
the foot that presses on the ground as the heel is raised;
and P, is the power at the end of the lever, the large muscle
in the calf of the leg, that raises the heel.




54            PHYSIOLOGY AND HYGIENE.
81. Third Kind of Lever. —In the third form of
lever the power is between the weight and the fulcrum. A
common example of this is seen in the raising of a ladder.
The fixed foot of the ladder is the fulcrum, the ladder itself
is the weight, and the power is applied as far from the fulcrum as it can be. Fig. 29 represents a lever of this kind.
FIG. 29.
THIRD KIND OF LEVER.
This form of lever is more frequently used than the other
forms in the human body. We have an example of it in
bending the forearm  upon the arm as seen in Fig. 30, in
which 1 is the bone of the arm; 2, the bones of the forearm;
4, the muscle which bends the forearm upon the arm; 5, its
double-headed attachment above; and 6, its attachment to
FIG. 80.
2'8
the radius, one of the bones of the forearm. In this case
the fulcrum is at 8, the joint of the elbow, the weight is the
hand with whatever it holds, and the power is applied at the
point where the tendon is fastened to the radius, that is,
as in the case of the ladder, between the fulcrum and the
weight. The muscle which straightens the forearm upon
the arm is represented at 7.




THIE MUSCLES.                   55
82. Time and Power.-In the management of the
three kinds of levers there are two different objects aimed at,
under different circumstances. One object is to move a
great weight with a small power. Here quickness is not
aimed at, but the weight is moved slowly. The other object
is to move the weight quickly, an object inconsistent with
the moving of any very heavy weight. When the object is
to move a heavy weight slowly, the lever is so managed as
to get a good purchase, as it is expressed.
Thus in the case of the lever of the second kind, Fig. 27, if
the weight be a heavy one, the power is commonly applied
at some distance from the weight. The nearer the power is
to the weight, the greater must it be to move the weight.
The smaller the power, the further must it be from the
weight.
But though a smalf power, if at a distance from  the
weight, answers to raise it, yet in this case the power must
move through a considerable space to move the weight but
little; while to raise the weight to the same height, a power
nearer to it passes through but little space. This will be
made clear by Fig. 31. F is the fulcrum, and W the weight.
If the lever, A, be raised to the line B, the dotted lines will
show the different spaces which the power passes through,
according to its distance from the weight. If the power be
at P, it passes through the space indicated by the dotted line
FIG 71.
w     p   A             P
a in moving the weight W to c. But if it be at p, it passes
through a much shorter space, b, in raising the weight to
the same height.  The more important, therefore, in this
form of lever, quickness of movement is, the nearer to the
weight is the power applied.




56           PHYSIOLOGY AND HYGIENE.
Let us look at the application of these principles to the
example of this kind of lever, which was cited from the
human body, represented in Fig. 28, the raising of the
weight of the body on the foot in walking.  The power
is here applied quite near to the weight, for quickness
in raising the heel in walking and running is of great importance. By having the heel project farther behind, the
muscle could be attached farther from the weight, and thus
act with more power. But there would in this case be a
sacrifice of quickness of movement, and besides this, the
lengthened heel would present a very awkward and ugly
appearance.
But it is in examples of levers of the third kind that we
find these principles best illustrated. This form of lever is
much more often used in the mechanism of the muscles
than the other forms. Refer to the example given of this
lever in the action of the biceps muscle in bending the forearm, as shown in Fig. 30. In this case it is of much more
importance to move small weights quickly, than to move
heavy ones slowly. Therefore the power is applied quite
near to the fulcrum. The tendon of the biceps, as you see,
is fastened to the main bone of the forearm near the fulcrum,
the elbow. The point where the power is applied would
pass through but little space, in moving a weight through
a considerable one. The lower jaw, in its upward motion,
is a lever of the same kind. In this case, force, rather than
quickness, is required in breaking and grinding the food.
Here, therefore, the power, the action of the muscle, is applied farther from the fulcrum than in the case of the biceps
muscle of the arm, and nearer to the weight to be moved,
or the point where the resistance is which is to be overcome.
It is applied also in a different direction-a point which will
be considered in another connection.
The muscles which move the lower jaw upward can be
seen in Fig. 32. One is the large spreading muscle b, the
swelling of which, in its contraction, we can feel, if we place
the fingers on the temple while moving the lower jaw upward. The other is the short strong muscle c, the fiont




THE MUSCLES.                    57
edge of which is so far forward, that one-third at least of
the lower jaw-bone is embraced by this muscle.
Now, if you compare this bone as a lever, with the forearm
as acted upon by the biceps, you will at once see that the
FIG. 32.
-----
MUSCLES OF FACE AND NECK.
power is applied much nearer to the weight, or the resistance to be overcome, in the case of the jaw, than in the
case of the arm. It is so even when the resistance to be
overcome is at the front teeth; and it is much more so
when the resistance is at the back part of the mouth, as when
we are grinding our food. Here, indeed, a portion of the
muscular force is brought to bear upon the resistance in a
direct line. It is not merely because the back teeth are
stronger than the front ones, but also because the power is
nearer the resistance, that we can crack a nut more easily
with the back, than we can with the front teeth.
83. Mechanical Disadvantage.-It is clear that
the biceps muscle acts, as it is expressed, at a mechanical




58            PHYSIOLOGY AND HYGIENE.
disadvantage, if we regard mere power or force, and leave
out of view quickness of motion. If it were inserted further
down on the forearm, nearer tile hand, it could raise much
greater weights than it now can. A similar statement can1
be made of most of the other muscles of the body.
Bat force is sacrificed for the sake of quickness in most
cases, because the latter is more important.  In the few
cases in which force is the more important, as in the case
just cited of the lower jaw, the reverse arrangement is provided. This gain in quickness can be illustrated by Fig. 33.
F being the fulcrum, the power in raising the weight, W,
FIG. 33.
F                    b
\  P                   P
to c, if acting at P, passes through the space indicated by the
dotted line a. But if it act at p, it will pass through all
the space b, and of course raise the weight more slowly than
when acting at P.
Most of the muscles work at a mechanical disadvantage
in another way. Observe the direction in which the muscle
acts on the, bone to be moved. This is seldom at right
angles, and therefore a considerable part of the force exerted
is lost. This can be made clear by Fig. 34. Let b represent the bone of the arm, and r its fulcrum, or point of
support in the shoulder. You readily see that if the bone
be acted on by a muscle, rn, at right-angles to it, it will require less force to move it to a given point than would be
required if the same muscle were placed in the position




THE MUSCL.S.                    59
represented by n. For the muscle n, acting obliquely on
the bone, would expend a part of its force in pressing the
end of the bone upward against the socket of the joint at r.
FIG. 34.
But in this case also, what is lost in power is gained in
quickness of movement. This can be shown by the figure.
We will suppose that the muscle contracts or shortens itself
half of the length of the tendon. If the muscle were placed
as at in, the bone would be carried to the line a, c. But
if the muscle be placed as at n, the same degree of contraction would raise the bone to the line a, d, the point of
the bone where the tendon of the muscle is attached moving
in the curved line as marked.
It, of course, requires much more power for the obliquely
placed muscle, n, to raise the bone to the line a, d, than for
the muscle rn, to raise it to a, c; and therefore a much
larger muscle is needed than there would be if it acted at
right-angles to -the bone as at en. And the muscle which
raises the arm at the shoulder, acting as it does at so great
disadvantage, is a very large muscle. The muscle, n, in the
figure, represents only the line of its action, and not at all
its shape. If you observe the various motions of the arm
in which this muscle has a part, you will appreciate the
necessity of so arranging it as to secure quickness of movement.  This was the chief object to be aimed at in its
arrangement; and the second and less important object,
power, is secured, so far as it is needed, by simply making
the muscle a large one.




;60          PHYSIOLOGY AND HYGIENE.
84. Plan by which the lMechanical Disadvantage is Overcome.-The mechanical disadvantage,
which was noticed as resulting from the oblique
FIG. 35. action of the muscles, is in part obviated by a
very simple contrivance. It is done by making
the tendon of the muscle work over ail enlarge7 —-r  ment of the bones at the joints.
The operation of this contrivance can be made
clear by Figs. 35 and 36. Let r and o (Fig. 35)
be the two bones of a joint, and let the muscle
FIG. 36.  m be attached to the bone o at i. As it contracts,
almost all its force will be spent in drawing the
— r  bone o upward against the bone r, because it
acts almost entirely in a line with the bones.
i...!   But let the ends of the bones be enlarged as in
-— o  Fig. 36, and you see that the direction of the
tendon of the muscle m is so changed where it
is attached to the bone, that the muscle can now very
easily make the lower bone turn upon the upper.
The enlargement then of the bones at the joints, which
is needed to give the requisite extent
FIG. 37.     of surface for working them, answers
\\t.  also another good purpose in thus
altering the direction of force in the
muscles. In the case of the kneejoint there is an additional contriv/    ance for making this change of
c    direction still greater.  A movable
bone, the patella or kneepan, besides
acting as a protection to the joint,
C \  Ie    effects also the purpose referred to.
The manner in which it does this
can be made plain by Fig. 37, in
which a represents the end of the
thigh-bone; b, the end of the large
bone of the leg articulating with it;
c, the patella; d, the large tendon which comes from the
muscle above, and is fixed into the patella; and e, the ten



THE MUSCLES.                  61
don which goes from the patella to the large bone of the leg
below. The dotted line shows how much the direction of
the force of the muscle is changed by this arrangement.
The movement performed by this muscle is throwing the
leg and foot forward, which it is by the above arrangement
of the patella enabled to do with great ease in walking, and
with great force in the act of kicking.
85. The Pltley.-The pulley is used in the arrangement of the muscles, though by no means so often as the
lever. It serves, whenever it is used, to change the direction of the force.
At the wrist and the ankle there are broad ligaments
which bind down the tendons of the muscles, and sustain
to them the relation of pulleys. If it were not for these
ligaments the tendons at these joints would fly out continually when the muscles are in action, making projecting
cords under the skin. And if the skin were removed, the
tendons would be in a position similar to that represented
FIG. 38.
at A, in Fig. 38. In this Figure, C is a tendon of the
great toe in its position as bound down by ligaments.




62           PHYSIOLOGY AND HYGIENE.
Now if the muscle were in the position represented by A, it
is plain that it would act at a greater mechanical advantage
than in the position C; but the toe would not be moved so
quickly; and besides, if the tendons projected in this way,
the foot would be a very cumbrous piece of machinery, compared with what it is now, with the tendons bound down
around the slender ankle. So that both beauty and use are
secured by the arrangement.
There is a beautiful application of the pulley in the case
of the muscle that draws down the lower jaw, called the
digastric muscle. It is represented in Fig. 39, in which a
is one end of the muscle attached behind the ear, and b is
the other end attached to the inside of the lower part of the
chin.
FIG. 39.
DIGASTRIC MUSCLE.
It is muscular at the two ends, and tendinous in its middle
part. This middle part runs through a loop or ring in a
small muscle as represented in the Figure. This little muscle
is fastened above to a small process of bone under the ear,
and below to the hyoid, or U-shaped bone, c, which is situated just above the larynx. Now when the jaw is to be
drawn down, the two fleshy ends of the digacstric muscle contract, and the middle tendinous part works in the ring provided in the little muscle. This muscle is so slender, that
its loop is of itself hardly strong enough, as we should




THE MUSCLES.                   63
suppose, for the tendon of so large a muscle as the digastric
to work in. And we accordingly find that there is an
additional security in a strong ligament, which fastens the
tendon of the digastric muscle to the hyoid bone.
This ligament (which is not represented in the figure,
because it would confuse your view of the pulley-action of
the parts) is sufficiently long to allow of all the freedom of
motion necessary to drawing the jaw downward. You see
at once that one object of this arrangement of the digastric
muscle is to secure beauty of form in the neck. A muscle
extending from the top of the chest to the chin in a straight
direction would very effectually draw down the lower jaw,
but it would be a great deformity. This is avoided by the
pulley-arrangement of the digastric muscle.
But this muscle answers another purpose besides drawing
down the jaw. If, while the jaw be held fast by muscles
which draw it upward, the digastric contracts, it will draw
up, as you can readily see by the Figure, the hyoid bone, c,
and with it, of course, the larynx which is attached to it.
Now precisely this set of motions occurs when we swallow.
The mouth is shut by the drawing up of the jaw, and then
the contraction of the digastric muscle draws up the larynx,
as you can perceive if you place your fingers on the larynx,
or Adam's apple, as it is called, when you perform the act of
swallowing. The little muscle in which the loop is, renders
some assistance to the digastric in thus drawing up the hyoid
bone and the larnyx, as you can see by the Figure.
86. Muscles of the Eye.-There are six muscles
that move the eye-ball. Five of them are represented in
Fig. 40. There are four straight muscles, three of which are
marked a, b, c; the fourth is behind b, only the upper edge
of it being seen in the Figure. These muscles are,at their
origin in the back part of the socket of the eye, arranged
round the optic nerve, and passing forward, are attached to
the sclerotic coat, the firm white coat of the eye. The two
lateral muscles, b and its opposite, move the eye to the one
side and the other, and the two muscles, a and c, perform
the up and down motions.




C4            PHYSIOLOGY AND HYGIENE.
But there are certain oblique rolling motions of the eyeball which can not be executed by these straight muscles.
For these motions two muscles are provided, one of which
has a pulley-arrangement, as represented in the Figure.
FIG. 40.
This muscle, s, has a long tendon which passes through a
ring of cartilage in the roof of the socket, and then turning
back is fastened as you see to the upper part of the eyeball.
This muscle is under the direction of one nerve alone.
It is an involuntary muscle which performs the insensible
rolling motions of the eyeball, and like the other involuntary
muscles of the body, is at work while we are asleep, as well
as when we are awake. It is the muscle which rolls the eye
about tremulously when it is open in the insensible state
sometimes produced by disease.
87. Opsposing Mg Tscles.-Every muscle performing
a motion has its opposing muscle or muscles, which perform
the opposite motion. In the case of any two opposing muscles the one must be in some measure relaxed while the
other is in action. Thus in alternately bending the elbow,
and straightening it, there is alternate action and relaxation
in the two opposite muscles 4 and 7, as represented in Fig.
30. So in moving the head back and forth the muscles in
front and rear are alternately contracted and relaxed.
There is indeed in every muscle some amount of contraction which is independent of action through the nerves,
whether it be reflex, or produced by the will. For this
reason the muscles cut off in amputation of a limb retract.
So also if the muscles on one side of the face be palsied,
those on the other side draw the mouth to that side. The




THE MUSCLES.                   65
mouth is held in the middle of the face by the equal action
of pairs of muscles. The head, too, is held in equilibrium
in the same way.
In what is called wry-neck, this tonic contraction, as it is
sometimes termed, is greater in the muscles on one side
than it is on the other. In some cases a cure can be effected
only by dividing the contracted muscles. In strabismus, or
squinting, one of the straight muscles of the eyeball contracts too strongly for its opposing muscle, and as in wryneck, dividing the contracting muscle is often necessary to
remedy the difficulty.
88. Compounnd 3-1uscular Action.-Most motions are not performed by single muscles, but by the joint
and agreeing action of several, and sometimes many muscles.
And as these muscles may vary to a great extent in their
degree of contraction, the motions produced by them are
not only compound, but are exceedingly varied. In Fig. 32
you see a pair of muscles, one of which is marked h, which
extend from the large protuberances behind the ears to the
top of the breast-bone.
When they contract equally, the head is bent straight forward in the middle line between the muscles, and a line
drawn from the middle of the forehead down to the breastbone would strike exactly at the point where these two
muscles unite. But if one muscle contracts more strongly
than the other, the head as its bows forward turns toward
the side on which is the strongest contraction. And as the
degrees of contraction in these two muscles may be varied,
so there may be a variation in the degree of inclination of
the head to one side or the other, as it is bent forward.
If then a variety in the direction of motion may be produced by variation in the degrees of action in two muscles,
one can readily see that an almost infinite variety of motion
must result from this variation, where many muscles are
called into action.
89. MJuscles of the Tongue.-There is no part of
the body which exemplifies in so palpable a manner the
compound and diversified character of muscular motion as




66            PHYSIOLOGY AND HYGIENE.
the tongue. It is mostly a bundle of muscular fibres, apparently mingled together in confusion, but really arranged
in perfect order, so that the tongue can be moved with great
definiteness in all directions, forward, backward, upward,
downward, to either side, and in all intermediate directions.
But all this wonderful variety of movement is produced
in obedience to the definite action of nerves, whose fibres are
mingled with the muscular fibres of the tongue. And in
order to produce each motion there is an agreement of
action not only between many of these fibres, but also between
multitudes of them.
90. View of the JMuscles.-The muscles are of various shapes and sizes, according to the motions which they
are designed to produce, and the circumstances in which
they are placed. They are round, long, short, flat, fanshaped, circular, serrated, &c. At a (Fig. 41) is the very
large muscle that makes the fleshy prominence at the upper
part of the arm, and the office of which is to raise the arm,
carrying it out from the body; its fibres are not all arranged
alike, but lie in different directions. The result is, that
while the arm is raised by the muscle as a whole, it may be
carried at the same time forward or backward by the varying action of these different fibres.
There are many of the muscles of the body which are
thus made to produce various results by variation of the
action of different parts of the same muscle. And the regulation of this variation by the nerves is one of the most
wonderful and mysterious things which we find in our study
of the nervous system.
For each fibre,in the cases referred to,is told, as we may
express it, just how much it must do in order to produce the
requisite general motion of the muscle. It is manifestly much
more wonderful thus to produce various but accurately
graduated contraction in different parts of the muscle, than
to produce a uniform contraction in all its fibres.
At b is the biceps muscle, which bends the forearm upon
the arm, and at c is another muscle that assists the biceps.
At e is the large muscle in the back of the arm, which acts




THE MUSCLES.
FIG. 41.
MUSCLES OF THE BODY.




68            PHYSIOLOGY AND HYGIENE.
in opposition to the biceps, and straightens the forearm upon
the arm. At d is a muscle which rolls the radius outwards,
and thus turns the palm of the hand upward as seen in the
Figure.
At g is a very large broad muscle coming from the whole
length of the back. At the axilla or arm-pit, its fibres are
collected, twisted, and folded upon each other, and it is fastened
by a stout tendon to the upper and back part of the bone of
the arm. Its office is to pull the arm backwards and downwards.
At h is a serrated muscle which, rising from the ribs, goes
to the shoulder-blade, and serves to draw the shoulder-blade
forwards. At i is one of the broad muscles of the abdomen. At I and 17 are two large muscles that move the
thigh. At o and 2p, as seen on the right thigh, and at n, as
seen on the left, are three large muscles, which are fastened
to the kneepan, and serve to throw the leg forward.
At q is the tendon that forms the outer hamstring, and
at r are the two tendons which form the inner one. The
muscles to which these tendons belong, serve to bend the
leg upon the thigh, drawing it upward and backward. At s
is the muscle which makes the bulk of the calf of the leg.
It moves the heel upward and backward, and it is seen
in t in the right leg of the Figure.  Its strong tendon
which is attached to the top of the heel-bone is called, on
account of its strength, the tendon of Achilles. This muscle
is in Fig. 28 the power P which raises the weight of the
body, W, on the fulcrum, F, as the heel is raised from the
ground in walking.
In Fig. 42 you have a rear view of the muscles. At a is a
very broad muscle, which, rising from the back, is attached
to different parts of the shoulder-blade. You can see that
this irregularly-shaped muscle will move the shoulder-blade
variously, according to the various action of the different
fibres of the muscle, which run in so different directions.
At c, you see the rear part of the muscle that raises the
arm. At b is the extensive muscle that you saw in Fig. 41
at g, which draws the arm backward. At e is a large muscle




THE MUSCLES.                     69
FIG. 42.
9,,
n~' i
---- 0
REAR VIEW OF THE MUSCLES.




70            PHYSIOLOGY AND HYGIENE.
that draws the thigh backward. At g, ]h, and f are the
muscles whose tendons form the two hamstrings. At i is
the muscle that forms the calf of the leg, and raises the heel.
91. The Bones are not all that the ]Muscles
rnove.-Thus far the bones have been especially spoken
of as being moved by the muscles. But other parts are
moved by them also. In the cas3 of the voice, the little
muscles move cartilages to which the vocal ligaments are
attached. The tongue and the palate are moved by muscles.
Muscles move the skin. The mouth, the eyelids, the eycbrows, &c., are moved by them. In many animals the skin
is moved extensively by muscles, as, for example, when the
horse shakes his skin to get rid of the biting flies.
92. Synmmnetry of Arranyementt. —The muscles
moving the fingers are placed mostly in the forearm, while
their slender tendons pass over the surface of the bones in the
wrist. The flowing outline of the arm is thus secured, and
the hand is made a light, and at the same time a strong apparatus.  Substantially the same can be said of the arrangement of the muscles and tendons in the leg and foot.
There is a contrivance in a muscle that bends the toes
which will be noticed here. Its four tendons pass to the
last bones in the toes, and in doing so they go through the
tendons of the muscle that bends the second joints. For
this purpose, the latter divide near the ends where they join
the bones. In the fingers, also, a similar arrangement is
made for the tendons of the second and third joints. This
FIG. 43.
~           bc
is represented in Fig. 43, in which e is the tendon which
goes to the last bone c through the division inf, which goes
to the second bone b. It is manifest that this is the best
way of packing the tendons, as we may express it. Any




THE MUSCLES.                   71
other conceivable arrangement would add to the bulk of the
finger. As they are represented in the figure they are raised
up, instead of being closely packed down upon the bone, as
they are in reality.
93. Modes of Action of the Miuscles.-Your attention is called to one mode of action, in which a large number
of the muscles are called into play, on account of its analogy
to an expedient often used in mechanics. This, represented
by Fig. 44, is called the toggle-joint.
Let c, a, and c, b, represent two bars connected together,
like a carpenter's folding rule, by a hinge or
joint at c. Suppose the two ends, a and b, to    FIG. 44.
be fitted into the two blocks represented in    a
the Figure. If now the block at b is fixed,
and the block at a is movable, and force be
applied to the joint c carrying it towards d,
the block at a will be pressed upward with   c0.-d
considerable force. If, on the other hand, the
block at b is movable, and that at a is fixed,
the block at b will be pressed downward. We
see this latter form of the contrivance applied  b
in printing-presses.                      TOGGLE -JOIrd'.
In the human body this toggle-joint is used
in both ways. When one stoops to take a heavy weight
upon his back or shoulder, he puts both the knee and the
hip-joints in the condition of the toggle-joint when it is
bent; and then as he straightens up, the weight is raised
by an action of the joints precisely similar to that of the
toggle-joint in machinery. In the case of the knee, the
straightening of the joint is done by the muscles on the
front part of the thigh; that draw up the kneepan with the
tendon attached to it.
This is using the principle of the toggle-joint in pressing
utpward. It is also sometimes used in pressing downward.
In crushing any thing with the heel, we give great force to
the blow on the principle of the toggle-joint, by flexing the
knee and straightening the limb as we bring down the heel
upon the thing to be crushed. In pushing any thing before us,




~72          PHYSIOLOGY AND HYGIENE.
we bend the elbow as preparatory to the act, and then thrust
the arm out straight, thus exemplifying the toggle-joint.
The horse gives great force to his kick in a similar manner.
The great power exerted by beasts of draught and burden is
to be referred mainly to the principle of the toggle-joint.
When a horse is to draw a heavy load, he bends all his limbs,
especially the hinder ones, and then as he straightens them,
he starts the load. In this case the ground is the fixed block
of the mechanism, the body of the horse to which the load
is attached is the movable one, and his limbs are so many
toggle-joints. By this application of the principle we see
draught-horses move very heavy loads.
94. The lHand. —The hand is the most wonderful of
all parts of the body, in regard to variety and complication
of movement. There are over fifty muscles, which are engaged in the various motions of the upper extremity, all of
which, of course, have more or less reference to the hand.
Indeed the hand is the part of the upper extremity to which
all its other parts are tributary, and therefore we may
properly consider all these muscles as in a great measure
belonging to the hand.
If now you call to mind the fact, that each one of these
muscles can vary the amount of its contraction in all degrees,
from the most powerful action down to the slightest movement, you can readily see that fifty muscles with this power
of variation can produce an almost endless number of combinations of motion. The variety would be exceedingly great,
even if every muscle, whenever it acted, had always the same
amount of contraction.  But the power of varying the
amount of contraction multiplies the variety to an inconceivable extent.
95. The Miuscular Sense.-The question arises,
how in all the diversified action of the muscles their nice
adjustment is effected. How do the muscles know, as we
may express it, just how much to do in each movement?
When, for example, you reach your hand up to touch some
object, how does each muscle know just what degree of contraction is necessary to make the hand go with precision to




THE MUSCLES.                    73
the particular point arrived at? And so when one is playing
on an instrument with the fingers, as the piano, varying
their pressure continually in accordance with the desired
loudness of the sound, how does each muscle know just what
amount of contraction is required of it in each movement?
Though the senses of vision and touch afford some assistance
in the guidance of muscular action in such cases, something
else is manifestly necessary.
Sir Charles Bell, therefore, supposes that there is what he
calls a muscular sense, which acts as a guide to the muscles,
in connection with the senses of sight and touch. In some
cas3s it is the sole guide. On this subject, Sir Charles says,' When a blind man, or a man with his eyes shut, stands
upright, neither leaning upon nor touching aught; by what
means is it that he maintains the erect position? The symmetry of his body is not the cause; the statue of the finest
proportion must be soldered to its pedestal, or the wind will
cast it down.
"How is it, then, that a man sustains the perpendicular
posture, or inclines in due degree towards the winds that
blow upon him? It is obvious that he has a sense by which
he knows the inclination of his body, and that he has a
ready aptitude to adjust it, and to correct any deviation
from the perpendicular. What sense then is this? He
touches nothing, and sees nothing; there is no organ of
sense hitherto observed which can serve him, or in any
degree aid him. Is it not that sense which is exhibited
so early in the infant, in the fear of falling? Is it not the
full development of that property which was early shown in
the struggle of the infant while it yet lay in the nurse's
arms'?
"It can be only by the adjustment of muscles that the
limbs are stiffened, the body firmly balanced, and kept erect.
There is no source of knowledge, but a sense of the degree
of exertion in his muscular frame, by which a man can
know the position of his body and limbs, while he has no
point of vision to direct his efforts, or the contact of any
external body.
4




74 tPHYSIOLOGY AND HYGIENE.
In truth, we stand by so fine an exercise of this power,
and the muscles are, from habit, directed with so much precision, and with ani effort so slight, that we do not know
how we stand. But if we attempt to walk on a narrow ledge,
or stand in a situation where we are in danger of falling, or
rest onil one foot, we become then subject to apprehension;
the actions of the muscles are, as it were, magnified and
demonstrative of the degree in which they are excited."
CHAPTER VI.
LANGUAGE OF THE MUSCLES.
963 All T17ought Expressed  by  Muscular
Contractility.-As the nerves of sensation are the inlets
of all knowledge to the mind, the nerves of motion are the
outlets by which all knowledge is communicated. Thought
and feeling are expressed only by muscular motion.
It is chiefly by the voice that thought and feeling are
communicated. And every variation of note, or of articulation, is caused by the action of muscles. When the muscles of the hand, by writing, communicate to others thought
and feeling, they merely translate the language of the muscles of the vocal organs into conventional signs. Leaving
the language of these vocal muscles for another chapter, in
this we will notice the language of the other muscles of the
body and especially of those of the face.
97. Muscles of Expressiotn  in  the Face.The particular muscles of expression in the face, are
represented in Fig. 45. There is a thin flat muscle covering
the whole top of the head, represented at 1, 2, and 3; 3
being its thin tendinous part. It is fastened to the large
bones behind, and in front its fibres end in the skin of the
forehead and the eyebrows, and in the circular muscle of
the eyelids, 4. When it contracts, therefore, it raises the




THE LANGUAGE OF THE MUSCLES.              75
skin of the forehead and the eyebrows; and if it contract
strongly, it wrinkles the forehead. The circular muscle of
the eyelids, 4, when it contracts closes the eye. This and
the large frontal muscle just described, must have much to
do with the expression of the countenance.
FIG. 45.
2 /(
MUSCLES OF THE FACE.
A very important though small muscle, not seen in the
figure, may be seen at a, in Fig. 32. It is attached to the
bone at the side of the top of the nose, and is inserted into
the skin of the eyebrow. It is called the corrugator supercilii, or wrinkler of the eyebrow. From the agency which
this muscle has in the expression of certain passions and
emotions, comes the word in so common use, supercilious.
Though a little muscle, it is truly a supercilious one.
At 7 is the circular muscle of the mouth, orbicularis oris.
When this contracts it closes the lips, and if it act strongly
it pushes them out. This is the muscle with which, in part,
pouting is done. At 8 is a muscle which is fastened above
to the bone of the nose, and runs down, its fibres ending in




76            PHYSIOLOGY AND HYGIE1 E.
the wing of the nose, and in the upper lip. When it contracts, therefore, it moves the wing of the nose outward,
and draws up the lip. You see this muscle in action in
some emotions, the nostrils appearing spread out. At 9 is a
muscle which raises the lip, and at 10 and 11 are two
muscles, that raise the corner of the mouth, carrying it a
little to one side. At 13 is the muscle which acts in opposition to the two last. It pulls the corner of the mouth
down. At 12 is the muscle which pulls down the lower lip.
At 18 is the muscle in the side of the mouth, which draws
the corner of the mouth backward, and also serves to press
the cheek inward, and thus prevent the food from getting
outside of the teeth when we are chewing it. This muscle
also, by its compressing power, forces out the air from the
mouth when the cheeks are distended, as in blowing a horn
or a trumpet. Hence it is called buccinator from buccinare,
to blow a trumpet. At 15 is a large muscle which closes
the lower jaw against the upper, and although its chief use
is to masticate the food, it has some agency in the expression
of the countenance, in fixing the teeth firmly together, as
in the expression of rage. There are three muscles which
move the ear: 19, moving it upward; 17, forward; and 21,
backward. These have but little power in man, but in some
animals they move the ear considerably, and are prominent
agents of expression.
98. Mluscles about the Mouth. —In Fig. 46 the
muscles about the mouth, which have so much to do with
the expression of the countenance, are very distinctly shown.
At a is the muscle which draws up the wing of the nose and
the lip; b raises the lip; c raises the corner of the mouth;
d and e raise the corner of the mouth, and at the same time
carry it outward; in draws it outward; m draws it downward and outward, in which action it is assisted by a broad
thin muscle, o, which, situated just under the skin, comes
up from the neck; I draws the lower lip downward; and i
is the circular muscle which closes the lips, and thrusts
them out in pouting. At hI is a short muscle which is
fastened to the sockets of the teeth, and has its fibres ending




THE LANGUAGE OF THE MUSCLES.            7
in the skin of the chin. It therefore draws the chin up
when it contracts. It has so much agency in the expression
of scorn and contempt that it has been called the superbus.
It is by the action of this muscle, together with the circular
muscle i, that the expression termed pouting is produced.
FIG,. 46,
C\          M
MUSCLES ABOUr THE MOUTH,
Most of the muscles which have been described are in pairs;
and in every pair both muscles contract always exactly alike,
unless affected by disease. We laugh and frown and weep
on both sides alike. All of these muscles of expression in
the face are governed in their action by the branches of one
nerve, the respiratory nerve of the face. When this nerve,
therefore, is paralyzed on one side, and not on the other, as
is no uncommon occurrence, these muscles on the paralyzed
side are motionless, and the individual can laugh and frown
and weep on only one side of the face.
No one muscle is devoted to the expression of one emotion
or passion; expression is commonly the result of the combined action of many muscles. By virtue of this combination, the same muscle often takes a part in the expression
of various emotions.




78            PHYSIOLOGY AND HYGIENE.
99. Action of Particular Muscles in Expressinfg Einotions.-When the frontal muscle (1, 2, 3, Fig. 45)
contracts it raises the eyebrows. This motion expresses either
doubt or surprise, and the observer determines which it is, by
the expression of other parts of the countenance accompanying it, or in other words, by the action of other muscles in
the face. When this muscle contracts very strongly, it draws
up the eyebrows so much, as to push up the skin of the
forehead, and wrinkle it. This, as you will soon see, is one
of the many motions of the face which make up the expression of great bodily fear. In joy this muscle acts moderately; raising the eyebrow, therefore, but a little. This
muscle often acts in connection with the corrucator supercilii, the wrinkler of the eyebrow. The muscle which draws
the corner of the mouth down is in action while the slperbus
(It, Fig. 46,) is drawing up the chin which pushes up the lip
before it. At the same time the muscle which draws up the
wing of the nose and the lip (a, Fig. 46,) contracts to some
extent, producing an arching of the mouth and a peculiar
shape of the wings of the nose. The upper lip is arched by
the action of this muscle in such a way as to fit the arching
upward of the lower lip, produced by the superbus and the
muscle which draws down the corner of the mouth.
In the expression just described, and illustrated by the
figure, it can be seen that the muscle which draws down the
corner of the mouth has a considerable agency. Now, this
muscle is the chief agent in the expression of sorrow, as you
saw in the first part of this chapter. The difference in the
two cases lies in the combination of action of the muscles.
Thus, in sorrow the muscle which draws down the corner
of the mouth, does not have the sltperbuts to act with it, as
in the case of the passion. So also, in some forms of grief,
the corrugyator supercilii acts quite strongly, where the grief
is represented as caused by bodily pain.
In quiet sorrow this muscle is not in action, but there is
a general languor relaxing the muscles of the face, while
the corners of the mouth are slightly depressed. It is a
state of the muscles directly opposite to that which exists




THE LANGUAGE OF THE MUSCLES.;:9
when there is a calm quiet pleasure. Then most of the
muscles are in a state of gentle action, and the corners of
the mouth are a little raised, giving the radiance of a light
smile to the whole countenance. The frontal muscle
slightly raising the eyebrows, adds. to the effect.
100. Jlovementts of the Eye in Exlpression.
-The muscles of the eye, that is, those which move the
eyeball, have some agency in certain expressions of the
countenance. Thus, the fixing of the eve upon an admired object makes a part of the expression of admiration.
In the expression of devotion the eye turns instinctively
upward.  There are certain involuntary motions of the
eyeball, which have much to do with expression in certain
states of the body, and in certain emotions. These motions
are performed by the oblique muscles. When the straight
muscles which ordinarily control the motions of the eye
lose their power from a state of general insensibility, the
eye is given over to the action of these oblique muscles,
which are involuntary, and therefore is rolled about in its
socket, being turned upward all the time, so that only the
white of the eye is seen. This occurs in sleep, in fainting,
in the stupor of disease, and in the approach of death.
The loss of power in the voluntary muscles of the eyeball and eyelid is often seen ludicrously exhibited in the
intoxicated man. He squints and sees double from deficiency of action in the straight muscles of the eyeball.
The oblique involuntary muscles of course roll the eye in
proportion to the deficiency of these straight muscles. The
voluntary muscle too, which holds up the upper lid, fails to
do its duty, and the lid is constantly disposed to fall over
the eye. The frontal muscle is therefore called upon to aid
it. Hence, in the effort of the drunkard to keep his eyes
open, you see him raise the eyebrows, the eyelids of course
being dragged up after them slightly.
101. Comr,it(nation of JMuSscUlar Actiont.-But
we do not get a full view of the combinations of muscular
action ih expression, if we confine our observations to the
countenance. The muscles of other parts of the body, and




80           PHYSIOLOGY AND HYGIENE.
sometimes of the whole frame, are brought into action in
connection with the muscles of the face, in expressing
thought and feeling. The attitudes and motions of other
parts of the body correspond with the attitudes and motions of the countenance, so as to produce a harmonious
effect. The hand is more used than any other part in aid
of the countenance in expression; but the whole body is
often brought more or less into action. The character of a
passion can sometimes be inferred merely from the attitude or from the mode of walking, as you see one at a distance.
102. Action of the Respiratory Mithscles. —But
it is the muscles of the respiratory organs which sympathize
most with the muscles of the face in expression. This
sympathy is the result of a nervous connection, and the
nerve of expression in the face is therefore sometimes called
the respiratory nerve of the face. In laughing the individual draws in a full breath, and then lets it out in short
interrupted jets, the muscles of the throat, neck and chest,
especially the diaphragm, being convulsively agitated. And
if the laughter be strong and continued, he holds his sides,
which become really sore, from the violent action of the
respiratory muscles in this expression of his emotions. In
weeping too, these same muscles are affected. The diaphragm acts spasmodically, the breathing is cut short by
sobbing, the inspiration is quick, and the expiration is slow,
and often with a melancholy note. But it is not alone in
these marked cases that the respiratory muscles are seen to
act, their action is plainly noticeable in many of the slighter
expressions of feeling.
103. The Habitual Expression of the Countenance after 1Death.-The habitual expression of the
countenance, depending as it does upon the habitual condition of the muscles. is seen after death. In the state of
relaxation which occurs immediately at death the face is
very inexpressive, because its muscles, together with those
of the whole body, are so entirely relaxed. But very soon they
begin to contract, and they assume that degree of contrac



DIGESTION.                  81
tion to which they were habituated during life, and therefore give to the countenance its habitual expression.
CHARACTER.          CONTRACTILE.
I FUNCTION.        MOTION  Voluntary.
Involuntary.
MUSCLES.                         BY TENDONS TO THE
ATTACHMENT.    BONES.
tNOT SO ATTACHED.
ARRANGEMENT.{ DEEP-SEATED.
SUPERFICIAL.
CHAPTER VII.
DIGESTION.
104. Summary of the Process of Digestion.
Under the term digestion are included all those processes
which are necessary to effect the separation from the food
of its nutritious portion, and the introduction of it into the
circulation. A summary of these processes may be thus
given. The food is broken up and ground in the mouth,
and it is at the same time mixed with the saliva. It is
then taken into the stomach, where it is kept in constant
motion under the solvent action of a fluid of a peculiar
character. When it is brought into the right condition, it
is passed from the stomach into the intestines. Here it is
acted upon by two fluids-the bile, the secretion of the liver,
and the secretion of another gland, the pancreas or sweetbread. These secretions have some agency in separatin 
from the mass its nutritious portion, and this is absorbed
or taken up, in the form of a milky fluid, by little vessels
lying on the surface of the inner membrane of the intes



82           PHYSIOLOGY AND HYGIENE.
tines. These vessels unite to form a large tube, through
which the milky fluid is poured into the circulation, to
replenish the blood.
105. Teeth Various, accordinig to Different
Kinds of Food.-Mastication is an important part of
the process of digestion. The teeth, which perform this
act, are very hard bodies. The body of a tooth is composed
of two substances. The inner part is called the ivory, and
the outer, which is exceedingly hard, is called the enamel.
The teeth are of different shapes for different modes of
action. There are long and pointed teeth, for tearing;
others for cutting, which have a sharp edge; and others
for grinding, which have for this purpose a broad and
irregular surface.
The teeth are differently shaped in different animals,
according to the kinds of food which they -eat. Thus, the
herbivorous, or vegetable-eating animals, have grinding teeth
to bruise their food; while the carnivorous, or flesh-eating
animals, have sharp-edged teeth,and long-pointed teeth, by
which their food is torn and cut in pieces. And it is to be
observed, that the movement of the jaws always corresponds
to the character of the teeth.
In the carnivorous animals, the motion of the lower jaw
upon the upper is a mere up-and-down, or hinge-like
motion. As they have no grinding teeth, there is no need
of any lateral motion. But in the animals that have grinding teeth, there is a lateral motion, to enable them to grind.
You see this difference very plainly, if you observe the dog
and the horse while they are eating. In Fig. 47 you see
represented the teeth of a carnivorous animal. The front
teeth are long and pointed, for rending, while the back
teeth have a sharp edge for cutting.
In Fig. 48 you see represented the broad and irregular
grinding surfaces of the teeth of herbivorous animals. In
animals that live on insects, the teeth present conical
points, which press into corresponding depressions in the
opposite jaw, as represented in Fig. 49. In those that live
on soft fruits, the teeth are rounded, as in Fig. 50. These




DIGESTIOX.                    80
are quite in contrast with the tearing teeth of the carnivorous, and the grinding teeth of the herbivorous animals.
FIG. 47.
FIG. 48.
TEETH OF HERBIVOROUS
ANIIMAL.
TEETH OF CARNIVOROUS ANIMAL.
There is an arrangement of the enamel and the ivory in
the teeth of the herbivora which ought not to pass unnoticed.
Instead of having the enamel cover the ivory, as in the
teeth of the carnivora, the two substances are arranged in
FIG. 49.                        FIG. 50.
TEETH OF FRUGIVOROUS
ANIMAL.
TEETHI OF INSECTIVOROUS ANIMAL.
upright layers, as seen in Fig. 48. The object of this is plain.
The ivory wears away more readily than the harder enamel,
and, therefore, the surfaces of the teeth always present projecting hard ridges, fitting them for grinding thoroughly.
A miller would say, that these are stones that never need
picking.
106. ]Mfan an Omnivorous Animal.-So perfect
is the correspondence of the teeth with the kind of food on
which the animal lives, that the skillful naturalist can
infer very correctly, from the examination of the teeth




84            PHYSIOLOGY AND HYGIENE.
alone, the character of the food on which an animal lives,
and even the general arrangement of its structure.
As man has the three kinds of teeth which I have noticed,
he is said to be omnivorous, or an eater of all kinds of food.
In him, the front teeth are the cutting ones; what are
called the stomach and eye-teeth are the tearing ones; and
the large back teeth are shaped for grinding. It will be
observed that the tearing teeth, as they have not very sharp
points and are no longer than the other teeth, have but
little power when compared with the long and sharp tearing
teeth of a carnivorous animal, as seen in Fig. 47. As 1lanll
can use instruments to cut his food in pieces, he does not
need so much power in his teeth as carnivorous animals
have. Allowance should be made for this in estimating
the amount of carnivorous adaptation in man.
O1T. Substitutes for Teeth.-There are a few of
the Mammalia that have no teeth. This is the case with
the common whale. In his case, instead of teeth, there
hang down from the upper jaw, as represented in Fig. 51,
FIG. 52.         FIG. 51.
WHALEBONE.    SKULL OF WHALE.
plates of a fibrous substance, called whalebone, which have
their fibres separated at their free extremities, so as to make
a sort of sieve. This is intended to catch the small animals, which the whale devours in great numbers.
To obtain these it swims with its mouth opened and thus
fills it with water. The water is strained through the




DIGESTION.                    85
fibrous whalebone, and the small animals retained. Birds,
too, have no teeth. Their place is supplied in part by a
contrivance in the stomach itself, for the breaking up of the
food. This will be described in another part of this chapter.
108. Salivary Glands.-While the food is cut and
ground by the teeth, it is at the same time thoroughly
moistened by the saliva, which is poured forth from certain
glands ill the neighborhood. There are three pairs of these
glands. Fig. 53 shows the glands on one side. The parotid
FIG. 53.
SALIVARY GLANDS.
gland, 1, is the largest. This is situated in front of the
lower part of the ear. It is the seat of the swelling in the
disease called mumps. Its duct, 2, passes over one large
muscle and between the fibres of another, and pours its
contents into the mouth opposite the second small grinder
of the upper jaw. If you press on this part of the cheek,
you can feel in the mouth an increased flow of the saliva.
The submaxillary gland, 3, is situated inside the lower
jaw at its lower part; and its duct, 4, opens into the
mouth at the side of the froenum of the tongue. The sublingual gland, 5, lies under the tongue, and discharges its
secretion by ducts at the side of that organ.




86           PHYSIOLOGY AND HYGIENE.
109. Action  of the Salivary Glands.-These
glands are especially active when we are eating; and it is commonly estimated that, during an ordinary meal, about eight
ounces of saliva are poured into the mouth. This large
amount is wanted to moisten the food thoroughly before it is
swallowed; and it also has some chemical influence in preparing the food for the action of the gastric juice in the
stomach. More saliva than usual is needed, also, when we are
speaking, in order to keep the parts properly lubricated, for
the passage of the air in and out during speaking dries up
the saliva by evaporation. And, accordingly, the motion of
the parts at such times stimulates a larger flow, just as pressure on the cheek will do it, as before remarked. This result
is favored by the course of the duct of the parotid gland,
which, as you have seen, passes over one large muscle, and
then through the body of another.
Chewing excites an increased flow of the saliva; and the
tobacco chewer does a real injury to the salivary glands, by
keeping them  constantly in excessive operation, to say
nothing of the ruinous effects of this drug on the system at
large.
110. Flow  of Saliva affected by Sympathy.
-It is supposed that, besides the mere mechanical stimulus
of the motion of the parts, the stimulus of sympathy is also
concerned in exciting these glands to increased action. The
glands are supposed to be affected in this way by the stimulation of the food on the surface of the mouth, about the
orifices of their ducts. That sympathy does have an influence
on their secretion is evident from the very familiar fact,
that the thought of food will often, as it is expressed, cause
the mouth to water.
1 ll.  Difference  ini  the  Character of  the
Saliva. — The fact that these glands do not all secrete the
same kind of fluid, has led to an interesting discovery in
relation to them. The submaxillary glands secrete a viscid
fluid, while that which is poured forth by the parotid and
sublingual glands is perfectly limpid. Now it has been
found, by various observations and experiments on animals,




DIGESTION. 7, 
that while the teeth are cutting and grinding the food, and
the parotid and sublingual glands are pouring out the saliva
to moisten it, no secretion comes from the submaxillary
glands.
But these glands pour out their viscid fluid the moment
that the tongue thrusts the food back towards the throat,
in the beginning of the act of swallowing. The special object of this viscid fluid is then to cover the food, so that it
may, to use a common expression, slip down easily into
the stomach; and it has nothing to do with the moistening
of the food, this being the particular office of the other two
pairs of glands.
112. Swallowing. —When the food has been ground
by the teeth, and moistened by the saliva, it is carried by
the act of swallowing into the stomach. This act, simple
as it may appear to you, is a very complicated one, and is
performed by the conjoined and agreeing action of many
different muscles. The food is first thrust back over the
surface of the tongue into the large cavity in the back of
the throat, called the pharynx.  Into the pharynx two
tubes open-the eosophagus or gullet, which is the passage
into the stomach, and the trachea* or windpipe, the passage
to the lungs.
As the cesophagus lies behind the trachea, the food, in
passing to it, must go directly over the opening into the
trachea. To prevent the food from entering the trachea,
therefore, there is a little tongue-shaped body, called the
epiglottis, extending back from the root of the tongue, and
acting as a lid to the glottis, the opening into the trachea.
Wheii we are swallowing, this lid is shut down; but it is
always raised up when we are breathing or speaking. When
we swallow, not only does the lid shut down, but the larynx
rises to meet the lid, as you may readily perceive, if you
place your fingers upon what is called Adam's apple while
* This term is sometimes used, as here, to mean the whole of the
tube conducting to the lungs, including the larynx, which is at the top
of this tube, and sometimes it is restricted to that part of the tube
which is below the larynx.




88            PHYSIOLOGY AND HYGIENE.
you are swallowing. In Fig. 54, you have a side view of the
parts engaged in swallowing, as if the head were divided
ilto two halves by a vertical section. At i, is the cavity of
the nostril; at h, are the lips; a is the divided bone of the
chin; b is the tongue, between which and the spinal column,
is f, the large cavity of the pharynx. In front of this cavity
hangs the palate, g, as a door or valve, to direct the air coming from the trachea, d, either through the mouth or through
FIG. 54.
VERTICAL SECTION OF THE THROAT.
the nostrils, according to its position. The esophagus, e, is
behind the trachea, and the epiglottis, c, shuts down when we
swallow, to let the food pass over it into the oesophagus. In'
Fig. 55, you have a view of the same parts from the rear.
At 1, is a section of the bones at the base of the skull; 3, 3,
are the cavities of the nostrils; 2, 2, the walls of the pharynx
spread apart; 5, the pendulous palate; 6, 6, the arch of the
palate; 8, the root of the tongue; 9, the epiglottis, and 10, the
glottis, or opening into the larynx; 13, the (esophagus; 14,
the trachea.  The pharynx, you see, is a funnel-shaped
cavity, tapering down to the cesophagus, the opening of
which is considerably below the opening of the trachea.




DIGESTION.                     89
113. ActionL of the CFso-              FIG. 55.
phagus.- -When the food enters the oesophagus, it is carried.
through that tube into the stomach by the action of muscular            v      I -2
fibres. These fibres are represented
in Fig. 56. The circular fibres are
seen at a and b. These are removed at c, so as to show  the
longitudinal fibres. It is by the
consent of action between these
different sets of fibres that the
food is propelled through the
esophagus.
As the food descends, a dilatation of the circular fibres must
VIEW OF TIIE THROAT FROM
everywhere take place where the  BVIEW OF TE THROAT FROM.
food is, and a contraction of them
immediately behind it-the dilatation mak-      FIG. 56.
ing the way for it, and the contraction foreing it along. And in animals that chew the
cud, these actions force the food from  the
stomaech into the mouth.                    a
114. The Gastric Juice.-The food
being introduced into the stomach, is here
subjected to the action of the gastric juice.
This is a peculiar fluid, somewhat acid in
its character, which is secreted by very minute follicles, or bag-like cavities, situated in
the substance of the mucous membrane.
Ordinarily there is none of this fluid in the
stomach when no food is there. Dr. Beaumont made some very interesting observations on this, as well as many other points,
in the remarkable case which fell under his
care. His patient, Alexis St. Martin, had
received a wound in his left side by the
bursting  of a gun. The wound, which   LAID OPENU




90            PHYSIOLOGY AND HYGIENE.
opened into the stomach, never entirely closed, but an
orifice remained, through which Dr. Beaumont could look
into,and observe what was going on in the stomach.
He describes the mucous membrane, in its healthy state,
as having a velvet-like appearance, with a pale pink color,
and as being covered with a very thin, transparent, viscid
mucus. On introducing some food, or irritating the mucous
membrane mechanically, he saw, by the aid of a magnifying glass, "innumerable lucid points" projecting on the
surface, and from these exuded a pure, limpid, colorless
fluid. These points were the follicles which secrete the
gastric juice, rendered turgescent by being stimulated to
action.
115. Quantity of Gastric Juice.-The amount
of gastric juice secreted is generally about in proportion to
the amount of food which the necessities of the system require. W\Xhen the quantity of food taken is very much
more than is required, there can not be a sufficient amount
of gastric juice secreted to digest all of it; and some
must therefore remain undigested, and will prove a source
of irritation to the stomach. If the amount. of food taken
from  day to day is not very excessive, but is only a
little above the proper quantity, there will be enough
gastric juice made to digest it; but the daily overtaxing
of the powers of the secreting follicles will, after a while,
produce derangement of the stomach, and perhaps permanent disease.
116. Eunction of the Gastric Juice.-The action of the gastric juice upon the food is of a chemical
nature. In order that it may act effectually on all portions
of the contents of the stomach, this organ is kept in constant motion by the fibres of its muscular coat. These
fibres are so arranged that, as they contract and relax, they
keep up a sort of churning of the contents, and thus effect
a thorough mixture of them with the gastric juice. In
Fig. 57, you see these fibres represented. At 1, is the opening of the cesophagus into the stomach; and at 4, is the part
which opens into the intestine. The fibres are in different




DIGESTION.                     91
layers, running in different directions. The outer peritoneal
coat, 5, 5, is dissected off and turned back, showing some of
FIG. 5 7.
MUSCULAR FIBRES OF THE STOMACH.
the fibres that run lengthwise of the organ, 6; and some
that run crosswise, 7; and others, 8, that run obliquely.
You can readily see what effect the contraction of these
different fibres will have on the shape of the stomach. The
contraction of the longitudinal fibres, 6, brings the large,
bulging end of the stomach, 2, and the small end, 3, nearer
together.  The transverse fibres, when they contract, diminish the capacity of the stomach transversely. And the
oblique fibres modify these two motions by their oblique
action.
117. Action of the Prylorus.-By the combined
chemical and mechanical action of the stomach, its contents
are, after a little time-in three or four hours-reduced to
a uniform  greyish, semi-fluid mass, called chyme. While
tili3 process has been going on, the communication between
the stomach and the intestines has been entirely closed by
a valve, called the pylorus. This is represented at 5, in
Fig. 58, which presents a view of the inside of the stomach.
This valve is made of a fold of both the mucous and the
muscular coats of the stomach. It is a very faithful sen



9J2           PHYSIOLOGY AND HYGIENE.
tinel, as is indicated by its name, which is derived from two
Greek words, signifying to guard the gate. It will not
ordinarily permit any undigested food to pass it.
While the process of digestion is going on, the motions
produced by the muscular fibres cause the contents to move
about, and of course they are thrown against the pylorus,
as well as any other part of the stomach. But the valve
remains closed, until some portion comes against it that is
thoroughly changed to chyme, and is therefore fit to pass
on into the intestine. It opens to let this pass.
FIG. 58.
INTERIOR OF THE STOMACH AND SMALL INTESTINE.
Toward the conclusion of the digestion of a meal, small
quantities pass at first, and after a while, the contents pass
quite rapidly through the valve.
Although this sentinel-valve thus performs its duty so
faithfully in relation to nutritive substances, it seems to let
other substances pass very readily. Solid substances, swallowed by mistake, as buttons, pieces of money, the pits and
skins of various fruits, often pass the valve without any
trouble. The valve seems to be on duty as a sentinel only
during the process of digestion; and, if the attempt to go
through with this process prove unavailing, the pylorus,




DIGESTION.                    93
though it let such hard substances as have been mentioned
pass without difficulty, resists the passage of the undigested
food, sometimes causing much uneasiness, and even perhaps
pain, by so doing. In such a case, either the valve after a
time gives over its resistance, or, holding out, the action of
the stomach is reversed, and the offending matter is thrown
off by vomiting.
118. Bad Habits in  Eating.-The process of
digestion, as it has been described, is a regular process, requiring a certain average period of time for its completion.
If, during the progress of it, fresh food be introduced, its
regularity is broken in upon, and the process stops. Then,
too, if, immediately after the completion of the process, a
new supply of food be taken, harm is done, because the organ
has not its needed interval of rest. For these reasons, the
practice of eating between meals is a very injurious one.
Eating fast does harm, because,-lst, the food is not
sufficiently ground; 2d, it is not mixed thoroughly with
the saliva; and, 3d, more food is taken than would be sufficient to satisfy the hunger if the individual ate slowly, and,
therefore, more than can be easily digested. Great variety
in food stimulates the appetite unduly, and too much is
consequently eaten. Moderate exercise, if it be not violent,
facilitates digestion. An experiment was once tried upon
two dogs, which was thought to prove that exercise hinders
digestion.
Two dogs were fed freely, and while one was left to lie
still, the other was made to run about violently. Both dogs
were killed after an hour or two, and it was found that,
while digestion had gone on thoroughly in the dog that was
allowed to remain quiet, in the other the food was undigested. This only proved that violent exercise, taken immediately after eating, impedes digestion.  It has been
found, on the other hand, that light exercise promotes the
process; and daily experience, among laborers, shows, that
even very strong exercise does not interfere with it, if a
little interval of rest be allowed, so that the process may be
fairly begun.




39-           PHYSIOLOGY AND HYGIEN'E.
119. Cause of Hunger.-The sensation of hunger
has been attributed to various causes,-as the empty state
of the stomach, the presence of the gastric juice irritating
the mucous membrane, &c. It cannot arise from emptiness; for, if so, it should occur sooner than it does after
eating, and should not be absent in disease, as it often is
for a long time, when the stomach is almost entirely empty.
It can not arise from irritation by the gastric juice; for
it was found by Dr. Beaumont, in his observations of the
stomach of Alexis St. Martin, that this fluid is not secreted
till after food is introduced into the stomach. The cause
of hunger is evidently in the state of the system. It is a
state of want.
Nutriment is needed by the formative vessels, the builders
and repairers of the system, which make their wants known
as distinctly as the bricklayer does, when he calls for more
brick and mortar. - Through the nerves, an impression is
communicated to the stomach, and the sensation of hunger
is the result.
That the sensation results from impressions made upon
the nerves of the stomach is evident from the fact that it
can be temporarily relieved by putting indigestible substances into the stomach. These produce the effect by
causing other sensations, which take the place, for the time
being, of the sensation of hunger. After, however, the momentary effect is over, the sensation of hunger returns in
its full force. The cause, then, of the sensation is in the
system at large, but its seat seems to be in the stomach.
If disease has impoverished the system, so soon as the
stomach is in a condition to respond to the call of the formative vessels that set themselves at work to repair the
waste, the hunger is often excessive. In order to have the
sensation of hunger, not only must there be a want in the
system at large, but the stomach must be in a state fitted to
receive the notice of this want. And fortunately it is seldom
in this state except when in a condition to do its work. If
it were otherwise, food would often be introduced when it
could not be digested.




DIGESTION.                    95
1o0. Sensations of Hffinger Affected by the
3ltld. -Mental impressions sometimes incapacitate the
brain for receiving the notice of the want of the system.
In this case, the mental impression in the brain counteracts
the impression conveyed from the stomach, and so neutralizes the sensation of hunger. Thus, grief often destroys
the appetite for food.
121. Thirst. —Nearly the same remarks can be made
in relation to thirst, that have been made in regard to hunger.
This sensation seems to have its seat in the fauces or throat.
Its cause is evidently not there; for the mouth and throat
may be very dry, and yet there may be little or no thirst;
while, on the other hand, there may be much thirst, although
the mouth and throat are moist. The cause of the sensation is, like the cause of hunger, in the system at large; and,
therefore, no local cause, producing a dryness of the throat,
can cause thirst independent of a general condition.
122. Arrangerment of the Orgatis of Digestion.-Fig. 59 exhibits the organs of digestion as they present themselves in a front view, except that they are somewhat
separated from each other, insteadl of being as closely packed,
as they are in the abdomen. The large end of the stomach
lies to the left side,* and at this end is the spleen. The pancreas is behind the right end of the stomach. Above the
stomach, and mostly to the right side, is the largest organ
in the abdomen, the liver. In the Figure, it is represented
as turned upward. The stomach is directly connected with
the small intestines at the pylorus. At the end of this long
and winding tract begin the large intestines. The duct of
the gall bladder, and that of the pancreas, open into the
swall intestine at its beginning.
The office of the spleen has not yet been ascertained.
Neither has that of the worm-like appendage at the beginning of the large intestines. The omenturn, or caul, which
hangs like a curtain from the front part of the stomach down
in front of the intestines, is not represented in the Figure.
* As this is a front view, the right side of the Figure is the left side
of the body.




96             PHYSIOLOGY AND HYGIENE.
123. The Mesentery.-There is one arrangement in
the abdomen which must not pass unnoticed. If the intesFIG. 59.
v'I~~~~~.  t ~'
SPLEEN.
GALL BLADDIr).......
LARGE INTESLARGE INTESTINES.............  SMALL INTESI   ~~~~~~~~~TINES.
BEGINNING OF
LARGE INTESTINES.
WORM-LIKE AP --------—'lPENDAGE.
SMALL INTESTINES.
DIGESTIVE ORGANS.
tines were left to lie loose in this cavity, they would constantly be subject to displacement and injury. They are
therefore fastened to the backbone by an arrangement.which secures them from any such accident, and at the same
time allows of a sufficiently free motion of different parts
of this tube. It is this. The intestinal tube makes the
margin of a broad sheet of membrane, the other edge of
which is gathered up and fastened to the spinal column.




DIGESTION.                     97
The device is like a ruffle with a puffed edging. The membranous sheet is called the mesentery.  As the intestinal
tube, the puffed edging, is much longer than the ruffle
itself, the mesentery, it is gathered on to the ruffle, as a
seamstress would express it. Now, the mesentery is composed of two folds of the peritoneum, the smooth, shining,
ou'ter covering of the intestines.
The arrangement will be easily understood by the diagram
in Fig. 60, which represents a section of the intestine with
the mesentery. The cavity of
the intestine, a, is lined by the        FIG. 60.
mucous membrane represented
by the inner circle. Next comes                      C
the muscular coat, and next the
peritoneal, the outer, which, in-   O
stead of making a circular tube,
as the other two coats do, passes
backward on both sides of the
intestine, to make the mesentery,   PLAN OF THE MESENTERY.
b. After being attached to the
spine by means of cellular tissue, it is reflected off to pass
over other portions of the intestine, as seen at c, c.
Between the two layers of the peritoneal membrane, in
the mesentery, is considerable space, as seen at b. This
space is filled up with blood-vessels, nerves, and lacteals with
their small glands, soon to be described, all bound together
by the common packing material of the body, the cellular
tissue. You see, therefore, that the mesentery subserves
more than one use. Besides fastening the whole tract of
the intestinal canal to the spine, so as to guard it against
accident, it acts as a secure medium for the passage of
the blood-vessels and nerves to the intestines. And, besides, it contains the little tubes which convey all the
nutriment into the blood for the growth and repair of the
body.
124. Chymne, Cjhyle.-The chyme, as it passes into
the small intestine from the stomach, has mingled with it
the bile and the secretion of the pancreas. These are poured




98            PHYSIOLOGY AND HYGIENE.
into the intestine at the point represented at 6, in Fig. 58.
These secretions undoubtedly have some agency in separating
the nutritious part of the chyme which is afterwards absorbed by the innumerable small vessels, called lacteals,
situated in the mucous membrane. This nutritious part
of the chyme is a milky fluid, called the chyle. The lacteals
which absorb it are little tubes or ducts. These enter
certain glands, called the mesenteric glands, and then pass
on, as seen in Fig. 61, to pour their contents into the
thoracic duct.
FIG. 61.
0
OF
SECTION OF INTESTINE SHOWING THlE LACTEALS.
125.: Tloracic Duct.-This duct, which is about the
size of a common quill, running up on the left side of the




DIGESTION.                    99
aorta, the great artery of the heart, pours its contents into
the junction of two veins at the top of the chest. The
mode of the joining of this duct with these veins is calculated to facilitate the discharge of the chyle. As the two
large currents in the veins, v and v, in Fig. 62, unite,
FIG. 62.
JUNCTION OF THE THORACIC DUCT WITH THE VEINS.
there is created, by the forward motion of these currents,
a tendency to a vacuum at the angle at which they meet,
the point where the thoracic duct, T, D, opens.  There
is, therefore, a suction power, as it is termed, exerted upon
the fluid in this duct. The chyle, thus mingling with the
blood, becomes a part of it.
126. Digestive Arpparatus iti, Different Anirnals.-The digestive apparatus varies much in different
animals, according to the kinds of food on which they live.
As a general rule, the more the food differs in character
from the animal itself, the more complicated and extensive
is the apparatus. Thus, the herbivorous animals have a
very long alimentary canal, and the beginning of it, the
stomach, is a complicated organ. While, on the other hand,
in the carnivora, the flesh which they eat being very much
like their own flesh, and, therefore, not requiring a very complex process of assimilation, the stomach is a simple organ,
and the alimentary canal is very short. In the sheep, for
example, the alimentary canal is about twenty-eight times




100           PHYSIOLOGY AND HYGIENE.
the length of the body, but that of the lion only three times
his length. In man, who lives on a mixed diet, the alimentary
canal is about six times the length of the body.
12T. Digestion in the Sheep.-The stomach is
more complicated in animals that chew the cud than in
any others. It has four distinct cavities, and a singular
mechanism is called into operation in managing the food as
it passes through them. In Fig. 63, you have a representation of the stomachs of the sheep, as they appear exteriorly.
As the animal crops the food, it passes into the first stomach,
which is little else than a great reservoir to hold and soak
it. Then it passes into the second stomach, from which it is
returned into the mouth. On being swallowed again, it passes
from  the cesophagus into the third, and thence into the
fourth stomach. In Fig. 64, you see the interior of these four
stomachs; and by the aid of this illustration I will describe
the process of digestion in the sheep more particularly. You
see the very large first stomach, or paunch, in which the
food is accumulated. It is not yet masticated thoroughly,
for the animal has swallowed it as fast as he could, and
packed it away in this reservoir. From this it is passed, in
small quantities at a time, into the second stomach, the
honeycomnb, so called from the peculiar network of folds in
it. Here the food is rolled up into balls by the action of the
muscular fibres in this network. Each ball of food is passed
ulp through the cesophagus into the mouth, where it is
chewed and thoroughly mixed with the saliva.
Then it is swallowed, and, as it passes from the cesophagus, instead of going into the paunch, as it did when swallowed the first time, it is directed through the groove seen
in the Figure into the third stomach, the manyplies. This
has many folds, like the leaves of a book, so that the food is
exposed to a large surface in this cavity. It passes from this
to the fourth stomach, the reed. Here, and here only, it is
acted upon by the gastric juice. This, therefore, is the true
stomach, all the other cavities furnishing only preparatory
steps to the true process of digestion. It is from this fourth
stomach that what is called the rennet is taken.




DIGESTION.                         101
When fluid matter is swallowed, it goes directly into
the second stomach, and not into the first, the paunch; so
that, in the case of the sheep, the drink goes one way and
FIG. 63.
(ESOPHAGUS.
ORIFICE OF
STOMACH.   --- ------
D STOMACH..
INTESTINE.
O       m   QQ          e
STOMACHS OF THE SHEEP.
FIG. 64.
(EESOPHAGUS.-_ —-..
GROOVE.' -
MANYPLIES. -
REED. -...
INTESTINE.
INTERIOR OF THE STOMACHS OF THE SHEEP.




102           PHYSIOLOGY ANSD HYGIENE.
the solid food another. And, what is still more singular,
while the animal is a suckling, the milk passes into the
fourth stomach through only the third, which has its folds
so closed together as to form a mere tube to conduct it to its
destination.  And the great paunch and the honeycomb
are wholly useless until the animal begins to crop its food
for itself.
128. Digestive Apparatus in Birds. —In birds,
the digestive apparatus is necessarily very peculiar, from the
fact that they do not masticate their food. They have, on
this account, an arrangement in the stomach itself for
grinding the food. In the cavity called the gizzard are two
opposing surfaces, made very hard, so that by rubbing
together they bruise the grains; and while the food is thus
ground, as between two millstones, the gastric juice is
poured down upon it from above. This arrangement is
seen in Fig. 65, which represents the digestive apparatus in
the turkey laid open.
At b is the gizzard, showing the two hard surfaces, which
are rubbed together by the stout muscles that make the
great bulk of the organ. Above, at a, are the glands which
pour forth the gastric juice. And above this part of the
stomach there is, in all grain-eating birds, a large sac bulging out from the  esophagus, called the crop, which is a
reservoir for the food, just as the paunch is in the ruminating animals. In those birds that live on flesh or fish there
is no such grinding apparatus. The walls of the stomach
are quite thin, and it presents no hard surfaces.
The kind of food, the mode of life, and the purpose
which the animal is designed to fulfill, are the circumstances which govern the variations of the digestive apparatus. The proportion which the digestive apparatus bears
to other parts varies very much; and in some of the
lower orders of animals, the body seems to be all stomach.
In such cases, the only appendages are those which seize
the food and direct it into the orifice of this organ. This
is the case with the hydra, represented in Fig. 1. And,
what is very singular, the outside of the body of this animal




DIGESTION.                   103
is just as capable of acting as a stomach as its inside. For
when the creature is turned inside out, it will go on catching and digesting its food as usuaL
FIG. 65.
STOMACH OF THIE TURKEY.
But, wide as the variations are in the digestive apparatus of animals, the same object is aimed at in all-the
assimilation of nutrient substances to the animal, to produce a material from which its structure can. be built and
kept in repair. There is, therefore, much that is common
to them all in the modes in which this object is accomplished. And even the analogy which exists between the




104             PHYSIOLOGY AND HYGIENE.
animal and plant, in regard to assimilation, does not relate
to the fact alone, but in some measure to the modes in
which the process is effected.
Not yet understood
by the pupil.
5 5
s;'.. 
Co  
E-4
OrD




CHAPTER VIII.
CIRCULATION  OF  THE  BLOOD.
129. Apparatus of the Circutlation.-In the
last chapter was described the manner in which the blood
is made from the food. The blood, thus prepared, is circulated in every part of the body, that it may be used for the
purposes of construction and repair. The apparatus by
which this is done acts, as we have seen, as the common
carrier of the material which is used everywhere in the
body by the laborers, the builders, to whom it is thus
brought.
This apparatus consists of several parts-a great central
organ, the heart; the arteries, the tubes by which the blood
is conducted to all parts of the body; the veins, other
tubes, which bring the blood back to the heart; and the
capillaries, a network of exceedingly minute vessels, through
which the blood passes as it goes from the terminations of
the arteries into the beginnings of the veins.
The blood goes from the heart through a large artery,
called the aorta, which sends forth branches; and these
divide and subdivide, so that the extreme arteries, through
which the blood flows into the capillary network, are very
minute. And the veins which receive the blood from this
network to carry it back to the heart, are equally minute;
but joining together, as they proceed toward the heart,
they are at length all united into two great venous trunks,
one from above and the other from below, which pour
their contents into this organ.
The capillaries, taking their name from the Latin word
capilla, a hair, are so small that they can not be seen
by the naked eye. In any small cut, the blood which oozes
out comes from multitudes of these vessels. They serve to
hold the blood, while the formative cells, that construct




106           lHYSIOLOGY AND) HYGIENE.
and repair the body, may select such materials as they need
for their purposes.
130. The Kleart.-The heart is a great central forcing and suction pump, in the midst of this circulating apparatus.  When it contracts, it forces the blood out through
the aorta and its branching arteries into all parts of the
system. And when it enlarges or dilates itself, it, by suction, as it is termed, fills itself with the blood returning from
the system through the veins.
131. The Arteries.-The arteries differ from  the
veins in their structure and arrangement. The arteries are
firm though elastic tubes, while the veins are lax in their
structure.  The object of the difference is obvious. As the
blood is forced into the arteries by the powerful action of
the heart, it is necessary that they should be strong and
firm.
When a dilatation does occur in an artery, it is called an
aneurisnz. But the arteries need to be firm, not only for
the sake of security against rupture, but also that the force
of the heart may propel the blood to the extremities of the
arterial system. If the arteries were lax tubes, like the
veins, the impulse would soon be lost in the yielding tubes,
and the blood would move very sluggishly in the small
arteries at a distance from the heart.
What we call the pulse, is caused by this impulse. If the
arteries were lax tubes, the pulse would not be felt at any
great distance from the heart. Instead of being distinct,
as it now is, with every beat of the heart almost to the very
extremities of the arterial system, it would be rendered confused by the yielding of the tubes, even quite near the heart,
and at a distance from that organ it would be entirely lost.
Besides the firmness of the arteries, there is another circumstance which favors the free flow of blood through
them. It is their mode of division. The branch of an
artery leaves the main trunk at a sharp angle, making thus
only a slight deviation from the direction of the main current; while, on the other hand, in the veins where the current flows in an opposite direction, the branch unites with




' THIE CIRCULATION.               107
the trunk at nearly a right angle. This difference is represented in Fig. 66; 1 being the artery, and 2 the vein.
FIG. 66.
1          2
ARTERY AND VEIN.
132. The Veins.-The venous system has a much
greater capacity than the arterial. That is, all the veins of
the body are together capable of holding more blood than
all the arteries are. And the blood moves very rapidly and
directly from the heart through the arteries, but comes
back to the heart quite slowly through the veins. Every
thing is arranged to promote this rapid circulation through
the arteries, while the venous system is calculated for a slow
but sure progress of the blood back to the heart.
To secure this, valves, made of folds of the inner lining
of the veins, are so arranged as to prevent the blood from
flowing in the wrong direction. Fig. 67 represents a vein
cut open so as to show these valves. A shows the valves as
they ippear when the vein is laid open and spread out; B,
as they appear when the vein is simply laid open; and C
represents the appearance of the outside of the vein where
there are valves. The need wvhich there is of this help to
the circulation through the veins is obvious. The suction
power of the heart is not competent, unaided, to move the




108          PHYSIOLOGY AND HYGIENE.
blood throughout all the lax venous system. These pocketlike valves, therefore, are made in the veins to assist the
circulation there.
FIG. 67.
A         B     C
VALVES IN THE VEINS.
Every movement of the muscles or other parts about the
veins tends to keep the blood in motion, and the valves
serve to prevent this motion from taking the wrong direction. The difference in force and velocity with which
the blood moves in the arteries and in the veins, is made
manifest when they are wounded. The blood flows from a
wounded vein in a slow and steady stream. From an artery
it flows rapidly, showing the impulse of the heart in its jets,
which correspond exactly with the pulse. Hence comes the
danger in wounding an artery, while the wound of a vein is
ordinarily attended with no danger.
133. Protection  to the Arter'ies.-Accordingly,
we find the arteries so placed, that they can not easily be
wounded, while many of the veins are quite freely exposed.
The arteries are deeply seated, except in some few cases
where this is impossible; but the veins are often superficially situated. You can see this, for example, in the bend
of the arm. Some large veins appear there just under the
skin, while the artery which supplies the arm is embedded
among the muscles and tendons. In every part of the body,
the most secure spot is chosen for an artery. Thus, at the
knee-joint, the artery, instead of running over the surface




THE CIRCULATION.                109
of bone, where it would be liable to be wounded, lies deep
in the ham at the rear of the joint. The same is true of
the elbow-joint, just alluded to, and of other parts of the
body. Although there are arteries everywhere, they are uniformly so deeply seated, that it is only in a few localities
that you can readily find one. You can feel one pulsating at
the wrist, and another on the temple.
134. Mode of Stopping a Bleeding Artery.It will be proper here to give some practical instruction,
in regard to stopping the flow of blood from a wounded
artery; as many lives have been lost from the ignorance of
bystanders when such accidents have happened. Enveloping the part in cloths, which is so commonly done at such
times, does no good, but only serves to catch and conceal
the blood as it flows.
Pressure upon the artery, on that side of the wound
which is toward the heart, will of course interrupt the supply
of blood from this organ to the wound. Firm pressure with
the thumb will do it. But the pressure must be made at the
right point, that is, directly upon the artery. You may not,
in all cases, press upon the right spot at once. If you do
not, the blood will continue to flow. In this case press at
different points, until you find the point at which you see
that pressure stops the flow of blood from the wound. But
you may not be able to find the right spot. If you can not,
you can tie a slip of strong cloth or a handkerchief around
the limb above the wound, and twist a stick in it until the
bleeding stops. In one or the other of these ways, you can
prevent the loss of blood until the surgeon arrives to take
charge of the case.
135. Co mnn rnication between Arteries.-Although there is no such free communication between
arteries as exists between the capillaries, there is some
amount of communication, and particularly in certain parts
of the body. And it is well that it is so, for it sometimes
helps the surgeon to save a limb, when he could not do it
if there were no communication.
An artery has three coats, one of which is a strong fibrous




110          PHYSIOLOGY AND HYGIENE.
one. When this is thinned or ruptured, the other two coats
bulge out, forming a pulsating tumor.  And, as the blood
is constantly pumped into this by the force of the heart, it
enlarges, and at length it may burst, and the life of the
patient be destroyed by the loss of blood. When an aneurism formed in a limb, as for example in the ham, the
surgeon, in former times, used to save the life of the patient
by amputating the limb above the aneurism. Putting a ligature round the artery above the aneurism would of course
stop the flow of blood into it; but it was supposed that the
limb would die, in that case, from the want of a proper
supply of blood.
But it was found, at length, that this was not so; and
surgeons now, in such cases, cure the disease, and save the
limb too, by tying the artery. Immediately after the operation the limb is cold, and there is plainly very little circulation in it. But in a few hours the circulation becomes free,
and in a little time it is as well established as ever. This
is effected by the communications which exist between the
branches which go off from the artery above the aneurism,
and those which go off below it. It is obvious, however,
that this would not be thoroughly effected if no change
took place in the size of the communicating arteries. But
this change does occur. Some of them become enlarged to
meet the necessity of the case.
This is a most interesting fact; and so is also the factthat these communications between branches of arteries are
very common in the neighborhood of those places in the
body where aneurism, from strains produced by violent and
sudden motion, is peculiarly apt to appear. This same provision avails, of course, when aneurism is cured by pressure
made upon the artery above it, a measure which modern
surgery has found in many cases to be as effectual as tying
the artery.
136. Action of the Hleart Illustrated.-There
have been great differences of opinion among physiologists
in regard to the proportionate amounts of agency that the
different parts of the apparatus have in carrying on the cir



THE CIRCULATION.                  11I
culation. The heart manifestly exerts the chief agency,
both by its forcing and its suction power. You can get a
clear idea of the manner in which it exerts these two forces
in this way: Fill a ball of india-rubber, to which a tube is
attached, with water, and inmerse the tube in a vessel of
water. If you press the sides of the ball together, some of
the water is forced out into the vessel. This represents the
contraction of the heart. If, now, you allow the ball by its
elasticity to resume its round shape, the water rushes into
it from the vessel. This represents the dilatation of the
heart.
The dilatation of the ball results from its elasticity; and
it is supposed by some that the dilatation of the heart
results from the same cause, its contraction alone being
produced by muscular action.  Whether this is so or not,
the dilatation is an active one, and the blood rushes into the
heart from the veins by suction, as it is termed. The dilatation is so active that, as has been shown by experiments
on animals, even a great amount of pressure is not able to
prevent its taking place.
13,?. Actioun of the Capillaries.-But, great as
the agency of the heart is, it is not true that it is the only
moving power, and that the arteries and veins are mere
passive conducting tubes. There are various phenomena
which show that the arteries, the capillaries, and even the
lax veins, exert a considerable agency in circulating the
blood. We will merely allude to some of these phenomena.
Determinations of biood to particular parts show that
the blood-vessels have an active agency in the circulation.
In inflammation of any part, there is an increased activity
of the particular portion of the circulating apparatus supplying that part. In the act of blushing, there is a local
activity of the circulation somewhat independent of the
heart. This is also true of the circumscribed flush of
hectic.
138. Circulation  in  the Liver.-There is one
portion of the circulation in which the active agency of
the capillaries is especially manifest. The veins, receiving




112           PHYSIOLOGY AND HYGIENE.
the blood from all parts of the body, at length are all
united into two veins, which empty their contents into the
heart. But there is a very remarkable exception to this.
The veins which collect the blood from the viscera in the
abdomen unite in one large trunk, called the vena portre;
and this, instead of pouring its contents into the large vein
that goes up to the heart, divides, like an artery, into
branches, which take all this blood to the liver for the
manufacture of bile. Fig. 68 represents this circulation
of the vena portre. 1, 1, are the veins coming from  the
intestines; 2 is the trunk of the vena portae; and 3, 3, are
branches of it distributed in the liver.
FIG. 63.
CIRCULATION OF VENOUS BLOOD IN THE LIVER.
There must be, in this case, some propelling power in
the capillaries, and some, also, in the veins. If there
were not, another subordinate heart would obviously be
needed in the vena portae, to pump up the blood from all
the veins of the abdominal viscera, and then to send it
through all its branches into the capillaries of the liver.




THE CIRCULATION.                113
139. Why the Veins are Ftll and the Arteries
Empty after Death. —The veins have a less active
agency in the circulation than any of the other parts of
the apparatus. It is for this reason that commonly after
death the veins are found quite full of blood, while the
arteries are nearly empty. The apparatus of the circulation may be regarded as forming a circle of organs in this
order —the heart, the arteries, the capillaries, and the veins.
The blood is constantly going the rounds of this circle.
It is plain that, as the apparatus is about to stop, there
must be an accumulation in the weakest, least active, and
most relaxed of this circle of organs. The arteries and
capillaries force the blood into the veins to the last moment
of life. This effect probably extends no further than the
smaller veins; but the heart, by its active dilatation, draws
the blood from them into the larger veins. And as these
two forces, at the two ends of the venous system, are at
work up to the last moment, the whole of this system is
filled with blood.
The fact that the large arteries are commonly found
nearly empty of blood after death, gave the ancients the
idea that air circulated in arteries, while blood circulated
in veins. Hence the name, artery, is derived from two
Greek words, signifying to hold air. And hence, also, by
long established custom in common language, the blood is
spoken of as running in our veins; and it would sound
strangely if, in common and especially in poetical language,
we should speak of it as running in our arteries also. Although there were from time to time some glimpses of the
true idea of the circulation, it was not really developed and
demonstrated till about two hundred and fifty years ago.
140. Changes wrought in the Blood.-A step
farther in the development of the plan of the circulation will
now be taken. We have seen that the office of the arteries is
to conduct the blood to the network of capillaries, and that
in the capillaries the blood has reached its place of destination where it is to be used. The formative cells, appended
to the capillaries, take from the blood what they need for




114           PHYSIOLOGY AND HYGIENE.
their various purposes, and at the same time there is added
to the blood refuse matter from the waste of the tissues.
The blood, then, is changed while it is in the capillaries.
In the arteries it was red; but, after passing through the
capillaries, it appears in the veins of a purple color. It
is also as much changed in other properties. It is no
longer fitted to nourish the body. It would even prove a
poison to any organ into whose capillaries it should flow.
If, for example, it, instead of bright arterial blood, should
be sent to the brain, that organ would cease to do its office;
insensibility would ensue, and life would soon be destroyed,
if the flow of red blood could not be established.
141. Charisge takes place in the Lungs.-This
purple blood, which comes back to the heart from the
capillaries by the veins, must, therefore, be in some way
changed to red blood, before it is again sent all over the
system through the arteries. This change is effected in
the lungs. As the purple blood returns to the heart, it is
sent by the heart to the lungs, in order to be exposed to the
air before it is sent again over the system. For this purpose
there is a second circulation, and the heart is made a double
organ; or rather, there are in effect two hearts for the two
circulations, for the two sides of the heart have no communication with each other. The apparatus for all this is
very complicated, but it can be made clear to you.
142. Course  of Circulation.-First examine diagram 69, which is intended to represent merely the course of
the circulation, without regard to proportionate size of parts,
or to minutiae in the arrangement of the apparatus. Let a
represent the right side of the heart, c the left side, b the
lungs, and d the general system of the body. The arrows
show the direction in which the blood flows. In all the
shaded part the blood is venous or purple, and in the part
not shaded it is arterial or red. We will now trace on
the Figure the course of the circulation. We will start at
a, the right side of the heart. The blood received here, of
a purple color, from the whole body by the veins, is sent by
the heart to b, the lungs. Here it changes to red blood,




THE CIRCULATION.                  115
and passes by veins back to the heart-but, observe, it is to
the left side of the heart, c. It is now sent by this left
half of the heart to all parts of the system, represented by
FIG. 69.
DIAGRAM SHOWING THE COURSE OF THE CIRCULATION.
d. Here, in the capillaries, it is changed to purple blood,
and goes back by veins to the right side of the heart, a, the
place where we started.
143. Two  Circulations anl Two IHearts.You see, then, that there are two separate circulati ns, one
through the general system, and the other through the
lungs alone. In both circulations the blood is sent from the
heart by arteries, and is brought back to it by veins. But
notice that, while in the general circulation the red blood
is in the arteries, and the purple in the veins, in the circulation through the lungs this is reversed-the red blood is in
the veins, and the purple is in the arteries. So, also, while
the change of the blood in the capillaries of the general
system is from red to purple, in the capillaries of the lungs
it is from purple to red.
144. Vaciles.-There are not only two sides or halves
of the heart, separated entirely from each other, but each of
these sides has two apartments, with valves or folding-doors
between them, so arranged that the blood can pass one
way through them, but not the other. There are also
valves at the beginning of the great artery of the heart, the
aorta. These are so arranged that the blood can go freely




116            PHYSIOLOGY AND HYGIENE.
out of the heart into the artery, but not a drop can get back
from  the artery into the heart. There are similar valves,
also, at the beginning of the great pulmonary artery by
which the purple blood is sent from the heart to the lungs.
In Fig. 70 is represented a section of the right side of
the heart, for the purpose of giving you an idea of the
relative size and position of the two apartments. The
auricle, a, so called because a part of it has some resemblance to an ear, receives the blood from the whole system by two large veins, b, b, called the
FIG. 70.     venme cavce.  From  the auricle it passes
a          into the ventricle, v, which by its contractions sends it to the lungs through
the pulmonary artery, f.  The valve between the auricle and ventricle is composed of three membranous sheets, which
-V  are held at their edges by small tendinous
cords, dc, just as a sail is held by the ropes
d          at its corners.  This valve permits the
SECTION OF THE   blood to pass from  the auricle into the
RIGHT SIDE OF
THE HEART.    ventricle; but when it attempts to pass
back from the ventricle to the auricle,
it pushes back the sheets of the valve until their edges meet
in the center, they being prevented from going too far back
by the tendinous cords.
There are also valves at e, the beginning of the pulmonary
artery, which allow the blood to pass through them into
the artery, but no blood can pass through them from the
artery back into the ventricle.
145.  Relation  between  the  Aitricles  andc
JTentricles.-The auricle and ventricle act in this way
in propelling the blood.  When the auricle contracts, the
ventricle dJilates* to receive the blood from the auricle. The
valves between them are open while this is taking place.
* This dilatation is an active one, as was stated in 136, when speaking
of the heart as a whole. The ventricle does not dilate because the
blood is forced into it, but the blood rushes into it because it dilates.




THE  CIRCULATION-.                117
But the next moment the ventricle contracts and the
auricle dilates. If the valves between them should now be
open, the blood would be forced back into the auricle. But
the membranous sheets of these valves shut upon each
other as the ventricle contracts, and thus prevent the blood
from going back. It therefore is discharged through the
pulmonary artery, f, the valves there being open. When
the ventricle dilates, the blood would, from  suction, enter
it from the artery as well as from the auricle, if the valves at
the orifice of the artery should remain open. They are accordingly shut when the ventricle dilates.
When, therefore, the auricle dilates and the ventricle
contracts, the valves between the auricle and ventricle are
closed, and those at the mouth of the pulmonary artery
are open; and, on the other hand, when the ventricle dilates
and the auricle contracts, the valves between them are open,
and those of the pulmonary artery are closed.
Dr. Carpenter has a very good illustration of the relation
of the actions of the auricle and ventricle, in a representation given in Fig. 71. The apparatus which is represented
consists of two pumps, a and b, the pistons of which move
up and down alternately. These are connected with a pipe,
c,f, in which there are two valves, d and e, opening in the
direction of the arrows. The portion c of the pipe represents the venous trunk discharging its blood into the heart,
and the portion f, the artery which is the outlet for the
blood. The pump, a, represents the auricle, and the pump,
b, the ventricle. When the piston in a is raised, the fluid
enters through c to fill it by suction, as it is termed. When,
now, its piston is lowered, the fluid is forced through the
valve d into the pump, b, (which represents the ventricle,)
whose piston is at the same time raised to receive it. And
when the piston in b is lowered in its turn, the fluid being
prevented from returning into a, by the valve d, is forced
through the valve e into if, representing the discharging
tube, the artery. At the same time, a fresh supply of fluid
is received into a by the raising of its piston.
The auricle and ventricle of one side of the heart, the




118           PHYSIOLOGY AND HYGIENE.
right side, have been described. The left side is constructed
very much in the same way. You will observe, in Fig. 70,
that the ventricle is much more capacious than the auricle.
FIG. 71.
The auricle is indeed the antechamber to the ventricle.
The ventricle, too, has much thicker walls. It is made
very strong, because it does the principal part of the work.
The size of the whole heart is about that of the closed hand
of the individual.
146. Valves of the Aorta.-Your attention is now
called to a more particular view of the valves of the heart.
We will take, first, the valves which are at the beginning
of the aorta, the great artery of the body, going out from
the left ventricle. These are very much like the valves of
the veins seen in Fig. 67. There are three of them. They
are like little pockets arranged around the orifice of the
artery, and looking toward the tube of the artery.
Of course, when the ventricle contracts, and forces the
blood into the artery, these pockets are pressed by the blood
flat against the sides of the artery. But when the ventricle
dilates. and the blood attempts to go back from the artery
into the ventricle, it gets into these pockets, and bulges
them out toward the heart, and thus the mouth of the
artery is closed. But if these pocket-like valves had plain
curved edges, they would not effect a perfect closure. * There




THE CIRCULATION.                  119
would be a liktle space in the very middle of the orifice of
the artery which would be left open. This is made plain
by Fig. 72, which represents the orifice of the artery with its
closed valves, as it would appear seen
from  the interior of the heart, if the
three valves had plain curved edges.
There would be a space left between
them. But this difficulty is remedied
by a very simple contrivance.  A little  
fleshy projection is placed upon the
middle point of the edge of each valve,
of such a size that the three projections together just fill the space A.
When, therefore, the valves are closed, no blood can go
back from the artery into the ventricle. This arrangement
is shown in Fig. 73, in which the aorta, a, is laid open and
spread out, so as to show the three valves with their
projections on the edges. At b and c, are the openings of
the two arteries that supply the walls of the heart with
FIG. 73.
VALVES OF THE AORTA.
blood for their growth and repair, for the heart is constructed and repaired from its own blood. The valves at
the orifice of the pulmonary artery are arranged in the
same manner as those which are at the orifice of the aorta.




120          PHYSIOLOGY AND HYGIENE.
147. Arranzgement of the Valves between the
A ur*icles acnd  Ventricles.-The valves which are
between the auricles and the ventricles, are folds of strong
white membrane, their edges being held by numerous
small tendinous cords. And these cords are manned, as we
may express it, by muscles attached to the walls of the
heart. The office of these muscles is to hold on to the cords
that are fastened to the edges of the valves, and prevent
these sheets of membrane from flapping back too far when
the powerful ventricle contracts. If this were not done,
the consequence would be, that when the ventricle contracts
with prodigious force, as sometimes occurs when the circulation is in a state of great excitement, the light tendinous
fastenings would be ruptured by the pressure of the blood
upon the valves. As arranged, however', the strong but
yielding muscular bundles, to which these tendons are
attached, regulate with great exactness the closing of the
valves.
148. No Valves at the Openings of the Vence
Cave. Why?-In looking at Fig. 70, observe that, while
there are valves between the auricle and ventricle, and at
the mouth of the artery going out from the ventricle, there
are none at the openings of the two vence cavwa, the veins
that pour their contents into the auricle. Why is this?
Why is there no need of valves here to prevent a regurgitation into these veins when the auricle contracts? It is
because that, as the auricle contracts, there is at the same
time the dilatation of the strong ventricle, making, of
course, a suction in that direction so powerful as to counteract most fully any tendency to regurgitation into the veins.
149. General View of all the Parts of the
tJeart. —Having thus examined the heart in detail, you
are now prepared to look at it as a whole. Fig. 74 presents
a front view of the heart, in which a is the right auricle,
receiving the purple blood from the whole body by two
large veins, h and i, called the venc cavce; b is the right ventricle, that receives the blood from the right auricle, and
sends it to the lungs by the pubnonary artery, f; c is the




7THE CIiiCULATiON.                 1l
left au.ricle, which receives the red blood from the lungs, by
the pulmonary veins, g, g, g; d is the left ventricle that
receives the blood from the left auricle, and sends it all
over the body through the aorta, e.
You observe that you see but a part of the left auricle
and ventricle, they lying partly behind the right ventricle.
FiG. 74.
FRONT VIEW OF THE HEART.
You do not see the very beginning of the aorta, for, as it
rises from the left ventricle, it is at first concealed behind
the top of the right ventricle and the beginning of the pulmonary artery. It then forms an arch, from which it sends
forth branches to the head and upper extremities; and it
afterwards passes down behind the heart, to supply with its
branches the trunk of the body and the lower extremities.




1120?2      PHYSIOLOGY AND HYGIENE.
In the line of division between the two ventricles, b and d,
you see one of the coronary arteries, as they are called, which,
coming from the beginning of the aorta, supply the walls of
the heart with blood.
150. Course of the Blood through the differet  Cavities of the lHeart.-To make you quite familiar with the relations of the different parts of this complicated organ, and with the course of the blood through its
different apartments, in Fig. 75 is given a map of the
FIG. 75.
Nat
parts below by the ascending cava. These veins pour the
- 1
rz,
MAP OF THE cIRcULATION.
heart, with the names placed upon the parts. The dark
blood is received from all parts of the body by the vence cavcefrom the parts above by the descending cava, and from the
parts below by the ascending cava. These veins pour the
blood into the right auricle. From this it passes into the




TITE CIRCULATION.                  123
right ventricle, which sends it by the pulmonary artery to
the lungs. From thie lungs it returns by the pulmonary veins
to the left auricle. It then passes into the left ventricle,
firom which it is sent by the aorta to all parts of the body.
151. Relation of the Heart to the Luqngs.-In
Fig. 76 is represented the heart, situated between the two
lungs, with the arteries which carry blood from it, and the
veins which pour their blood into it. The lungs are represented as being.drawn apart to the right and left in front, so
as to expose fully the heart and its vessels. The sac containing the heart, and the packing cellular tissue, are reFIG. 76.
b    a   b
cI!
d'TI
e     i!  ij 
LUNGS, HEART, AND PRINCIPAL BLOOD-VESSELS.
moved, so as to lay the heart and its vessels bare. At a is
the trachea or wind-pipe; on each side of it are the two
arteries, the carotids, which go to the head; c is the artery
which goes to the arm; b, b, are the jugular veins coming
from the head, d, d, the veins from the arms, all emptying
their contents, as you see, into the descending cava; e is the
right auricle, receiving the blood from the two cave; f the




124           PHYSIOLOGY AND HYGIENE.
ascending cava; g the right ventricle, i the left ventricle,
and h the descending aorta.
152. Causes of the two Sonalds of the Hearst.The harmony of action between the two sides is preserved
by having the two auricles act together, and the two ventricles act together. And this action produces two sounds,
which may be heard by applying the ear to the left side
of the chest. The first sound is rather a prolonged and
heavy one, the second is light and quick.  The first
sound occurs when the strong action of the heart is performed, that is, when the ventricles contract. It is owing
to several causes. One of these is the impulse of the heart
against the walls of the chest.
Another is the flapping together of the valves between the
auricles and the ventricles, to prevent the blood from regurgitating into the auricles, when the ventricles contract
to force out their contents. The light and quick second
sound is caused principally by the flapping together of the
valves at the mouths of the aorta and the pulmonary artery
when the ventricles dilate. The pulse is produced by the impulse given to the blood by the contraction of the ventricles.
There is, therefore, a pulse in the arteries of the circulation
through the lungs, as well as in those of the circulation
through the general system. Wherever there is an artery
there is pulsation.
153. Miovement of the Heart as a Whole.-The
impulse of the heart against the front wall of the chest on
the left side is easily explained. The aorta, in going from
the heart, makes an arch upward and backward, to go down
in front of the spine; and it is the tendency to straighten
out, produced in this arch by the force of the blood thrown
into it by the ventricle, that causes the throwing of the heart
forward by a spring. This is easily seen as illustrated by
Fig. 77, in which a is the spinal column; b, the front wall
of the chest; d, the heart; and c, the arch of the aorta.
When the heart throws the blood into this arched tube.
tends to straighten it; but as the aorta is fastened to the
fixed spine behind, there can be -no impression made in




THE CIRCULATION.                  125
that direction. The straightening of the arch must therefore occur in the other direction, to the front; and the
heart is thrown a little forward, as represented by the dotted
lines. The change of position thus produced is indeed but
slight, but it is sufficient to cause the
impulse.                                     FIG. 77.
154. Pe r i c ar d i tn.- The,
heart is inclosed in a sac, called the                 b
pericardium, which, at its upper part,    /
is fastened all around the vessels that
proceed from  the heart. This sac is
lined on the inside by a serous membrane, which also lines the outside of
the heart, being reflected over upon it
from  the pericardium.  This membrane forms, therefore, a sac without
any outlet. This is made plain by
Fig. 78. In this diagram, showing the plan of the serous
membrane of the pericardium, a, a, are the auricles; v, v, the
ventricles; b, c, the vessels proceeding from the heart; p the
serous membrane lining the outside of the heart; p', the same
membrane reflected from the upper part of the heart and
FIG. 78.
PLAN OF THE PERICARDIUM.
covers the inside of the pericardium. Now, this sac is kept
moist by a fluid exuding from its whole surface, so that,




126            PHYSIOLOGY AND HYGIENE.
as that part of it which covers the outside of the heart, in the
motions of that organ, rubs against that part which lines the
pericardium, the lubrication prevents any injury from the
friction. This lubricating fluid is continually renewed, the
exhalants and the absorbents balancing each other in their
action.  When the exhalants secrete more fluid than the absorbents can take up, the excess accumulates, making what
is called dropsy of the heart.
155. Action, of the Heasrt Imvoluntary.-The
heart, as you have seen, is a complex arrangement of muscles.
And these muscles are wholly involuntary; that is, they are
not at all under the direct con trol of the will. No one can,
by an exercise of the will, make his heart beat slower or
faster. As will be seen in another chapter, this organ is kept
at work by its nervous connection with the spinal marrow.
It has no repose, as the voluntary muscles have, unless you
call the intervals between the contractions and dilatations of
its several parts intervals of repose.
The amount of work which it does in a lifetime is enormous. The heart of an adult beats, that is, each one of the
four chambers of this organ dilates and contracts, about 70
times in a minute.  This would make 100,800 times in 24
hours, 36,792,000 times in a year, and 2,575,440,000 times in
a life of 70 years.  In children, the action of the heart is
much more rapid, and in disease it sometimes reaches in
them 160 or even 200 beats in a minute.
The two circulations of the general system  and of the
lungs are ever going on.  The blood is ever moving in all
the cavities of the heart, in every artery, and vein, and
capillary. It never stops till it is arrested by death.
NOTE.-The heart moves in an ordinary lifetime, more than a quarter
of a million of tons of blood. It can raise its own weight 20,250 feet in
an hour. An active climber can accomplish only 4,00) feet an hour,
or one twentieth of the work done by the heart, while the best locomotive can raise its own weight through only 2,700 feet in the same tVinle.




RESPIRATION.                   127
0
spong bo       d     eilg t
r~i   0
F         _      _




128           PHYSIOLOGY AND HYGIENE.
lights; and you can learn what they are in man by observing
the lights of other animals. They are composed chiefly of
air-tubes, air-cells, blood-vessels and nerves, packed together
with the common packing material of the body, cellular
tissue. The spongy lightness of the lungs is owing to the
air-cells or vesicles. You can get some idea of the proportion of these cells to the solid part of the organs if you inflate the lungs of some animal, as the sheep or calf, by blowing into the windpipe. These cells are exceedingly minute,
and in them a marked change is effected in the blood.
The capillaries holding the blood, branch out on the walls
of the cells, and the blood is acted upon by the air through the
pores of the vessels. The process of respiration introduces
the air freely into these cells. The air enters through the
windpipe, which branches out into tubes called bronchia
which divide and subdivide, till they become very minute,
and then end in the air-cells. These cells are estimated to
be about the oTotith of an inch in diameter. Some calculations have been made in regard to the extent of surface
which they would all make if they could be spread out in
one sheet. There is of course no great accuracy in such calculations; but we can readily see that the aggregate surface
must be immense, and, therefore, the blood is thus very extensively exposed to the action of the air. In Fig. 79 is
represented the lung of one side, (d; the branches of the bronchi of the other lung, c, at the lower part of which, e, they
are represented as they branch out minutely to open into the
air-cells; b is the trachea or windpipe, and a is the larynx
at the top of it. It is through a chink called the glottis, in
the larynx, that a'l the air passes as it goes into and out
from the lungs. This will be particularly described hereafter.
15t. Relative Situation  of the Heart awrel
Lungqs.-In Fig. 76, in the last chapter, you see represented the relative situations of the heart and lungs, the
lungs being somewhat separated, however, from the heart,
to the right and left, in order to show that organ fully. In
their natural position they are close to the heart, and cover




RESPIRATION.                 129
up all of it, except a small portion in front and to the left
side, where its beating is so plainly felt. Both the heart
FIG. 79.
6
LUNGS AND AIR-TUBES.
and the lungs are suspended in the chest to the upper part
of the walls of this cavity, and are fastened also to the spinal
column in the rear. The large vessels of the heart, and the
bronchi of the lungs, serve as the principal means of suspending these organs, as is shown in the Figure.
158. Pleura.-The lungs are covered by a white,
shining membrane called the pleura, which also lines the
inside of the walls of the chest. This is always kept lubricated by a watery fluid, so that, as the lungs expand and
the chest moves, the friction will be attended with no inconvenience or injury.
-159. The Lungs not Connecte(d to the Walls
of the Chest.-You may perhaps ask why, as the lungs
follow the walls of the chest in its expansion, they could
not have been fastened to these walls throughout their whole




130           PHYSIOLOGY AND HYGIENE.
surface. The principal reason probably is that, if this were
the case, the intimate vascular connection which would
exist between the walls of the chest and the lungs, would
expose the delicate texture of these organs more frequently
to injury from external violence. As it is now, the effusion, or the inflammation, consequent upon a blow on the
chest, is not apt to affect the lung in the neighborhood,
because it has no direct connection with it by nerves and
blood-vessels.
160. 3Mlechanismn   of Breathimlg.-You are now
prepared to see by what mechanism the air is alternately
introduced to and expelled from  the lungs.  The chest
incloses a large space, which can be made much greater by
certain movements of its walls.
It is this expansion of the cavity of the chest, effected by
certain muscles, which causes the air to rush into the chest
through the trachea, just as air rushes into the bellows
when the space within is enlarged by the separation of their
walls.
In Fig. 80 is shown the framework of the chest. At b, b,
is the spinal column, the grand pillar supporting the walls
of this cavity. The ribs, c, c, go from this with a large
curve round to the breastbone, a, in front. The ribs, however, do not join directly with the breastbone, but there are
cartilages intervening, as seen in the Figure.  The collarbone goes from this breastbone across to the top of the
shoulder. The ribs are twelve on each side.  The lowest
two are attached only to the spine, and are called floating
ribs. The whole is so constructed as to allow a very considerable expansion of the cavity. As the chest is kept in
constant motion, lightness in its wails is an object of some
importance; and, at the same time, it is necessary that the
structure should be a strong one, in order to effectually guard
the lungs from injury. Both of these objects are secured,
by having the walls in front and at the side composed of so
many bones, well bound together by the muscles which
move them. The cartilages which connect the ribs to the
breastbone are a great safeguard. They give elasticity to




RESPIRATION.                  1.1
the structure as a whole, and the ribs are not very liable to
be broken, because of the yielding of the cartilages with
which they are connected.
FIG. 80.
161. Framnework of the Chest.-This framework
is filled out with connecting material, chiefly muscles, which
effect the expansion of the chest in inspiration. First, there
is a large expanse of muscle and tendon called the diaphragm,
stretching across the lower part of the chest and separating
its contents from the contents of the abdomen below. The
edge of this muscle is fastened to the spine behind, to the
end of the breastbone before, and all around the lower ribs.
It is arched upward; and against its concave surface press
upward the liver and stomach, while the lungs and the
heart press downward against its convex surface. The diaphragm is represented in Fig. 81. The ribs are cut away in
front, so as to give a front view of the cavity of the chest,
C, c, the lungs and heart being entirely removed. D D is
the diaphragm, very high in the central portion, which is




132          JPHYSIOLOGY AND HYGIEN3E.
tendinous, but descending very low at its edges at the sides
and in the rear.
FIG. 81.
DIAPHRAGMo
Front View.
162. Inspiration and Expi)r-ation.-The Dia1phragmn. —If all the muscular fibres in the diaphragm
contract, the arch will be flattened, and thus the room in
the chest will be enlarged. To occupy this additional space
the air rushes in through the windpipe. This is inspiration.
In expiration, the reverse movement takes place-the arch
of the diaphragm rises, and compressing the lungs, forces
the air out of them through the trachea. In inspiration, as
the diaphragm is flattened, it pushes down before it the stomach, liver, &c.,,rnd hence the pressing out of the abdomen,
which is so sensibly felt, if the hand be placed upon it during
the act of inspiration. In expiration, on the other hand,
the abdominal walls retreat inward. These two opposite
states of the arch of the diaphragm, and of the walls of the
abdomen, are represented in Fig. 82. It is a side view, the




RESPIRATION.        13
ribs being cut away. C c is the cavity of the chest, and C a,
the cavity of the abdomen. The diaphragm and the abdomen are represented as they are in expiration. The dotted
FIG. 82.
/'                  A
DIAPHRAGM.
Side View.
line marks the flattening of the arch of the diaphragm, and
the projection of the abdomen, as they occur in inspiration.
It is supposed that in ordinary expiration, there is little, if
any, muscular action-that, as the diaphragm, which in
inspiration pushed down the stomach and liver, and thus
thrust out the walls of the abdomen, ceases to contract and
relaxes, the mere elasticity of the parts below, and especially
of the abdominal walls, restores the former condition of
things, and so the diaphragm is carried upward, and expiration results. When, however, the expiration is at all forci



PHYSIOLOGY AND) HYGIENE.
ble, it is produced in part by the action of the muscles of
the abdomen and some of the muscles about the chest.
163. Other Sllttscees, besides the Diaphraugmt,
Act in, lnspiratioon. —While this dome-shaped muscle,
the diaphragm, is the principal agent by which the chest is
enlarged, there are other muscles which render assistance.
In Fig. 83, a is the spine; c, c, c, the ribs; b, the breastbone;
d, the collar-bone; g, the diaphragm. You observe, on the
FIG. 83.
a          c
d
contract, the effect is to raise the first rib, and all the others
upward.  The result is the more effectually secured.y
e w
WALLS OF THE CHEST.
right side of the chest, certain muscles, i, extending from
the spinal column in the neck to the first rib. When these
contract, the effect is to raise the first rib, and all the others
being attached to it, of course follow.  As the ribs in Fig.
80 slant downward fiom the spine toward the front, the
result is, that all the ribs are carried together forward and
upward. The result is the more effectually secured 1 7




RESPIRATION.                    1 3
muscles which pass from rib to rib, as seen at e, e, e, e, Fig. 83.
In this Figure, the ribs, c, c, c, are left bare on the left side,
to show the arch of the diaphragm, y, the dotted line indicating it on the right side.
164. Arransgement of Muscles betiween the
Jibs.-There are two layers of muscles connecting the
ribs, the fibres of which cross each other, as represented at
M, in Fig. 84. R R are parts of two ribs. The spaces
FIG. 84.
between the ribs are filled with muscular fibres, arranged as
represented in the Figure.
These muscles between the ribs not only help to raise all
the ribs as a body, but they bring each rib nearer to the one
above it. This increases the expansion of the chest, especially as the ribs are so joined to the spine, that if a rib be
moved upward, it must be carried outward as well as forward. It is evident that by the operations of these muscles
in the neck and between the ribs, the diameter of the chest
will be increased from front to rear, and also from side to
side.
The chest is expanded, then, by two motions-by flattening
the arch of the diaphragm, and by raising the ribs. In
ordinary quiet respiration, this expansion is effected chiefly
by the diaphragm.  But when there is a call for more active
respiration, as in violent exercise, the muscles which raise
the ribs act strongly, and hence the heaving of the chest,
as it is called. Their action is violent when from disease, as
in asthma, for example, it is difficult to introduce sufficient
air into the lungs.
1,d5. BResuet  of an   Openinrg  tbhrouf/gh  the,
IVall of the Chest.-The lungs, heart, &c., accurately




136           PHYSIOLOGY AND HYGIENE.
fill the chest in all the variations of size to which its cavity
is subjected in respiration. For, when the chest is expanded,
the spongy lungs swell out to follow its walls, and the air
rushes in through the trachea to fill the expanding aircells. If, now, there were an opening through the walls of
the chest, communicating with the outside of the lung,
when the chest expanded, the air would rush in at this
opening as well as through the trachea, and the lung would
be compressed in proportion to the freeness of the opening. This has sometimes occurred from disease and from
wounds. If a free opening were made at the same time in
both sides, both lungs would be compressed, and death
would be produced by suffocation, as really as if some
obstruction in the windpipe prevented the air from entering
the lungs.
1'66. Change int the Blood effected in the Ai'rcells.-As has been said, the change in the blood, from
purple to red, is effected in the air-cells. The blood and the
air are brought very near together for this purpose; and yet
they are kept entirely separate. It is supposed that the air
in the cells acts upon the blood through the pores of the
vessels containing it, which branch out on the walls of the
cells; for if dark venous blood be inclosed in a bladder, the
air will act through the pores of the bladder, and gradually
change the outer portion of the blood to a red color.
167'.  Variable amount of Work done by the
Air-cells.-These air-vesicles, then, do an important work.
The change which is effected in them is immediately essential to the continuance of health, and even of life. If the
air be in any way shut out from them death occurs at onc,.
And so important is it that they should do their work well,
that extraordinary provisions are made to secure an abundance of room for them  under all circumstances. For the
cavity of the chest, as you have seen in this chapter, can be
expanded to a very great extent. It would indeed be difficult to conceive how a greater range of expansion could be
secured. As the air-cells are called upon to do more work
att some times than at others, there are special provisions for




RESPIRATION.                      137
a larger dilatation of the chest than is required in ordinary
quiet respiration.  Thus when, from  violent exercise, the
blood is coursing rapidly through the lungs, and more air is
therefore needed to change it to red arterial blood, the chest
is largely expanded by calling into action muscles, which do
but little, if any thing, in ordinary breathing.*
168. Injury  done to  the  Air-cells by Compression of the Chest.-As the apparatus of respiration
is so especially arranged to secure room for the lungs under
all circumstances, it must be very deleterious to the health
of the body to interfere with this arrangement. If the expansion of the chest in breathing be limited by any pressure,
every air-cell must be embarrassed in doing its part in
changing the blood.
Either all of them must be unduly contracted, or some of
them must become obliterated, so that there will not be as
many vesicles as there should be.  In either case, the organ
is disabled in proportion to the amount of the compression.
The blood is not so good as it would be if there were enough
vesicles, and they could perform their work without constraint.  The vigor of the system is therefore lessened.  And,
besides, the lungs themselves, from this unnatural confinement, are especially liable to disease.t
Vigorous exercise undoubtedly causes much injury to
lungs that are thus confined. If the chest be left free to ex* It is a curious fact that the mechanism of respiration is somewhat
different in the two sexes. In men the diaphragm takes the larger
share in the process, the upper ribs moving comparatively little; in
women the reverse is the case, the respiratory act being largely costal.
-HUXLEY.
f The volume of air which remains in the lungs (Residual air) after
a forced expiration, is from 75 to 100 cubic inches. An equal additional
volume (Supplemental air) remains in the chest after an ordinary expiration.
In ordinary breathing, 20 to 30 cubic inches (Tidal air) pass in and
out. A forced inspiration will add 100 cubic inches (Complemental air)
to the volume. Then after a forced inspiration the lungs contain 100 +
100 + 30 + 100= 330 cubic inches of air. After an ordinary inspiration
100 + 100 -+ 30=230 cubic inches.




138           PHYSIOLOGY AND HYGIENE.
pand to its fullest extent when occasion requires, this injury
is avoided. For when the strongly and rapidly contracting
heart pumps the blood in such quantities into the lungs, the
widely expanding chest draws in the due amount of air to
change the extra amount of blood. All the air-vesicles are
ready to do their duty, and, therefore, no violence is done to
the delicate texture of the lungs.
But if these organs be compressed, the dilatation of those
vesicles that are not obliterated, in the midst of the commotion of the difficult respiration, is very unequally effected,
and some of them are stretched beyond their proper dimensions. At the same time, the blood must be here and there
obstructed in its passage through the lungs, producing what
is termed congestion. And if this violence be frequently repeated, permanent disease will be the result.
From  the considerations in the last two paragraphs it is
manifest, that the interference with the due expansion of
the lungs, which so commonly results from the modes of
dress in the female sex, must be one of the prominent causes
of consumption, to say nothing of other diseases arising from
this cause.
This interference is effected in two ways-chiefly by compression of the chest directly, but also by the pressure which
the load of clothing hanging from  the waist must make
upon the upper part of the abdomen.  This latter cause
interferes with that forward movement of the abdomen
which is necessary to the flattening of the arch of the diaphragm in the act of inspiration.
The extent to which compression of the chest is sometimes carried is seen by comparing the two outlines in Fig.
85. One is an outline of the Venus de Medicis, the universally recognized beau ideal of beauty of form in the female,
and the other is an outline of the form of a lady with an
artificially small waist. In Fig. 86 is represented the framework of the chest of its natural size, and as it is sometimes
contracted by fashion. The Figures representing the contraction of the chest may appear at the present time as caricatures, for a very small waist is not considered now to be so




RESPIRATION.                   139
essential to beauty in the female form, as it was twenty-five
years ago. The truth, as uttered by medical men, has had
some effect. But the evil is remedied only in part.  The
chest of the female is still too much begirt, in obedience to
FIG. 85.
the tyranny of fashion, to allow of the free expansion to
secure which such special pains are taken by nature. The
FIG. 86.
evil begins in childhood.  The chest is moulded during its
growth to the shape which fashion prescribes. It could not
be done after the chest has attained its full size. The torture
of the compression necessary to do it could not be endured.
In childhood, therefore, while the boy's chest is left to
grow in its natural shape and dimensions, the girl is begirt




140           PHYSIOLOGY AND HYGIENE.
so tightly as to embarrass her respiration, because nature is
too ungenteelly large ill her patterns.
169. Cause of Death in  Dro,?niy,/t.-. — It is the
interruption of the change which is effected by the air upon
the blood in the lungs, that produces death in drowning.
The very common supposition, that considerable water gets
into the lungs in drowning, is erroneous. Very little water
ordinarily gets in-not enough to occasion any embarrassment.
The difficulty is, that the air is kept out, and not that the
water gets in. The drowning person makes attempts to
inspire, but the moment that the water reaches the epiglottis,
the door of the windpipe, it causes at once, by its irritation,
a spasmodic closure of the epiglottis, so that almost no
water is introduced. In the mean time, the purple blood
continues to be thrown by the right ventricle of the heart
into the lungs. But the little air contained there soon
parts with its oxygen; and then the change in the blood
ceases to occur, and dark blood is sent fiom the lungs to
the heart, and thence to all the organs. These can not
go on to do their duty without the stimulus of arterial
blood.
The brain, therefore, gives out, and there is insensibility.
The muscles cease to act, and all motion is gone. If a good
supply of arterial blood could be furnished to all the organs
until breathing could be again commenced, life would be
preserved, and there is provision for such a supply in certain animals that can remain under water for some time..iTO. Singular Provision in the Whale. —For
example, in the whale there are large reservoirs for containing arterial blood, which can be used for the supply of the
organs while he remains under water. When the supply
begins to be exhausted, the animal of course has those
uncomfortable sensations which a predominance of purple
blood is so apt to produce. He manifests his uneasiness by
his puffing and blowing, as he rises to the surface to -et a fresh
supply of air, and with it a fresh supply of artterial blood in
the reservoirs.




RESPIRATION.                    141
1TJ. Respiration in Fishes.-The apparatus of
respiration varies in different animals. It appears in three
forms-lungs, gills, and tracheai or air-tubes. The gills of
the fish are arranged in fringed laminit, in order to present
by all their minute divisions a large surface;
and these delicate organs are covered with a lid  FIG. l.
to protect them from injury. The blood-vessels,
which contain the blood to be changed,branchl
out on the surface of the fringes of the ]aminas,
just as the blood-vessels in lungs branch out
on the surface of the air-vesicles.  The air
which is to change it is mingled with the water.
It acts upon the blood, as the water containing
it, after being taken into the mouth of the fish,
passes out through these laminae, as through a
sieve. That the air in the water is the cause
of the change can be proved by experiment.
If a fish be placed in a vessel with its orifice
closed, so that no air can enter, it will soon die 
from suffocation, because the air in so small a
portion of water is soon used up. Although
the fish can not with his gills use air that is not
mingled with water, it is supposed that it is
merely because the gills soon become dry when
exposed to the air, and that the air would act
on the blood in the gills if they were only kept
moist.  Indeed, in the land-crab, that has the
power of living for some time out of the water,
it has been found that there is a gland in the
gill-chamber which furnishes a secretion to keep
the gills moist.
Gills differ much in their shape and arrangement in the various aquatic animals. In Fig.
87 is represented the arenicola or lob-worm. LOB-WORMI.
Here the gills are in.the form of tufts arranged
along the outside of the body. They take a somewhat similar
form in the larv.e of many aquatic insects, as seen in Fig.
88. A large surface is presented to the air contained in the




14 z2          PHYSIOLOGY AND HYGIENE.
water by the delicate and beautifully arborescent gills of
these animals.
FIG. 88.    1T2.  Respiration in Insects.-In insects, we find the respiration effected by trachlew
or air-tubes.  These go into all parts of the body,
and the air contained in them  acts upon the
blood in the tissues of the body.  The insect,
therefore, has no  distinct respiratory organs
situated in any one part of the body, but the
air is carried into every part. This seems to be
necessary on account of the feeble circulation
in the insect.
The trachem which, as Cuvier says, conduct
LARVA OF THE the air in search of the blood, as the blood has
MAY-FLY.  no means of travelling in search of air, open on
the surface by stigmata, as they are called, which are of
various shapes and number in different insects.  In the
grasshopper there are twenty-four, arranged in four rows.
You can suffocate an insect by simply covering the stigmata
with varnish.
In Fig. 89 are represented the trachece in an insect, the
nepa or water-scorpion.  The trachee, as you see, send
branches out in every direction, so that air is introduced
into every part of the body. There are lungs, so to speak,
everywhere in the insect.
173. Respiration  ion Birds.-The apparatus of
respiration is largely developed in birds for two objects-to
provide for the extensive change in the blood which is required by their great activity, and to give lightness to the
body.
To secure these objects there are air-sacs connected with
the lungs, and located in different parts of the body; and in
birds that fly rapidly and are long upon the wing, these sacs
are very extensive, and even many of the bones are made
hollow, and are connected with the air-sacs.
By this arrangement, the air is introduced extensively to
the blood in the capillaries on the walls of these sacs, and at
the same time the body is made very light. And the heat




RESPIRATION.                       143
generated by the effort of flying must expand the air in the
cair-sacs and swell them out, and thus make the body lighter.
In Fig. 90 is seen this arrangement of air-sacs in the ostrich,
The lungs, 1, 1, are quite small, but the air-sacs, c, c, c, are
very large.  The orifices by which they communicate with the
lungs are as shown in the Figure.  In birds of great powers of
FIG. 89
1ST PAMS OP
LEGS.
CHEST.
WING CUT O —-K
A-...... AIR-SACS.
2D PAIR OF._.
LEGS.
3d PAIR.
STnIGATA. ---------
RESPIRATORY APPARATUS OF THE WATER-SCORPION.
flight, the air-sacs are much more extensive. This arrangemeint of air-sacs in different parts of the body of the bird
i,ears some analogy to the tracheae distributed in the bodies
of insects.




144           PHYSIOLOGY AND HYGIENE.
174. Changes produced  i*n  the Air in the
Lungs.-You have seen that the object of the apparatus
of respiration is to change venous blood into arterial, and
you have also seen how the air is introduced to the blood in
order to effect this change.
FIG. 90.
LUNGS OF THE OSTRICH.
And now the interesting inquiry arises, what are the
actual changes which occur, both in the blood and in the
air, in the lungs. If you take a tumbler filled with limewater, and breathe into it through a tube, the lime-water will
become turbid, and will soon deposit a sediment. This is
chalk, or carbonate of lime, formed by the union of the carbonic acid gas exhaled from the lungs with the lime in the
lime-water. Whence comes this carbonic acid gas, and how
is it formed? In order to answer this question satisfactorily,




RESPIRATiON.                   145
we must learn something of the chemical constitution of the
air which we brcathe.
It is composed of two gases, oxygen and nitrogen. 1n
every 103 parts of common air, there are 79 parts of nitrogen
and 21 of oxygen. It is found that the oxygen is that constituent of the air which is necessary to life. If an animal
be placed in a closed jar filled with common air, he will soon
die, and the oxygen will be found to have disappeared, while
the nitrogen will remain very nearly as at first.
If, noW, one animal is placed in a jar of nitrogen, and
another in a jar of oxygen, the one in tile nitrogen will die
immediately, while the other will be very lively until the
oxygen is mostly used up by his lungs. The animal in the
pure oxygen will breathe at first more rapidly than the animal
in the jar of common air; and it is thought that oxygen is
too stimulating for the lungs, and therefore needs to be
diluted with the nitrogen, since the latter is always found in
the air that we breathe.
1o5. Change takes place in the Capillaries.In the case of both the animal in the jar of air, and that in
the jar of oxygen, carbonic acid is found to have taken
the place of the oxygen which has disappeared. This gas is
made, by a union of oxygen with carbon or charcoal. It was
formerly supposed that this union is effected in the lungsthat carbon is thrown off from the venous blood in the lungs,
and that the oxygen of the air there unites with it, and so
carbonic acid appears in the air expired from  the chest.
But it has been discovered that the exchange is not made
in the lungs. The oxygen is absorbed by the blood, and(
goes with it to the heart to be sent all over the system.
And it is in the capillaries that the oxygen unites with
carbon to form carbonic acid.
The union takes place while the blood is changing from
arterial to venous, and is an essential part of the change.
The carbonic acid thus formed in the capillaries, is brought
back to the' heart in the venous blood, and is discharged
from the system in the lungs. That the change takes place
as stated h:        ndantly proved in various ways.




146           PHYSIOLOGY AND HYGIENE.
It has been found by experiments which will not be de.
tailed, tlhat carbonic iacid exists inll considerallle anount in
venous blood; while, on the other hLand, illre is minuch oxygen in arterial blood. The inference from this is, that oxygen unites with the blood as it passes through the lungs,
goes with it to the capillaries, and there unites with the
carbon, giving us the carbonic acid which we find in the
blood in the veins, after it has passed into them from the
capillaries.
It has been found, also, that if frogs or other cold-blooded
animals be placed.in hydrogen or nitrogen (gases which
produce no injurious effect on them) they will give off for
some time nearly as much carbonic acid as they would have
done in common air.
In this case, as no oxygen is introduced into the lungs,
the carbonic acid cannot come from any union effected in
these organs between carbon and oxygen, but it must be
discharged by exhalation from the blood as it is passing
through the lungs. Of course the discharge of the carbonic
acid ceases after a little time; for, there being no new supply
of oxygen by way of the lungs, as there is when the animal
is breathing common air, there can be no new formation of
carbonic acid.
But even cold-blooded animals can not live in these gases
for any great length of time, for oxygen is needed for the
continuance of their functions. And in the warm-blooded
animals, a constant supply of it is necessary-they will
die if cut off from this supply even for a short time.
176. Charnges piroduced in the Blood by the
Air.-The change which takes place in the blood as it
passes through the lungs, occurs to some extent when the
blood is exposed to the air in any way. Thus, if blood be
drawn from a vein into a bowl, the surface of it becomes red
by the action of the air upon it. Carbonic acid is discharged
from it, and the oxygen of the air takes its place, uniting
with the blood, just as the process occurs in the lungs. A
larger part of the blood will be thus changed, if it be shaken
so as to expose more of it to the air. The change takes place




RESPIRATION.                  147
to some extent even if a membrane be interposed, as when
the blood is inclosed in a bladder. The oxygen of the air,
in this case, is introduced through the bladder, and the carbonic acid gas escapes through it. Precisely in this way is
the change effected in the lungs, as already stated.
The blood is separated from the air by being confined in
blood-vessels, and the air in the vesicles acts upon it through
the walls of these vessels. And, as the blood is divided into
innumerable little streams, every part of it is acted upon by
the air in the vesicles. Though the texture of the lungs is
exceedingly delicate, yet the blood is confined to its limits,
even though it courses through these organs with great
rapidity, and it never mingles with the air except as a consequence of actual disease.
1;v'". Quantity of Carbonic Acid given out
by the Lungs.-The quantity of carbonic acid discharged
from the lungs in the course of twenty-four hours is very
great. Many experiments have been tried and calculations
made to ascertain its amount, from which it is estimated
that there is at least three-quarters of a pound of charcoal in
the carbonic acid thrown off from the lungs of a commonsized adult in the course of twenty-four hours.*.1 8. Necessity of Ventildtion. —This gas is a
deadly poison. When accumulated in a considerable amount,
as when charcoal is burned in an open furnace in a close
room, it may prove immediately destructive to life. And in
the very prevalent neglect of ventilation, the frequent accumulation of this gas from the respiration must prove more
or less injurious to the health.
Whenever the proper amount of oxygen gas is withheld
from the lungs, and carbonic acid takes its place, the quality
of the blood is impaired from incompleteness of the change
effected in the lungs, and the vigor of the body must in this
way be lessened, to say nothing of the deleterious influence
of this gas upon the nervous system. Though the results
* Three-fourths of a pound of carbon united with oxygen will form
two and three-fourths pounds of carbonic acid.




148           PHYSIOLOGY AND HYGIENE.
are not immediate and palpable, great injury is continually
done to the health of multitudes by the accumulation of this
gas, in small close apartments, and in crowded assemblies.
A congregation of twelve hundred people throw off from
their lungs in two hours an amount of carbonic acid that
contains seventy-five pounds of charcoal.  And yet little
pains is commonly taken to carry off this vast quantity of
poisonous gas, and replace it with pure air. *
1'T9. Carbonic Acid Exhaled from  the Luntgs
of Animals Absorbed by Plants.-As so much oxygen is absorbed in the lungs of all animals, and so much carbonic acid is thrown out from them, the inquiry arises how
the air is replenished with oxygen, and is cleared of the carl)onic acid which is thus so largely mixed with it. It is
found that this is accomplished, to a great extent at least,
by the leaves of plants. The process which goes on in these
lungs, as they may be called, of the plants, is quite the reverse of that which is going on in the lungs of animals.
The carbon of the carbonic acid which is thrown off from
the lungs of animals is absorbed by the leaves of plants, and
the leaves replenish the air with the oxygen, which is so
constantly and abundantly absorbed in the lungs of the animal creation. Thus the animal and vegetable kingdoms are
sources of supply to each other.
It may be thought that there would be a surplus of oxygen in the atmosphere in warm climates, whei'e the vegetation is so luxuriant; while, on the other hand, there would
be an accumulation of carbonic acid gas in the colder regions.
This would be so, if the air were not so movable that the
equilibrium is readily secured in either case.
180. Light Necessary. —It is an interesting fact,
that the presence of light is necessary to the process which
has been described as going on in the leaves of plants. Each
leaf may be considered as a laboratory, and the light as the
* It is estimated or perhaps determined that each individual ought
to have at least 800 cubic feet of space to himself, this space to be
constantly supplied with pure air, with provision for the exit of the
foul air, or-in other words-this space to be perfectly ventilated.




RESPIRATION.                  149
chief agent inll effecting the chemical cllanges that occur in
it. And it is found that no artificial light can do the work.
It is only the light of the sun that is competent to this
chemistry.
And as these innumerable laboratories are everywhere at
work, absorbing  the carbon and exhaling the oxygen, to
purify the air rendered noxious by the laboratories of thle
animal creation, we must confess it to be a mystery how
the chemistry of the lungs of animals and that of the
leaves of plants should be kept so nicely balanced. The
balance is so strictly maintained, that the cllemical compo;sition of the air is always found to be almost exactly the
sallle.
181. Aninmal t eat.-The heat of the body is maintained by the union which takes place in the capillaries
between the carbon and hydrogen of the system, and the
oxygen which is introduced into the blood through the
lungs. It is a process analogous to combustion. When
carbon or charcoal is burned in a vessel containing air, the
oxygen unites with the carbon, and carbonic acid gas is
formed.
The same union occurs in this case between carbon and
oxygen that we find occurring in the capillaries. A sort of
combustion is going on in every part of our bodies. And,
as heat is evolved in the one case, so it is in the other.
The same can be said of the burning of hydrogen and oxygen together. Heat is caused by the union thus produced
between them, and so it is when they unite in the body.
The water which is exhaled from the lungs comes from this
union of oxygen and hydrogen.
It was formerly supposed that the union between the oxygen and the carbon and hydrogen takes place in the lungs,
and that the heat is made there, and then is distributed over
the whole system. But it was objected to this supposition,
that it made the lungs a sort of furnace for the rest of the
body, and that, if the supposition were correct, there ought
to be a much higher degree of heat in these organs than
anywhere else, which is not the case. It was at length dis



150           PHYSIOLOGY AND HYGIENE.
covered that the union between the oxygen and the calrbon and hydrogen occurs in the capillaries of the body
instead of the lungs; that the combustion that proclucsthe heat occurs throughout the system, instead of in one
locality.
182. Three Soaurces of Ftel. —The fuel for this
combustion comes from three sources. One of these is the
waste of the tissues. This filrnishes a considerable amount
of the carbon and hydrogen for the union with the oxygen,
in all animals that are subjected, from their activity, to mucll
wear and tear of the system.
Another source of the fuel for combustion is food.  The
oils, sugars, and starchy kinds of food are devoted in a great
measure to this particular purpose. These furnish a sort of
floating fuel, as we may express it, which is carried about in
the blood. Hence, we see that our diet must necessarily be
varied according to the weather and the climate.
In cold weather the heat of the body is more rapidly
abstracted than in warm weather, and, therefore, we need
then more of that food which affords a supply]v of carbon and
hvdrogen.  Similarly, the enormous quantity of oily food
often consumed by inhabitants of very cold climates is
burned, as we may say, in the capillaries to keep up the
animal heat. Of course, keeping the body warm by fire
and clothing relieves from the necessity of taking any large
quantities of fuel-malking food. In the most favorable circurnstances there is a need of variation in diet to suit the
weather and the climate, and we make this variation for the
most part instinctively.  Indeed there is a marked provision
in nature for it.
While there is a large amlount of fat in the bears and seals
and whales which afford food for the Esquimaux and Greenlander, there is very little in the animals which furnish a
part of the diet of the inhabitants of tropical climates.
Still another source of animal heat is the store of fat
which is laid up in the body. One design of this accumulation of fat in different parts of the body seems to be to
provide for the heat when other sources fail. Thus, when




RESPIRATIOX.                  151
disease destroys the appetite, and thus cuts off the supply
of food, the fat wastes away, or rather is burned up, to keep
up the temperature of the body. The fat is the great means
of maintaining the requisite temperature when hibernating
animals become torpid for the winter. They become very fat
in the autumn, before crawling into their winter quarters,
and in the spring they come out very lean, their fat having
been consumed in keeping up even the low degree of temperature required during this time.
183. Atnimal H-eat  diffeirs in, Cold  and
Wagrn-bloodeds  Aitimals. —As the amount of heat
produced, when charcoal is burned in air, or when oxygen
and hydrogen are burned together, depends upon the quantities of carbon and hlydrogen that unite with the oxygen,
so, also, the degree of animal heat depends upon the quantities of carbon and hydrogen that unite with the oxygen in
the capillaries. This may be illustrated by referring to the
effects of exercise on the heat of the body.
When the circulation is quickened by exercise, the blood
passes more rapidly than usual through the lungs, the respiration is consequently quickened, more air is introduced
into the lungs, and therefore oxygen is more rapidly absorbed by the blood. At the same time, the action of the
muscles effects a waste of their tissue, so that more carbon and hydrogen are ready to be released to be united
with the increased oxygen. Hence comes the heat produced
by exercise.
So, too, those animals which are the most active, ordinarily have the most animal heat, and have the most extensive respiratory apparatus, so that there may be a free supply
of absorbed oxygen to unite with the carbon and hydrogen
of the changing tissues. It is in birds and insects that this
union takes place most largely, and in them, therefore, the
respiratory apparatus is very largely developed. This is made
necessary by their muscular activity, which produces so
much waste matter that must be removed from the system.
Cold-blooded animals, on the other hand, are very inactive. There is not, therefore, much wear and tear of the




1o2) 5 11PHYSIOLOGY AND HYGIENE.
tissues. There is comp:tratively little waste, therefore, to be
thrown off. And so but little oxygen needs to be introduced into the lungs, and consequently little heat is generated.  To,iealize fully the contrast between the warmblooded and the cold-bloodled animals in these respects,
observe, as the representative of the one class, a canary bird,
and a frog as the representative of the other.
The frog is generally quiet, and only now and then takes
a leap, or croaks; but the bird is ever in restless motion, and
sings much of the time with all his might. The bird is
warm with the heat generated by the constant union of
oxygen with carbon and hydrogen in its capillaries; but
the frog is nearly as cold as the water in which he is immnersed. The bird breathes rapidly, to let the oxygen of
the air largely into his lungs; but the frog seems scarcely
to breathe at all, so scanty is the supply of oxygen which
lie needs.
184. Uniformity  of Animal Heat in  the
Warmn-blooded  Animals. - Cold-blooded  animals
are very nearly of the same temperature with the substances
that are around them; but warm-blooded animals have a
certain degree of temperature, which they maintain with
considerable uniformity under all variations of temperature
in the atmosphere.  This in man is about ninety-eight
degrees Fahrenheit.  This is above the temperature of the
surrounding air, except in exceedingly hot weather. The
human body is therefore always giving off heat.
But the amount of heat which the human body can bear
for a short time is much greater than the facts above alluded
to would lead us to suppose. It was long taken for granted,
that it could not safely bear, even for a short time, a heat
much higher than that which is endured in hot climates.
The truth on this subject was at length discovered by accident.
185. Interesting Experim ents.-Two Frenchmen were employed by government, in 1760, to devise some
method of destroying an insect which infested the grain at
that time. The result of their experiments was the dis



RESPIRATION.                   153
covery, that by subjecting the grain to a certain degree of heat
in an oven the insect was destroyed, while the grain was not
injured. While they were trying their experiments, a girl
offered to go into the oven and mark the height of the
mercury in the thermometer.  It stood at 260~0; and, after
remaining there for ten minutes, which she found that
she could do without ally great inconvenience, she marked
it at 288~, that is, 76~'above the boiling point of water.
These facts led to the famous experiments of Dr. Fordyc:l
and Sir Charles Blagden, in England.  With wooden shoes,
tied on with list, they went into a room in which the thermomneter showed the air to be at 260~. Their watch-chains
were so hot that they could scarcely touch them, and eggs
were roasted hard in twenty minutes, and beefsteak was
cooked in thirty-three minutes. And yet the same air that
produced these results was breathed by them with impunity.
and it raised the heat of the body but very little.
The air which was breathed out fiom  the lungs was so
much cooler than the air of the room, that it was refreshingly cool to the nostrils, and to the fingers as they blowed
upon them. In such cases, the evil effects of the heat are
prevented chiefly by the great amount of perspiration that
occurs, the vaporization of this abstracting the heat, which
would otherwise accumulate in the body and produce disastrous results. The exhalation from  the lungs, also, lias
some influence.
186. Different Degrees of Torpor ina  Hibernating.  Animals.-In the state of hibernation, to which
reference has several times been made, the torpidity varies
in degree in different animals. In cild-blooded animals, respiration and circulation may, in this state, cease altogether.
In them  the movements of life are often, perhaps we may
say generally, as fully suspended as they are in the seed that
is kept from heat and moisture. They may be preserved in
this state for a long time and yet revive.
Serpents and frogs have been kept in an ice-house for
three years, and then have been revived on being brouglht
out into a warm atmosphere.  In the warm-blooded animals




154           PHYSIOLOGY AND HYGIENE.
that hibernate,the torpidity is less deep than in those which
are cold-blooded.  In them  the respiration and the circulation become very slow, but never entirely cease. Indeed
some species take food with them into their winter quarters,
and occasionally wake up sailficiently to eat. But most of
them  are in a quiet, deep sleepl, from  which they do not
arouse at all till the winter is past.
In this state, as life is nearly, sometimes quite, at a stand,
there is little wear and tear, and therefore little chalnge inl
the tissues, and so there is need of the introduction of but
little oxygen by the respiration.  Dr. MI. Hall, in his experiments and observations, found that the bat, when completely
torpid, consumed no oxygen, and discharged no carlbonic
acid from the lungs, although its circulation was not entirely
suspended.
1S'. Relation of Activity to Quantity of Air.
The more active is the respiration of animals, the less able
are they to bear a deprivation of air. A warm-blooded land
animal will die if it be under the water only a few minutes;
but a cold-blooded animal can live under the water for some
time, because it is not in so urgent need of oxygen. And,
for the same reason, a warm-blooded animal, in a state of
hibernation, may be kept under water for a long time without destroying life, although when in its active state it would
die on being kept under water for only a few minutes.
188. General Sautnmary.- The extensive play
which the respiration has in the vital operations of the
system has been shown. You have seen what the chemical changes are, which it effects directly in the lungs,
and indirectly in the system.  And you have seen howv
the animal heat is produced by these changes, and how
it is so regulated, that it seldom  varies from  its fixed
standard.  But it is to be remembered that, while the
lungs, and even the capillaries everywhere are thus chemical laboratories, the nervous system  exerts a constant
influence upon this chemistry of the body. This is espe,cially seen in regard to the production of heat, but it is
true of the whole range of the chemical operations. The




FORMATION AND REPAIR.              155
laboratories would all cease their work if their nervous connections were destroyed.
CHAPTER X.
FORMATION  AND  REPAIR,
189. Pormcative  Cells appended to the Capillaries.-The building and the repairing of the various
structures of the body are done by vessels appended to the
capillaries. The capillaries having received from the arteries the blood, the building material, the formative vessels
select from it, while it is in these capillaries, whatever they
need for their purposes. Those vessels which, for example,
form bone, select from the blood very different constituents
from those which make nerve or muscle.
190. Co0ncert of Action. —These builders of the
body not only have the power of selecting their building
materials from the blood, but they work in concert. Each
company of builders work together in harmony, as if they
were under intelligent leaders. And though different companies may be in close proximity, there is no disagreement
nor interference. For example, the builders of a tooth and
the builders of the gum around it, do not encroach on each
other; but each do their appropriate work within their
assigned limits. Even when different structures are intermingled, as when tendon and muscle mingle together at
their place of union, there is no confusion in the work of the
two sets of laborers.
191. Concert of Action shown in P:'oduching
different Shapies.-The concert of action which we
observe in the different sets of formative vessels is to be
looked at fiom another point of view. It is such that they
give a definite aud peculiar shape to the structure which
they make. Each bone differs in shape from every other




156           PHYSIOLOGY AN~D HLYGIENE.
bono, each muscle from every other muscle; an(l so of other
parts. There is very great variety of shape in the structures
of the body; and each shape can be determined only by a
certain concert among the builders,
This concert of action may be looked at from still another
point of view. In the growth, that is, the construction of
any part, the addition is made by the formative vessels Et
every point of the part, and not upon tl:e outside merely.
As these builders are at work enlarging the part in the
growth from infancy to childhood, they must so act in concert as to preserve the same general form in the part dluring
all the successive stages of growth. And, as all the different
structures of the body enlarge together, there must be agreement between different sets; else there would be encroachment and confusion.
192. Change of Action. —But this concert of action
appears the most wonderful when a new action, or change of
action, is called for. In the transition from childhood to
youth, for example, the builders of the apparatus of the voice,
the larynx, all at once become unusually active in their work,
and a great enlargement of this musical instrument, for such
it is, takes place, so that it may now utter the grave notes
of manhood.
Soon, too, the beard-builders begin their new work upon
the face. And during the period of childhood new operations have been continually instituted among the builders
of the teeth, as one tooth after another has made its appearance, and as the new set have replaced the old.
To effect each one of these changes, there must be concert of action among the formative vessels; and there must
be a most wonderful concert among the different successive
sets of builders, to make all these series of operations work
out at length the general result.
-193. Tadpole Saed 1F rog. — This change of action in
the formative vessels is strikingly exemplified in some animals. We refer to those that entirely change their formsn
during the period of their existence.  One example will be
given; the common frog. He is at first what is termed a




FORMIATION AND REPAIR.                 15 
tadpole, and goes through many successive changes to become
a complete frog.  These changes are represented in the
following figures.  The relative sizes are not preserved, the
tadpole state being represented relatively much too large, for
thel purpose of showing more clearly the development of the
legs.  Tihe young tadpole is represented in Fig. 91.  It has
a large head and body, and a long fiat tail by which it swiims
easily.  There are no prominences to indicate the putting
forth of any thing like limbs.  It has gills, in the form  of
loose fringes on each side of tile head.
FIG. 92.
FIG. 91.                          FIG. 93.
FIG. 94.
FIG. 95.
FIG. 96.
These gills after a time disappear, and it has another set
of gills arranged under a fold of skin very much like the
gills of a fish.  The form is then as in Fig. 92.  The next
change is this.  The hind legs begin to grow out as seen in
Fig. 93.  Next, the four legs appear as seen in Fig. 94.  The
tail is still very large.  This now gradually disappears while
the legs grow as represented in Fig. 95.
In Fig. 96, representing the perfect frog, the tail has
entirely disappeared. With these exterior changes interior
ones have been going on also. The animal, which was at




158           PHYSIOLOGY AND HYGIENE.
first like a real fish, breathing with gills and swimming in
water, has lost its gills, and has now a pair of lungs; and it
is no longer able to remain long under water, but must
conle to the surface to breathe the air.
194. Chang;    e of' Action  to  meet ntew  ENrige1ic ies.-The change of action in the formative vessels,
which is soiletimes called for by accident and disease,
exhibits in an interesting manner the concert between
these vessels as influenced by circumstances. When a bone
is broken, these formative vessels set themselves at work to
repair the injury, by forming new bone between and around
the two ends of bone, which new bone we call callus.
1915. lI austration front Processes of IJflamnmattiont.-Concert of action under successive changes is
strikingly exhibited in the processes of inflammation. The
following account of these processes is from a work published by the author, entitled "Physician and Patient."
"You see a swelling. It after a while begins to soften.
There is matter in it, but it is not yet very near the surface. But soon, at some point, it comes nearer and nearer
to the surface, the wall of the abscess thus becoming constantly more thin, till, at length, it opens and discharges.
The discharge continues till the swelling is nearly all gone,
and the remainder is absorbed, and the part is restored
to its natural state.
"Just look for a moment at the complicated character of
this apparently simple operation. Here is quite a large
deposition of substance which is to be removed; and this
is the object to be effected. Observe how it is done. The
softening of the swelling is not a mere change of solid substances into a fluid, as if by decay, but it is the result of an
active process, which we call suppuration. When this process is properly performed good pus is made, or as the old
writers in medicine rather quaintly expressed it, laldable pus.
1" This process of suppuration, when it is well done, does
not go on here and there in the swelling, making it like
a honeycomb with a multitude of little abscesses; but there
is a concert, an agreement of action by the vessels of the




FORMATION AND REPAIR.                159
pIart, as really as if they worked intelligently. It is this
concert of action which not only makes the line of movement in the abscess, but points it towards the surface,
instead  of giving it some other direction, laterally or
inward, upon some of the internal organs.
"Three different offices are performed by the vessels in
the different quarters of the abscess. While some of these
little workmen are forming the pus, there are others thinning the wall of the abscess in the direction of the surface,
by absorbing or taking up the substance there; while there
are others still, in the rear, and at the sides of the abscess,
depositing substance, in order to make a barrier to prevent
the pus from being diffused in the surrounding parts.
"When the absorbents have completed their passage for
the pus through the skin, the pus is gradually discharged
from  its reservoir, and the'occupation' of the pus-makers
is soon'gone.' The wall-builders also cease their work,
and while the vacancy becomes filled up by contraction and
deposition, the wall of defense, so carefully maintained so
long as needed, is now taken up by the absorbents-workmen which seem to know just when, as well as how, to do
their duty."
196. Foormation of all Parts fromit the Blood.
-Thus, all the solids and fluids in the body are madc from
the blood. Even the heart itself is made from the blood
which it pumps into the aorta; for from this aorta go out
small arteries, to carry blood to the walls of the heart for
its growth and repair.
197. Witste. —Not only is there construction going on
in every part of the system, but there is waste also. The
wear and tear of the ever-moving, machinery continually
makes some of the particles useless, and these must in
some way be removed. Let us see how this is done.
198. Two Kinds of Waste Maltter. —There are
two kinds of waste particles; and for the disposal of them
two different plans are pursued. Some of the waste particles, though wholly useless where they are, can be rendered
fit to be used again by being subjected to certain processes.




1(,0          PHYSIOLOGY AND HYGIENE.
These, therefore, are not thrown out of the system, but
are taken up by absorbents, and are carried where the
necessary processes can be applied to them; and then they
are introduced into the blood. to make again a part of the
building material.
But there are some waste particle3 that cannot be used
again; and these are so mlanaged as to be got rid of at
various outlets of the system. These two kinds of particles
are taken up by two different sets of absorbents. The
selecting power which they thus exert is as unerring as if
they were possessed of intelligence.
199. Lynmphatics. - The  particles which can be
used again are taken up by absorbents, which are termed
lymphatics.  These vessels are much like the lacteals, the
absorbents in the intestines. They unite together, as they
come from  all parts of the body, into two trunks.  One oi
these is the thoracic duct, which is the common duct both
of the lymphatics and the lacteals (Fig. 6), and in which
the chyle and the lymph, as the fluid in the lymphatics is
called, are mingled together.
The other trunk, which receives the lymph from but a
small part of the body, empties its contents into a large
vein at the right side of the top of the chest. The largest
part of the lymph, therefore, unites with the chyle, and is
poured with it into the circulation, and the rest reaches
the same destination by another way. It all becomes with
the chyle a part of the blood. But before this it passes,
like the chyle, through glands, in order to fit it to becomD
again a part of the building-material of the body. These
glands are everywhere in the track of the lymphatics.
They are often enlarged from disease, and then they can be
readily felt. In relation to this appropriation of waste particles, it may be truly said that man lives in part upon
his own flesh.
Those waste particles which are entirely useless are taken
up by the veins directly into the circulation. They then
travel the rounds with the blood, and are thrown off from
the system by organs fitted for that purpose. These organs




FORMATION AND IREPAIR.                   161
are the lungs, the skin, tile liver, the kidneys, etc. Each
of these excretory organs is fitted to throw off its particular
part of the waste.  Thus the lungs excrete a kind different
from that which the skin does; and so of the rest.
200. Excretiolt adtd  Secr etion.-It is interesting
to observe that some of the excretory organs perform other
functions besides that of mere excretion.*  Thus the lungs,
while they excrete carbon, absorb oxygen, without which
life could not go on.  At the same time, too, they act as the
bellows for the organ of the voice, the larynx, as you will
see in the chapter on that subject.  So, also, the liver, while
it excretes what would be noxious if it remained in the
blood, puts its excretion into such a form, that it proves, as
you saw in the chapter on digestion, an auxiliary in some
of the processes of the digestive organs.
201. The Skis*. — The skin, while it is an extensive
excreting organ, performs other important offices.  It serves
as a firm  yet very flexible and soft covering to the body,
protecting its internal parts from injury. It is highly endowed with nerves for two purposes-the one, that it may
act as a sentinel to warn of danger; and the other, that it
may be the seat of the sense of touch.  What is very commonly spoken of as the skin, is not really the skin, but only
a covering for it.
202. Cuticle.-When the skin is rubbed off, as it is expressed, it is only this covering of the skin, or cuticle, which
is removed. The skin which is raised by a blister is this
cuticle.  The great object of the cuticle is to protect the
true skin, which is very fully supplied with nerves for
the purposes mentioned above, and which therefore, if uncovered, would prove a source of severe suffering. As it is,
* The words excretion and secretion, are often applied to the same
thing. Excretion, strictly speaking, should be applied only to something to be thrown off, and not to something formed to be used. But
sometimes an excretion is so formed that it can be used, and then the
word secretion is also applicable to it. Thus the bile, while it is an
excretion containing noxious particles to be thrown off from the system,
is put to use, and so it is as often called a secretion as anll excretion.




1G;2          PHYSIOLOGY AND HYGIENE.
the cuticle protects the skin effectually, and yet does not
interfere with its functions as the organ of the sense of touch.
It is of so slight and so soft a texture, that the nerves of
touch may readily receive impressions through it. It is
composed of many layers of minute round cells, the outermost layers being made up of these
FIG. 97.        cells broken and emptied of the
fluid which they contained.
203. Trute Sk in.-The true
skin, which the cuticle covers, is of
- 5,:a afibrous texture, with a good supply
of both nerves and blood-vessels.
On the surface of this true skin
next to the cuticle are eminences
called papilla. In these are seated
b  the extremities of the nerves of
X:~    ~~/i i'touch. Fig. 97 represents a highly
magnified section of a bit of the
the cuticle; c is the true skin; b
4(~/1/" "represents the papillae.,204. Tubi'ny in the Skin,.I/,V iji gYou observe a tube which runs
a> li   up through the cutis or true skin
c  and the cuticle, and in the latter
takes a spiral course. This is the
I~l [l~,,~~~ [~     discharging tube of the sweat-gland,
l, lying within the true skin, and
f |       Msurrounded with globules of fat.
These glands are more numerous
/ in some parts of the skin than in
others. They are particularly nunmerous on the palms of the hands,
and on the soles of the feet.
Mr. E. Wilson counted, with the
aid of the microscope, 3528 of them
Vertical sectionof the  in a square inch on the palm of the
SOLE OF THE FOOT.    hand.  Reckoning the length of




FORMATION AND REPAIRS.              1(3
one of these at one quarter of an inch, it gives 882 inches
or 73- feet of tubing in this small space. He calculated the
amount of this tubing in the skin of the whole body as
being 48,600 yards, or nearly 28 miles. The amount of
excretion from the seven nlillions of these tubes, which
open on the surface of the skin, is very great.
205. Insensible Persspiratioit,-The perspiration
is ordinarily insensible, as it is termed; that' is, it is in the
form  of vapor. But sometimes, as in vigorous exercise,
when the sweat-glands are rendered very active, chiefly to
prevent too great an accumulation of heat, the perspiration
becomes sensible.
206. Sebaceouts Glands.-There is another set of
glands in the skin, called sebaceous glands, which secrete
an oily fluid. They also have thin tubes like the sweatglands. They are most abundant where the skin specially
needs an oily lubrication, as where there are folds in the
skin,or hairs, or where the skin is exposed to friction, or to the drying at-    FIG. 98.
mosphere. They are very abundant on
the face and head. Every hair has sebaceous glands connected with it, as represented in Fig. 98; in which b is the
hair emerging from  the skin; a a are
the sebaceous glands pouring their se-       -a
cretion by thin tubes into the tube or
canal in which the hair grows; c the
root of the hair surrounded with fat
globules.
207. Influe))ce of Labor on 
lWeanr and Teal', an Jd on AbsorpStion -By the facts developed in this
chapter, it is thus seen that there is constant change going on in all parts of the
body.  Particles which have become
HAIR
riseless are taken up by the absorbents   and sebaceo,glands.
while the formative vessels deposit
others to take their places. The rapidity with which this




164           PHYSIOLOGY AND HYGIENE.
change occurs, depends mostly upon the activity of the
individual. The busy laborer, whether the labor be bodily
or mental, requires more nourishment than the indolent
man, because there is more waste in his case, from the wear
and tear occasioned by motion or thought, and there is
therefore a necessity for a larger supply of repairing material.
The difference, it is true, is not so great in regard to
mental labor, as in regard to that of the body; but still it
is very apparent.  This dependence of the amount of
change in the system upon the degree of activity is very
manifest, if we compare different animals in this respect.
The frog and the canary bird, in regard to respiration, have
been already contrasted, and they can be contrasted in this
respect also. As the frog makes but little exertion either
of body or mind, there is but little change in his body, and
but little nutriment is required to supply the small waste
that occurs. But in the ever active canary there is much
waste from this action, and therefore there must be much
eating to supply the material of repair.
208. CGhaange Varies inl Different Parts of
the Body, and iAl the sane Bod y at Diferrent
Ti'nes. —The relation thus seen to exist between the
amount of change and the degree of activity, is exemplified in a comparison between differenE parts of the body.
In those which are most actively used the change of decay
and repair is going on most constantly. The active muscles and nerves are continually changing; while the bones,
which are only passive instruments of motion, are changed
very slowly.
And it is a significant fact, that in the case of the muscles and nerves, the waste particles are to a large extent of
the entirely useless kind, for they are mostly absorbed by the
veins, these tissues containing but few lymphatics. That
is, whenever we think, or feel, or move, we render entirely
useless quantities of the particles which make up the structure of the muscular and nervous systems, and these are
got rid of at the proper outlets, while other particles immediately take their places.




CELL-LIFE.                  165
209. Life a Result of Death.-In this constant
change going on in the body, life and death may be said to
be brought into very near companionship. Every act of
the mind, and every movement of the body, breaks down
some of the structure; and the particles, which are no
longer fitted to maintain the living functions, must be
taken away as refuse dead matter, and new particles
endowed with vital affinities must take their place.
Action, destruction, repair, are the successive events
which are ever occurring in every part of our frame. Action is followed by destruction, and in proportion to its
intensity; and repair is necessary to fit it for further action.
And so through life the nutritive functions are thus struggling against the tendency to decay and death, till at length
at the appointed limit the struggle is given over, the vital
affinities release their hold, and the common laws of dead
matter take possession of the body.
CHAPTER XI.
CELL-LIFE.
210. The Formative  Vessels shown by the
M]icroscope to be Cells.-It is found by the aid of the
microscope, that all the minute operations of the system
are performed by the agency of cells. They are not such
cells as are found in the cellular tissue, which are mere
interstices, communicating together, but they are bladders
or sacs, and are filled either with a fluid alone, or with a fluid
containing some grains of solid substance, termed molecules. The usual form of the cell when it first appears is
globular or spheroidal. It is seldom, however, seen in this
form; for, besides the change of form from the pressure of




166           PHYSIOLOGY AND HYGIENE.
neighboring cells, the cells themselves often assume various
shapes from other causes.
211. Seent in  the Bootd  and in Amost other
Parrts.-Cells can be seen in the blood. If the web of the
foot of a live frog be placed under the microscope, they
may be seen sweeping along in the blood-vessels, like so
many little bladders, varying their shape, according as they
press on each other, or on the sides of the vessel. This is
very well represented in Fig. 99, in which a portion of the
web of a frog's foot is seen as magnified 110 diameters,
The dark irregular spots which you see, as at 3, 3, are pigment cells, which give the color to the part.
FIG. 99.
CAPILLARIES IN THE WEB OF A FROG'S FOOT.
Cells may be seen, not only in the blood, but also in most of
the other fluids, as well as in the solids. The solid parts of animal bodies are composed either of cells, or of structures pro



CELL-LIFE.                    167
duced by cells, oi of a mixture of these structures with cells.
The sarne can be sail also of plants. Cells, therefore, are the
real formative vessels in both classes of organized beings.
212. Cells ini the Lower A'ni#m3als.-'We have very striking exhibitions of the cells in FIG. 100.
the lower orders of animals. The Hydra, arepresentation of which is given in Fig. 1, seems to be
made up of little else than cells. If you observe
under the microscope one of its arms, as it moves'~
about, the motion appears to be a motion of the
cells upon each other. There are no fibres to be    0
seen, to which the motion can be attributed.
Fig. 100 represents one of these arms highly mag-   0
nified. The cells, as you see, have somewhat of      o
a spiral arrangement.
213. Character and Color of Tisstes                O
dependent ont the Contents of Cells. —   (KO
COO
The character of many of the tissues in the body    0oy0)
depends on the contents of the cells.'The cell    00 0
itself, or the cell-wall, as it is termed, is con-  o~07O
sidered to be always the same. But the contents
vary, and this variation  makes generally the    CELLS
variation in the character, and in the color also,  in the arm of
of the various textures.
For example, all the glands are constructed essentially on
the same plan; and their difference depends upon the contents of the cells in them. Thus the liver differs from the
tear-gland, chiefly because the former has cells which fill
themselves from the blood with the components of bile,
while the other has cells which fill themselves with the
components of the tears.
The color of various parts, as the iris of the eye, the skin
of the dark-colored, the hair, &c., depends upon a coloring
matter which constitutes either a part or the whole of the
contents of particular cells.
214. Selecting Power of the Cells.-It is clear,
from the facts which have been stated, that the cells have a
selecting power. In the body they take from the common




1 68          PHYSIOLOGY AND HYGIENE.
pabulum or material, the blood, such constituents or substances as they need for their particular purposes. Illustrations of this have already been given, in speaking of the
difference in the glands. Every cell contains its own peculiar constituents, which it has taken from the blood. For
example, there are fat-cells which receive fatty matter from
the blood, rejecting everything else; pigmentary cells receiving nothing but coloring matter from the blood, &c. The
same thing appears too in plants. There are cells which
receive from the sap volatile oil; others, fixed oil; others,
starch; others, coloring matter, &e.
Fluids, and sometimes gases, enter the cells continually.
The pores through which they enter are not visible even
through the microscope, but of course such pores must exist.
Their entrance is controlled by the selecting power to which
allusion has been made.
2 15. Cells Real Laboratories. —Not only is there
a selecting power in. the cell, but there is often a converting power, by which new compounds are formed from the
constituents introduced into it.  The cell in this case,
though so small as to be seen only by a microscope of
considerable power, is a real laboratory, effecting chemical
changes in its contents. There can often be seen quite a
brisk movement in the molecules in the cell while these
changes are going on.
216. Differenlt Offices of Cells.-Cells, as has been
already stated, do not all perform the same office, but there
are cells for a great variety of purposes.
There are different kinds of cells in the blood. There are
colored and colorless ones. The office of the colorless ones
has not yet been satisfactorily determined. But we know
more about the colored ones. These give the red color to
the blood. They are not red when looked at singly, but are
of a yellow  cast; and the red color appears only when
several are together.
217. Office of Red Cells int  the Blood.-One
office of these colored cells is to carry oxygen to all parts of
the system, and return the catrbonic acid to the lungs to be




CELL-LIFE.    1.9
thrown off. By carrying these cargoes back and forth in
the circulation, these little cells perform a very important
office. A very valuable part of the cargo of these cells is
iron. In low states of the system, when the red cells are
deficient, the administration of iron in some form is often
found to be very effectual, in connection with a good diet,
in remedying the deficiency.
The proportion of these red cells varies much in different
animals. It is largest in those which are the most active.
The proportion is greater generally in birds than in the
mammalia, and it is much greater in the latter than in reptiles or fishes. In man it varies much in different inldividuals. These cells are abundant in the ruddy, strong, and
active; while they are less numerous in the inactive, pale,
and feeble.
218. Jlanner in  which Absorption is Per-'formed by Cells.-There are cells for absorption, and
cells for secretion and excretion.  It has been said in the
chapter on Digestion, that the vessels called lacteals absorb
chyle from the contents of the intestine. It was formerly
supposed that they did this through their open mouths on
the surface of the mucous membrane. But the absorption
is accomplished by cells, which are developed for this purpose at the extremities of the lacteals. They take up the
chyle and discharge it into the lacteals, and they are dissolved away in the very act of emptying themselves.
A new crop therefore of cells appears every time the process of absorption is to be performed. And, what is still
more curious, every time that absorption is to take place,
there is cast off, as a preparatory step, a sort of pavement
of cells from over every point in the mucous membrane
where there is an extremity of a lacteal. The absorbing cells
are thus uncovered, so that they can perform their duty.
All this can be made clear by the following diagram. The
surface of the mucous membrane of the intestine is not a
perfectly smooth surface, but examined by a microscope, it
is seen to be covered with eminences and depressions. Absorption takes -place on the eminences, while the depressions
8




170           PHYSIOLOGY AND HYGIENE.
are the seats of secretion. In the diagram, Fig. 101, you
have a representation of the arrangement of one of the
eminences highly magnified. A represents it as it is in the
intervals of digestion when absorption is not going on, and
FIG. 101.
A                    A
b           aab
AGRAM  ABSORPTION IN A   O  MEMBRANE.
DIAGRAM SHOWING ABSORPTION IN A MUCOUS MEMBRANE.
B as it is during absorption; a a are the absorbent vessels
or lacteals; b b basement membrane, as it is termed, an
exceedingly thin membrane acting as a basement to the
pavement cells c c; d d the absorbing cells. When absorption is not going on, the prominence is somewhat shrunken,
and the pavement cells cover it. There are some granules
or small grains, d, in A, which are, it is supposed, the germs
of the absorbing cells, which you see developed in B. When
absorption is taking place the prominence is swelled out as
represented, the lacteal vessels are full, and the absorbing
cells appear at their extremities, while the pavement cells
have been thrown off, so that the chyle may have free access
to the absorbing cells through the pores or interstices of the
basement membrane.
219. JManner in which Secretion is Effected
by them.-While absorption thus goes on in the eminences, secretion takes place in the depressions. The diagram, Fig. 102, represents one of these depressions, or follicles, as they are termed, in two opposite states, when secreting, and when not secreting. TIn A, secretion is not going




CELL-LIFE.                    171
on, and the cells e, in the follicle, remain quiet. In B, on
the other hand, secretion is taking place, and it is done by
the casting off of cells, as represented. These cells discharge their fluid contents into the cavity of the intestine,
and disappear, while other cells take their places. These
FIG. 102.
A
B    c                c
DIAGRAM SHOWING SECRETION IN A MUCOUS MEMBRANE.
follicles are really little glands. And the various glands,
the salivary glands, the liver, the pancreas, &c., are made up
essentially of such follicles arranged in different ways.
220. Muscles made up of Cells. —There are some
cells which are devoted entirely to the production of motion,
for an ordinary muscle is composed of great numbers of
chains of cells included in sheaths bound together. A
muscle appears to the naked eye to be made up of fibres.
Each one of these fibres is found by the microscope to be
composed of from 500 to 800fibrillae, or minute fibres. And
FIG. 103.
a                     b
FIBRE OF A MUSCLE.
each of these fibrillke is a series or chain of cells. In Fig.
103, a, is represented a fibre as seen under the microscope,
showing the fibrillea of which it is composed. They are




172            PHYSIOLOGY AND HYGIENE.
separated at the broken end by the violence in tearing the.fibre. In b, you see one of the fibrillee very highly magnified, showing that it is a chain of cells. In
FIm. 104.  the diagram, Fig. 104, is represented the cona    dition of a fibrilla in the two states of contraction and relaxation. In a it is relaxed.
In b it is contracted, the cells being shortened, and at the same time widened. And
as all the cells in the muscle are thus widened
when the muscle contracts, we see the cause
of the well known swelling out of muscles
when they are in action. That you may form
some idea of the size of these cells in muscles, I will state that in the space of the
square of a tenth part of an inch, thus, o,
there are over 100,000 of these cells.
221. Hoofs, Horns, 2Nails,  and
Teeth made by Celts.-There are cells
whose office is to make certain solid deposits.
MSCUAR.: Hoofs, horns, nails, and teeth are made in
a relaxd;b contracted. this way.  Even the hard enamel of the
teeth is constructed by cells. They deposit
it in the form of prisms of hexagonal shape as seen in Fig.
105, which represents a vertical section of enamel as seen
Fig. 105.
VERTICAL SECTION OF ENAMEL.
under the microscope. Their shape is more plainly seen
in A, Fig. 106, which represents a transverse section of




CELL-LIFE.                   173
enamel. The line of these prisms is generally wavy, but
they are for the most part parallel to each other. At B are
some of these prisms separated. They are more magnified
here than in Fig. 105.
FIG. 106.
ENAMEL.
A, Transverse section. B, Separated prisms of it.
222. Nerves composed of Tubes made from
Cells.-The nerves are bundles of tubes of exceeding
fineness. They vary from  & —th to Toko6-th of an inch in
diameter. Now, each of these little tubes, or tubuli, as
they are called, was once a chain of cells. The cells in
each chain or row, as the microscope has shown, gradually
became incorporated together to become a tube, and in this
tube is contained the true nervous matter.
And it is supposed that each of these tubuli preserves
itself separate and distinct, from its origin in the brain, or
some other of the central organs
of the nervous system, to its         FIG. 107.
termination in some fibre, or   A
on some surface. For no cont-   0 
munications between the tubuli   0
have ever been found by any   0
nmicroscopist.  The manner in   0
which these tubuli are made   0
from cells may be illustrated by
the diagram in Fig. 107, in which the steps by which the
row of cells A becomes the tube B are represented.
223. All Organized Substances built up by
Cells.-All animated nature is built up by cells. The first




174            PHYSIOLOGY AND HYGIENE.
thing which comes from the supposed germ is a cell. And
this single cell is the parent of all the cells which build up
the whole structure, whatever it be. It is by these cells thus
produced, that all plants and animals are constructed. "A
globular mass," says Carpenter, " containing a large number
of cells is formed before any diversity of parts shows itself;
and it is by the subsequent development, from this mass, of
different sets of cells, of which some are changed into
cartilage, others into nerve, others into muscle, others into
vessels, and so on, that the several parts of the tody are
ultimately formed."
224. Arrangement of the Parts of the Eqg.By an examination of different eggs at different stages of
the process of hatching, the various steps in the development of the animal have been observed and noted. In the
middle of the egg is the yellow yolk, composed of albumen
and oil globules. It is surrounded by an exceedingly thin
sac, which keeps it separate from the albumen, or white of
the egg that envelopes it. The yolk b, Fig. 108, is lighter
FIG. 108.
SECTION OF A BIRD'S EGG.
than the white, and it therefore always seeks the highest
point in the egg. But it is held down by two very delicate
ligaments e, e, connecting it with the white lining of the
shell. And you will observe, too, that the cicatricula, or




CELL-LIFE.                  175
germ-spot, a, which is a collection of cells beginning the
process which is to form the animal, being lighter than the
yolk is always at the top of it, in order to receive the
warmth from the body of the bird as it sets upon its eggs.
There is at the blunt end of the egg,f, a bubble of air
which is intended as an invigorating draught for the lungs
of the young bird preparatory to its bursting its shell.
225. Successioan of Cells in the Yolk before
the Animal isformed.-When the processes preparatory to the formation of the animal commence, the yolk
itself is composed in part of cells, as represented in Fig. 109,
A. In the midst of it there is a germinal spot, a, with a
vesicle in it. b. This vesicle produces a cluster of cell&
FIG. 109.
A;~          B  e.\ I Alit
DEVELOPMENT OF CELLS IN THE YOLK DURING INCUBATION.
But these cells, and those which in part compose the yolk
are temporary, and all disappear. Before, however, the
cluster of cells in the germinal spot disappear, there are
seen in the midst of them two twin cells. These multiply;
and what is singular, they do it by doubling, so that there
are successively 4, 8, 16, 32, &c. At length there is a mass
of them like a mulberry, as at e, in B. This mass then




176           PHYSIOLOGY AND HYGIENE.
sends off cells at its edges which makes a layer, f, all round
the yolk as represented in C. A second layer, g, is formed
inside of the first as seen in D. In the case of the higher
animals a third layer is added.
226. Dlevelopment of Organs.-There is no formation of the animal yet. Soon, however, a single large cell
appears in the center of the mulberry-shaped mass of cells,
and from this begins the formation of the animal. All the
other parts of the egg-the cells, the yolk, the white-are
tributary to the action which proceeds from this cell.
Within its wall is a ring-like nucleus. This takes the shape
of a pear, and then it is afterward very much like a violin.
From this nucleus are produced cells which form all the
various parts of the animal, the heart, lungs, stomach,
brain, limbs, &c. And these are made of the yolk and the
white of the egg.
From the views which have been presented in this chapter it is manifest, that the grand distinction between organized
and unorganized szubstances is to be found in this Cell-life of
the organized. In unorganized substances particles or molecules are the only things which we know of as being concerned in their formation. But in the construction of
organized substances or beings, every thing is done by the
agency of cells. And in this cell-life of the living world we
have another beautiful example of the divers and almost
numberless results which the Creator works out by simple
and single means.
As gravitation holds atoms together in masses of every size
from the minutest to the largest, and keeps the mighty orbs
in their appointed circuits, so cell-organization constructs
and moves all living things, however small, however large,
and however diversified.
22'. The Power of the Deity showrn  in the
]iinute Operations of Xature. —As we examine
the various workings of this cell-life, we can not but perceive the truth of the old adage, Natura in minimis
maxima est-nature is greatest in the smallest things. The
power of mere bulk or mere force we can comprehend by




CELL-LIFE.                   17 7
mental addition, however great that, power may he. We can
imagine a power which we see, to be indefinitely multiplied,
and thus can form  the idea of immense power.  But
when with the microscope we see minute cells working out
such results as we have contemplated in this chapter, and
inquire how it is done, we see that there is a hidden power
here that utterly defies our conception. The mechanics and
the chemistry of the cell, who can understand them?
From the inscrutable movements of this hidden power, at
work wherever life is, in the cells, its laboratories, we get a
higher idea of Omnipotence than we can get from the
grandest and most terrific exhibitions of mere force. We get
from them the idea of an all-pervading, as well as an allwise power, working not merely in every locality, but at
every point of the universe. And the revelations which the
microscope makes to us seem to draw us very near to the
Infinite. As we gaze with wonder and delight at the secret
operations of his power thus opened to us, we seem almost
to be admitted to his presence; and even our awakened
curiosity, amid the wonders now brought into our field of
vision, does not suffice to remove the awe which almost
oppresses us.
How great is the inner beauty of the living world around
us! We admire the symmetrical forms, and the beautiful
colors which nature presents to us in such variety; but
there is an inner world of beauties throughout nature, still
more perfect and resplendent, which is hidden from the
naked eye of man, though it is all open to the Omniscient.
If you would get some idea of the beauty of this inner
world, take the most delicately beautiful of all the specimens
of man's workmanship, and examine it with a microscope;
and then compare it with some living texture or coloring.
Compare in this way, for example, the most perfect painting
of a flower with the flower itself. The painting loses all its
beauty as it is magnified; but in the bosom of the flower
the microscope develops to you beauties far transcending
those which are seen by the unassisted eye. Even such living structures as are unattractive to the naked eye, present




178           PHYSIOLOGY AND HYGIENE.
under the microscope wonderful beauty in the delicate lines
of their textures.
It is true of every one who has used this instrument in
his observation of nature, that he is impressed with the fact
that, great as is the beauty of nature, as we look out upon it,
it is vastly inferior both in kind and in amount to that
inner beauty seen so completely by the all-seeing Eye, and
now developed to us in part by the skill and ingenuity of
man. And it suggests to us the hope, that in a new state
of being, and with higher faculties, we shall be able to look
farther into these inner beauties of the universe, than we
now can with all the aids which our ingenuity can devise.*
CHAPTER XII.
THE NERVOUS SYSTENM
228. Process of Nutrition  in  Plants and
Animals quite alike. —Thus far we have contemplated
man merely as a structure. We have observed the means
by which the body is built and is kept in repair. We have
seen that the functions of nutrition in man and all animals
have much in common with those of plants. So far as
these functions are concerned, they vary from plants only
in the modes by which the nutrition is effected.
The absorbents in the root of the plant do for the plant
what the lacteals in the digestive organs do for the animal,
the difference between them being only according to the
differing circumstances. So also, circulation and formation
are in all essential points the same in these two different
departments of animated nature.
* I could not find it in my heart to cut out the above paragraphs
relating to the power of the Deity shown in the minute operations of
nature; though they contain little of direct instruction, the reading of
them can not fail to make a good impression. —ED.




THE NERVOUS SYSTEM.               179
229.  The  Nervous System- the Essential
Difference between Plants and Antimals.-The
functions which have been treated in the previous chapters,
as being common to plants and animals, are called the functions of organic life, because they concern merely the structure, the organization. But there are other functions. The
body, with all its complicated parts, is constructed and kept
in repair for certain uses.
These uses are secured by the nervous system,-a system
which is superadded to what the animal has in common
with the plant, and which, therefore, constitutes the essential
difference.between the animal and the plant. This system
furnishes the means of the relations of the animal to the
world around him.
He receives his impressions from external things through
this system; and through it he acts upon external things..He feels through the nerves, and by the nerves excites those
motions by which he acts on both material and immaterial
existences.
The functions, therefore, which are performed through
this system, are called functions of animal life, in distinction
from the functions of organic life, which are common to
vegetables and animals. They are sometimes also called
functions of relation, in view of the relations which it establishes between sentient and moving beings, and all external
things.
230. The Nervous System  and its Subordihnate  Imnstruments. -The nerves do not themselves
move, but they excite motion in muscles, and these move
bones and other parts. Neither is sensation performed by the
nerves alone. The different senses, for example, have different organs, with arrangements differing according to the
kind of sensation. Mere nerves alone do not see, or hear, or
taste, or smell, or touch.
There are special organs constructed for these purposes;
and through these,the nerves receive impressions. Thus the
nerve of sight can not of itself see; but the eye being there,
so formed as to have pictured on a membrane the images of




180          IPHYSIOLOGY AND HYGIENE.
objects, the nerve receives an impression from these images,
and this impression is transmitted through the trunk of the
nerve to the brain, where the mind takes cognizance of it;
and this constitutes seeing.
231. The Lighther theb Rank the more ContplUcatedl the 3Nervoits Systeim.-The nervous system in
the lower orders of animals is very simple, and forms an exceedingly small part of the animal. But, a, wAe rise in the
scale, we find that, as the limits of relation to external things
enlarge, this system becomes more prominent; till, in man,
in whom  these relations, both mental and physical, are
much more extensive than in any other animal, it is very
prominent and greatly complicated.
232. All KnotColed   e Acquired and CommutCnicated bty Nerves. —A  child as it first opens its eyes
upon this world, knows nothing at the outset of shapes, or
colors, or distances, or any other relations of things. This
is all to be learned through the nerves and their subordinate
organs.  And as all knowledge is acquired through the
nerves, so it is communicated through nerves to others.
It is communicated by the motions that are excited in
the muscles by the nerves; by the motions of the countenance
varying its expression; by the motions of the limbs, or
gestures; but especially by the motions which produce and
articulate the voice. Thought andfeeliny can be commnunicated in no other way than by muscular motion.
233. Parts of the Nervouts Systemn.-The nervous
system may be considered as having three parts: 1, certain
central parts, as the brain and spinal marrow; 2, nervous
trunks, which going from these central parts divide and subdivide, as the arteries do, till they become exceedingly
minute; and 3, the nervous expansion in the organs, having
a relation to the nervous trunks similar to that which the
capillaries bear to the arteries.
In what we call sensation we suppose that an impression
is produced in the nervous expansion, that the trunk serves
to transmit it, and that through the nervous center, the
brain, it is communicated to the mind.




THE NERVOUS SYSTEM.               181
234. Conditions _Necessarcy to Sensation and
Motion.-Let us see now what is necessary to this compound act, termed sensation. First, it is necessary that
the organ where the nerve is expanded be in a condition
to let the nerve receive the impression. If the eye be so
injured in its textures that the impression can not be made
on the nerve, there can be no vision.
It is necessary, also, that the trunk of the nerve be in a
proper condition. If the nerve of vision be pressed upon
by a tumor, there will be no impression transmitted from
the images formed in the eye. So, too, if a nerve going to
any part of the body be cut off, there can be no transmission
of impressions to the brain from that part.
Again, it is necessary to sensation that the brain should
be in a state to communicate the impression to the mind.
If the brain be pressed upon strongly by a depression of the
skull from violence, or by effusion of blood by the rupture
of an artery, as sometimes occurs in apoplexy, there can be
no sensation.
Excitement of mind, too, sometimes prevents the occurrence of sensation, by its action upon the connection between
the mind and the brain. Thle pain of a wound received in
battle is often unfelt, until the excitement of the battle is
over. The aching of a tooth is often stopped by the excitement consequent upon going to the dentist to have it extracted.
In these cases the cause of the pain is acting all the while
upon the nervous extremity, and the trunk of the nerve is
capable of transmitting the impression, but the state of the
mind is such, and such is the consequent condition of the
brain, that the sensation does not occur-one link in the
necessary chain is defective.  The same can be said as
regards the necessity of each of these links of the chain, in
relation to voluntary motion, as well as to sensation.
235. General Plan of the Nervous System.In Fig. 110 there is presented a general view of this system,
-the central organs with the nerves going out from them.
At a is the cerebrum, the upper large brain, filling up a con



182           PHYSIOLOGY A~N-D HYGIENE.
FTG. 110.
c~~-~sg~"/, ~, —a/
0:t~  — ~7,4~~~~~~~~-a,q
---.~~~~~~~~~~~~~~~~ lV
-— I
NERVOUS Tt1/iKS IN A MAN.




THE NERVOUS SYSTEM.               183
siderable portion of the skull; at b is the cerebellum, the
smaller brain, lying beneath the cerebrum at its back part:
at c is the great facial nerve, the chief nerve of the face; the
spinal marrow, cld, sends off branches on either side in its
whole length; at e is the brachial plexus, a bundle of nerves
coming from the spinal marrow, which here unite together,
and are then distributed to all parts of the arm; at i is a
similar plexus from which are distributed nerves to the lower
extremity; f, g, and h point to different nerves in the arm,
and 1, mi, n, and o to different nerves in the leg. You observe
that the whole of this nervous system is divided into exactly
similar halves. The cerebrum and the cerebellum are both
double organs, and the nerves of one side are just like those
of the other.
FIo. 11 1
i k m —BRAIN AND NERVES.
236. Hemispheres and Lobes of the Brsain.Having thus noticed the general arrangement of the nervous
system, observe next the arrangement and structure of the
brain which are seen in Fig. 111. This Figure presents to




1S!t          PHYSIOLOGY AND HYGIENE.
view a perpendicular section of the brain, as made from front
to rear, dividing it into two halves. You have here a view
of the inner surface of one hemisphere, as it is termled, of the
cerebrum, the large upper brain, which is commonly described
as having three lobes or divisions: a, the anterior; b, the
middle; and c, the posterior. At f is the broad band of
white fibrous matter, which unites the two halves or hemriispheres, of course divided in the section; at d is the cerebellum, showing a peculiar arrangement, called the arbor
vitw, or tree of life; at g is the beginning of the optic
nerve which goes to the eye; 1 is the olfactory nerve; e is
the commencement of the spinal marrow.
237 ". Distt'ibutiow  of NYerves.-The many nerves
which you see, are distributed to various parts of the face;
the nerve at h goes to the tongue; at i, to the throat; and
at m. to one of the muscles of the eye. From the beginning
of the spinal marrow go forth many nerves, one of which,
k, is a very important one, as it sends off branches to the
lungs, the heart, and the stomach. It is this part of the
nervous system, the top of the spinal cord, that is most
immediately essential to the continuance of life. For it
is through their nervous connections with the top of the
spinal marrow, that the heart and lungs continue to perform
their duty.
238. Functions of Respiration  and Circulatiosn depeind on the Spinal Coa'd. —It has been
ascertained, by experiments upon animals, that the cerebrum, and even the cerebellum, may be destroyed, and yet
the animal will continue to breathe, and the circulation
will go on for some time. But the moment that this part of
the spinal cord is destroyed, from which the heart and lungs
are supplied with nerves, the breathing and the circulation
stop and the animal dies. So, too, in apoplexy, if the
effusion of blood take place at the top of the spinal marrow, death will occur, and in much shorter timle, than if
the effusion take place in the cerebrum or cerebellum.
239. Cerebrun.- You observe that the cerebrum
has deep irregular furrows on its surface, and that it pre



THE NERVOUS SYSTEM.               185
sents undulating tortuous projections. These are called
the convolu iions of the brain. Into the furrows between
them  dips down the membrane, in which branch out the
arteries that supply the brain with blood, and the veins
that return it from this organ.
This memebrane is, from  its soft and delicate texture,
called the pia Mater (soft mother), while the stout fibrous
membrane which lies outside of this next to the bony
covering is called the dura mater (or hard mother). The
names are entirely inappropriate, for the latter serves as a
protection to the brain, and the former is merely a vehicle
or medium for the entrance of the blood-vessels into the
brain. There is another membrane lying between these
which is called the araclhzoid membrane, because in its
tenuity and delicacy it resembles the spider's web. It is
one of the serous membranes, and it serves as a protecting
envelope to the brain, and at the same time, by its serum,
keeps this organ bedewed with moisture over its whole
surface.
240. Graq/ and White Su bs-aWnces.-Th e substance
of which the brain is composed is very soft, something like
blanc-mange. It is the softest organ in the body. In color
it is not uniform throughout. All around the white inner
part of the brain there is a thick layer of gray substance.
In Fig. 112 you have a horizontal section of the brain,
showing the proportions and arrangement of the gray and
the white substances. As the gray substance dips down,
as you see in the figure, into all the furrows, its extent is
greater than would at first view be supposed. In the middle is represented the broad band connecting the two hemispheres of the brain.  You observe in Fig. 111 and Fig. 112,
that there is no apparent arrangement of the external parts
of the brain which would give countenance to the idea of
the phrenologist in relatibn to its division into particular
organs. The convolutions, far from presenting any welldefined arrangement, are exceedingly irregular.
241. The  Gr'ay Sub:9talnce made  of Cells;
the lWhite, of Thubes.-The gray substance, which is




186           PHYSIOLOGY AND HYGIENE.
FIG. 112.
SECTION OF THE BRAIN,
sometimes called the cortical (bark-like) substance, because
it surrounds the white central part of the brain, is made up
of cells, while the white part, is composed of exceedingly
minute tubes. These tubes are continued into the nerves,
and as they hold the nervous matter, they constitute the
medium of communication between the brain and all parts
of the body.
This function of communication is the sole function of
the white nervous matter. In the brain this white matter
is a mere collection of tubes, and these branching out in
bundles form the nerves. These tubes are supposed to be
entirely separate from  each other, from their beginning in
the brain to their termination in the various parts of the
body, for the microscope has never discovered any union
between them at any point.




THE NERVOUS SYSTEM.              187
The brain, then, is a great central organ of communication, where innumerable minute tubes are brought together,
each of which is connected with some one moving fibre, or
some one sensitive point in the body. Those which are
connected with muscular fibres transmit impressions from
the brain, and those which are connected with sensitive
points transmit impressions to
it. Of the size of these tubes        FIG. 113.
you can judge by Fig. 113,
which shows some of them as
they appear magnified 350 diameters.
2412. Office of the Gray
]Mattei'.-The office of the
gray substance, it is quite well
ascertained, is very different
from that of the white substance,
as the difference in its structure
would lead us to suppose. It is           TUBUL
NERVOUS TUBULI,
more intimately connected with   Magnified 350 diameters.
the mental operations than the
white substance. When, for example, motion is produced in
obedience to the will, the impression producing the motion
is transmitted through the white matter, but the cause of
this impression does not act directly on this matter. The
impression is caused by the action of the mind on the gray
matter, and the white substance serves only to transmit it.
The gray matter, therefore, has a more active agency than
the white in the production of the phenomena of the mind
and the nervous system. It is the first link in the chain of
connection between the spiritual and the physical in our
nature. Hence, in examining the brains of animals, we find
that the higher the intelligence is, the more abundant is the
gray substance; and it is especially abundant in man, in
consequence of the large development of the convolutions.
243. The Gray Sitbstance well sutpplied with
Arterial Blood. —A due supply of arterial blood is absolutely essential to the vigorous performance of the functions




188           PHYSIOLOGY AND HYGIENE.
of the gray substance. If the supply be cut off in any way,
as by the failure of the heart's action in fainting, insensibility and loss of the power of motion are the consequence.
While the gray substance is on the outside of the brain, it is
on the inside of the spinal marrow.
244. Ganglions and Plexuses.-It is also on the
inside of the little bodies called ganglions, scattered here
and there, as depositories of nervous force-little brains, as
we may term them. These ganglions are not merely a part
of the apparatus of communication, as are the plexuses,
which are mere combinations of nervous trunks, as seen
in Fig. 115, t t being the trunks, which, after uniting with
each other in various ways, again separate to go to their
different destinations.
FIG. 114.
FIG. 115.
At g, in Fig. 114, is a ganglion into which the fibres, f, of
the nerve, n, run. They then separate again into branches
b. These ganglions produce nervous force, and therefore
are composed like the brain in part of gray substance. The
spinal marrow, too, produces as well as transmits, and so
this substance forms a part of it.
245. Changes in the Nerve Cells. —This gray
substance, as it is in constant operation, is subject to much




THE NERVOUS SYSTEM.               189
wear and tear, as we may express it, and therefore the
changes of repair are constantly going on in its structure.
Hence the necessity for so large a supply of blood as is
secured by the network of vessels, among which the cells
peculiar to this substance are scattered.
246. Ternmination of the Xervous Libres. —
The extremities of the fibres, or rather of the tubuli, (Fig.
113) of the nerves terminate variously. The most common
termination is in loops, as seen in Fig. 116, which represents the termination of the nerves as seen through the
microscope in a thin perpendicular section of the skin of
FIG. 116.
NERVES OF TOUCH IN THE SKIN OF THE THUMB.
the thumb. The three eminences in this figure are those
of the papillc, as they are termed, which you can see, if
you look at the ball of the thumb, are arranged in curvilinear rows. In Fig. 117 you see this same loop-like arrangement of the nervous tubuli, as seen through the microscope,
on the sensitive sac that lines the cavity of a tooth, the
entrance for the nerves and blood-vessels of this sac being
at the end of the root.
24T. Pacinian  Corpuscles, their Office not
known. —One very singular termination of the nervous
tubuli, is in what are called Pacinian corpuscles, after
Pacini, the first microscopist that discovered them. They
are found attached to the nerves in the hand and foot more
often than any where else. Their structure, which is seen
highly magnified in Fig. 118, A, is very curious. They are




190          PHYSIOLOGY AND HYGIENE.
attached to the branches of the nerves, on which they cluster by little peduncles or stalks. At a is the peduncle; b is
FIG. 117.               FIG. 118.
A           B
NERVES IN A TOOTH.         PACINIAN CORPUSCLES.
the nervous fibre or tubulus; f is its termination in the
corpuscle. In B is represented a portion of a nerve of a
finger, with clusters of these corpuscles of about the natural
size. Of what use these singular bodies are we know not.
It has been supposed by some that they are minute electrical batteries, because they bear some resemblance to the
electrical organs found in some fishes.
248. Healing of Nerves.-There is a wonderful
fact in regard to the healing of wounded nerves which must
not pass unnoticed. You know that if a nerve be divided,
no impressions can be transmitted through it to and from
the brain. But the two cut ends of the nerves can grow
together, and the communication can thus be more or less
restored. Sometimes it is perfect as before. Now, if you




THE NERVOUS SYSTEM.              191
call to mind the structure of a nervous trunk, you will see
that this is passing wonderful. It is made up, you will
recollect, of tubuli which are entirely separate from each
other, and each one of these goes, from its origin in the
nervous center to its destination, by itself. It is difficult to
conceive, therefore, how the nerve can be healed without
creating confusion.
249. Nrice Fitting of the lTubutli.-For to avoid
this, it would seem to be necessary that each little tube at
its cut end must unite with its corresponding end, and not
with the end of some tube with which it has no relation.
For example, if the nerve distributed to the hand were cut,
it would no.t do, as it seems to us, to have tubuli which go
to the thumb unite with those which go to a finger.
And besides, as it will soon be shown you that the tubuli,
through which the impression that produces motion is
transmitted, are separate from those which transmit the
impression that causes sensation, it would not do for a
tubulus of one kind to unite in the healing with one of
the other kind.
That there is, however, a very accurate union effected, is
manifest from the observations of M. Brown S6quard.
He examined in animals nerves which were divided twelve
months before, and could not discover the point of division even with the aid of the microscope. If the tubuli
were not all made perfectly continuous as before the
nerve was divided, the microscope would have revealed the
defect.
But it takes time to effect this adjustment of the tubuli,
for it was found by Dr. Haighton that after dividing nerves,
their functions were not restored till some time after they
were apparently healed.
250. New  Nervous Connections  Formed.Taking this view of this interesting point, the difficulty is
greatly enhanced, when we look at the union of parts that
did not originally belong together, as, for example, when a
piece of skin is dissected from the forehead, and is twisted
down so as to be made to grow on to the nose to supply a




192           PHYSIOLOGY AND HYGIENE.
deficiency there. Here entirely new relations are established between the nerves of the divided parts, and, as we
should expect, there is confusion in the sensations. The
patient, at first, whenever the new part of his nose is
touched, refers the sensation to the forehead. But this
confusion of the sensations is after awhile removed. And
it is curious to observe, that while the old nervous connections are breaking up, and the new ones are becoming
established, there is an interval of partial, sometimes entire,
insensibility in the part. How these new relations can be
established consistently with the known arrangement of
the tubuli in the nerves is a mystery.
251. Nerves of the Spintal Marrow   Comnpound.-The nerves through which the mind sends its
messages to the muscles, are not the same as those through
which it receives impressions in sensation. In and about
the face, the nerves of motion and sensation are, for the
most part, entirely separate from each other. But in other
parts of the body, the fibres or tubuli for motion and sensation are mingled together in the same nervous trunk, inclosed in one sheath.
It is found that each of the nerves, coming out from each
side of the spinal marrow, has two roots, which unite,
FIG. 119.   and are inclosed in one sheath.  This
arrangement is represented in Fig. 119, in
which a is a portion of the spinal cord;
dcl the anterior root; b the posterior root; e
c   the trunk formed by the union of these two
roots; and f a branch of the nerve. At c,
on the posterior root is one of the ganglions,
or little brains, previously mentioned. Why
SPINAL CORD. they are placed on these posterior roots, and
not on the anterior, or why they are placed
here at all, we know not.
252. Different Nerves for Different Offices.It has been ascertained by many experiments on animals,
that the posterior roots are composed of tubuli, which bring
impressions to the spinal marrow; while the anterior are




THE NERVOUS SYSTEM.                 193
composed of tubuli which carry impressions from the spinal
marrow. For, if the spinal cord of an animal be laid bare,
and a posterior root be irritated, pain is produced; but
if an anterior root be irritated, violent motions are caused
in the parts to which the nerve is distributed. That is,
the posterior root is a nerve of sensation, and the anterior
a nerve of motion. It is a matter of convenience that
they unite and are mingled together in the same sheath,
for they are to be distributed in the same parts. In and
about the face the nerves of motion and sensation are kept
for the most part separate, as before stated, merely because
it would be no convenience in any case to put them together
in one sheath.
253. Nerves of Special Sensation.-But not only
are there different nerves for sensation and for motion,
but there are also different nerves for different kinds of sensation. Thus, in the eye, the optic nerve which transmits
the impressions from the images formed on the retina, as
will be shown in the Chapter on the Eye, is wholly separate
from the nerve by which any pain or irritation is felt in this
organ. The latter is called a nerve of common sensationthe former a nerve of special sensation. So in the nose,
the nerve that takes cognizance of odors is a different one
from that by which irritation of the lining membrane is felt.
The snuff-taker smells the snuff with one nerve, and feels
tingling with another.
Each set of nerves is fitted for its own peculiar office, and
has for this its own peculiar susceptibility. Thus, the nerves
of touch are insensible to light, and, on the other hand, the
nerves of vision are insensible to touch. If, therefore, the
nerve of vision be paralyzed, but the nerve of common sensation in the eye be unimpaired, although there is no seeing,
the eye is as sensible to irritation as ever.
On the other hand, if the nerve of vision be unimpaired,
and the nerve of common sensation be paralyzed, as sometimes happens, the individual can see, but he has lost the
sentinel that stands guard over the eye, and by its warning
of pain keeps it from injury. What, therefore, is flying in




194          PHYSIOLOGY AND HYGIENE.
the atmosphere may lodge in the eye, and though it produce no pain, it will excite inflammation by irritating the
capillaries.
When the nerve of common sensation is in a healthy
state, the moment any thing gets into the eye great pain is
produced, and the tears flow and the eyelids are in constant
motion; and by these instinctive means, as we may term
them, the irritating substance is removed. But when this
nerve is paralyzed, although the irritating substance produces no pain, it gradually causes inflammation in the delicate vascular texture of the eye.
2,54. Different Deyrees of Sensibility in  the
Various Parts of the Body. —Different parts of the
body are endowed with different degrees of sensibility, according to their necessities, in relation to the warning of
danger. Thus the skin is the most sensitive part or organ
of the body, that it may warn at once of the approach of
danger; while the internal parts have much less sensibility,
and some of them have none. In the performance of operations, therefore, the great suffering is in the cutting of the
skin. There is very little sensibility in the muscles, and
there is none in the bones.
The following fact illustrates the use of the sensibility of
the skin in the prevention of injury. A man who had lost
all sensibility in his right hand, but retained the power of
motion, lifted the cover of a pan when it was burning hot.
Although he was not aware of any effect at the moment,
the consequence was the loss of the skin of the fingers and
of the palm of the hand, laying bare the muscles and
tendons.
255. Inflamed Parts very Sensitive.-Although
there is so little sensibility in the internal parts in their
healthy condition, yet when they become inflamed they
become painful, sometimes acutely so.  Thus, an inflamed bone is the seat of severe pain; and the tendons,
although nearly insensible ordinarily, become very painful
when inflamed, as any one that has a deep-seated felon can
testify. The question as to the cause of this change of




THE NERVOUS SYSTEM.               195
sensibility we will not stop to discuss, but that there is a
benevolent object in it is very manifest. If inflammation
caused no pain in such parts, it might go on to a destructive
extent without the person's being aware of the danger, and
therefore without his applying for medical aid.
256. Nerves not Sensitive.-It was formerly supposed that a nerve must of course have an exquisite sensibility. But there is no sensibility in nerves devoted to
motion. Neither is there any in the brain itself. Portions
of it can be cut off without producing any pain. The heart,
too, is insensible to the touch. A case proving this fell under
the observation of Harvey, the discoverer of the circulation
of the blood. This absence of sensibility in the heart is not
because it is not well endowed with nerves. It is well
endowed, but with nerves which are devoted to another
purpose. They are nerves of sympathy, which establish a
connection with every part of the body, making this organ
to be so easily affected by motion, by disease, and by every
passing emotion of the mind.
25T. Respiratory Nerve of the Pace.-In the
face we have an example of different sets of nerves for
different classes of motions. All those motions that are
used in the expressions of the countenance are associated
by a certain nerve. Sometimes this nerve of expression is
paralyzed on one side. The result is, that while the individual can masticate equally well on both sides, he can
laugh, and cry, and frown, only on one side, and he can not
close the eye on the side affected.
258. Paralysis of the Respiratory Nerve of
the Eace.-In Fig. 120 is a representation of this condition of things. The left eye cannot be closed by any effort,
and the left side of the face is wholly devoid of expression.
This nerve of expression is often paralyzed by itself, the
other nerves in the neighborhood, both of sensation and
of motion, being entirely unaffected.  This has been
called the respiratory nerve of the face, because it controls motions which are connected with the movements
of respiration. If you observe how the various passions and




196           PHYSIOLOGY AND HYGIENE.
emotions are expressed, you will see that there is a natural
association between the muscles of the face and those of the
FIG. 120.
PARALYSIS OF THE NERVE OF EXPRESSION
on one side of the face.
chest in this expression. This is very obvious in laughing
and in weeping. When the nerve of expression, or facial
respiratory nerve, is paralyzed, all the motions of the face
connected with the respiration are absent.
Though the individual may sob in weeping, or send forth
the rapid expirations of laughter, yet the face on the
side where the nerve is paralyzed will be perfectly quiescent. So, too, those movements of the nostrils which are
sometimes used in expression, are rendered impossible.




THE NERVOUS SYSTEM.                197
Sneezing and sniffing up can not be done on the affected
side. Neither can the individual whistle, because a branch
of this nerve goes to the muscles at the corner of the
mouth.
259. Nerves of the'Eye.-The eye has six different
nerves, each having its distinct office and its separate
origin in the brain for a different service. 1. The optic
nerve, whose sole office is to transmit impressions from
the images formed in the eye to the brain. 2. A nerve of
common sensation, through which any irritation in the eye
is felt. 3. A nerve which is distributed to the muscles of
the eye generally, and to no other parts of this organ. 4. A
nerve which goes only to one of the oblique muscles of the
eye. This is an involuntary muscle which performs the insensible rolling motions of the eyeball, and is associated with
the muscles of expression in the countenance by means of
nervous connections. 5. A nerve which goes to another
single muscle, which turns the eye outward. 6. A branch
of the respiratory nerve, which regulates the motion of the
eyelids, and has much to do, therefore, with the expressions
of the countenance.
260. Paralysis affecting Different Nerves.Attention has been incidentally called to the fact, that one
nerve may be paralyzed, while others distributed to the
same parts are entirely unaffected. So, too, in the nerves
which go out from the spinal marrow, composed of tubuli
of motion and sensation mingled together, one set of the
tubuli may be affected while the other is not; for in paralysis it is often the case that sensibility remains while the
power of motion is gone, and vice versa.
Sir Charles Bell relates an interesting case, in which the
paralysis was different in the two sides of the body. A
mother was seized with a paralysis, in consequence of which
there was a loss of muscular power on one side, and a loss
of sensibility on the other. She could hold her child with
the arm of the side which retained its power of motion but
had lost its sensibility, but only when she was looking




198         PHYSIOLOGY AND HYGIENE.
at it. She could not feel her child on the arm, and therefore when her attention was drawn to any thing else, and
she ceased to have her eyes fixed on the child, the muscles
having no overseer, as we may say, to keep them at work,
were relaxed at once, and the child would fall from her
arm.
261. Nerves, tho'ugh having Different Offices,
all alike in Sti'ucture.-The microscope shows us
that the nerves of motion and of common and special sensation are all alike in their structure, and chemistry shows
us that they are alike also in their composition. The question arises, then, why the impression producing motion can
not be transmitted by the same nerve with the impression
causing sensation. The reason is evidently not to be found
in the nervous trunk itself, as this is the same in all cases.
It is in the circumstances of the two ends of the nervethat which is in the nervous center whence it arises, and that
which is expanded in some part of the body. The nervous
tubuli which end in the fibres of a muscle can not transmit
impression to the brain from the skin over the muscle,
because they do not go to the skin at all. There are other
tubuli that are distributed there for that purpose, mingled
indeed in most cases with the tubuli for motion, but yet
kept entirely distinct from them.
And besides, there is probably something in the structure of the extremities of a nerve of sensation. which
differs from that of a nerve of motion, so as to make it
impossible for a nerve of motion to receive the impression
producing sensation, even where the impression is made
directly upon the muscle itself. There is also probably a
different ending of the nerves of sensation and motion
in the nervous center, the brain, or spinal marrow, that
makes the one kind incapable of performing the duties of
the other kind.
262. Products of Nervous Action. —We have
thus far contemplated nervous action, for the most part,
only in two forms-as producing either sensation or voluntary motion. In sensation the action is from the extremity




THE NERVOUS SYSTEM.              199
of the nerve to the nervous center; but in motion it is
from the center to the extremities of the nerves, as they
are expanded among the fibres of the muscles. This voluntary motion, you see, may arise in consequence of sensation,
as when you withdraw the hand from the fire, if the heat
be painful; or it may occur without a preceding sensation,
as when the thinking mind wills to perform certain motions for effecting some purpose.
In either case it is supposed that the gray vesicular or
cellular substance of the brain is in immediate connection
with the mind, and that the white tubular matter of the
brain and the nerves serves only for transmission. That
is, both in sensation and in motion the effective physical
agency is in the vesicular gray substance. This is the
working part of the telegraphic apparatus of the mind,
while the innumerable tubuli of the white matter of the
brain and nerves are the communicating wires.
263. Involunttary Action.-Much of the muscular
motion of the body is produced without the agency of the
will, and sometimes even in opposition to it. This is true
of the motions caused by emotions in the mind. For example, the muscular motions in sobbing and in laughing
often occur in opposition to the strong action of the will.
In this case, the emotion produces its effect upon the gray
vesicular substance, and is transmitted through the nerves
to the muscles.
There are some common motions which are performed
to a greater or less extent without the agency of the will.
The muscles which perform them are called involuntary
muscles. The muscles of respiration, for example, ordinarily act without our willing them to do so. If they did not,
respiration would stop when we sleep, or be stopped by
disease. But the will can quicken these muscles in their
action. They are therefore not wholly involuntary.
But there are some purely involuntary muscles. The
muscular coat of the stomach, which was spoken of in the
Chapter on Digestion, as being constantly in motion when
the stomach is filled with food, is of this character. No




200          PHYSIOLOGY AND HYGIENE.
effort of the will can quicken or retard the action of this
muscle.  That exceedingly compound muscular engine,
the heart, is a collection of purely involuntary muscles.
264. Excitor and 13iiotor Nerves.-We have already
alluded to the two roots which unite to make up each nerve
that comes from the spine. One of these roots is composed
of tubuli through which impressions are transmitted to the
spinal marrow; and the other contains tubuli, through
which an impression is transmitted from the spinal marrow to the muscles, causing them to contract. Each nerve,
then, coming from the spine, is made up of two distinct
nerves, or two distinct sets of tubuli. One of these is called
an excitor nerve, the other a motor nerve.
In the case of the muscles of respiration, every time
that they act, an impression is transmitted from the lungs
through an excitor nerve to the spinal marrow, the gray
vesicular substance there responding to this impression,
and sending in consequence an impression by a motor nerve
to the muscles. So, also, the presence of food in the
stomach produces an impression which is transmitted
through the excitor nerve, and another impression is returned through the motor nerve, exciting the muscular
coat to action. And in the act of swallowing an impression
is transmitted from the food thrust back into the throat
and then impressions are returned to the many muscles
engaged in this compound act. The action of the nerves
illustrated by these examples is termed their reflex action,
because the impression transmitted by one nerve to the
spinal marrow is reflectedfrom it by another.
265. Sensation does not Accompany Nervous Action.-In some cases the impression is accompanied with actual sensation, and sometimes not, the
action being confined to the spinal marrow. Thus, in
the action of respiration, the impression carried from
the lungs by the excitor nerves comes from the presence of dark blood in the lungs. Ordinarily, a mere impression, and nothing like sensation, is transmitted. The
respiratory muscles, most of the time, go on to do their




THE NERVOUS SYSTEM.              201
work, in obedience to the impressions communicated from
the lungs, without any recognition of the process by the
mind.
But when there is embarrassment in the lungs, the quiet
process, carried on through the agency of the spinal marrow alone, is not adequate to meet the exigency. In some
way, the brain becomes a party in the operation. The act
of breathing is now accompanied with positive sensations,
and there is a mixture of voluntary and involuntary muscular action.
266. The Spinal iMarrow  Performs  Two
Separate Fitunctions.-The spinal marrow, then, performs two separate functions-one, by itself, in producing involuntary motion; and another, in connection
with the brain, in producing voluntary motion and sensation.
The arrangement by which it does two things which are
so different from each other, will be clear to you, if you
bear in mind the fact that the spinal marrow, like the
brain, is composed of the two nervous substances, the white
tubular, and the gray vesicular substance.
When the spinal marrow acts as a mere medium of communication for the brain, the transmission is made directly
through the tubes of the white substance to and from the
brain-to the brain in sensation, and from it in voluntary
motion. Thus, when a sensation is felt in the foot, the
impression made there is transmitted through the nerve to
the spinal marrow, and up through the white part of this
organ to the brain. It touches none of the gray substance
of the spinal marrow, but goes to the gray substance of the
brain. And when the foot is moved, an impression is returned from the brain through the white part of the spinal
marrow, and then through the nerve which goes from it to
the muscles that move the foot.
But, on the other hand, when the spinal marrow acts by
itself, independently of the brain, producing what is called
reflex action, the impressions that are transmitted, some of
them begin, and some end, in the gray substance of the




202           PHYSIOLOGY AND HYGIENE.
spinal marrow. The -impression on an excitor nerve ends
there, and the impression on a motor nerve begins there, the
latter resulting from the former, except when motion is
produced by disease in the spinal marrow itself. Thus, in
breathing, an impression goes from the lungs through excitor nerves to the gray substance, and that is the end of it;
but another impression begins there as a result of it, and is
transmitted to the involuntary muscles moving the chest.
261. The Brain Rests-the Spiial iMarrowo
does not. —One marked distinction between the brain
and spinal marrow is, that the brain has its intervals of rest;
but the functions of the spinal marrow never cease for a
moment as long as life continues. In sleep the brain is
more or less at rest, and it is in a state of entire torpor when
the sleep is profound. But daring sleep the heart beats,
the respiratory muscles work the chest, and the muscular
coat of the stomach churns the food if there be any there.
For these motions, with many others, are dependent upon
the spinal marrow, and not upon the brain; and so, while
the brain sleeps, the spinal marrow keeps up the operations
of the system that are essential to the continuance of life.
But beside the motions that have been mentioned, as
being kept up by the spinal marrow, when the brain is torpid from any cause, there are other motions which can be
excited by stimulating nerves that are connected with the
spine. For example, the act of swallowing can be produced
by pouring a liquid into the mouth, and motion can be produced in the muscles of a limb by irritating the limb at
different points. So, too, if a man be paralyzed in his lower
limbs by a blow upon the spinal column, these parts, which
he cannot move by his will, can be excited to motion by
irritation with electricity or other agents.
It may be remarked that the voluntary muscles often act
involuntarily. In animals from which the head has been removed, the voluntary muscles can be excited to involuntary
action, resembling voluntary movements, although of course
with the removal of the head were destroyed all sensation
and all exercise of the will. A pigeon, whose cerebrum had




THE NERVOUS SYSTEM.               203
been removed, would fly when thrown into the air, would
run when it was pushed, and would drink when its beak
was put into the water. There was no sensibility and no
will in this case, for these cannot be without the cerebrum.
The movements were involuntary, though performed by
voluntary muscles. Now as these facts prove that voluntary muscles are, through their connection with the spinal
marrow, capable of acting as involuntary muscles also, the
question arises whether they do not much of the time act
in part as involuntary muscles, and sometimes wholly so.
268. Walkiyg.-When we are walking we use voluntary muscles. But manifestly a distinct act of the will is
not put forth for every motion performed in walking. The
mind may be at the same time fixed upon something else;
and there seems ordinarily to be only an occasional action
of the will, as when we change our course, or when some
obstacle is in the way, requiring a variation from the regular consecutive series of movements. There is a distinct
action of the will when the movements begin; but after this
the motions seem for the most part almost automatic, and
are probably produced by the reflex action of the spinal
marrow, the will interfering only when occasion requires.:269. Braint  not Directly Essential to Life.
— Many experiments have been tried upon animals with reference to the functions of the brain and of the spinal marrow. It was formerly supposed that the brain was the only
center of nervous power, and that it was immediately essential to the preservation of life. But these experiments have
shown that this is far from being the truth. The brain, it
has been found, has nothing to do directly with the maintenance of life. Animals live for some time after the brain
is destroyed. A pigeon was kept alive for some months
after its cerebrum was removed.
Its condition was very much like that of a man the
functions of whose cerebrum are suspended by the pressure
of a fractured portion of the skull. Although, like him,
the animal had lost all sensation and voluntary motion, yet,
like him, it continued to breathe, and its heart continued




204          PHYSIOLOGY AND HYGIENE.
to beat. Of course so extensive an injury of so important
an organ will at length cause death; but life continues long
enough in such cases to show that this organ is not immediately essential to its continuance.
270. Upper Part of the Spinal Cord directly
essential to Life. —The functions most essential to life,
the respiration and circulation, are, as you have seen, kept
up by the spinal marrow. The very upper part of this organ
is especially devoted to this purpose. You may take out
the brain of an animal, and destroy all its spinal marrow,
except this upper portion of it, and the animal will stiil
breathe, and its heart will beat. But if you destroy just this
small portion of the spinal marrow, though you leave the
rest of it and the brain untouched, the animal will die at
once from the cessation of the respiration and the circulation.
271. Effects Produced by Cutting the Spinal
Cord.-If after cutting off the head of a frog, you divide
the spinal marrow in the back, you can still produce involuntary motions in both the upper and lower extremities. But
the same irritation will not produce them at the same time
in both together, for the division of the spinal marrow in the
back separates it into two independent parts. When, therefore, you irritate the upper extremities, the motion is confined to them, and the lower extremities are quiescent. And
if you irritate the lower extremities, the motion produced
there does not extend to the upper. The division can be
repeated with similar results.
If the spinal marrow be divided above and below the
origin of a pair of nerves so as to separate this point wholly
from the rest of the nervous system, reflex action can be
excited in the nerves connected with this point. That is, an
irritation of the parts supplied by the excitor nerve of this
little segment of the spinal marrow will produce an impression in that segment, which will be reflected by the motor
nerve to the muscles.
The gray substance of the spinal marrow may, therefore,
be regarded as a chain of little brains, in some measure separate from eacll other. But while there are thus many centers




THE VOICE.                   205
of reflex action, there is only one center of sensation and
voluntary motion, and that center, the brain, is connected
with the mind.
2r2. Two  Systems of Nerves, Cerebro-Spinal
and Sympathetic. —The system of nerves which we
have been examining is termed the cerebro-spinal, from its
two great central organs, the brain and spinal marrow.
But there is another nervous system, the functions ofwhich
are involved in much mystery. It is called the system of
the great sympathetic, or the sympathetic system. Sometimes it is called the nervous system of organic life, because
it is intimately and extensively connected with the nutritive processes; while the system that we have been considering is called the nervous system of animal life, because it
regulates the functions peculiar to animals: sensation, and
spontaneous motion.
While the sympathetic system is thus connected with the
nutritive processes, it is also supposed to be the means of
effecting the sympathetic connection between different parts
of the body, and to serve as the medium through which the
passions and emotions of the mind produce their effects upon
the functions of the different organs. In this system there
are many ganglions or little brains, which communicate with
each other by nerves.
The structure and functions of the nervous system have
thus been described to such an extent as will prepare you
for the consideration of those subordinate organs, by which
the purposes of this system are accomplished.
CHAPTER XIII.
THE  VOICE.
2M?. The Vocal Apparatus.-The apparatus of
the voice is truly a musical instrument. We can see therefore, in its construction and arrangement, the applica



206          PHYSIOLOGY AND HYGIENE.
tion of those principles which usually regulate the production of musical sounds, and which man observes in making
the various instruments which his ingenuity has invented to
delight the ear.
As the apparatus of the voice is really a wind instrument,
we will first develop the principles on which
FIG. 121.   wind instruments  produce  the  various
^.d     musical notes, and then show you the resemblance between these instruments and
the set of organs which are engaged in
producing the notes of the voice.
Wind instruments are of two kinds-those
that have an inflexible mouthpiece, and those
in which the sounds are produced by a vibrating reed. The horn, trombone, trumpet,
flute, fife, flageolet, flute-stop and other
stops of the organ, &c., are instruments of
the first kind.
i 2 4. Causes affecting the Variation of Pitch.-The variation of notes
produced in these instruments may be thus
explained. The column of air contained in
the tube is the vibrating body from which
l  proceeds the sound. Any thing, then, that
affects the size or form of the column of air
affects the note. The length, the breadth,
and the mode of producing the vibrations
are the cause of the variation of the note.
The holes in the side of a flute are for
the purpose of altering the length of the
confined column of air. In the trombone this
is done by sliding one part of the instrument
a        upon the other.  The general rule is, the
longer is the column of air the more grave
is the note. Thus in the flute, the lowest note that can
be produced by the instrument is made by covering all the
holes, so that you have a column of confined air the whole
length of the tube. The highest note, on the other hand,




THE VOICE.                  207
which the instrument is capable of producing, is made by
so arranging the fingers as to allow the air to escape at the
first hole.
2T5. Size and Width of Vibr ating Column of
Air affecting the Note.-Fig. 121 is a representation
of one of the pipes of the flute-stop of the organ, which is a
wooden box, made very much after the manner of a boy's
whistle. At a is the passage for the introduction of the air;
b is the inclosed column of air, the vibration of which produces the sound; c is the place of escape for the air; and d
is a movable plug, by means of which the vibrating column
of air can be made longer or shorter, according to the note
desired. In tuning the organ, if the pipe gives too low a
note the plug is moved downward, thus shortening the
column of inclosed air, but if too high a note, the plug is
raised up.
The same rule applies to the width of the vibrating column
of air. The wider the column the graver the note, and vice
versa. Observe, also, that in a long, slender column of air, as
in the trombone, by giving the current of air from the mouth
a great velocity a high note may be produced; but where, as
in the ophicleide, the column is both wide and long, it is
difficult to do this, because it is difficult to produce a quick
vibration in so large a body of air, with all the suddenness
and force with which we can move it.
In those instruments which have no expedient for altering the length of the column of air, such as the common
horn, the various notes are produced by narrowing or widening the orifice by the agency of the lips, as the case requires,
at the same time giving, by the varied velocity with which
the air is forced into the instrument, a quicker or slower
vibration to the air. Grave sounds are produced by a wide,
and acute by a narrow opening.
2"6. Reed Instruments.- In reed instruments the
variations in note are produced in a different manner. The
clarionet, hautboy, bassoon, the reed stops in the organ, &c.,
are instruments of this sort. It is the vibration of the thin
plate called the reed that causes the sound. The longer this




208           PHYSIOLOGY ANDI) HYGIENE.
plate is, the slower are the vibrations, and therefore the
graver is the note. The principle can be well illustrated
in the reed stops of the organ. The reeds in the different
pipes are made of different lengths, according to the notes
which they are to produce. In a reed instrument played by
the mouth, the clarionet for example, the rapidity of the
vibrations is regulated by the pressure of the lips. In producing a high note the lips press firmly on the reed and
leave but a small portion of it to vibrate; while in producing a low note the lips press less firmly on the reed, and
leave a large portion of it to vibrate.
27T. Storinged Instrullents —This same principle
also applies to stringed instruments. Thus in the piano,
the grave notes come from long and large strings, while the
higher notes come from slender and short ones. In the
violin the strings are all of the same length, the larger strings
giving the graver notes, and the smaller the higher ones.
The notes are varied also in the case of each string by varying the tension. They are varied too while playing on the
instrument by varying the length of the vibrating strings
by the pressure of the fingers.
2r8. Tutbe connected twith the Reed.-The reed
is frequently connected with a tube. This contains a column
of air through which the sound caused by the vibration of
the reed must pass. Unless, then, the vibration of this
column of air corresponds with the vibration of the reed, it
will alter the note. It always does alter the note to some
extent. It never raises it, but always makes it more grave.
That is, the vibration, in passing from the reed to the
column of air, becomes less rapid and coarser, as is always
the case when vibration passes from any substance to
another.
But the tube is so constructed that there may be as little
change in this respect as possible. Holes are therefore
properly placed in the side of the tube, so that with the
fingers the column of confined air may, in the case of every
note, be placed in correspondence with the vibration of the
reed.




THE VOICE.                  209
Suppose the tube to be long and without holes; in this
case low notes could be easily produced, but attempt a
high note and you would fail. The reason is obvious. The
low note is caused by a low and coarse vibration of the reed,
for the transmission of which a long column of air is fitted.
But if a high note be attempted, the slow vibration of the
long column of air disagrees with the quick vibration of the
reed, and very much flattens the sound as it passes through
the tube after coming from the reed.
As already suggested, the object of the tube is to secure
the combined effect of a reed and a wind instrument.
The tube makes the reed speak, as it is expressed; that
is, it gives intensity and an agreeable character to the
sound. If you disconnect the reed of the hautboy or bassoon, for example, from its tube, and blow upon it, you
can produce all the variety of notes, but the sound is disagreeable; but by connecting the tube with the reed you
produce a comnpound sound, as we may call it, which has a
sweet and rich melody.
We will now examine the apparatus of the voice, and see
how far the principles which have been developed in relation
to common musical instruments are applicable to this
instrument.
2W9. Description, of the Organ of the Voice.Just at the root of the tongue, as described in the Chapter
on the Bones, is a small bone, shaped so much like the Greek
letter v that it is called the hyoid or TT-like bone. The
curved portion of this bone is towards the root of the tongue,
and its two ends point backward toward the pharynx. With
this bone is connected a long cartilaginous tube extending to
the lungs, called the trachea, or windpipe. It is through this
tube, as you have already learned, that the air goes back and
forth from the lungs in respiration and speech. It is composed of a great number of rings of cartilage connected
together by membranous parts.
280. Lar'nyx.-But it is the upper part of the windpipe, that part which is immediately below the U-like bone,
which claims our attention as the seat of the formation of




210            PHYSIOLOGY AND HYGIENE.
the voice. This part is called the larynx. It is formed of
five cartilages, the arrangement of which will now be shown.
The largest of these cartilages, the one which forms most
of the body of this music-box, as we may call it, is the
thyroid. It is the pomurn Adami, or Adam's apple, which
is so easily felt in the top of the neck. This cartilage forms
the front and sides of the larnyx, but it is open behind.
The cricoid cartilage is shaped very much like a seal ring,
and this resemblance gives it its name. The narrow part
of it is situated directly under the thyroid cartilage, in its
front and at its sides, but the broad,
FIG. 122.       seal-like part of it is behind, projecting upward and filling a part of
the open space left by the deficiency
XI?~ of the thyroid in the rear. A side
view of these parts is given in Fig.
11!~I    Z  1 I  122, in which 1 is the U-like bone;
4 is the thyroid cartilage; and 6 the
cricoid. At 8 is the back part of the
cricoid, filling up a part of the space
8     in the open rear of the thyroid; 3
is a horn-shaped projection of the
6 - l   thyroid, and five is a smaller one
below, projecting  over  the  outside of the cricoid; 2 is a strong
membrane or ligament connecting
Side view of     the hyoid or U-like bone with the
THE LARYNX.       top of the thyroid; 9 is the epiglottis, drawn up by a hook; and at 7
are the rings of the trachea. The epiglottis is composed in
part of cartilage. It is the lid of the larynx, shutting down
when we swallow, so that the food or drink may pass over
it, and being raised up when we breathe or speak.
There are two small cartilages which are not seen in this
figure, called arytenoid cartilages, from two Greek words,
meaning ladle and shape, because they bear some resemblance in form to ladles. They stand in the open space
in the rear part of the thyroid, on the top of the cricoid




THE VOICE.                   211
cartilage. They are the pillars to which the vocal chords
or ligaments are attached behind. These two cartilages are
movable, having a regular joint with the upper edge of
the cricoid. There are small muscles which pull them in
different directions, and thus change the degree of tension
and the position of the vocal ligaments, and of course vary the
pitch of the sound produced by the vibration of the ligaments.
281. Vocal Ligyamzets.-Fig. 123, is a diagram
showing the arrangement of these ligaments. It represents
a view of them  as you look down
into the larnyx, in which a is the       FIG. 123.
front of the thyroid cartilage, and         a
bb are the two arytenoid cartilages.
To these you see are attached two
sheets of membrane, which are also
fastened all around to the inside of
the thyroid. If these movable posts,
as we may call them, to which the         b   b
ligaments are thus attached, be   Diagram showing the action of the
drawn backward, it is obvious that    VOCAL LIGAMENTS.
it will make the ligaments more
tense. If they are separated from each other, the opening
between the ligaments will be widened. If they are brought
nearer together, this opening will be narrowed, and the forward
part of the free edge of each liga-     FIG. 124.
ment will be prevented from vibrating, because it will here be brought
in contact with the other ligament.
Now  there are small muscles
which are attached to the arytenoid
cartilages for the purpose of mov-  / 
ing them as was pointed out. The
figure here presented is a mere diagranl, to show the arrangement of
the ligaments for the production of
the various notes of the voice. In THE VOCAL LIGAMENTS.
Fig. 124 is represented the actual appearance of the ligaments and the arytenoid cartilages, as you look down upon




212          PHYSIOLOGY AND HYGIENE.
them. The ligaments, you observe, are thicker at their free
edges than any where else.
The true vocal ligaments have been described. But there
is another pair of ligaments directly above them, the space
between which is the real opening into the larnyx, upon
which the epiglottis shuts down when we swallow. In Fig.
125 is a diagram representing the plan of these two pairs of
ligaments, as shown by a perpenFIG. 125.      dicular section from side to side.
B B represents the vocal ligaments,
C C the upper ligaments, and V V
the two recesses between them.
282f. The Lower the True
C     C  A'Vocal Chords.-We know that
-  it is the lower ligaments that are
-  the true vocal chords, because the
parts above these, even the upper
B  B\         ligaments, may be, all cut away,
and yet a vocal sound may be produced; while if an opening be
made into the larynx below the
lower ligaments the voice will be
destroyed.
Magendie, a French physiologist, speaks of a man who,
on account of an opening in the larnyx, was never able to
speak without pressing his cravat tightly against this opening, in order to prevent the air from eLcaping through it.
Many experiments have been tried with the larnyx after
death to verify the results above stated. The lower ligaments, then, are the vocal chords, by the vibration of which
all the different notes of the voice are produced. And the
other parts of the vocal apparatus serve only to modify the
sound caused by the ligaments. The lungs act merely as
the "wind-chest," to hold the air which, being forced out,
strikes on the ligaments, and makes them vibrate.
283. Principles  of Mlisical Instrunments
applied to the Vocal Apparatus. — Let us now
apply to this apparatus the principles already developed, as




THE VOICE.                  213
regulating the variation of note in common musical instruments. The size of the aperture, through which the sound
is thrown out, influences the note-of this fact we have a
familiar example in whistling. And as you have seen that the
size of the opening between the vocal ligaments is varied
by the muscles moving the arytenoid cartilages, this variation must have an influence upon the note of the voice.
But this is not the only cause of the variation of the
note. As shown in relation to the reed, and to the strings
of stringed instruments, so also here, the larger and less tense
are the vibrating bodies, the vocal chords, the graver is the
note. You have seen how these chords or ligaments are
varied in tension by the action of the muscles that move
the arytenoid cartilages. You have also seen that, as these
cartilages are brought near together by the muscles, the
length of the free vibrating edges of the ligaments is shortened, because the edges are brought together in their anterior part (Fig. 123).
Magendie verified this by observation. He opened the
throat of a noisy dog in such a way that he could look
directly upon the vocal ligaments. When the sounds were
grave, he observed that the ligaments vibrated in their
whole length, and that the air passed out through the whole
length of the chink between them. But when the sounds
were on a high note, the ligaments did not vibrate in their
anterior part, but only in the posterior, and the air passed
out. only at the open part.
284. Resemblance between the Instruments
of the Voice and  Common Mliusical Instrumnents. —The sound as it comes from the larynx passes
through a tube, just as the sound coming from a reed does
in a reed instrument. In other words, there is a body of
inclosed air extending from the larynx to the outlets of the
mouth and nose, which vibrates in transmitting the sound
from the larynx. This body of air is not so simple in its
form as that is which is inclosed in the tube of common
reed instruments. It has three outlets, the mouth and the
two nostrils. The sound of the voice seldom comes out




214           PHYSIOLOGY AND HYGIENE.
from the orifices of the nostrils, but almost always from the
mouth. In humming it comes altogether from the nostrils.
In ordinary speaking and singing the cavities of the nose
act as reverberating cavities, the sound which reverberates
there issuing from the mouth.
285. Tube of the Vocal Apparatus like that
of a Reed Instrument.-You have seen that the
tube connected with the reed in the reed instrument is so
constructed, that the length of the confined column of air
can be changed, in producing the different notes; the vibration of the air thus being brought into correspondence with
that of the reed.
If you place your finger on the front of the larynx, and
then sound various notes, you will feel the larynx rise when
you sound a high note, and fall when you sound a grave
one. The object of this movement is to alter the distance
from the larynx to the outlet of the mouth-in other words,
to alter the length of the column of air in the tube-so that
it may correspond in its vibration with the vibration of the
vocal chords. But the size of this column of air is altered
in another way. It is altered in its width, which is quite as
effectual in changing the vibration as an alteration of
length.  The tube of the vocal instrument you readily
see can be altered in its width by the muscles of the throat
and mouth.
The object of the tube of the reed instrument is to make
the reed speak, as it is termed; that is, to give intensity
and an agreeable character to the sound. If the voice
should come directly from the larynx without passing
through the tube attached to it, it would be as disagreeable
as the sound of a reed when separated from its tube.
The voice gets most of its melody after it is made in the
larynx, as it passes out through the column of air in the
throat and mouth. And it is the variations of this tube
produced by the muscles that surround it that give to the
voice its variety of tone as well as its melody, thus constituting one of the great excellencies of the vocal instrument
in comparison with all common musical instruments.




THE VOICE.                   215
286. Delicacy  of the  Action  of the  Vocal
luscles.-To have some conception of the variety of the
motions of the muscles concerned in the modulation of the
voice, listen to some singer whose voice can command with
ease and freedom a great extent of the scale. For every
note that you hear there is a distinct and particular adjustment of the vocal ligaments, and of course a particular degree of contraction of the little muscles that move them.
It is calculated that the ligaments vary in length only
about the J of an inch in producing all the notes of the
voice. Now the natural compass of the voice (that is, its
range from its lowest to its highest note) in most singers is
about two octaves or 24 semitones. Within each semitone
a singer of ordinary capability can produce 5 or 6 distinct
notes; so that for the whole number of notes that he can
sound distinctly 120 is a moderate estimate. He therefore
produces 120 different states of tension in the vocal ligaments. And as the variation in their length for passing
from the lowest of these 120 notes to the highest is only
the Ith of an inch, the variation required to pass from one
note to another will be only the 6 -,th of an inch. A very
expert singer can produce a much more delicate action than
this, and distinctly appreciate the result by his ear.
28T. Importandce of Keeping the Chest Pall
of Air.-The skillful singer or speaker exhibits much
skill in managing the muscles of the "wind-chest."  He
keeps it all the time well supplied with air, so that but a
comparatively slight action of the expiratory muscles will
suffice to throw the air against the vocal ligaments with the
requisite force. But an unskillful singer or speaker much
of the time has his chest poorly supplied with air, and so
speaks or sings, as it is expressed, from the top of the chest.
It costs him, therefore, so much labor to throw out the air
with sufficient force, that he is soon tired out.
The necessity for keeping the chest full of air, in order to
work the vocal apparatus easily, may be illustrated by reference to the bagpipe. If the bag containing the air be well
filled, a slight pressure of the arm upon it will force the air




216           PHYSIOLOGY AND HYGIENE.
through the pipe with sufficient rapidity to produce the
sound. But if the bag be flaccid from the little quantity
of air in it, a very strong pressure of the arm will be required to produce the same effect.
288. lThilng out the Vocal Mutscles.-But it is
not the muscles of the chest only that are tired out in the
unskillful singer or speaker, but also the muscles of the
larynx and the throat. And a frequent tiring of these
muscles weakens the parts, and often at length produces
disease. Much of the throat-disease of public speakers
comes from this cause, and is a nervous disease, the affection
of the lining membrane of the throat being often a mere
accompaniment.
This result is more apt to occur when the nervous force
of the system generally is impaired. It is also more apt to
occur in those who speak in a uniform and somewhat
monotonous manner, than in those who speak with much
variety. A continuation of precisely the same muscular
effort for any length of time is apt to produce painful
exhaustion, while a much greater amount of varied muscular effort may be put forth without weariness, or even with
pleasure.
289. Parts  Engaged  in  the Articulation
of the Toice.-We will now observe the agency of the
different parts of this compound vocal tube in the articulation of the voice. Each letter, whether it be a vowel
or a consonant, requires a particular position of the different parts of the vocal tube. In some letters the tongue
is the chief agent in articulation, in others the lips, in
others the teeth, in others the palate, and there are some in
the formation of which the cavities of the nose have an
important agency.
290. The Tongue less Essential than Coinmnonly Supposed.-The tongue has been considered so
essential to speech, that tongue and language are often used
synonymously. But though it does perform an important
part in articulation, it is not absolutely essential. A boy,
who lost his tongue by disease at the age of eight years, was




THE VOICE.                   217
exhibited publicly because he could talk without a tongue.
A girl, who lost from disease the whole of her tongue, together with the uvula (the little round body which hangs
down from the middle of the arch of the palate), could talk
and swallow as well as any one. So perfect was her articulation, that she could pronounce with exactness those letters
which commonly require the agency of the tip of the tongue.
She could sing finely, articulating with the same clearness
as when she talked.
29 1. Dentals. —Some of the letters are formed principally by the teeth, as c, t, s, z. They are therefore called
Dentals. It is the too frequent and bungling employment
of some of these which constitutes lisping. Those who have
a tongue too large for the mouth are apt to lisp. In advanced
age, when the teeth are lost, we find this defect of lisping.
The reason is obvious. When the teeth are gone, the sockets
gradually become obliterated, and that part of the jaw-bone
where the teeth were, of course diminishes in size, making
the mouth too small for the tongue.
2!)2f. Labials.-The letters, in the articulation of
which the lips takes the lead, are b, p, mi, f, v, w, &c.,
and are called labials. Children, when they first begin to
talk, use labials freely, because they can see in others the motions necessary for their pronunciation, and are led to imitate
them. Hence the endearing terms used by the child to the
parent are, in all languages, or nearly all, composed of labials
and vowels. And, too, it is from the delight which the child
takes in repeating over and over these terms, that we have
the word papa and manma, instead of pa and mna. The same
thing can be observed in other languages as well as the
English.
293, Reverberiation in some Letters in the
2Vtasal Cavities. —The nasal cavities, it is obvious, must
have a great influence in articulation. The letters in and n
are partly nasal. In pronouncing m at the end of a syllable,
as am, em, or oan, we close the lips, and the sound issuing
from the larynx reverberates in the cavities of the nose. You
can perceive this reverberation by pressing gently upon the
10




218          PHYSIOLOGY AND HYGIENE.
nostrils with the fingers while pronouncing this letter.
The same can be said of n, except that in pronouncing it
we press the tip of the tongue against the roof of the mouth
just behind the front teeth, preventing the passage of the
air out through the mouth in this way, instead of doing it
by closing the lips, as in articulating m.
294. Speaking through the Nose. —In what is
commonly called speaking through the nose the reverberlation mentioned above is disagreeably strong. The popular
idea of it is incorrect, for this fault occurs in those who have
some obstruction to the free passage of the air through the
nose. This obstruction acts like the pressing of the nostrils
with the fingers, confining more or less the body of air contained in the nasal passages. It is the vibration of this air
thus partially confined in tortuous passages that produces the
nasal twang. Any thing, therefore, which prevents the free
outlet of the air from the nose will occasion it. Pressing the
fingers on the nostrils while speaking will produce it.
295. Whtispering.-When no sound is produced by
the ligaments of the larynx, as is the case in whispering, the
noise produced by the passage of the air through the cavities
of the vocal apparatus can be so articulated, as to be heard
distinctly at a considerable distance. Persons, therefore,
who have entirely lost the voice can converse. In whispering the vocal ligaments are relaxed as they are when we
simply breathe. But the sound of whispering has its high
and low notes like the vocal sound. The variation of note
is caused by variation of the size of the column of air contained in the vocal tube.
296. Contrivances to Imitate Articulation.Various attempts have been made to imitate the articulation
of sounds by mechanism, but with very limited success. In
1779 a prize was offered by the Academy of Science at
St. Petersburg, for the best dissertation on the theory of
vowel sounds, and it was awarded to G. R. Kratzanstein, an
account of whose experiments was published in the Transactions of the Academy. He found that the sound of the
four vowels, A, E, O and U, might be produced by blowing




THE EAR.                   219
through a reed into tubes, the forms of which are represented in Figures 126, 127, 128, 129 and 130, and that the
FIG. 126. FIG. 127. FIG. 128.  FIG. 129. FIG. 130.
A              0 ~
sound of I, as pronounced by the French and other European
nations, could be produced by blowing into the tube, Fig.
130, at a, without using the reed.
CHAPTER XIV.
THE  EAR.
IN the last chapter the production of sound by the vocal
apparatus was mentioned. In this chapter it is proposed to
show how the impression of sound is transmitted to the
brain, in order to produce the sensation of hearing.
297'. Difference between a Sound and a Noise.
-Sound may be produced by the vibration of any substance;
though some bodies are better fitted to produce it than others,
and are therefore called sonorous.  When the vibrations
which cause sound are equal, a musical sound results; but
if they are unequal, we have a discordant sound, or what we
ordinarily call a noise. Sound is transmitted from the point
where it originates, in all directions. And its vibrations
gradually lessen, just as the ripples lessen which are produced by dropping a stone into the water.
298. Reflection  of Sound.-The vibrations of




220           PHYSIOLOGY AND HYGIENE.
sound are reflected by objects against which they strike.
For this reason the voice can be heard at a much greater
distance if it be transmitted along a wall than whnen it is
uttered in an open space. This may be illustrated on Fig.
131. Let A B represent a wall, and C the position of the
FIG. 131.
a;......B
A ail| / l; g 2 AM i/ ||Xg ||SB
ear. If the bell at D be rung, besides the vibrations which
come to the ear at C in the direct line C D, a vibration striking the wall at F will come to the ear in the line F C, and
the same can be said of other points along the wall. An
accumulation of vibrations, therefore, comes to the ear at C,
which therefore receives a louder sound from the bell than
it would if the bell were rung in a perfectly open space.
For the same reason a speaker can be heard much more
easily within walls than in the open air. The sound is
reflected, and, therefore, in some measure concentrated by
the walls.
299. Speaking Tube.-In speaking tubes this reflection and concentration are carried to a still greater extent.
Sound can in this way be heard at a great distance from its
source. M. Biot found that when he spoke in a whisper at
one end of a tube, over three thousand feet in length, he
was distinctly heard at the other end; so entirely do the
walls of the tube prevent the diffusion of the vibration in
the air around. Speaking tubes are therefore used to a
great extent in large manufactories, where directions need
to be given continually to workmen in different parts of the
establishment. The flexible tube, now so commonly made
use of by deaf persons, furnishes another illustration. The




THE EAR.                    221
vibrations of the voice received by the trumpet-shaped end
are transmitted through the tube to the ear.
300. Difference  in, the  Transimission  of
Sound through Solids, Liquids an d Gases.Sound may be transmitted through any substance, whether
it be solid, liquid, or gaseous. It cannot be transmitted
through a vacuum, for there is nothing there to vibrate.
Sound differs in this respect from light, which passes as
readily through a vacuum as it does through any transparent
substance.
A pistol fired on the summit of a mountain, gives not
nearly so loud a report as when it is fired in the valley below.
The more solid the medium is for the transmission of
sound, the more readily is it transmitted. The scratching
of a pin at the end of a long log may be heard by. the ear
applied to the other end, although it can not be heard through
the air, at even the distance of a few feet. A deaf gentleman,
resting the bowl of his pipe on his daughter's piano-forte as
he smoked, found that he could hear the music with great
distinctness; and many deaf persons can hear conversation,
by holding a stick between their teeth, while the other end
rests against the teeth of the person speaking.
Water is a much letter conductor of sonorous vibration
than air, though it is not so good an one as a solid substance.
The force of the vibration is lessened more gradually in
water than in air, and its rate of progress in water is, according to Chladni, 4,900 feet in a second, or between four and
five times as great as in air.
301.  Sonorous  Vibration  does  cnot pass
readily from  one lMedium  to Another.-Thus,
although the scratch on the log is heard so easily by the ear
at the other end, if the ear be removed a little from the log,
it does not hear the sound, because the vibration is so much
lessened in passing from the solid wood to the air. It is
clear that the more unlike two substances are, when sound
passes from one to the other, the more will the force of the
vibration be lessened; for the more unlike they are, the less
easily will the one take the vibration from the other.




222           PHYSIOLOGY AND HYGIENE.
For this reason, a sonorous vibration, produced in a solid
body, may be transmitted to water with much less loss of
intensity or force, than occurs when it is transmitted to air.
And it may be remarked in this connection, that when vibrations are transmitted to a fluid, from air or from a solid, an
intervening membrane is of essential service, for it presents a firm surface upon which the vibrations can be received.
302.  Hearing  a  Comtlpound  Process. —The
vibrations of sound, passing into the ear by a tube, strike at
the bottom of that tube upon a membrane called a drum.
The air can go no farther, for this drum is perfectly air-tight.
It communicates its vibrations, however, to the drum, which
transmits them to a chain of four little bones, the last of
which transmits them to another drum, covering an opening
into various winding passages in solid bone. In these
passages is contained a limpid fluid, which is put in motion
by the vibrations of the drum last mentioned.
So much for the mere mechanical part of the process. In
the winding passages are spread out the minute fibres of the
nerve of hearing. The vibrations of the liquid in these halls
of audience make an impression upon these nerves, which
is communicated to the brain through the trunk of the
nerve, and this completes the whole process necessary to the
production of the sensation of hearing.
303. The Parts of the Apparatus of Heariing
Described.-The parts of the apparatus of hearing may
be seen in Fig. 132. The internal portions are made rather
larger than natural, in order that the construction of the
ear may be clearer. At a b c is the external ear; at d is the
entrance to the tube of the ear, f; g is the drum of the ear at
the end of this tube, called the membrane of the tympanum;
h is the cavity of the tympanum, the chain of bones which it
contains being left out, so that the plan of the apparatus may
be more clear to you; k is the Eustachian tube, which
makes a communication between the back of the throat
and the cavity of the tympanum; n is a part of the
winding passages, shaped like a snail's shell, and therefore
called the cochlea; at m are three other winding passages,




THE EAR.                    223
called, from their form, semi-circular canals; and at I is the
vestibule, or common hall of entrance to all these winding
passages.
FIG. 132
eA.        b
VERTICAL SECTION OF THE ORGAN OF HEARING.
In the wall of the tympanum, on the side opposite to
the drum of the ear, you see two holes. These open into
the winding passages, the larger one into their vestibule or
entrance hall. Each of these holes is covered by a membrane, and to the membrane of the larger one is attached
the last of the chain of bones. At o is the trunk of the
nerve of hearing, and at e e is the bone that encloses these
parts, which is so hard that it is called the petrous, or rocklike bone.
304. Externat Ear.-The object of the external ear
is to collect the waves of sound, and direct them into the
tube of the ear. There have been many speculations in
regard to the use of the prominences and ridges of the




224          PHYSIOLOGY AND HYGIENE.
external ear, but they are fanciful and groundless; and its
surface is thus diversified, probably for the sake of comeliness. If the object were to give it the best shape and
construction for collecting the vibrations of sound, it would
have had a different shape altogether, and would have been
provided with muscles which could turn it in different
directions, as is the case with many animals. The shape of
the external ear is much better in many animals than it is
in man, if we consider its object to be merely the collection of
the waves of sound. The endowment is in this case, as well
as in every other, according to the necessities of the case.
305. Tube.-The tube of the ear is about an inch long
in the adult. It is formed of cartilage like the external car,
and ends at the drum. At its entrance are hairs which
afford some protection against intruders.  But the chief
protection is the bitter wax, which is secreted by little
glands, situated in the skin of the tube. The odor from
this secretion so effectually keeps out the insects from this
open entrance, that it is quite a rare occurrence to have an
insect get into the ear. And when one does get in, the
wax envelopes him, and commonly soon destroys him.
~306. Drium  ancd Bones. —The drum  of the car,
which makes the closed end of the tube above described, as
seen at g, Fig. 132, is very thin and transparent. On the
other side of it is the cavity of the tympanum h. In this
cavity are the four bones. These
FIG. 133.       are represented in Fig. 133, enlarged so that you can see their
shape  distinctly.   They  are
named from their shapes.
They are the malleus or hammer m; the incus or anvil i; the
os orbiculare, or round bone o,
the smallest bone in the body;
and the stapes or stirrup-bone.
The long handle of the hammer h is fastened to the middle
of the drum of the ear. The little round bone is fixed
between the slender end of the anvil, and the top of the




THE EAR.                    225
stirrup-bone. In Fig. 134 you have a representation of
these bones, together with the drum of the ear. While the
end of the handle of the hammer is fastened to the middle
of the drum, the base of the stirrup is
fastened to another drum, covering the    FIG. 134.
hole or window, opening into the vestibule of the winding passages.
There are three very delicate muscles
which move these bones. One of them
relaxes the drum of the ear, and another
makes it more tense; and thus the drum
DRUM OF THE EAR
is put into the right states of tension, to    With the bones.
accommodate it to the various kinds of
vibration that come to it. This is a matter of some importance, for it is plain that while a relaxed drum can vibrate
properly to grave sounds that enter the ear, it must be tense,
in order to respond properly to the vibrations of the air in
the higher notes.
307. Eustachiaa   n Tube.-The cavity of the tympanum (h, Fig. 132) containing the little bones, which is
beyond the drum, communicates with the mouth by the
Eustachian tube k. If you shut your mouth, and close the
nostrils with the fingers, and then perform the action of
blowing, you will feel the air enter the Eustachian tubes, and
fill the cavity of the tympanum. The chief object of this
communication is to have air on the inside as well as the
outside of the drum, so that it may vibrate freely.
308. WVinding Passages of the Internal Ear.
-These are inclosed, as already stated, in the most solid
bone in the body. They are called together, very appropriately, the labyrinth, sometimes the internal ear. This is
really the essential part of the apparatus. Here are the true
halls of audience, where the nerve receives the messages
from without, and transmits them to the brain. The drum
of the ear and the chain of little bones may be destroyed,
and yet, if these winding passages remain entire, with the
membranes over the two windows that open into them, the
hearing will not be lost; though it will be less perfect than




226           PHYSIOLOGY AND HYGIENE.
it is when the whole of the apparatus is there, and in good
order.
309. The Winlding Passages.-The labyrinth is
represented much magnified in Fig. 135. The middle part
of it, v, is the vestibule. From
FIG. 135.       this go out the semi-circular
canals, x, y, z, on the upper
X,     side, and on the lower the
winding passages of the cochlea, k. At o you see the openQ    ing called the fenestra ovalis,
p       1       lY11z or oval window. This is cov-'VD/E//           ered by a membrane, on which
presses the base of the stirrupbone. You see another opening, r, which is called the fenestra rotunda, or round window. This is covered with a
membrane.  Both of these
openings you see in Fig. 132
in the wall of the tympanum, opposite to the drum of the
ear.
310. Principles of Transmission of Sound
observed in the Arrangement. —It will be proper to
say a word here in relation to the choice of a fluid, instead
of a solid or an aeriform substance, as the medium through
which the impression of the vibration of sound is communicated to the nerve. It is better than a solid would be,
because no arrangement of a vibrating solid with the minute
fibres of the branches of the nerve could be effectual, and at
the same time so little liable to derangement, as the arrangement of nervous fibres immersed in a liquid, and the whole
inclosed in solid walls of bone.
It is better than air would be, for at least two reasons.
1st. The vibrations of sound are communicated with much
more ease and rapidity through water than through air.
This we see to be a consideration of some importance, when




THE EAR.                    227
we look at the complicated and winding passages that contain the fluid.
2d. There is not so much loss in the force of the vibration
in the transmission from the solid stirrup-bone through
the membrane to the fluid, as there would be if the transmission were to air.
311. Steps of the Process of Hearing given
in their Order. —Having thus described the parts of the
organ of hearing, we will trace the steps of the process of
hearing, as it must occur in the case of every sound that
we hear. The vibrating air enters the tube of the ear,
and, reaching the drum, produces a vibration there. This
vibration is communicated to the chain of bones, which
pass it on. It is transmitted from the last of this chain
of bones, the stirrup-bone, to the membrane covering the
fenestra ovalis, and from this to the fluid contained in all
the passages of the labyrinth.
The vibration goes through all the semi-circular canals in
one direction, and in another up one gallery of the cochlea,
and down the other. In all these cavities, are spread out in
various ways the filaments of the nerve which receive the
impression of the vibration. This impression is transmitted
from the extremities of the nerve, through its trunk, to the
brain, where the mind receives it. All this together constitutes hearing; and all of it occurs in the case of any sound
which we hear, however closely it may follow any other
sound.
Most of our hearing is done precisely in the way described,
but not all. We sometimes hear directly through the bone
surrounding the labyrinth. If you place a watch between
the teeth. you hear the ticking; and it gives a very different
sound from what it does when held to the ear, because the
sonorous vibration is transmitted directly from the teeth
through the solid bones of the skull,
312.  Complicated  Apparatus, producing
Simple Results.-Though the apparatus of the ear is
complicated, the mechanical result is a simple one-it is a




228          PHYSIOLOGY AND HYGIENE.
mere trembling of a fluid inclosed in winding cavities of
bone. But simple as the result is, it is made, through the
beautiful nervous connections of the ear with the brain, one
of the chief inlets of knowledge to the mind.
Thus intimately in the human body are the simplest
mechanical results connected with the complicated and
diversified operations of the mind. In the process of hearing the drum of the ear is to be considered one end of the
apparatus, and the gray portion of the brain the other. The
drum simply vibrates; and instantaneously the mind receives
a distinct impression from the vesicles of the gray matter.
And thus is the communication established between the
immaterial mind, and the vibrations of the material substances with which it is surrounded.
CHAPTER XV.
THE EYE,
313. Seeing, a Compound Process. —The sensation of sight is the result of a compound process, which
may be divided into two distinct parts. The one part is
purely mechanical, and the apparatus for it is constructed
according to the common principles which we find illustrated in optical instruments. The object of its arrangements is to form distinct images of objects in the back part
of the eye. The other part of the process is executed by the
nerve of vision, called the optic nerve.
314. Refraction of Light. —The rays of light coming from any luminous point go in straight lines in all directions, just as the vibrations of sound do, and, like them,
become less intense the farther they are diffused. Wllen




THE EAR.                     229
they pass from one medium into another they are bent out
of their straight course, or refracted, unless they' pass from
one to the other in lines perpendicular to the surface of the
medium which they enter.
315. RLefractiont as Light passes fr~ot  a
Rarer into a Dlenser Medium, ofr Vice Versa.
-This may be illustrated by the following experiment,
Place a coin, a, in the bottom of a basin, as represented inl
Fig. 136, and then withdraw from
it so far that the coin may be hid-       FIG. 136.
den from  your eye by the edge of
the  basin, as represented in the
figure.  Keeping your eye fixed in'
that position, pour some water into.:
the basin up to the level, c. The coin 
will again become visible to your eye.
The reason is, that the rays of light,
as they come from  the water into     a
the rarer medium, the air, are refracted or bent downwards, that is, from the perpendicular.
The effect of this may be seen in the figure. A ray of light,
coming from the coin in the direction a, d, does not pass to
d, but is bent downward, and so passes to the eye at e. The
coin, therefore, is seen by the eye at e, but it is not seen in
its true direction from the eye, which is in the line e, c, a,
for we always judge of the place of an object by the direction
in which the rays from it strike the eye. The only point
from which the eye can see the coin in its true position is
at b, in a perpendicular line directly over it. A ray that
passes from one medium to another in a line perpendicular
to the surface of the medium into which it passes is not bent
out of its course.
While rays that pass from a dense medium into a rarer, as
from water into air, are bentfrom the perpendicular, those,
on the other hand, which pass from a rarer medium into a
denser, as from air into water, are bent towards the perpendicular. Thus if in Fig. 136 a be the position of the eye of
a fish, and where the eye is, at e, there be an insect, the fish




230           PHYSIOLOGY AND HYGIENE.
can see it, because the ray that strikes the surface of the
water, c, is refracted or bent towards the perpendicular line,
b, a. He does not see the insect, however, in its true direction, a, c, e, but it appears to him to be at d.
316. Refraction  by  Convex  Lenses.-When
light passes from one medium into another of different
density which presents a convex or concave surface, instead
of a flat one, a very great change is produced in the direction
of its rays. Thus suppose, as represented in Fig. 137, three
FIG. 137.
doa       -— 9t at
diverging rays coming from  a point, a, through the air,
enter a convex surface of glass, b, b'. The central ray a, c,
enters the glass in a direction perpendicular to its surface, and
therefore does not bend from its course. But the ray a, d,
enters very obliquely, and is bent towards the perpendicular
at that point, e, and passes on in the direction f. So likewise the ray a, g, is bent towards the perpendicular h, and
passes on in the line i. These rays diverging in the air have
become converging in the glass, and the point at which they
meet is called the focus. To this point all the other rays
entering the convex glass converge also.
31T. Refraction  by  Concave Lenses.-But if
the surface of the glass be concave, as represented in Fig.
138, the diverging rays which enter it will be made to
diverge still more. The ray, a, c, being perpendicular to the
surface is unchanged in its course; but the ray, a, d, is bent




THE EYE.                     231
towards the perpendicular, e, into the line f, and the ray,
a, j, is bent towards the perpendicular h into the line i.
FIG. 138.
I       I
In the case of both the concave and the convex lens, the
greater the curvature, the greater is the change of direction
in the rays. The greater the curvature, therefore, the
sooner are the rays brought to a focus in the case of the
convex lens.
FIG. 139.
DIFFERENT PARTS OF THE EYE.
318. Description of the Coats of the Eye.-The
arrangement of the different parts of the eye is shown by
Fig. 139, which is a mere map of a section of the eye, through




2 33 2        PHYSIOLOGY AND HYGIENE.
its middle part from front to rear. It is intended to represent the arrangement of the parts distinctly, without strict
regard to proportion. The eye has three coats, as they are
called. At a is the thick strong white coat, called the sclerotic coat, from a Greek word meaning hard. This, which
is commonly called the white of the eye, gives to the eyeball
its firmness. Into it the cornea, e, fits like a watch-glass
into its case. The sclerotic and cornea then make the outer
coat of the eye.
Next comes the choroid coat, b. This is a very vascular
coat, containing the minute branches of blood-vessels which
nourish other parts of the eye. It is of a dark color, for
reasons which will be stated in another place. Its color is
owing to coloring matter contained in pigment cells, which
lie along on the inner surface of this coat, next to the inner
coat of the eye, the retina, c. The retina is a thin membrane, being principally composed of the expansion of the
optic nerve, d.
319. Humnors of the Eye.-The eye has three
humors, as they are termed. The first is the aqueous or
watery humor, f, which is in a chamber between the transparent cornea, e, and the crystalline humor, or lens, h.
This chamber is divided into two parts by the iris, g, g, the
pupil being the circular communicating door between them.
The part of the chamber which is in front of the iris is much
larger than that which is behind it. The crystalline humor,
or lens, as it is more often called, has the consistency of half
dissolved glue. At i is the vitreous humor, filling up a large
part of the cavity of the eye. It is called vitreous from its
glassy appearance. It is a clear jelly-like substance, having
about the tenacity of white of egg. It is contained in an exceedingly thin and delicate sac, and this is divided into cells
which contain the liquid.
320. Arrangement of the _Front Part of the
Eyeball.-Fig. 140 is a map of the front part of the eye,
in which the parts are more minutely delineated than in Fig.
139. At 2 is the sclerotic coat; 3, the cornea; b, the crystalline lens; a, a, a, the aqueous humor; 7, 7, the iris; 4,




THE EAR.                      233
the choroid coat; 8, the retina; c, c, the vitreous humor'
and 9, the sac containing it. Around the inside of the
chamber containing the aqueous humor is a very thin membrane (represented as you see by
a line), which secretes the humor.       FIG. 140.
In this membrane, as in the case
of every other closed sac in the
body, there are both exhalants
and absorbents, so that the fluid
may be changed as necessity requires.?..
There is another thin mem-            7
brane of the eye which has not
yet been described. It is repre-  3 a 
sented by a line, 1, in the figure.
It is the conjunctiva, so called
because it unites or conjoins the
ball of the eye with the eyelids.
It covers the cornea, passes back
a little way on the white of the
eye, and then turns forward to           2
line the eyelid. It is the seat of\ \\ 89
the most common form of inflammation in the eye. It is very vascular, as is shown by its
distended vessels when it is inflamed. It is exceedingly sensitive, and hence the great pain which is occasioned by any
thing, even the smallest mote, that gets into the eye.
321. Ciliary Processes.-At 6 in Fig. 140, is one
of the ciliary processes, as they are called, from their resemblance to the eyelashes. There is a circular row of them,
numbering from sixty to eighty, so arranged as to resemble
the disk of a radiated flower. In Fig. 141 they are represented as they appear in looking at them from behind, the
back part of the eye being removed. At 1 is the divided
edge of the three coats; 2, the pupil; 3, the iris; 4, the
ciliary processes. At 5 is the anterior edge of the retina,
at the beginning of these processes, presenting, as you
see, a scalloped appearance. The processes come from  the




234           PHYSIOLOGY AND HYGIENE.
choroid coat, and are united at their origin by a ring of
ligamentous substance to the sclerotic coat.  The exact
operation of this beautiful mechanism is not known, but
FIG. 141.
CILIARY PROCESSES
it is pretty well ascertained, that muscular fibres are so connected with these processes, that when they contract they
draw the crystalline lens forward.
322. Object of the Apparatus to Form Images
of Objects on the Retina.-The object of all this apparatus, here described, is the formation of images of objects in
the back part of the eye upon the retina, so that the optic
nerve expanded there may carry impressions from them to
the brain. The rays of light coming from an object pass
through first the cornea, then the aqueous humor, then the
crystalline lens, and lastly the vitreous humor to the retina,
where they, so to speak, daguerreotype the object. The fact
that such an image is formed has often been proved by
observation on the eyes of animals.
If the eye of a rabbit be cleansed from the fat and
muscles at its back part, and a candle be held in front of it,
you can see the image of the candle through the sclerotic
coat, formed upon the retina. So if you take the eye of an
ox, and carefully pare off the back part, so as to leave it very




THE EYE.                     235
thin, a distinct image of any thing placed in front of the eye
may be seen at the back part.
323. Images  on  the Retina Inverted.-The
image, however, will be inverted, as represented in Fig. 142.
FIG. 142.
For the sake of clearness two rays only are represented as
coming from each of the two ends of the object, a, c. These
rays cross each other in the middle of the eye, those from a
being brought to a focus at b, and those from c at d. As
all the other rays, coming from other points in the object, are
refracted in the same manner, a complete inverted picture
of it is thus formed. The cornea is, as you see by Fig. 139,
more convex than the sclerotic coat, so that it may act with
some power as a lens in making the rays converge.
324. Iris.-The iris is a circular curtain with a round
opening in its center, called the pupil.  The latter can be
varied in size to a considerable degree. On the iris depends
what is called the color of the eye, which is various, as blue,
nearly black, gray, hazel, &c. The chief office of the iris
is to regulate the quantity of light that enters the eye.
When the light is obscure, the opening in the
iris is widely dilated; but when there is much
light it is contracted; and if the light be
excessive, it is contracted almost to a point.  FIG. 143.
These motions are effected by peculiarly arranged muscular fibres, of which the iris is in
part composed.  There are two sets of fibres,
the circular and radiated, as represented in
Fig. 143. When the circular fibres contract,
the pupil is contracted; and when, on the other hand, the
radiated fibres contract, the pupil is dilated.
325. Crystalline Lens.-The crystalline lens is the




236           PHYSIOLOGY AND HYGIENE.
chief agent in the eye in concentrating the rays of light by
refraction. In Fig. 144 you have a side view of it. Its
anterior part, 1, is less convex than its posterior,
FIa. 144.  2. In Fig. 145 is a magnified view of the lens
hardened in spirit and cut open, so as to show
the different layers of which it is formed. The
1 IlL 2  layers are more and more hard as you go towards
the center. The object of this arrangement and
Cystalline Lens. of the peculiar shape of the lens, is not as yet
understood.
326. Choroid Coat.-The choroid coat (b, Fig. 139)
contains quite a large share of the
FIG. 145.      minute blood-vessels and nerves of
the eye, and serves for a medium
by which they pass to other parts
of this organ.  But it serves another important purpose by means
of its dark pigment. It makes a
dark chamber of the back part of
the eye where the optic nerve is
expanded. The object of this is to
secure distinctness in the images
formed upon the retina.
32f. Want of Pigment in the Choroid of the
Albino. —The pigment is deficient in the iris of the
albino; and the bright red or pinky hue of the iris in his
case is owing to the blood in the minute blood-vessels, with
which this part is so well supplied. Those animals that use
their eyes mostly in daylight have the pigment of the
choroid of the darkest color; while, on the other hand,
those that need to see most clearly at night, as the owl,
either have none of this pigment, or have it of a very light
color.
328. The Retina.-The retina is a soft grayish delicate membrane, formed chiefly of the expansion of the
optic nerve. Here the images are formed, and the minute
fibres of nerve in this membrane receive impressions from
these images, which are transmitted to the brain by the




THE EYE.                      237
trunk of the nerve. This nerve has the same relation to
light that the nerve of hearing has to sound, the nerve of
smell to odors, or the nerve of touch to the qualities of
bodies that we feel. And it is curious to observe that the
termination of the nerve of sight on the surface of the retina
is arranged in papillae, just as the terminations of the nerves
of touch are. In Fig. 146 is represented a portion of the
retina of a frog magnified three hundred times.  The upper rows of papillae,     FIG. 146.
which are without dots, are seen sideways.
329. SphIerical Aberration. —
There is a defect in the operation of
lenses in optical instruments, which is
termed spherical aberration. This can be
explained on Fig. 147, which represents a lens, L, L', with
some of the rays as they pass through it. Now the rays
R' R" R"' are brought to a focus at F; while the rays R L
and R"" L' come to a focus much nearer, at 1. It is found by
FIG. 147.
a  -----------------—. —---—.. L
D'\WB= "-"''IB
------- -_ _ __ —   F
experiment, that if the central portion of the lens be covered,
so that the rays R' R" R"' cannot pass, a distinct image
will be formed on a screen put at 1. And, on the other
hand, if the outer portion of the lens be covered, so that
the outer rays are intercepted, then the middle rays, R' R"' R'"
will form an image on a screen at F. But if the whole lens
be used, no distinct image is formed, anywhere. If you




238           PHYSIOLOGY AND HYGIENE.
place the screen at 1, it will receive, with the rays that come
to a focus there, rays that have their focus at F.
In the eye the iris acts as the diaphragm or stop to
the crystalline lens which is behind it, as was indicated in
Fig. 139. Ordinarily, by means of this stop, the rays pass
through only the central part of the lens.
330. Chlromatic Aberration.-Another difficulty
attending the operation of a common lens is what is termed
chromatic aberration. Every ray of white light consists of
a mixture of rays of seven different colors. Some of these
colors are more easily refracted than others, and therefore
on passing through a lens will come to a focus sooner. This
of course is apt to make some confusion in the color and
the distinctness of objects, when seen through a single lens,
or through several if they are alike.
The difficulty has been remedied, and it is said that the
hint of the remedy was taken from the arrangement of the
eye. At any rate, the defect is avoided by having lenses
made of different materials, just as is the case in the eye.
Thus if two lenses be used, one of which is made of flint
and the other of common glass, the difficulty disappears.
In the eye it is perfectly avoided by the passage of the rays
through so many different materials, before they reach the
retina.
There is also an arrangement in the eye by which it
adapts itself to different distances in looking at objects. If
we look through a telescope at a near object, and then turn
it towards one at a distance, we can not see the latter distinctly until we adjust the lenses to suit the distance. But
in the eye how quickly the adjustment is made! It is done,
ordinarily, without any conscious effort on our part. We
look at an object at a few inches distance, and in an instant
turn the eye and see an object afar off with almost equal
distinctness. There has been much discussion in regard to
the means by which this adjustment is effected, but the
probability is that, as the lens is very elastic, it is kept in a
state of tension by the elasticity of the suspensory ligament,
and consequently is somewhat flattened. Now, if the ciliary




THE EYE.                     239
muscle contracts, it will draw the ligaments away from the
lens, or diminish the elastic tension on the lens. The
lens, consequently, will become more convex, but will return
to its former shape, when the ciliary muscle ceases to
contract.
331. Difficulty in the Near-sighted.-In some
cases this power of adjustment is counteracted by defect
in the structure of the eye. Thus, in the near-sighted,
either the cornea or -the crystalline lens, or both, are too
convex; or, the crystalline lens is too far from the retina.
The result is, that the rays of light coming from a distant
object come to a focus before they reach the retina, as represented in Fig. 148. All objects, therefore, are seen indisFIG. 148.
tinctly except those which are brought near to the eye.
This defect is remedied by the use of a concave lens, which
counteracts the effect' of the too highly refractive power of
the eye by making the rays divergent, instead of parallel,
before entering the eye.
332. The  FPar-sighted.-In  the far-sighted the
difficulty is of an opposite character. The refractive power
FIG. 149
of the eye is too feeble. This is owing either to too little
convexity of the cornea or of the crystalline lens, or of




240           PHYSIOLOGY AND HYGIENE.
both; or, to too great nearness of the crystalline lens to the
retina. In this case the rays coming from a near object do
not come to a focus soon enough. The focus of the rays
coming from any point of the object is behind the retina,
as seen in Fig. 149, in which the rays from two points are
represented as prolonged till they meet. This defect is
palliated by the use of convex glasses.
333. Correspondence of Actio'n between the
two Eyes. —It is an interesting and wonderful fact, that
as we look at an object with both eyes, although there are
two images formed, and therefore two impressions carried
to the brain by the two nerves, yet but a single impression
is produced in the mind. To produce this it is manifest
that there must be a very exact correspondence in the two
eyes as optical instruments. The two images must be similar, and must be formed on corresponding parts of the
retina in both eyes.
Thus, if there be a range of objects, as at A, B, C, in Fig.
150, the impression of each will be a single one in the mind,
FIG. 150.
because the picture of each of these objects is on the same
part of the retina in both eyes, a, b, c, and a,, bl, c'.  But if
you press with your finger one of the eyes a little out of its
place, all these objects will appear double, because their
images will occupy different parts of the retina in the two
eyes.




THE EYE.                   241
334. The Two  Images of an  Object in the
Two lEyes cnot Exactly Alike.-While it is necessary
to single vision when both eyes are used, that the image of
the object should occupy corresponding portions of the
retina in the two eyes, it is not true that these two images
are exactly alike. You can verify this by a simple experiment. If you hold a book before your eyes, with its back
towards you and in a vertical direction, you see the back of
the book and its sides at once, as a single object. If now,
still holding the book in the same position, you shut one
eye, you see but one side of the cover of the book-that one
which is on the same side with the open eye. And so with
the other eye. The plain inference is, that when you look
at the book with both eyes, the image formed in the right
eye is composed of the back of the book and the cover of
the right side, while the image in the left eye is composed
of the back of the book and the cover of the left side.
From these two distinct images, two distinct impressions
are sent to the brain; and yet but a single impression is
recognized there by the mind, for the book is seen as a single
object. This single impression must, therefore, result in
some way from a mingling of-the two impressions transmitted along the two optic nerves.
The statements in the last paragraph are beautifully
illustrated by the instrument contrived by Professor Wheatstone, which he calls the stereoscope. In using this instrument, you look at two pictures of the same object with the
two eyes, and yet you see but one thing-that is, but one
impression is produced in the mind, although two different
pictures are made in the two eyes, and of course two different impressions are conveyed to the brain.
Thus, the two representations of a dog, seen in Fig. 151,
are seen in the instrument as a single dog. You observe
that they are shaded differently. They are representations
of the two pictures, which a dog in this position would
make on the retina in both of the eyes of a person looking
at him. When you look at them in the instrument, the
single dog that you see stands out more than either of the
11




242. PHYSIOLOGY AND HYGIENE.
two representations, as seen when they are not in the instrument. The reason is obvious., In the two images formed
in the eyes, as you look into the instrument, are all the
lines of light and shade which you would see in looking
FIG. 151.
at a real dog with both eyes; while either one of these
representations contains only a part of these lines.
335. Rude  mnitatio~n of the Stereoscope.-You
can imitate in some good degree the effect of the stereoscope,
by placing the end of a small book between these figures,
and letting the other end rest against the nose and forehead,
thus separating the eyes from each other. If now you look
intently at the two figures, you will in a few moments find
them approximate each other, till at length they mingle
together, and you will see but a single dog, standing out
like a statue.
336. Visual Angle.-Let us look now at the means
by which we gain the experience that is necessary to correct
vision. One means is the appreciation of the space occupied
by objects in the field of vision. This is measured by what
is *termed the visual anzyle-that is, the angle which is
formed by two lines ciming from the extremlities of an ob



THE EYE.                     243
ject, and meeting in the eye, as represented in Fig. 152. In
this way we get the idea of, magnitude.
FIG. 152.
But it is manifest that it alone can not give us this idea
correctly. It would do so, if all objects were at equal
distances from the eye. But if they are at different distances,
something evidently must be known of those distances, to
estimate the magnitude of the objects by the visual angle,
which they subtend. The arrow at A B will appear just as
large as the larger one at A' B', because it will occupy the
same space a b on the retina, and subtend the same angle.
But if it is known that the one is nearer to you than the
other, allowance is made for this in the estimation of the
size.
The hand, held up to keep the rays of the sun from the
eyes, would look as large as the sun itself, if one did not
know how near it is; and the sunr and moon appear to us
-to have about the same magnitude, because we do not fully
realize the fact that the sun is ninety-two millions of miles
from us, while the moon is only two hundred and forty
thousand.
33". Distance of Objects Estimated by their
Distictutess. —Another means which we use in getting
a correct idea of objects by vision, is the degree of distinctness in their lines, and shadows, and colors. The fact is
learned very early by the child, that the nearer objects are,
the greater is their distinctness; and he makes use of this
fact continually in estimating both their distance and their
magnitude. By this means, however, he estimates the latter
less directly than he does the former.




244           PHYSIOLOGY AND HYGIENE.
He makes use of his notion of its distance gained, by its
degree of distinctness. Many mistakes are made in the use of
this means of judging the distance of objects. Thus, a very
bright light will often appear to be nearer than one that is
less bright. When the atmosphere is very clear, mountains
and other objects appear nearer to us than they do when the
atmosphere is thick and hazy.
338. Size of Objects Estimated  by  Coinparison.-Another means of making a correct estimate
of the distance and magnitude of objects is, comparison
with other objects which are familiar to us. Thus, we get
our ideas of the size of animals from objects in their neighborhood. The artist makes use of this means of comniunicating ideas of size. Figures of men are placed near large
buildings for this purpose. A notion of the great size of
the elephant is given by placing his keeper at his side. We
are not ordinarily aware how dependent we are upon such
comparisons, in estimating the magnitude of objects. For
example, a person upon a giddy height suddenly turned his
eye upon some huts below at a river's side; they appeared
to be dog-kennels, till a man issued from the door of one of
them, and thus, by affording a means of comparison, dispelled the illusion.
339. All,Images on the Retina (to inot Prodtce Im2pressionts in the ]W[ind.-When it is said
that images of objects are formed upon the retina, and that.
impressions are transmitted from them to the brain, this is
far from stating all that is true on this point. Many of the
images pictured upon the retina do not transmit impressions
to the mind. The sensation of seeing is, therefore, in relation to them incomplete-only the beginning of the process
is effected.
This can be verified by a simple experiment. If you hold
a finger near the eyes (at some ten or twelve inches from
them), and a finger of the other hand at a greater distance,
but in the same direction, and then look at the near finger,
you will perceive that the other finger appears double. So,
on the other hand, if you look at the distant finger, the




THE EYE.                    245
near one appears double. The reason of this can be made
clear to you by Fig. 153. The two eyes, L and R, being
directed so that their axes
converge on the object A, the        FIG. 153.
middle  points of the  two
images correspond with the
middle points of the retina in
the two eyes, a and a.
The images thus corresponding in their place on the
retina, the impressions carried
from them by the two optic
nerves to the brain correspond
also, and so the vision is single.
But the image of the object B
is formed in the two eyes, in
parts of the retina that do not
correspond, b and b.  They
are both on the inside of the
middle points, a a, that is, towards the nose; whereas the outward part of the retina in
one eye corresponds with the inward part in the other eye,
and vice versa.
340. The "Bulind  Spot." —The sensibility of the
different parts of the retina to light varies greatly. The
point of entrance of the optic nerve is not sensitive to light,
as may be proved by a very simple experiment. Close the
left eye, and look steadily with the right at the letter A on
the page, held at a distance ten or twelve inches.
A                                      B
The letter B will be seen quite plainly, as well as the
letter A. Now, move the book slowly toward the eye, which
must be kept steadily fixed upon the letter A. At a
certain point the letter B will disappear, but as the book
is brought still closer it will again come into view. This
results from the fact that, in the first position of the book,
the image of the letter B falls between that of the letter A
and the entrance of the optic nerve; while, in the second




246           PHYSIOLOGY AND HYGIENE.
position, it falls on the entrance of the optic nerve itself; and
in the third, inside that point. So long as the image of the
letter rests upon the entrance of the optic nerve it is not
perceived, and hence this region of the retina is called the
blind spot.
34 1. Defenses of the Eyie.-The means by which
so delicate an organ as the eye is protected from injury, are
worthy of notice.  Observe first its situation.  Parapets
of bone surround it, and receive most of the blows that
come upon that part of the face. Above is the strong
arch of bone, forming the lower part of the forehead.
Then there are the cheek bones, and the bones of the
nose. Thus, walled in, in all directions, by these prominences, the eye is seldom hurt, except by a direct thrust.
And besides being thus protected by surrounding bones,
it reposes upon a soft cushion of fat, which yields, if the
eye be pushed backward by violence. Indeed it is pushed
backward effectually by the muscle that.closes the eyelids
whenever an impending blow is anticipated, and it is thus
sunk farther back in its cushioned recess, amid the projecting parapets, and of course receives less of the force of
the blow than it otherwise would. This muscle, also, by
its instantaneous action, prevents many light particles from
flying into the eye. Such particles are also often prevented
from entering the eye, by being intercepted by the eyelashes.
The eyebrow, besides being an ornament, protects the eye
from harm, by preventing the salt perspiration from running down into the eye, and irritating it. It acts as a
thatched roof, projecting from the arch over the eye, and
letting the perspiration from the forehead evaporate from
it. The eyelashes also serve to keep the perspiration of the
eyelids from entering the eye.
The structure of the eyelids is such, that the freest motion is allowed, while they afford by their firmness considerable protection to the organ. They derive their firmness
from a fibrous cartilage, which makes the body of each lid.
You can readily see that this cartilage, making an even




THE EYE.                     247
pressure on the surface of the eye, must often prove an
effectual defense against direct thrusts. If the weapon hit
this cartilage, it acts as a firm shield, to ward off the blow
from the eye behind it.
And even that part of the lid which is intended by its
laxness to allow free motion to the lid, the skin, is often
an effectual defense. If an impending blow be seen, and
the eye be instantaneously and forcibly shut, the wrinkled
skin forms a soft cushion over the eye, and thus not only
covers it up, but serves materially to deaden the force of
the blow.
342. Tear Alpparatus.-The tear apparatus affords
the eye material protection. The bland tears keep the
organ properly lubricated,
so that its constant motions          FIG. 154.
occasion no irritation. And
if any thing gets into the
eye, the tears are manufac-     ~          ~      c
tured abundantly, for the   6 - 
purpose of washing out the
intruding substance. Fishes
have no need of a tear apparatus, as their eyes are
washed  constantly  by the
water in which they live.
In Fig. 154 is represented
the  tear apparatus.  The
tears are secreted by a small
gland, called the lachrymtal       TEAR APPARATUS.
gland, situated at a, in the
orbit under the arch of the forehead, and near the outer
angle of the eye. At b are the ducts which empty the tears
in upon the surface of the eye on the inside of the upper
lid.
By the constant motions of the organs the tears are diffused over its whole surface, and thus continually wash the
eye. The arrangement for carrying off the fluid is this.
It flows through a tube, d, e, into the nose. This tube has




248           PHYSIOLOGY AND HYGIENE.
at its beginning in the eye two branches, c, c, which open
on the edges of the two lids at the inner corner of the eye.
These open mouths, that drink up the tears as they flow
to them, you can very readily see. The drain of the eye,
which thus conveys the lachrymal fluid to the nose, is ordinarily capable of taking care of all the tears made by the
gland.
But when an uncommon amount is made, as in weeping,
it cannot receive all the tears, and they therefore overflow
their banks, the edges of the eyelids. And sometimes there
is a constant overflow from obstruction of the drain by
disease. The continual weeping of the eye, when this obstruction exists, will give you some idea of the amount of
fluid which the lachrymal glands make.
343. Oilign the Eyelashes.-Along on the edge
of each eyelid are some very small glands which secrete an
oily substance. This serves two purposes. It oils the eyelashes, and also prevents the tears, when they are only in
ordinary quantity, from being diffused over the edges of the
eyelids in the constant motions of the eye.
This exceedingly small quantity of oily substance suffices
to keep the tears in the eye where they are needed. There
is also a curious provision for directing the tears to the
mouths of the ducts when the lids are
FIG. 15.5.   closed. When brought together their edges
unite in such a manner as to form with
the surface of the eye a triangular channel for the tears to run in. This is made
-o.       clear by the diagram in Fig. 155, in which
the line b represents the surface of the eye,
and a the edges of the lids, showing a section of the canal between them.
344. Nictitating JMetmbrane in
the Eyes of Birlds.-We  had intended
to notice some of the peculiarities of the eyes of different
classes of animals. We will, however, notice but one-the
nictitating membrane in the eyes of birds. When not in
use it is gathered up in the inner corner of the eye. When




HYGIENE.                    249
it is stretched over the organ we see that it is a thin translucent membrane.  It is very elastic, so that as soon as
the muscles sweep it quickly over the
eye, it flies back at once to the corner    FIG. 156.
where it is so snugly folded. In Fig. 156
it is represented as half way over the
front of the eye. In Fig. 157 are seen
the curiously arranged muscles that move
it. One of the muscles, g, arises from the ii.
ball of the eye at its upper part, and
running back, forms the trunk of the
optic nerve, a tendon with a loop, through    FIG. 157.
which the tendon of the other muscle, p,
works.
This muscle arises from the lower part   k
of the ball of the eye, opposite to the
origin of the first muscle. Its tendon, t,
is fastened into the edge of the nictitating membrane. It acts through the loop       t
as a pulley, and you can see that the
muscle, g, assists it materially in effecting the very quick
motions of the membrane.
CHAPTER XVI.
HYGIENE,
AFTER having considered the construction of the machinery of the human system and the uses which the mind
makes of it, one naturally inquires what the conditions
are on which depend the full development of this complicated machinery and its daily repair?
345. Sources of our Knowledge of fHygiene.
-The principles and rules of Hygiene are to be learned




250           PHYSIOLOGY AND HYGIENE.
from two sources. 1. They are to be learned from Physiology. As we observe the functions of the different organs,
we can learn what those circumstances are which favor their
due performance, and what those are which interfere with
it. 2. They are to be learned, also, by observing the effects
of those agencies which are known to interfere with the
functions and to produce disease.
An exemplification of these two modes of learning the
principles of Hygiene in relation to a single point will
suffice. The study of the physiology of the chest shows us
that nature has, in the construction of its framework,
especially provided for giving ample room to the lungs;
and so we deduce a law of Hygiene, that the chest should
not in any way suffer compression. This is the first mode.
But the same law can be deduced by the second mode, that
is, by observing the results of compression of the chest.
Rules of hygiene generally have but little practical influence, unless the physiological facts upon which they are
based are understood. Although the evil effects of their
violation may be vividly portrayed, and even illustrated, as
in the case of the chest, by engravings, the impression upon
the mind is by no means so thorough and practical, as
when the same lesson is enforced by a clear knowledge
of the functions and arrangements of the organs and the
conditions necessary to their healthy action. Physiology,
therefore, should be studied as preparatory to a proper
appreciation of Hygiene.
Not only is a knowledge of Physiology essential to a
proper appreciation of the rules of Hygiene, but in many
cases they cannot be fully understood in their varied application without such a knowledge. With the very partial
and superficial knowledge of Physiology that is usually
communicated with Hygiene, these rules are for the most
part merely arbitrary.  And just so far as the principles
on which they are based are not understood, is there a
liability to mistake their application.
In considering the subject of hygiene, the natural division of Physiology should be kept in mind. There is a




HYGIENE.                   251
hygiene relating to the construction of the machinery of the
body, and there is also a hygiene relating to the uses of this
machinery. Besides, each organ has, to a certain extent, its
own hygiene. And yet, as all the organs are more or less
connected in sympathetic action, there is a general hygiene
of the system.
346. Ifyfgiene of Digestion.-Many of the points
in the hygiene of the digestive organs have been already
noticed in the physiology of digestion. Nothing more is
needed in addition to what is said there of the importance
of the thorough mastication of food, and of its having a
due amount of saliva mingled with it; of the evils resulting from eating too fast, from eating between meals, and
from eating a great variety of food; and of the influence
of exercise upon the process of digestion. There are some
other points, however, that remain to be noticed.
347. Quantity of Food to be Eaten. — No very
precise rules can be given as to the quantity of food that is
proper to be eaten. But a consideration of the physiological principles of digestion suggests rules that are sufficiently
definite for practical purposes. There must be such an
amount of food as will furnish sufficient chyle to keep the
blood, the building material of the body, in proper quantity.
The question arises, how shall we know what amount of
food is requisite for this purpose.
Fortunately, the want of the system and its supply are
commonly quite accurately indicated by the sensations.
The proper hygienic rule then on this point is, that we
should cease to eat when the sensations created by the want
of the system are removed-that is, when the hunger is
appeased, and the accompanying feeling of discomfort is
succeeded by a feeling of agreeable ease.
348. Mistakes as to Qulantity of Food.-But
there are mistakes often made in regard to these sensations.
They may be prevented from making a true report. Thus,
when eating is done too rapidly, more food than is needed
may be introduced into the stomach before the sensation
of ease and satisfaction is experienced. It is only when




252           PHYSIOLOGY AND HYGIENE.
suitable time is given to mastication, and the food is rather
gradually introduced, that this sensation indicates the proper
limit of eating.
Again, there is a very common mistake in regarding the
feeling of fulness instead of the sensation alluded to, as indicating the time for ceasing to eat. Those who adopt this
false rule generally make the stomach bear as much as it
can without absolute discomfort, and many daily overreach
this point. The result is, that this organ soon gives out
under this daily overworking; or, if the stomach be a strong
one, an injurious repletion is produced in the system.
Too little food is sometimes taken. Poverty is commonly
the cause. But sometimes it arises from false notions; as,
for example, the notion that the quantity of food should be
regulated by weight, or the more common notion, that we
should rise from  a meal with some appetite remaining.
The result is, that there is not a sufficient supply of chyle
to meet the wants of the system. The wear and tear create
a demand which is greater than the supply, and the body
therefore loses its fulness and its vigor.
349. Leng7th of Intervals between ]Meals. —In
determining the length of the intervals between the meals,
we should have regard to the time required for the completion of the process of digestion, and to the wants of the
system. Some articles are digested more rapidly than others,
but it commonly requires from three to four hours to complete the digestion of a meal. When the system is in a state
of action, its want of food, as indicated by its sensations,
shows itself a little time after the completion of the process
of digestion. The interval, then, between the meals should
not vary much from  five to six hours. If it be made
longer, some degree of exhaustion results; and if it be less,
disturbance of the digestive process may occur, from fhaving
the digestion of one meal begin before that of the previous
one is fairly finished.
350. Regulai'ity of Meals.-It is important that
the meals should be eaten at regular periods from day
to day. For the stomach, with its times of work and of




HYGIENE.                     253
rest, naturally contracts regular habits, a disturbance of
which is injurious. This obedience to habit in this organ
is manifest whenever any change is made in the time of
eating.
351. Quality of Pood.-The question is often asked,
whether such and such an article "is healthy," as if there
were essentially different degrees of suitableness in different
articles of diet. So far as digestion is concerned, any article
is healthy for any individual whose stomach can digest it
without difficulty. An article may be perfectly healthy for
one, and unhealthy for another. There are sometimes wide
differences in this respect, owing to unaccountable peculiarities. But even in regard to ordinary differences, the question
as to the propriety of any article of food is wholly an individual question.
Our food should be varied in the different seasons of the
year to a greater extent than is common. In the warmer
seasons it needs to be less stimulating, less heat-producing
than in the colder seasons. The fruits, each in its season,
should, in the warmer months, regularly form quite a large
proportion of our food. If used thus, they will tend to
prevent, rather than induce, the complaints peculiar to that
portion of the year.
352. Influence of the JMind on Dligestion.The state of the mind has much influence on the digestive
organs. This is sometimes strikingly exhibited in the loss
of appetite on the sudden reception of bad news. It is also
seen in the influence of continued sorrow upon the appetite
and the digestion. It is not strange, then, that one of the
prominent causes of dyspepsia is mental disturbance or depression. And a cheerful mind is very properly deemed to
be essential to easy and thorough digestion.
353. Hygiene of Respiration.-In order to understand fully the hygiene of respiration, it must be borne
in mind, that the great object of this function is to bring
the air into all the minute air-cells of the lungs, that it may
change the blood which is sent there for this purpose.
Anything, then, which interferes with the free introduction




254           PHYSIOLOGY AND HYGIENE.
of the air into these cells is a palpable violation of the laws
of health. And yet this interference is so commonly practised, that it is one of the prominent causes of disease.
354. ConLmpression of the Chest. —This interference is effected in two ways. It is done, first, by mechanical
compression of the chest. Although, as shown in the
Chapter on the Respiration, there are special pains taken
by the Framer of our bodies to provide, in the construction
of the chest, for the free introduction of air into the lungs
under all circumstances, this is often prevented by certain
prevalent modes of dress.
It must be observed that in the arrangement of the chest,
a free motion of its walls in the expansion of the lungs is
contemplated.  The dress, therefore, should always be so
loose as to admit of this free motion. If it is not, the air
is not freely admitted to all the air-cells, and therefore the
blood is not so fully changed, as nature requires; and the
health is impaired just in proportion to the degree in which
the due expansion of the chest is prevented.
Compression not only produces disease in the lungs, but,
by preventing these organs from effecting fully the requisite
change in the blood, it impairs the quality and lessens the
quantity of this building material, and thus diminishes the
nutrition and the vigor of the system, and therefore renders
it liable to a great variety of diseases, especially those of
which debility is a prominent characteristic.
355. Importance of a Good Supply of Pure
Air.-The free introduction of pure air into the lungs is
interfered with, secondly, by cutting off its supply. As you
learned in the Chapter on Respiration, the oxygen of the
air is used up in large quantities by the lunngs, and the carbonic acid gas thrown off takes it place. If, therefore,
there be not sufficient provision for the supply of fresh
relays of pure air, a mixture of air and carbonic acid gas
will be introduced into the lungs at every breath, so that
there will not be sufficient oxygen to effect thoroughly the
change in the blood.
In this respect, therefore, the result is the same as when




HYGIENE.                    255
too little air is admitted by reason of compression of the
chest. A portion of the requisite quantity of pure air is
shut out, in one case by diminishing the capacity of the
chest, and in the other by having the lungs in part occupied
by carbonic acid gas.
356. Bad  Results of Defective  Aeration
Seldom Atlppreciated.-The influence which this defective aeration of the blood, occasioned by these two causes,
exerts upon the health, is seldom appreciated. For unless
the deficiency be very great, no immediate obvious result is
produced. But though the deficiency may be comparatively
small, if it be continued from day to day for a long time,
the aggregate result of this steady depressing influence is a
serious one.
The destruction of health and of life that comes from
this imperceptible agency in every community is vast in
amount. But most persons seem to be insensible to this
fact. They need a narrative of such a destruction of life as
occurred in the Black Hole at Calcutta, to convince them
that a considerable quantity of fresh air is required by every
pair of lungs. And it is only by a description of an examination after death of some one who has been killed outright by extreme compression of the chest, that they can be
made sensible of the need that the lungs have of the room
that nature has given them. And even then the impression seems to be a momentary one.
If all the injury that is done by defective aeration of the
blood could be visibly traced out, we should then realize the
necessity of having just as many of the air-cells, those little
chemical laboratories, as nature designed, and of keeping
them well supplied with the fresh air which they require
for the life-giving work that they perform.
35-7. H-ygiene of the Circeulation.-The hygiene
of the circulation need not detain us long. The office of
the organs of the circulation is to circulate the blood, the
building material, everywhere. They never rest from their
work. But they work more actively when the muscular
system is in action than when it is at rest. As one lies in




256           PHYSIOLOGY AND HYGIENE.
bed, the circulation goes on steadily, but quietly. But on
rising and moving about, the circulation becomes more
active. Not only does the heart beat more quickly, but the
capillaries in every part of the body increase their action.
And, as more blood is carried to every part, there is more
done everywhere. We see this in the skin, in the increase
of the perspiration on exercise. When the muscular effort
is very great, the excitement of the circulation is violent and
tumultuous. The heart beats strongly and rapidly, and the
flushed face shows how active is the circulation in its extreme vessels, the capillaries.
358. Exercise Necessary to Iealth.-The occasional excitement of active exercise is absolutely essential to
the proper physical development. The body may sometimes,
indeed, maintain its proper bulk in a continued state of
muscular inaction; but its textures will not have the requisite strength and tone. That they may have these qualities,
it is necessary that the blood be often pumped into their
capillaries with the force that is given to the heart by active
exercise.
It is not the muscles alone that are rendered stronger and
firmer by exercise, but the same effect is produced in all the
textures, the bones, the ligaments, the veins, the skin, &c.
The great internal organs of the body are firmer, more fit to
perform their duty, and less liable to disease, if the circulation in them is excited daily by this means. Active exercise
makes the stomach digest better, the lungs perform the work
of aerating the blood more thoroughly, and the brain serve
the mind more easily and effectually; it therefore renders
one less liable to dyspepsia, to consumption and other diseases of the lungs, and to apoplexy and other diseases of
the brain and the nervous system.
But the activity of the circulation may be made so violent
by exercise as to do some damage. Though its organs are
capable of bearing much in this respect, there is some need
of caution. Harm is undoubtedly often done in trials of
strength when the effort is both violent and prolonged.
Vigorous action answers fully the purpose of developing




HYGIENE.                    257
power and firmness; but violent action is attended with
some hazard.
359. Hlygiene of Bormation and Rejpair.In considering the hygiene of formation and repair, it must
be borne in mind that there is constant change everywhere
in the system. Particles that have become useless in the
textures are continually taken. up and carried away in the
veins or the lymphatics, and other particles are put in their
places, being taken for this purpose from the blood in the
capillaries. This change is going on during all the period
of growth, as well as afterwards. The health and vigor of
the textures, and therefore of the system as a whole, are dependent upon the proper performance of this constant process of removal and fresh supply.
There are two conditions necessary to the due performance of this process. The first is, that the blood, the universal material for building and repairing, shall be of good
quality. This is secured when the digestive process, which
furnishes the blood, is well performed, and the lungs and
other organs, that purify the blood by discharging its refuse
matter, are in good condition. - The second condition is,
that the blood shall be often quickened in its course through
the organs by the excitement of exercise. This has been
mentioned in speaking of the hygiene of the circulation.
360. Necessity of a FM'ee Discharge of the
WaNste.-The necessity of having the waste matter that is
brought back from all parts of the body in the venous blood,
effectually discharged by the various organs designed for this
purpose, requires a particular notice. The lungs, the skin,
the liver, the kidneys, &c., must thoroughly evacuate this
waste, or its retention will impair the quality of the blood,
and thus interfere with the proper nutrition of the body, or,
in other words, with the process of formation and repair.
And the retention of this refuse in any considerable amount
is immediately productive of disease.
The lungs, while they take in oxygen from the air, discharge carbonic acid gas, that part of the waste of which it
is their duty to rid the system. If this carbon be retained,




258           PHYSIOLOGY AND HYGIENE.
the blood is impure in proportion to the degree of retention.
361. Functions of the Skin. — It is the duty of
the skin to discharge some portion of the refuse of the system in the sensible and insensible perspiration. The skin is
not a mere covering of the body, but it is also an active
organ, performing very important functions. It continually
discharges through its numberless pores a large quantity of
matter.
Although this matter is mostly in an insensible form, if
from inactivity of this organ it fail to be discharged, its retention renders the blood impure, and so does injury to the system. At least two pounds of matter are discharged from the
skin in twenty-four hours. This being the case, it is not at all
wonderful that activity of this organ should be so necessary
to health, and that the suspension of its secretions should
have so much influence in the production of disease.
36'?. Animal Heat. —In the Chapter on Respiration
you learned that the heat of the body is produced by the
change that takes place in the blood in the capillaries, as
it receives the waste particles, and as the new are deposited
in their places. This change makes a real combustion in
every capillary. The more rapid therefore is the change
the greater is the combustion, and of course, the greater is
the heat. Hence comes the increased heat of exercise.
Exercise makes more wear and tear, and so disengages in
the waste more carbon and hydrogen to unite with the increased amount of oxygen that comes in the quickly flowing
blood to the capillaries; and just as in combustion that is
attended with flame, the greater the amount of fuel the
greater is the heat. We have a familiar example of the production of heat by exciting the circulation, in the expedient often resorted to by laborers for xvarming the
hands, of striking them with a swinging motion upon the
shoulders.
The amount of heat produced in the body depends also
on the quality of the blood. The richer it is, the more oxygen it contains, and therefore, the brisker is the fire in the




HYGIENE.                    259
capillaries, and the greater is the heat. You see then why
it is that those who have a good state of the blood, and exercise much, maintain the heat of the system better, and so
need less clothing than those whose blood is weak, and who
exercise but little.
The heat of the body is maintained in all temperatures
of the atmosphere very nearly at 98~ Fahrenheit. This is,
you observe, much above even the highest temperature
that is agreeable to us. You see then that it is essential
to the comfort of the body that it be giving off heat continually to the surrounding atmosphere. If the atmosphere
be at 98~, the same temperature with the body, there is
great discomfort, from the fact that the heat is given off
too slowly.
It would not be parted with at all if the skin were not an
active organ. It is by the evaporation of the perspiration
thrown off by the skin that the extra heat is got rid of when
the air'-is so hot. The temperature in which the body is
generally most comfortable is about 70~. When the atmosphere goes below this, we need the ordinary expedients to
prevent a too rapid escape of the heat from the body.
The clothing and the heated air, with which we surround
ourselves to guard against the cold, do not act by communicating heat to the body, but simply by retarding its
escape.
Cold is a depressing agent, and exerts as such much influence in the production of disease. Statistics show this
in a striking manner. The statisticsof London, for example, prove that the mortality of a severe winter is much
greater than that of a mild one. And this difference is
found to be chiefly among the very young and very old,
because in them the power of generating heat is feebler
than in other classes.
The greater is this heat-producing power of the system,
the better does the system resist the depressing influence of
cold. All those means, therefore, which promote the vigor
qof tle body, are the best of the safeguards to be used against
this productive cause of disease and death. But, besides




260           PHYSIOLOGY AND HYGIENE.
thus fortifying the body internally against this depressing
agent, we have the means of outer defence alluded to,
in clothing and heated air. As there are many errors
committed in using these, they require a more particular
notice.
Clothing serves, as has been said, to shut in partially the
heat which is generated in the body. Its amount and character should be regulated by two circumstances-the degree
of the cold, and the amount of heat-generating power in the
system. The vigorous require less clothing than the weak,
because they have more of this power; so, also, the body
needs'less clothing when it is in exercise than when it is in
a state of rest, because in exercise it generates more heat.
And the same principles apply to heated air, for this is an
outer covering for the body, interposed between it and the
cold, like clothing, for the purpose of preventing the too
rapid escape of the heat generated within.
These plain principles are violated in various ways. Many,
from carelessness or from mistaken notions, are often unnecessarily exposed to the depressing influence of cold.
They are not sufficiently aware of the necessity of guarding
so much more thoroughly against the cold when at rest than
when exercising. And then, on the other hand, they add to
the effect by having too much clothing when in action, or
when in a warm place. When they thus suffer first from
too much heat, an after exposure to cold is exceedingly injurious.
The weak especially suffer from exposure to cold when
the body is at rest, and therefore, they should take special
pains to guard themselves against this depressing agent.
Any attempt on their part to harden themselves, as it is
expressed, by making use of as little clothing as the vigorous wear, particularly when the body is in a state of inaction, always does harm.
The very thin coverings so commonly seen on the feet
of delicate females are palpably inconsistent with this rule
of hygiene, and are in ridiculous contrast with the stout
coverings considered necessary for the feet of vigorous men.




HYGIENE.                    261
363. Cold Sometimes a Stimulant.-The depressing influence of cold sometimes produces a marked
immediate effect. But this is not generally the case. Commonly no harm is apparently done at the time, and so little
is thought of it. But if this influence be continued day
after day, its effects accumulate and become established.
The vigor of the system is more or less destroyed, and some
local disease may make its appearance. The debilitating
influence of cold is in this way a fruitful cause of disease,
not only in the abodes of poverty, but even among those
who have ample means of guarding against it.
Although cold is generally a depressing agent, it is often
indirectly a stimulating one. It is so when, in consequence
of its impression upon the skin, it excites what is termed a
reaction. Several circumstances are necessary to this result.
1. There must be the power of reaction in the system. There
may be so much debility that reaction can not be awakened.
2. If the system be in a state of rest, the application of cold
must be temporary. A continuous application of it would
be depressing, and would forbid reaction. 3. In an active
state of the body, reaction may be produced even when the
application is continuous. Thus the mere exercise of dressing may suffice to awaken reaction in a degree of temperature which would chill one through if he were sitting still.
364. Conditions on, which  Reaction  Depends.-The system may be accustomed to react under
the impression of cold in two ways. 1. By exercise in the
open air in cold weather. Those who have but little outdoor exercise in cold weather, have but little power of reaction, and therefore feel the depressing influence of the
cold whenever they are exposed to it. 2. By a judicious use
of cold bathing. The object of cold bathing, aside from
purposes of cleanliness, is to accustom the system to react
under the influence of cold. It is only when reaction occurs
under its use that it does good. It does positive harm when
reaction does not occur; and the harm done in this way
day after day, by depressing the vital powers, is sometimes
at length ruinous to the health.




262           PHYSIOLOGY AND HYGIENE.
365. Cold Bathing. —There is a want of proper discrimination in many writers on hygiene in regard to cold
bathing.  It is a mistaken ultraism  to say, as is often
said, that the preservation of health requires that the whole
body should be bathed every day in cold water. Neither
cleanliness nor the other purpose mentioned ordinarily requires so frequent and thorough bathing as this.  The
water may be applied to only a part of the body at a time,
and yet accomplish all that we wish. Indeed, some persons
of delicate constitution can not bathe the whole surface at
once with cold water. They may at first be able to apply it
to only a small part of the body.
But they may, with the aid of friction, after a while come
to apply it over a considerable portion of the surface, or
perhaps over the whole. In some persons this extension of
the limits of the bathing from day to day must be done very
cautiously; and there is occasionally one that can not bear
it at all over any considerable extent of surface. It is
necessary for some, in accustoming themselves to cold
bathing, to begin with using tepid water, making it from
day to day a little colder.
The best time for cold bathing is commonly in the latter
part of the forenoon, for the system is then in its most
vigorous state, and is therefore best prepared to react. But
in most persons reaction can be secured at the hour of rising,
and this is the most convenient time for bathing. Few can
use the cold bath with profit in the latter part of the day,
for the powers of the system are then more or less exhausted,
and full reaction is not easy. The soothing influence of the
warm bath is appropriate at that time. There are many
other points in regard to bathing that might be noticed, but
space will not permit it.
Thus far we have spoken mostly of the hygiene of the
body as a structure. But digestion, the circulation, &c, are
engaged in constructing and repairing organs for the use of
the mind. In this use, there is wear and tear, and hence
is the necessity of seasons of rest, that the needed daily repair of the organs may be effectually done. The mind uses




HYGIENE.                    263
the muscles and bones for motion, the various organs of the
senses in gaining a knowledge of the world around, and the
brain in thinking, willing and designing. Any of these
organs may be overworked, and after a certain amount of
work has been done, there needs to be an interval of rest
for repair. The repair is going on continually, while the
organs are at work; but it can not be done thoroughly
without these intervals of rest. Most of the repairing is
done in these periods. This simple statement suggests the
principles of hygiene in regard to the uses-which the mind
makes of the organs of the body. These will now be developed briefly in regard to the muscles, the senses, and
lastly the brain.
366. Exercise Necessary to the Develo2nnpmeut
of both the 3liuscles and the other Oryans.There is a certain amount of muscular exercise which is
essential to firm health. While no one can fall below this
amount without impairing the healthy vigor, the laborer
goes much beyond it without injury. There is a wide range,
therefore, in the amounts of muscular exertion that are consistent with health.
The exercise of the muscles is necessary to their full development. When a limb fails to be used, as, for example,
in palsy, the muscles become small and lose their firmness.
When, on the other hand, the muscles of any part of the
body are much used, they become more developed than
others less used. For example, the labor of the blacksmith
develops the muscles of his arms largely. The same thing
is true of the muscles of the leg-in the rope-dancer.  It is
only a general exercise of all the muscles of the body that
develops them in all parts of the frame in their due proportion.
But muscular exercise is also necessary to the proper
development of the other textures as well as the muscles.
There is one illustration of this influence of exercise which
deserves a particular notice, as it serves to prevent
deformity. In the universal vigor and firmness of the
textures which free exercise tends to produce, there is




264           PHYSIOLOGY AND HYGIENE.
ordinarily a precise equality between the two halves of the
body: the muscles on the two sides act with equal power;
the spinal column, the grand pillar of the trunk, is held
between the muscles that bind its twenty-four bones together with great exactness, and there is a beautiful symmetry in the whole frame.
But when, from  lack of exercise, there is want of firmness in the textures, this symmetry is apt to be lost during
the development of the frame, and the spinal column is
especially apt to become deformed.
36T. Deformity of the Spine.-There are two
immediate causes of this deformity, viz., irregular muscular
action, and irregular pressure. Weakened muscles are prone
to act irregularly; and structures that have lost their firmness, readily yield to any pressure that is laid upon them.
When there is firmness of texture, irregularities of pressure
are not apt to produce deformity, because the elasticity
prevents the permanent influence of such pressure. The
moment the pressure ceases, the elasticity of the part restores it to its usual shape. The firm regular action of the
muscles also tends to the same result.
Thus, in the case of the spinal column, if the posture of
the body be such that it is bent over to one side for some
time, the moment that the posture is altered, the elastic
cartilages resume their usual shape which has been temporarily changed by the unusual pressure, and the muscles
also that lie along this pillar of bones bring them at once
to their right position.
But if the cartilages have lost in some measure their
elasticity and the muscles are weak, the righting up of the
spinal column is not fully accomplished; and a succession
of slight failures in this respect will, after a while, produce
a permanent deformity in the direction of the most commonly assumed posture.
You can see all this exemplified if you observe the difference between males and females in regard to deformity of
the spine. This deformity is exceedingly common among
girls, while it is rare among lads. The simple reason is,




HYGIENE.                    265
that lads have the invigorating influence of free out-door
exercise. Too much influence is attributed to posture in
producing this deformity. Posture is often spoken of as
being the chief cause of it, and this view of the subject is
illustrated extensively with cuts, showing how the deformity is occasioned.
If this were the correct view, there should be much less
deformity among girls than among boys in our schools, for
the former sit in a crooked posture much less than the latter do. So far as posture does have an influence, it is quite
clear that the prim, fixed posture enjoined upon the girl
has a tendency to produce deformity, by adding to one of
the causes from which it proceeds, viz., the weakness of the
muscles. A fixed uniform posture wearies the muscles, but
variations of posture relieve them, and so prevent an exhaustion of their power.
The muscles of the back in the female are weakened, in
common with the other muscles, not only by a want of stirring out-door exercise, but also by a special cause of weakness in their case. The tight dress of the girl prevents
these muscles from having that free action which the loose
dress of the boy permits. You can see this in the difference of movement in the two cases. In the boy, the spine
is bent and twisted in all directions freely; but in the girl,
both custom and the stiff tightness of the dress require a
movement almost as if the spine were a single bone, instead
of being made up of twenty-four bones. The muscles in
her back, therefore, lose their power and fulness just as the
unused muscles of a palsied limb do.
368. Exercise should be Varied and  General.-Variety should be aimed at in the action of the
muscles. A continuous action of any set of muscles is
wearisome and painful. This is well exemplified in the
punishment once much in vogue in schools, of making the
offender hold a book out at arm's length for some time.
In the management of the muscles of the voice, the weariness caused by continued sameness of action is often experienced. The monotonous speaker or reader tires out thee
12




266           PHYSIOLOGY AND HYGIENE.
muscles much sooner than one who has great variety in his
tones.
369. Gymnastics and Calisthenics.-A  general exercise of all the muscles is essential both to symmetrical muscular development, and to the full attainment
of the invigorating effects of exercise. Gymnastics and
calisthenics are, in this respect, particularly beneficial.
These are, however, no better than any other exercises that
are so varied as to bring the muscles generally into action.
The varied exercises of walking, running, leaping, riding
on horseback, dancing, and active sports, are quite as good;
so also are the varied labors of the garden, if they be
pursued with interest and pleasure. There is no especial
benefit in the extreme variety of exercise sometimes aimed
at in gymnastics. Variety that is sufficient to bring into
general action the muscles of the body is all that is
requisite.
Gymnastics and calisthenics should always be considered
as subsidiary to the common exercises that have been mentioned, and should never be permitted to exclude them.
When they are made to do this, a temporary benefit is
reaped at the expense of a permanent injury. For after
the novelty of the round of exercises has passed away, they
are given up, and the common and now despised exercises
are not apt to be resumed. Habits of inaction, therefore,
are often confirmed, instead of being removed, by a systematic course of exercises under the high-sounding names
of gymnastics and calisthenics.
370. Effect of too severe Exercise.-But there
may be too much exercise. The toil of the laborer may be
so severe and long-continued, that the reparative process
in the intervals of rest is not competent to effect a full
repair of the muscles. A  gradual exhaustion of their
power, therefore, results. Much harm is thus often done
by severe unremitting toil.  Especially is this the case
when the excess of toil is exacted during the period of
growth.
It is necessary that exercise should be agreeable in order




HYGIENE.                    267
to produce its best effect on the system, on account of the
genial excitement which then accompanies it. For this
reason exercise should commonly not be solitary, and there
should, if possible, be some object connected with it. If
the observation of nature were made from the beginning
of education as prominent as claimed in the Preface that
it should be, there would be no lack of objects in the rambles in field and forest taken both for health and for the
pursuit of science.
3T1. Hygiene of the Senses.-Substantially what
has been said of the muscles may be said of the organs of
the senses. They require intervals of rest for thorough
repair. And they may be so overworked that complete reparation is rendered impossible, and their power be gradually
exhausted. The office of the senses is to receive impressions
from things around. Whatever gives an impression to any
organ of sense may be regarded as a stimulus to it. If
the stimulus be too great or too long continued, injury is
done. This is very obvious in regard to the eyes. They
are often injured by too much light. A word of caution
is needed in regard to the production of near-sightedness.
This is often caused in students and others by holding objects too near the eyes.
372. Necessity  of Seasons of Rest to  the
Brain. —We come now to the hygiene of the brain. This
is the great central organ or instrument of the mind, by
which it receives the impressions made upon the senses, compares and arranges the knowledge thus gathered, and originates those impressions that are made by it upon the world
around through the action of muscles. It is a very compound instrument. It needs, like the muscles, seasons of
rest for the full repair of the wear and tear occasioned in
its daily use.
It may be overworked, and then the repair will not
be complete, and gradual exhaustion of its powers will
result, occasioning disease in some form. A significant
illustration of the importance of seasons of rest for repair
in the case of the brain is furnished in the fact, that




^268         PHYSIOLOGY AND HYGIENE.
insanity is not apt to result from mental disturbance, unless
the subject of it fail to have his regular sleep. If he sleeps
well, the work of repair is so well done in the brain in its
nightly seasons of rest, that the disease, which might otherwise occur, is prevented.
With proper intervals of rest, the mind can perform a
large amount of labor without injury to the brain and
nervous system, if there be no undue excitement, and no
worrying and depressing anxiety. This is shown in the
length of life that so often accompanies the quiet but
laborious pursuits of science, while, on the other hand, the
excitement and anxiety of a life of business, especially as
it is ordinarily pursued in this country, are not favorable to
longevity.
373. Overworking the Brain.-It is especially
important that the brain, during the period of its growth,
should not be overworked. The reason is the same as
that for the caution, so universally observed, in regard to
putting too much labor upon the muscles of a young
horse. And yet there is buoyant activity in the child,
wvhich is disposed to show itself in the operations of the
brain as readily as in the action of the muscles. If this
activity be turned into proper channels, and be not too
much stimulated, no injury will be done to the delicate
textures of the brain.
Although much is said of the danger of over-stimulating
the brain of the child, the difficulty does not so much lie
here, as in the manner in which the mind is led to act.
There is commonly too much of mere drudgery, and df
storing the mind w'ith unintelligible, and therefore uninteresting matters. The mind, accordingly, is dissatisfied
and wearied. The tedium of the labor exhausts, and so
the brain is essentially impaired. When early education
shall become in all respects what it ought to be, greater
real acquisitions will be made without any injury to the
growing brain.
3'4. Influence of Quiet Cheerfulness.-It is
well known that undue mental excitement and the depres



HYGIENE.                   269
sion of anxiety are together apt to produce insanity.
Though they generally stop short of this result, they
always injure the health aud shorten life. A firm and
cheerful mind is favorable to longevity, but the anxious
and fretting are seldom, if ever, long-lived.
375. The Passions.-As the passions must have
much influence upon the action of the mind, and therefore
upon the state of the brain and nervous system, the proper
regulation of them is essential to health and longevity.
Much of the positive disease of the brain, and of the general nervous derangement so common among the educated
and refined, comes from the bad management of the passions.
376. Alcoholic Stimulants. -There are certain
articles in common use in the community, which produce
so deleterious an influence upon the system, that they demand a more extended notice than can be given them in
this chapter. Reference is made to alcohol and tobacco.
They act chiefly upon the brain and nervous system,
the former as a stimulant, and the latter as a sedative.
The use of opium is so limited compared with these,
that it will not be dwelt upon, especially as it is never defended.
No fact is more thoroughly demonstrated than that the
system has no need of alcoholic stimulants while in a state
of health. So far then as we look at mere necessity, these
articles are to be considered simply as medicines, required
only in diseased conditions. But it is said by some that
they can be used in small quantities without injury to
health. This cannot be claimed with any shadow of reason,
except with relation to very small quantities.
Entire abstinence is at least safe, and there are so many
other things supplied by a bounteous Providence to gratify
the taste and the appetite, that we can easily forego the
use of alcoholic stimulants; and we ought to be willing to
do so, if the good of others require it. The common use
of these articles as beverages is one of the most prolific of
the sources of disease; and it is a significant fact, that the




270           PHYSIOLOGY AND HYGIENE.
very moderate use, claimed by some to be innocuous, has a
strong tendency to pass into a larger use, even so large
that its deleterious influence upon health is palpable.
37". Tobacco an Active Poison. —The evidence is
quite as clear in relation to the injurious effects of tobacco.
This has sometimes been erroneously termed a stimulant.
The error arises from the well-known discomfort of the
habitual user of it when he is deprived of the use of this
drug. This discomfort has a depressing influence, and
when his system is brought again under the influence of
tobacco the depression is removed, not by any direct stimulating effect, but by the relief given to the uncomfortable
sensations.
Tobacco is really one of the purest sedatives we have. It
depresses vital action. It acts chiefly upon the nervous
system, and therefore has a strong tendency to produce
nervous diseases. While it is injurious to all, it is especially
so to those who have a low vital action, and are disposed to
nervous complaints.
Tobacco is so active a poison that extreme caution is required whenever it is administered, as it sometimes is, as a
medicine. The effects of even a small amount of it upon
one that is unaccustomed to its use are of the most decisive character. And that must be an exceedingly artificial
condition of the system, in which, by continued use of this
drug, large amounts come to be borne with little apparent
effect.
The evidence of the deleterious influence of tobacco
upon the system is as unequivocal as that in regard to the
influence of opium, and wonderfully strong is that slavery
to appetite that makes one persist in the use of this drug
in spite of such evidence.
378. Coffee and Tea. —Coffee and tea are often included in the same category with alcohol and tobacco.
Granting all that is claimed in regard to the injurious
effects of these articles, it is preposterous to class them
with such poisons. The evidence in regard to them is conflicting, and all that is settled as yet is, that in some persons




HYGIENE.                   271
they exert a bad influence upon the nervous system.
If this should be found to be true of a very large proportion of all who use them, the evidence would be conclusive against the propriety of their use as common
beverages. But as yet this has by no means been proved to
be true.
379. Poisonous Emanations.-There are certain
poisonous emanations, to which the human system is often
subjected, that are largely destructive of health and life.
They arise from decomposing filth of various kinds. Besides predisposing the system to the action of contagious
and epidemic causes of disease, they also of themselves
create disease. It is these emanations that render the close
air of a crowded city, especially in its narrow lanes, so
impure and fairly poisonous. And this impurity of the air
is one of the chief causes of the difference in disease and
mortality between the city and the country. The difference is greater than is generally supposed.
It has been found by statistics in England, that there are
24 per cent. more deaths from consumption, and 55 per
cent. more deaths from typhus, in cities than in the rural
districts, and the mortality from the diseases of childhood
is twice as great in the city as in the country. In what
way these emanations act we know not. But, although
much is to be attributed to a mere want of ventilation,
that is, to a lack of oxygen, there is no question that these
emanations often act as positive poisons to the system.
380. General I ieu of the Causes of Disease.
-In developing the principles of hygiene, we have noticed
many of the prominent causes of ill health and disease.
They are chiefly these: 1. A disregard in various ways of
the rules relating to the digestive process. 2. Compression
of the chest, especially during the period of growth. 3.
Deficiency in the supply of pure air to the lungs. 4. Failure to guard properly against the influence of cold and heat,
chiefly the former. 5. A lack of active exercise in the
open air. 6. Overworking the muscles. 7. Errors in the
management of the moral and intellectual powers. 8. The




272           PHYSIOLOGY AND HYGIENE.
influence of such articles as alcohol and tobacco. 9. Emanations from decomposing filth.
It is well thus to look at these causes grouped together,
endeavoring to give to each its due prominence. For various and exclusive views are often taken on this subject.
Quite commonly some of these causes are kept entirely out
of view, while others are strongly pressed upon our attention. Disease is generally a very compoound result, produced
by a concurrence of several of these causes, and sometimes
even of all of them.
These causes of disease, it will be observed, are more or
less under our control. Some of them are entirely so. A
knowledge of their operation, and an earnest endeavor to
remove them, would, therefore, vastly diminish the amount
of ill health and disease.
381. 0oOau  Control over the Cautses of Diseaese.
-It is true that there are some other causes of disease, of
which we know but little, and over which we have little or
no control. Such are the causes of various contagious and
epidemic diseases. But these really produce a much less
amount of disease than the causes which have been mentioned. Their action is occasional, and confined to localities;
not continual, and in all places. And besides, they may to
a great extent be shorn of their power, by guarding against
those causes of disease which are more or less under our
control. It is those who neglect to do this that commonly
become most readily the victims of contagions and epidemics.
382. Preventive   and  Curative  lieasures.There is much interest in the community in regard to the
cure of disease, but there is a blind indifference to its prevention. And yet vastly more can be done in the diminution
of disease by preventive than by curative measures. The
ravages of consumption, for example, can undoubtedly be
greatly lessened by preventing the operation of its principal
causes; and yet what is said about these causes is little
heeded, and the public attention is engrossed with the delusions of consumption-curers.




HYGIENE.                    273
It is emphatically true of this malady, that multitudes
more can be saved by preventive measures than by curative
ones. Against no disease call hygiene achieve greater victories.  The neglect to use preventive measures against
this and other diseases arises chiefly from the ignorance
of the principles on which these measures are based. The
prevalent indifference, therefore, to this subject can never
be fully removed, till the general introduction of Physiology
as a study into our schools shall make these principles
familiar to the mass of the community.




PART SECOND.
CHAPTER XVII.
CONNECTION OF THE MIND AND THE BODY,
THE Nervous System is to the mind the grand means of
communication with the world of material and immaterial
things around it.
This communication is maintained through organs subordinate to the nervous system. And you have seen that
through the senses all knowledge of external things is communicated to the mind, where it is used as the material of
thought and feeling; while, on the other hand, through
the muscles the mind produces all its impressions upon
external things.
Let us now look more thoroughly into the connection
which the nervous system establishes between the mind and
the body, and observe some of the higher and more intricate
phenomena which result from it.
383. The Brain the Organ of the JMlind.-The
brain is the organ of the mind. In this life there can be no
mental manifestations except through the agency of this
organ. The mind and the brain always act together as one
thing. This is manifest in regard to motion and sensation.
It is equally true of thought. The mind can think and
excite motion in the muscles only through the brain. The
proofs of this are various and abundant.
If a man by a blow upon his head have a portion of the
skull driven in upon the brain, so as to press upon it considerably, all sensation and power of motion are suspended.




CONNECTION OF THE MIND AND THE BODY.   275
His mental connection with the world around him is completely cut off. And furthermore, all mental action is arrested. The mind, thus shut in from the world around by
the suspension of sensation, does not go on to act independently of the compressed brain.
It may be remarked, that this degree of the suspension of
the mental functions depends upon the degree of effect produced upon the brain. If, for example, in the case of injury,
the pressure of the bone driven in upon the brain be not
very great, the suspension will be partial; but if the pressure
be considerable the suspension will be complete.
384. linsanity a Disease of the Organization.
-Insanity is always the result of disease in the organization.
This is so even when it is produced by moral causes acting
directly upon the mind. The insanity in such a case is an
indirect effect-the organization affected by the mind is
thrown into a diseased state and reacts upon the mind, influencing its manifestations.
If the mind thus acted upon were a spirit, separated
from the body, the result would be merely the feelings,
which the motives applied would naturally produce, and not
the unnatural feelings of insanity. It is not strictly proper,
then, to speak of a " mind diseased."
Let it not be understood that men tal derangement in every
case is to be attributed to disease that leaves such palpable
traces that the dissecting knife would reveal it if death were
to take place. There are diseased operations of the body
that are hidden from our view-so hidden, that they not
only leave no traces, but often develop no characteristic
bodily symptoms.
385. Situation of the Brain.-Observe for a moment the situation and the immediate connections of the
brain, the organ of the mind. It is fitly placed at the summit of the structure, inclosed by that noble dome which was
described in the Chapter on the Bones. And then observe
that, in its immediate neighborhood, are the organs of four
of the senses, sending their messages continually to the
mind. Especially notice that under the jutting arches of




276          PHYSIOLOGY AND HYGIENE.
the front of the dome are the ever-moving eyes, looking out
from their elevated place of observation; and at the sides of
the base of the dome are the halls of audience, ever open and
ready to transmit the messages that come to the soul through
the vibrations of the air. And there, too, in the very front
of this habitation of the mind is the face, indicating by the
delicate, quickly changing play of its muscles the thoughts
that are at work within. And lastly, there is the mouth,
the outlet for the voice, the chief agent of the outward manifestations of the mind.
Here then are clustered together in this small space, in
the immediate neighborhood of the mind's habitation, its
principal instruments of communication with the world
around. When we are listening to eloquence, whether it
be in the public assembly, or in the social circle, or in the
more private intercourse of friendship, and observe, as the
rich tones proceed from the mouth, the elevated and changeful expressions of the countenance, we are impressed with
the idea that, if it be the mind which constitutes the
image of God in man, the face of man thus situated in the
front of the mind's habitation is the fitting outward emblem
of that image.
386. Rapidity of Communication between
the -]ind and Body.-It is interesting to observe how
exceedingly rapid are the communications of the mind with
the different parts of the body. Notice what the process is,
or rather what the processes are, when you withdraw your
hand from any thing that hurts it, as heat for example. An
impression is produced upon the expanded nerve in the
part-this impression is sent along the nervous tubuli to the
brain-the mind there receives the impression-the mind in
return communicates an impression to the brain-this impression goes by another set of nervous tubuli to the muscles-they act, and the hand is withdrawn. If it took as
long to do all this as it has to describe it, the hand would be
very thoroughly burned before it is drawn away.
38T. Skill in the U.se of the MTuscles. —The use
which the mind makes of all the machinery of the senses




CONNECTION OF THE MIND AND THE BODY.   277
and of the organs of locomotion does not come to it at the
outset. It comes by training, and in some cases by very
long training. The child at first uses its muscles bunglingly.
It does not see or hear skillfully. It knows nothing at first
of the colors, or shapes, or distances of objects. It knows
nothing of the direction or distance of sounds. It has all
these things to learn. And for this purpose the organs of
sense and the muscles are put into exercise at once, and
the child begins its long process of learning on the day of its
birth.
Few have any conception of the amount of knowledge
which is acquired in the first of the child's life. Not only
is he born with absolutely no knowledge of the world of
things around him, but he has no skill in the use of the
instruments, the muscles and the senses, by which he is to
obtain his knowledge. These give him at first no very definite information; but by the constant exercise of them,
and by comparisons between the reports of the different
senses, he soon adds rapidly to his stock of knowledge, and
becomes skillful in the use of his means of gathering it.
388. Skill in the Use of the Senses aind the
iliscles.- Skill in the use of the muscles varies much in
different individuals. It is wonderful in the juggler, the rope
dancer, the skillful player on a musical instrument, and the
accomplished singer. You will have some conception of
what education can do for the muscles, if you contrast the
awkward balancing of the child in walking with the agile and
delicate balancings of the rope-dancer, or the aimless and
uncouth movements of the infant's hands with the rapid and
varied execution of the player on an instrument, or the monotonous and coarse sounds uttered in a child's first attempts
at singing with the varied melody of a skillful singer.
The senses are educated as well as the muscles. As you
see an infant reaching out his little'hands awkwardly
with his unskilled muscles towards an object, it is manifest
that he knows not at what distance the object is from him,
and that he does not readily adjust his eyes to its distance,
so as to see it clearly.




278          PHYSIOLOGY AND HYGIENE.
He after a while by practice acquires the power of doing
this. The same may be said of hearing. The little muscles
described to you as so nicely adjusting the eye for seeing at
different distances, and the ear for hearing various notes of
sound, require training, just as the muscles do with which
we walk or talk.
389. The Senses and  the  Muscles  I1utual
Teachers.- The senses and the muscles are mutual teachers in the education here described. Thus, in singing, the
accuracy of the sense of hearing in estimating sounds is
acquired through the action of the muscles of the voice
while the ear is listening. And on the other hand, skill in
executing sounds is acquired by these muscles under the
tuition of the ear. The dependence of the senses upon the
muscles is not absolute, however, as is that of the muscles
upon the senses.
The ear can be trained in the accurate appreciation of
sounds without any corresponding exercise of the muscles
of the voice, though the two processes are ordinarily to
a greater or less extent connected, and are corrective of
each other. But even when the ear is trained without any
aid from the muscles of the voice, the training is in some
measure a training of muscles.
For there are certain little muscles that regulate the tension of the drum of the ear, which undoubtedly go through
a process of training when we are learning to distinguish
accurately between different notes of sound. While the dependence of the senses upon the muscles is thus a partial
one, the dependence of the muscles upon the senses is, on
the other hand, complete.
Although the muscles have a sense of their own, a muscular sense, as Bell calls it, this is not adequate to be their
sole guide in action, but it serves as a mere auxiliary in this
respect. This absolute dependence of the muscles upon the
senses is very strikingly shown in the fact, that the deaf and
dumb are dumb simply because they are deaf. The voice
in them has no teacher.
390. The  Involuntary  Muscles not Edu



CONNECTION OF THE MIND AND THE BODY.   279
cated.-The education of the muscles does not extend to
those which are involuntary. Though respiration, for example, is a very complicated act of many muscles, these
muscles require no education to do their part skillfully.
We have no need to superintend them, for their constant
action is secured by an arrangement for nervous influence
which is independent of the mind.
So, while the mind sleeps, or when it is locked up in the
stupor of disease, these muscles continue to perform their
duty, as well as when we are awake. The same substantially
can be said of the muscles which perform the act of swallowing. Although this is a very compound, and, mechanically
considered, a very difficult act, it is performed as well in the
first hour of the child's life as it is at any future period.
The muscles that execute it need no training. And yet it
is only after long and diligent training that the purely voluntary muscles, as for example those of the hand, execute
movements which are no more complicated and difficult.
The reason for this difference is obvious. The movements
which are performed by the involuntary muscles, such as
breathing and swallowing, are immediately essential to the
preservation of life, and it is therefore necessary that they
should be well executed from the first. The voluntary muscles, on the other hand, instead of being devoted, like the
involuntary, to the maintenance of life, act as the instruments of the mind, and therefore the mind acquires the
power of using them skillfully only by dint of long-continued
training.
391. Association of Action in  the 2[uscles
without Mlental Action.-In the education of the
muscles, it is to be observed, that although the mind, during
the process of learning, at first takes distinct cognizance of
every movement, it after a while, as the education becomes
complete, takes little or no notice of many of the movements, except when some error occurs, or some obstacle
arises. Thus, when one is learning to sing or play a tune,
the mind, through the ear, at first takes a definite and distinct notice of every sound, and makes an appreciable exer



280          PHYSIOLOGY AND HYGIENE.
tion in every movement. But after the tune is learned, this
ceases to be the case, and the movements seem to be associated together, in some measure independently of mental
action.
So in learning to walk, the child notices each of his movements very distinctly. When, however, he has fully learned,
but little thought seems to be expended upon the motions,
except when some obstacle appears which interrupts their
regular succession. When one walks in a reverie, the mind
is most of the time wholly abstracted from the associated
movements which make up the compound act of walking.
In learning to read, the child makes a distinct mental
effort in regard to each letter, resorting to every aid which
will help to make the effort a successful one, even to
putting the finger on each letter as he looks along the line.
But as he becomes more and more skilled, the association
of action comes more and more into play.
392. Offices of the Cerebrurn  and  Cerebellum.-In the Chapter on the Nervous System, the different
offices of the different central organs of this system were
mentioned. The brain, as you have seen, is more especially
connected with the mind, and is the great instrument
through which mental manifestations are made. But it is
only a certain part of the brain, the cerebrum, a, Fig. 110,
that has this special connection with the mind. The cerebellum, b, Fig. 110, it is supposed, is especially devoted to
the motions of the body, for in different animals it is developed in proportion to the range and variety of motion.
From extended observations on this point in comparative
anatomy there seems to be good reason to conclude, that the
cerebellum is the great central apparatus for combining the
various compound motions of the body. It is uniformly
found to be larger in those animals that have great complication in their muscular movements, than in those in which
these movements are of a simple character.
Thus, in animals whose most complicated motion is walking, as the hoofed quadrupeds, the cerebellum is much smaller
than in those animals that climb and take hold of things




CONNECTION OF THE MIND AND THE BODY.   281
with their paws. In man it is much larger than in any
other animal, for he walks erect, and thus brings into action
a very large number of muscles in this delicate balancing
movement (for such it is), and then, in the individual parts
of the body, especially the hand, he executes a great range
of very complicated movements. It is more developed in
monkeys and apes than in any other of the inferior animals,
because, with their capability of extensive variety of posture,
and their power of seizing objects with their extremities,
they obviously come nearer to man than any other animal
in the varied combination of their muscular action.
The conclusions thus arrived at by comparative observations in animals have been confirmed by experiments. It
has been found by physiologists, that if the cerebellum be
removed with as little disturbance as possible to other parts,
although the sensibilities remain, and motions are performed,
the power of combining muscular actions in definite coimpound movements, such as flying, walking, &c., is lost.
In relation to the cerebrum, we find that the amount of
intelligence depends on the amount of its gray portion, the
-vesicular substance. In man, therefore, this part of the
cerebrum is very much greater than it is in any other animal.
It is the difference in the amount of the gray substance
which constitutes the grand distinction between the brain
of man and that of any of the higher orders of animals, for
in all other respects his brain seems to differ little from
theirs.
In looking at representations of the brain, as in Fig. 112,
it would seem at first view that the gray substance, the
working part of the cerebrum, is much less in amount than
the white portion, which serves only for transmission. But
this is not so. The eye is deceived, because the white substance is all together in one central mass, while the gray
substance is spread out in an external layer. This is very
plainly illustrated by Fig. 158. Here the area, a, contained
in the inner circle, strikes the eye as being larger than the
area, b, included between the two circles, and yet these areas
are precisely equal.




282           PHYSIOLOGY A"D IHYGIE1E.
Observe for a moment, in this connection, the concurrent
evidence by which we determine what the function of the
gray substance of the brain is. It comes from two sources.
The first is that which is furnished to us by the structure of
the cerebrum. As heretofore stated,'the gray portion is
made up of cells, while the white portion is composed of
tubuli. These tubuli are such as we find in the nerves, and
FIG. 1,58.
in fact are continuous with them. We very properly infer,
therefore, that as the nerves serve only for transmission, the
white part of the brain does the same. It has, therefore,
nothing to do with the thinking, and yet we know from
other facts that this is done in some part of the cerebrum.
So we necessarily infer that it must be done in the gray
substance. And here, to confirm the truth of this inference,
comes in one other source of evidence, viz., the comparison
between different animals in regard to the correspondence
between the amount of the gray substance and the amount
of intelligence.
393. Facial Anrgle.-The size of the anterior portion
of the brain, above referred to, may be estimated by the




CONNECTION OF THE MIND AND THE BODY.   283
measurement of the facial angle. This angle is formed by
drawing two lines as represented in Figures 159 and 160.
The line, a, b, is drawn from the most prominent part of the
forehead to the front of the upper jaw. The line, c, d, is
FIG. 159.               FIG. 160.
C                d    c                    Jd
lb                    b
intended to represent the line of the base of the brain, and
runs from the orifice of the ear along on the floor of the
cavity of the nose. It is manifest that the less prominent is
the forehead, that is, the less brain there is in the front part
of the head, the more acute will the angle be that is formed
by these lines. In Fig. 160, which represents the skull of a
negro, this angle is more acute than in the skull of the
European, Fig. 159. In animals this facial angle is much
more acute than in man. In the monkey tribe it varies
from 65~ to 30~, while in man its average is about 75~. The
ancient Greeks, wishing to give the aspect of great intellectual superiority to their statues of deities and heroes, made
it in them as high as 90~.
It is proper to remark here, that while it is clear that, as
a general rule, the amount of intelligence is to some extent
proportioned to the amount of the cerebrum, both in man
and in animals, the rule is not an invariable one. Size is
far from being the only measure of power in this case.
What differences there may be in intimate structure, to compare with the mental differences, we know not. Even where
the rule stated above holds good, the difference in mere bulk
is far from being proportionate to the mental difference.
The mind of a Newton or a Shakspeare is gigantic compared
with any common mind, but the brain in such cases is not
very much larger than ordinary brains.




284           PHYSIOLOGY AND HYGIENE.
394. Iliental Difference between Man and
other Animals.-In relation to the evidence drawn from
a comparison between different animals in regard to the
functions of the nervous system, there is one significant fact
which must not pass unnoticed. Though, as we rise in the
scale of animal life in our observations, we find every new
addition of functions coupled with some new additions of
structure until we come to the higher animals, we do not
find this to be so when we pass from them to man.
The brain, it is true, is larger in man than it is in them,
and has much more of the gray substance; but there are no
essential differences of structure in his brain, to correspond
with the added mental qualities which so decidedly distinguish him from the brutes. These qualities constitute something more than a difference of degree. It is a difference of
kind. And, therefore, it is a great and a significant fact, that
there is no corresponding difference of kind in the organization of the brain.
The distinction between man and other animals is a definite one. It is as definite as it would be if it were based
upon difference of organization. The barrier is fixed; and
not a step over it has any animal advanced, with all the
training which may have been expended upon him. No
animal, however intimate his intercourse with man, has ever
acquired man's habit of abstract reasoning, or manifested
any real knowledge of the difference between right and
wrong. Prof. Guyot does not speak too strongly when he
says, "I will even go farther than is ordinarily done, and I
will say, that there is an impassable chasm between the
mineral and the plant, between the plant and the animal;
an impassable chasm between the mere animal and man."
395. Sources of Evidence in regard to the
NVature of the Connection between Mind and
Body.-The nature of the connection of the mind and the
body is a great mystery. Still, there are many things which
we can know in relation to it. The sources of our knowledge on this subject are three, viz., the investigations of
Physiology, the testimony of Consciousness, and that of




CONNECTION OF THE MIND AND THE BODY.   285
Revelation. Each of these kinds of evidence throws light
upon the others. If, therefore, we use all of them, giving to
each its due limits and force, we shall come to some certain
and valuable conclusions. But if we take any one of them
alone, we shall be liable to be led into gross error.
In the investigation of this subject, there is in some physiologists a disposition to rely upon physiology alone, to the
exclusion of the other sources of evidence. In doing this
they are driven to this alternative: either they must be
content with a very limited knowledge of the subject, or they
must rely upon mere presumptive evidence for many of their
conclusions. And commonly the latter is the course which
they pursue. They are not content with the very limited
conclusions to which they are shut up by the absolute proof
furnished by physiology.
They boldly reason, therefore, upon what they deem to be
probable. And they are invariably led into error.
396. Endowments of Mlatter.-In order to get
definite ideas of the manner in which the erroneous conclusions are arrived at, let us view matter in its various states
and connections. Unorganized dead matter, in some important respects, is entirely different from living organized
matter. The distinction is a definite one. It is easily recognized, and none but dreamers in science have failed to see it.
Living matter is endowed with certain properties that
dead matter has not. They are termed vital properties.
They control to a certain extent the mechanical and chemical
properties which both forms of matter have in common.
Some suppose that what we call life is a single principle;
but others suppose the endowment to be compound, made
up of different principles or properties. But this question
we need not discuss. All that concerns the view here presented is the mere fact of the endowment.
Let us go a step farther. Some living beings have more
endowments than others. All have those of organic life in
common. But there is an animal life also, which by means
of the nervous system is superadded to the organic. And,
as we trace the animal kingdom from the lowest animal up




286           PHYSIOLOGY AND HYGIENE.
to man, we find the endowments connected with this system
multiplied as we advance, till in him they are more complicated and extensive than in any other animal.
This is especially true of intellectual endowments, those
which are merely instinctive being more developed in many,
perhaps we may say most, of the inferior animals. And in
man we find special mental endowments, of which other
animals present not the faintest trace.
391. Is Intelligence One of them?-Now the
question arises, whether intelligence is like life, a mere endowment of matter, or whether it is in some measure independent of it. In other words, whether it is a principle or
set of principles with which matter is endowed, or an immaterial something which acts through matter as its instrument. How much does bare physiology teach us on this
qunestion? It has often been claimed that it can teach us
much, and the most bold conclusions have sometimes been
ventured from this quarter. But mere speculation has in
all such cases been deemed to be proof. Physiology does
show us, as before stated, that the spiritual is in this world
always connected with the material, and that mind never
acts independently of the matter with which it is connected
in the brain. But it gives us no light upon the nature of
this connection. It is well for us to know how deficient are
its teachings on this point.
For all tlhat it can teach us, we know not but that the
mind may be a mere result of action in matter. It neither
tells us that it is so, or that it is not. It leaves us entirely
in the dark on this point. Indeed so far as it affords presumptive evidence, it appears to teach, that mental phenomena are results of matter, acting in consequence of certain endowments or tendencies imparted to it, just as secretion is in living substances, or chemical action in those
which are not living.
Accordingly those who have relied upon physiology alone
on this subject, have adopted various forms of materialism.
Some have supposed that thought is a mere product of
matter, and that the brain secretes it as the liver secretes




CONNECTION OF THE MIND AND THE BODY.   282 
bile. Others have taught that the mind is "a bundle of
instincts," each residing in some particular part of the brain
as its organ. This has been the doctrine of snome prominent
phrenologists.
Let us look at living matter in another point of view, and
see to what physiology alone, if at all venturesome in drawing conclusions, will lead us. Let us look at the origin and
growth of the thinking animal. Take, for example, an animal the formation of which we traced in the Chapter on
Cell-Life. The beginning of the bird as it forms in the egg
is a simple cell filled with a fluid. This produces other
cells, and soon the organs and the limbs of the animal are
formed. At length the animal bursts the shell, and comes
out not only a living and sentient being, but a thinking
being. It has a mind which feels desires and emotions, and
prompts the muscles to action to effect its purposes.
Organization here precedes the development of mind so
far as we can see, and therefore it would seem that mind is
a result of organization. Especially does this appear to be
so, when we find that the amount of mind in different animals is proportioned to the amount of a certain part of the
organization, the brain. All this is as true of man as it is
of other animals. And besides, we see in man that as the
organization becomes perfected, the intelligence is proportionably increased.
In infancy, when the organization of the brain is imperfect, the intelligence is small in amount, and grows with the
growth, and strengthens with the strength of the brain.
And as the mind thus grows with the body, it appears to
perish with the dissolution of the organization, and in the
case of the inferior animals undoubtedly does so.
But the evidence from physiology does not all tend to
materialism. There is some negative evidence which has a
different bearing, in the fact that, while man differs in his
spiritual nature so widely and so specifically from the inferior animals, his brain exhibits no corresponding specific
difference in structure, but only a difference in amount.
The difference in degrees of intelligence in the animals




288          PHYSIOLOGY AND HYGIENE.
below man is marked by a corresponding difference in the
amounts of the gray substance.
And if it were true that man, as some think, differed from
them only in having a higher degree of intelligence, we
should expect to find in him a mere increase of this substance. But as his mind differs from theirs not merely in
degree, but in kind also, we should have reason to expect,
if mind were wholly dependent on organization, that the
anatomist would find not only an increase in the quantity
of the gray substance, but also a difference in its structure.
398. Pthysiologist needs other Evidence.-It
is quite clear then, that the physiologist cannot well avoid
materialism, if, in examining the connection between the
mind and the body, he rejects all evidence beside that which
physiology furnishes. He can be saved from this result only
by being content with the narrow limits to which he is
shut up, if he confine himself to absolute proof. As we
have already seen, the positive knowledge that physiology
gives us on this subject is exceedingly narrow. We soon
come to the line that divides the known and the supposed.
And if we attempt to go beyond that, our conclusions as
to what is probable will quite certainly lead us to the result
pointed out.
The need, therefore, of the evidence drawn from the other
sources mentioned is most palpable. The physiologist must
confess himself to be under the necessity of going out of his
~physiology, in order to learn all that can be learned upon
this subject. At the best, there is much mystery in relation
to it which we cannot penetrate, with all the light that we
can bring to bear upon it. And the mystery is deep indeed,
when we call to our aid only the dim light of physiology.
It needs some other light to deliver us from the confusion
of ideas, into which we are introduced by the analogy existing between the phenomena of life and instinct and intelligence, in relation to their connection with the organization
of matter. Let us look then at the evidence which comes
from the other two sources, viz., our consciousness, and revelation.




CONNECTION OF THE MIND AND THE BODY.   289
399. Consco'ausness. — Every individual is conscious that, as he feels and thinks and acts, he, that is, his
mind or spirit, acts upon the structure of his body, and is
acted upon by it. It is not a consciousness that he, as a
material body, does all this. He feels that it is a power
within that does it, and he instinctively separates in his
ideas the power from  the different parts of the body, and
from the body as a whole. He is conscious, too, of a responsibility in relation to the thoughts and acts of the spirit
within. He has a knowledge of right and wrong, and has
self-reproach on doing wrong, and self-approbation on doing
right.
It is this consciousness of a self-acting immaterial spirit in
this material body, that constitutes the basis of all character,
and of all the moral relations of man to his fellow-man,
and to his Maker. Everybody acts upon the testimony of
this consciousness as being valid and -certain testimony.
And, however the physiologist may reason about matter
and mind, as if the latter were a mere product or endowment of the former, yet as a man, as a member of society,
as a subject of government and law, he cannot avoid acting
upon the ground that mind in a certain sense controls
matter, and is responsible for its acts independently of the
matter with which it is connected.
400.  Evidence front Consciousness  Confi-rmned by Revelation,.-Now the evidence which this
consciousness affords us should suffice to keep us from the
materialism into which physiology taken alone would be
apt to lead us. It shows us that, although the mind is developed with the material organization, and can act only
with it, it is not its mere product, nor one of its endowments. It shows us, on the other hand, that it is in some
measure independent of matter, and that its dependence
upon it is only a dependence of connection, matter being
the instrument of mind, through which it acts on external
things, and is acted upon by them. The evidence from this
source is of a positive character.
We are driven by it to the alternative of believing that
13




290           PHYSIOLOGY AND HYGIENE.
the mind is an immaterial, self-acting agent, in some measure independent of matter, or of harboring the impious and
monstrous belief that the Creator has implanted in the
bosom of man a lie, and that he is living a horrible farce,
acting in view of moral relations and responsibilities that
have no existence.
This positive testimony of our consciousness is confirmed
by the testimony of revelation. This is not done by any
formal array of proof. The existence of the spiritual part
of man as a self-acting responsible agent is assumed as a
fact that needs no proof. All the statements, and teachings,
and appeals of the Bible recognize it as a fact known to the
consciousness of every man. The Bible, therefore, may be
considered as simply affirming that the testimony of our
consciousness on this point is valid testimony.
But the Bible goes farther than this. It gives us one
great fact of which neither physiology nor our consciousness
could assure us, namely, the mind's immortality. Our consciousness could, it is true, give us presumptive evidence to
show that the soul with its high powers and aspirations is
to live after the death of the body. But it could furnish us
no absolute proof of the fact. And its presumptive evidence would be effectually rebutted by the presumptive
evidence from physiology, which, as you have seen, points
in another direction.
We are so familiar with the mind's immortality as a.
known fact, and we so uniformly think of it in connection
with the death of the body, that we are not aware how absolutely dependent we are upon revelation for all that we
know in relation to it. If there were no revelation, and
death were to us an unknown event, and we were now for
the first time called upon to witness the death of a friend,
how little should we know, and how confused would be our
thoughts in relation to the great mystery before us! "What
is it?" we should ask. "Is it sleep?  No. We neversaw
any one sleep thus. What is it? Who can tell us?" And
we should wonderingly watch to see some signs of awakening, not giving up all hope till decay begins its ravages on




CONNECTION OF THE MIND AND THE BODY.  291
the loved form before us. Then, as we should from the dictate of nature, consign to the earth the friend who was so
recently among us a breathing, moving, speaking man, now
a mere mass of decaying matter, we should feel that we bury
there not the body only, but all that belonged to that body
during life-the whole man.
Thought and feeling, as well as life and motion, would
appear to us, untaught of God, to be extinguished in the
grave. Even if some one should utter all tremblingly the
hope that there might be a subtle, spiritual part of our
friend that would some time, in some form, return again to
our society, that hope would at once be crushed by the reflection that whatever it was in our friend that thought and
felt, it came into existence with the body, was infantile when
the body was, grew with the growth of the body, and
strengthened with its strength, and therefore now, so far as
we can see, has perished with it. Nature utters no voice
to tell us otherwise. She emits no light to illuminate the
grave. Darkness and silence rest there, till the light of revelation shines upon it, and God proclaims man's immortality.
Your attention has been called to the three sources of
evidence in regard to the connection of the mind and the
body, and the character of the evidence furnished by each
has been indicated. It has been shown particularly that if
the attention be confined to that which is furnished by
physiology, the mind is apt to be led into materialism. But
the attention should not thus be confined. All the three
kinds of evidence should be employed and should be brought
to bear upon each other.
If this be done, the discrepancies in the evidence from
physiology are cleared up by the evidence afforded by consciousness and revelation, and we see the true value and
bearing of the fact, that the specific mental difference between
man and animals is not attended with a corresponding
structural difference. Though this fact operates merely as
conflicting evidence, when taken simply in connection with
the rest of the facts developed by physiology; when we
come, on the other hand, to take the whole range of evidence




292           PHYSIOLOGY AND HYGIENE.
from the three sources spoken of, it is exceedingly satisfactory as concurring with the testimony of consciousness and
revelation.
At the same time, those physiological phenomena, which
taken by themselves seem to show so strongly that the mind
is wholly dependent upon organization, are so interpreted
by the evidence from the other sources, that the dependence
is seen to be for the most part a dependence of connection
only, the brain being the instrument of the mind.
The evidence from consciousness and revelation is of the
most positive character, and can not be set aside by evidence
from any other source. Other evidence may serve to interpret it, but can not nullify it. The attempt is sometimes
made to set it aside by urging the presumptive evidence of
physiology, as if it were absolute proof. But most physiologists engage in no such futile and unchristian efforts, but
give due weight to the testimony of consciousness and revelation in all their investigations of the mysterious connection
of the mind and the body.
The influence of Carpenter, an English physiologist,
whose works are more extensively used by students than
those of any other physiologist, is especially to be commended
in this respect.  And although  skepticism  occasionally
utters its plausible falsities, deceiving the superficial and the
speculative, we have no fears from present indications that
the votaries of physiological science will, as a body, be arrayed in opposition to Christianity.
CHAPTER XVIII.
DIFFERENCES BETWEEN MAN AND THE INFERIOR
ANIMALS.
THE differences between man and the inferior animals have
been alluded to in different parts of this book, and especially




MAN AND THE INFERIOR ANIMALS.              293
in the preceding chapter. But it has been done only incidentally, and the subject demands at our hands a more
thorough and systematic investigation.
401. Views of Lord l3ionboddo.-Lord Monboddo
maintained that man is only an improvement on the monkey,
occurring as a result from the general tendency to advancement claimed to exist in nature. He seemed to think that
man bore a relation to the monkey somewhat like that which
the frog bears to the tadpole, and that as the tadpole becomes
the frog, so the race of man was produced by a change, at
some remote period of the creation, of the monkey into the
man.
This ridiculous notion of the erudite but fanciful Scotch
philosopher is really but another phase of the more recent
theory of gradation, or development, as it is sometimes
called, which in different forms is now advocated by so many
European philosophers. And, although few, comparatively,
adopt this theory definitely and fully, there is quite a disposition among many to obliterate the distinctions by which
the Creator has in so marked a manner separated man from
the inferior animals. It is well, therefore, that we should
have a clear idea of these distinctions.
It is often very loosely said that while man is governed
by reason, instinct rules in the animal.* If it be meant by
this that, as a general rule, reason predominates in man,
while instinct does so in animals, the statement is a correct
one. But if it be meant that animals are wholly governed
by instinct, and that man is distinguished from them as a
reasoning animal, it is not correct. For some animals do
reason, that is, if making inferences be considered as reasoning.
* Some explanation may be well here in relation to the different uses
made of the word animal in different connections. Here it is used in
contradistinction to man. So it is used in the expression, man and
animals. But as man is in certain senses an animal, whenever we wish
to recognize this fact we speak of other animals as the inferior animals.
And thus, in regard to animals, we speak of their higher and lower
orders, the higher of course being those that approximate nearest to
man.




294            HYSIOLOGY AND HYGIENE.
In tracing out the difference between man and animals no
attempt will be made to show what the nature of instinct is.
This is a great mystery, and all attempts to solve it have
utterly failed.  Let us examine some of the differences
between instinct and reason. In doing this it is not always
easy to say just where the one begins and the other ends, so
intimately are their phenomena often mingled together.
The actions of instinct are more unaccountable than
those of reason. In the operations of reason we see something of the processes by which results are reached. For
example, as a man travels over an unexplored country, we
can understand by what means he obtains a knowledge of
the country, in order to guide him on his journey. The
processes of his reasoning in regard to this we can comprehend.
But when an insect travels with unerring certainty to its
place of destination without any guide-marks that we can
see, or when a swarm of bees or a flock of birds wing their
flight to distant places, or when bees construct their honeycomb with the exactness of mathematics in obedience to the
best principles for such a structure, we can not understand
the processes which lead to the result. It seems to be produced by an impulse from a cause extraneous to the animal, guiding it as if it were a mere machine. The little intelligence of the animal seems to have only an incidental connection with this impulse. It, therefore, merely controls
somewhat the circumstances under which the instinct acts.
402. Instinct Governed by Invariable Rules.
-So little has the intelligence to do with the instinct, and
so nearly mechanical therefore are the actions of the latter,
that they are governed by an invariable rule. It is nearly
as invariable as are the movements of a machine. For this
reason there are no improvements or alterations in the acts
of instinct.
The bird and the bee, for instance, have no change of
fashion in their architecture from age to age. The honey that
fed John the Baptist, or that which was found by Samson
in the carcass of the lion, was deposited in the same hexag



MAN AND THE INFERIOR ANIMALS.           295
onal cells which are constructed by the bees of the present
day.
403. Contrivances in  the Nests of Birds.Each bird builds its nest precisely in the same way that
its ancestral birds have ever done. Most birds' nests are
constructed after the same general pattern. But sometimes
we observe striking peculiarities to subserve some special
purpose.
Fig. 161 represents the nest of the Baya, a little bird of
Hindoostan. It is in the shape of a bottle, and is made of
FIG. 161.
NEST OF THE BAYA.
long grass. It is suspended from a slender branch of a
tree, so that monkeys, serpents, &c., cannot reach it. The
entrance to the nest is made on the under side, so that these
animals cannot enter, while the bird itself can readily fly in.
It is divided into apartments, in one of which the female
sits upon the eggs, while in the other the male bird "solaces
his companion with his song whilst she is occupied in maternal cares." In Fig. 162 is seen the nest of another little
eastern bird, which with filaments of cotton taken from the
cotton plant, sews leaves together with its beak and feet, so
as to conceal the inclosed nest from its enemies.
404. Contrivances in  the  Honey-comnb. —




296            PHYSIOLOGY AND HYGIENE.
While there is no change in the acts of instinct they are
marked by perfection. There is nothing in which this perfection of instinct is better shown than in
FIG. 162.     the construction of the honeycomb. The
cells are made hexagonal, because in this
way all the space is occupied-there is
no waste of room. If the cells were
made circular, there would not only be a
waste of room, but a large quantity of'   material would be needed to fill up the
spaces between the cells. The difference
\   can be seen in the two Figures 163 and
164. Each comb, it is to be observed
farther, has two sets of cells, the ends of
one set being arranged against the ends
of the other in a peculiar manner. These
ends are not flat, but each one has three
plane surfaces, forming with each other
a particular angle soon to be noticed,
and uniting together at the center in a
point. In the arrangement of these cells,
NEST        therefore, a cell of one set does not lie
of the Tailor Bird.   end to end with a cell of another set.
Its three surfaces form a part of the bottom or end of three cells of the other set. This is made
FIG. 163.               FIG. 164.
clear by Fig. 165, in which a cell of one set is represented as it abuts against a cell of the other set by one of




MAN AND THE INFERIOR ANIMALS.            29s"
its surfaces, its other two surfaces forming a third part of
the ends of two other cells.
Now it has been found that the         FIG. 165.
angle formed at the edge of these
surfaces between the two sets of cells
is such as to secure the greatest
strength with the least amount of
material.  It was at one  time
thought that this was proved to be not exactly true. The
variation from the correct angle, made out by the calculations of the mathematicians, was indeed a slight one, but
still it was variation enough to show, if the calculations were
correct, that the workings of instinct were not perfect in
this case. But the investigations of Lord Brougham have
satisfactorily shown that the mathematicians were wrong in
their calculations, and that the bees are right.
405. Wonderful Operations of Instinct in
Cojtmmtunities amon g Animnals.-The perfection
of the operations of instinct is shown in the most wonderful manner in the regulation of communities of animals.
Here we see cooperation to produce results effected through
an irrational, and therefore in some measure a blind instinct.
This social instinct is most extensively exemplified among
the insect tribes, as for instance the bee and the wasp. The
structures resulting from the cooperation of multitudes
of little laborers guided by this instinct, are very interesting. Take but a single familiar example, the construction
of the nests of wasps. These insects make their building
material from the fibres of old wood. These they convert
by mastication into a pulp, which made into a thin layer,
becomes firm like paper. It is indeed a process very much
like the common process of paper-making invented by man,
and the first rude inventor may have got his idea from the
insect. With this substance the wasps build several ranges
of cells, which are hexagonal, like the cells in the comb of
the bee. These ranges of cells are placed parallel to each
other, at regular distances, with little supporting columns
between them, as seen in Fig. 166.




298           PHYSIOLOGY AND HYGIENE.
The number and variety of instincts of the ordinary hive
bees are very wonderful, but it would occupy too much
space to describe them.
FIG. 166.
NEST OF WASPS.
406. Exemplvified in the Beaver Commnunity.-The wonderful cooperation of animals in obedience
to social instinct, in the building of habitations and other
structures, is seen in several of the mammalia. But it is
most wonderful in the beaver, the following description of
whose habits in this respect is taken from Carpenter:
" During the summer it lives solitarily in burrows, which it
excavates for itself on the borders of lakes and streams; but
as the cold season approaches it quits its retreat and unites
itself with its fellows, to construct, in common with them,




MAN AND THE INFERIOR ANIMALS.            299
a winter residence. It is only in the most solitary places
that their architectural instinct fully develops itself. Having associated in troops of from two to three hundred each,
they choose a lake or river, which is deep enough to prevent
its being frozen to the bottom; and they generally prefer
running streams, for the sake of the convenience which
these afford in the transportation of the materials of their
erection.
"In order that the water may be kept up to a uniform
height, they begin by constructing a sloping dam; which
they form of branches interlaced one with another, the
intervals between them being filled up with stones and mud,
with which materials they give a coat of rough-cast to the
exterior also. When the dam passes across a running stream,
they make it convex towards the current; by which it is
caused to possess much greater strength than if it were
straight. This dam is usually eleven or twelve feet across
at its base, and is enlarged every year; and it frequently
becomes covered with vegetation so as to form a kind of
hedge.
"When the dam is completed, the community separates
into a certain number of families; and the beavers then
employ themselves in constructing huts, or in repairing
those of a preceding year. These cabins are built on the
margin of the water; they have usually an oval form, and
an internal diameter of six or seven feet. Their walls are
constructed, like the dam, of branches of trees; and they are
covered, on two of their sides, with a coating of mud.
Each has two chambers, one above the other, separated by a
floor; the upper one serves as the habitation of the beavers,
and the lower one as the magazine for the store of bark,
which they lay up for their provision. These chambers have
no other opening than one by which they pass out into the
water.
" It has been said that the flat oval tail of the beavers serves
them as a trowel, and is used by them in laying on the mud
of which their houses are partly composed; but it does not
appear that they use any other implements than their incisor




300           PHYSIOLOGY AND HYGIENTE.
teeth and fore-feet. With their strong incisors they cut
down the branches and even the trunks of trees which may
be suitable; and by the aid of their mouths and fore-feet,
they drag these from one place to another.
" When they establish themselves on the bank of a running
stream, they cut down trees above the point where they intend to construct their dwellings, set them afloat, and, profiting by the current, direct them to the required spot. It is
also with their feet that they dig up the earth they require
for mortar, from the banks or from the bottom of the water.
These operations are executed with extraordinary rapidity,
although they are carried on only during the night.  When
the neighborhood of man prevents the beavers from multiplying to the degree necessary to form  such associations,
and from possessing the tranquillity which they require for
the construction of the works just described, they no longer
build huts, but live in excavations in the banks of the
water."
40T. Blindness of Instinct Exemnplified.Instinct moves straight on to its result, and it does so
blindly. It exercises no intelligence in regard to the purpose for which the result is intended, or the circumstances
which tend to defeat this purpose. It evidently in some
cases never knows any thing of the purpose aimed at by its
acts, as, for example, when an animal makes provisions for
a progeny which it is never to see.
" It is scarcely possible," says Carpenter, " to point to any
actions better fitted to give an idea of the nature of instinct,
than those which are performed by various insects when
they deposit their eggs. These animals will never behold
their progeny; and can not acquire any notion from experience, therefore, of that which their eggs will produce;
nevertheless they have the remarkable habit of placing, in
the neighborhood of each of these bodies, a supply of aliment
fitted for the nourishment of the larva that is to proceed
from it; and this they do, even when they are themselves
living on food of an entirely different nature, such as would
not be adapted for the larva,




MAN AND THE INFERIOR ANIMALS.           301
"They can not be guided in such actions by any thing like
reason; for the data on which alone they could reason correctly, are wanting to them; so that they would be led to
conclusions altogether erroneous if they were not prompted
by an unerring instinct, to adopt the means best adapted
for the attainment of the required end."
408. Results of Instinct mingled with those
of Reason.-The results of reason are often mingled with
those of instinct in such a way that it is difficult to distinguish them from each other. But instinct is of itself wholly
irrational. If it were not so, it would avoid acting whenever action would evidently be useless.  But instinct has
not the eyes of reason to see when this is the case. It leads
the animal blindly on; so that, although under all ordinary
circumstances the object is accomplished definitely and in
the best manner, yet there is no capability of making provision for extraordinary circumstances. Therefore, actions
are occasionally performed which do not at all answer the
purpose which the instinct is designed to effect.
Instinct, though perfect in its action under the uniform
circumstances under which it is destined to act, is a kind of
blunderer when irregular circumstances arise. Instinct is a
strict routinist, while reason readily accommodates itself to
endlessly varying circumstances.  In illustration of the
above characteristic of instinct, take a few examples:
The hen will sit on pieces of chalk shaped like eggs,
as readily as she will sit on the eggs themselves. The fleshfly often lays its eggs in the carrion-flower, the odor of which
is so much like that of tainted meat as to deceive the insect.
409. Blindness of instinct Illust'rated in
the Beaver.-An amusing illustration of the blind disregard of circumstances in following out the promptings of
instinct is given by a gentleman, Mr. Broderip, in an account of a beaver which he caught when very young. As
soon as it was let out of its cage, and materials were placed
in its way, it began to build after the fashion followed by
these animals when they construct their dam in a stream
of water and build their habitations in its banks.  "Even




302          PHYSIOLOGY AND HYGIENE.
when it was only half grown," says Mr. B., "it would drag
along a large sweeping-brush, or a warming-pan, grasping
the handle with its teeth, so that the load came over its
shoulder; and would endeavor to lay this with other materials, in the mode employed by the beaver when in a state
of nature. The long and large materials were taken first:
and two of the largest were generally laid crosswise, with
one of the ends of each touching the wall, and the other
ends projecting out into the room. The area formed by the
cross-brushes and the wall, he would fill up with handbrushes, rush-baskets, books, boots, sticks, cloths, dried turf,
or any thing portable.
" As the work grew high, he supported himself on his tail,
which propped him up admirably; and he would often, after
laying on one of his building materials, sit up over against
it, appearing to consider his work, or as the country people
say,'judge it.' This pause was sometimes followed by
changing the position of the material judged; and sometimes
it was left in its place. After he had piled up his materials
in one part of the room (for he generally chose the same
place), he proceeded to wall up the space between the feet
of a chest of drawers which stood at a little distance from it,
high enough on its legs to make the bottom a roof for him;
using for this purpose dried turf and sticks, which he laid
very evenly, and filling up the interstices with bits of coal,
hay, cloth, or any thing he could pick up.
" This last place he seemed to appropriate for his dwelling;
the former work seemed to be intended for a dam. When
he had walled up the space between the feet of the chest of
drawers, he proceeded to carry in sticks, cloths, hay, cotton,
&c., and to make a nest; and when he had done, he would
sit up under the drawers, and comb himself with the nails of
his hind feet." If the instinct of this animal had been at
all rational, it would not have impelled him to construct a
dam and a dwelling in a common room, where they would
be of no use to him. Reason would have dictated the building of a nest and nothing more.
410. Care for Progeny.-The care which animals




MAN AND THE INFERIOR ANIMALS.            303
exercise in relation to their progeny seems to be governed
to a great extent, perhaps wholly, by a blind instinct. All
care is given up when care is no longer needed, and with it
what appears to be affection is given up also. In animals
there is no such lasting affection of the parent for the progeny as there is in main; for in them it is merely instinetive, and not rational and moral in its character, and it,
therefore, lasts only so long as it is needed to carry out the
purposes for which this particular instinct is designed. Indeed, in some cases there can be no affection in all the care
which is instinctively exercised by the parent, for it is put
forth for progeny which the animal is destined never to see.
And in those cases among animals in which the family
state exists, it is a mere temporary affair, and as soon as the
offspring is able to take care of itself it is no more to the
parent than any other animal of the same tribe is.
411. Some Animals  have  Intelligence  as
well as linstinct.-When this intelligence is shown in
the mere power of imitation it is of a low order. The parrot that learns to imitate man in speech is not nearly so
intelligent as some animals that have no such power. Some
animals have really a reasoning intelligence-that is, they
make rational inferences. Their reasoning is sometimes,
as before remarked, so mingled with the operations of instinct, that it is difficult to distinguish them accurately.
In the case of the beaver, who labored so faithfully in
obedience to a blind instinct, there was some exercise of
reason, as, for example, when he "judged" his work. But
it is difficult to point out definitely the line between instinct
and reason in such a case. There are some animals, however, in whom the workings of a reasoning intelligence are
to be seen with perfect distinctness. But their reasoning
differs from that of man.
The inferences which the reasoning animal makes are
individual; while man goes beyond this, and makes
general inferences, and therefore discovers general truths.
Newton's dog, Diamond, saw apples fall to the ground, as
well as his master. And he was capable of making some




304           PHYSIOLOGY AND HYGIENE.
inferences in regard to them; but they were individual
inferences.
For example, if an apple-tree were shaken, and the dog
were hit by a falling apple, whenever he saw other apples
falling he would infer that he might be hit again, and
would infer also that it was best for him to get out of
harm's way. This would be the extent of his reasonings.
But his master inquired into the cause of the fall of the
apple, and by considering this and other similar phenomena,
he deduced general principles, which govern the movements
both of the atoms and the worlds of the universe.
The inferences which are formed by animals are mere
results of the association of ideas, and the process, therefore, really hardly merits the appellation of reasoning.
Thus, in the case of Newton's dog, supposed above, the
idea of the falling apples was associated in his mind with
the hurt experienced when he was hit, and prompted the
getting out of harm's way.
When such associations are extended and complicated, it
appears at first thought as if the animal acted in view of
general truths arrived at by the same process of reasoning
that man employs. But it is a mere extension of mental
associations. Thus, Newton's dog probably associated the
idea of being hit and hurt with other falling bodies beside
apples. And so, too, various circumstances might come to
be associated with the falling of bodies, and thus complicate
the mental process which occurred when he saw any object
falling near him.
412. Reasoning in  Animals mere Mental
Association.-To show somewhat the extent to which
this mental association operates in the brute mind, some
examples will be given. A wren built its nest in a slate
quarry, where it was liable to great disturbance from the
blastings. It soon, however, learned to quit its nest and fly
off to a little distance, whenever the bell rang to warn the
workmen previous to a blast. As this was noticed, the bell
was sometimes rung when there was to be no blast, for the
sake of the amusement in seeing the poor bird fly away




MAN AND THE INFERIOR ANIMALS.           305
when there was no need of alarm. At length, however, it
ceased to be deceived in this way, and when it heard the bell
ring it looked out to see if the workmen started, and if they
did, then it would leave its nest.
In this case the bird merely learned to connect in its
mental associations two circumstances with the blasting,
instead of the one from which it at first took the warning.
The operation of this mental association is shown in a little
different manner in the following case:
Some horses in a field were supplied with water in a
trough which was occasionally filled from a pump. As the
supply was not always sufficient, one of the horses, more
sagacious than the rest, whenever he, on going to drink,
found the trough empty, pumped the water into it by taking hold of the pump-handle with his teeth, and moving
his head up and down. The other horses seeing this, would,
whenever they came to the trough and found it empty, tease
the one that knew how to pump, by biting and kicking
him till he would fill the trough for them.
In this case the horse that did the pumping associated in
his mind the motion of the pump-handle, as he had seen it
done by his master, with the supply of water. And while
they associated this supply with his pumping, he knew what
their teasing him meant, because he associated it with their
motions about the trough, indicating so plainly that what
they wanted was water.
A dog belonging to a Frenchman was observed to go
every Saturday, precisely at two o'clock, from his residence
at Locoyarne to iennebon, a distance of about three-quarters of a league. It was found that he went to a butcher's,
and for the purpose of getting a feast of tripe which he
could always have at that hour on Saturday, their day of
killing. It is also related of this dog, that at family prayers
he was always very quiet, till the last paternoster was commenced, and then he would uniformly get up and take his
station near the door, in order to make his exit immediately
on its being opened.
The narrator of these facts thinks that the first fact shows




306           PHYSIOLOGY AND HYGIENE.
that the dog could measure time and count the days of the
week. But this can not be so. The dog undoubtedly associated in his mind the time at which he could get the tripe
with something that occurred on Saturday at that hour at
his master's house, just as he associated the concluding of
family prayers with something that occurred as the last
paternoster was read, perhaps with some peculiarity in the
manner of his master when he came to that part of the
service.
4-13. Relation  between  Cause and  Effect
learned from  Association.-Animals learn the relation between cause and effect by this mental association, and
act upon the experience thus gained. This is manifest in the
examples cited. And it may be observed in many acts that
we witness occasionally in the higher animals. Thus, for
example, as a horse was cropping some grass, he took hold of
some that was so stout, and yet so loosely set in the ground,
that he pulled it up by the roots, and, as the dirt which was
on it troubled him, he very deliberately knocked it across
the bar of a fence till he got all the dirt out, and then went
on to eat it.
Here was a knowledge of cause and effect which was
derived from previous experience through mental association. You see the same thing when you see a cat jump up
and open the latch of a door, or a horse unbolt the stable
door to get out to his pasture. But in all such cases the
knowledge of cause and effect differs from the same knowledge in man in one important particular. In the animal it
is always an individual knowledge, that is, a knowledge of
individual facts; while in man it is often a knowledge which
has relation to general truths or principles.
From the facts stated in the last few paragraphs, it is
clear that Carpenter is not correct in saying that "the
mind of man differs from that of the lower animals rather
as to the degree in which the reasoning faculties are developed in him, than by any thing peculiar in their kind."
While there is much in common between them  in their
modes of mental action, especially if man be compared witll




MAN AND THE INFERIOR ANIMALS.            307
other animals in the period of his infancy and childhood,
there is, as you have seen, one attribute of the human mind
which is wholly peculiar to it, and never exists in any degree
in any other animal. And this attribute, the power of abstract reasoning, or in other words, the power of deducing
general truths or laws from collections of individual facts,
constitutes the great superiority of the human mind, in distinction from the mind of the brute.
414. Language.-It is this attribute which is the
source of language in man. This can be readily seen by
observing what is the nature of language. It is a collection
of corresponding vocal and written signs of an arbitrary
character, arranged according to certain general rules or
principles. Other animals do have a kind of language of a
very limited character. It is the language of natural signs.
It is composed of cries and motions, which vary in different
tribes of animals, so that each tribe may be said to have its
own natural language. But animals never invent and agree
upon any arbitrary signs, as is done continually by mankind
in the construction and extension of language. This they
can not do, because abstract reasoning is required for such
an invention. General principles are observed in the construction and arrangement of arbitrary signs, and, as has
been shown, brutes know nothing of principles.
415. The Source of Man's Belief in a Creator.-If he had not the power of deducing general truths
from individual facts, he could neither discover the truth that
there is a first great Cause, nor appreciate or even receive it,
if it were communicated to him. Not the faintest shade of
such an idea can be communicated to any of the inferior
animals, however high their mental manifestations may be,
and simply because the structure of their mind is such that
they know nothing of general principles.
Carpenter speaks of the disposition to believe in the existence of an unseen but powerful Being, which is found to
be universal even among the most degraded races of mankind, as a natural tendency, which he seems to think is implanted in the human breast by the Creator. But it ap



308           PHYSIOLOGY AND HYGIENE.
pears clear, that it is a mere natural result of the exercise of
the power that has just been mentioned.
416. Conscience.-Man differs from other animals
also in having a conscience, or a knowledge between right
and wrong, and a sense of obligation in relation to it. This
moral sense is supposed by some to be a mere result of the
exercise of the power of abstract reasoning. But others
suppose that the sense is implanted as a distinct quality or
power, and that the office of the reasoning power in relation
to it is to bring the evidence before it for its decision.
This point will not be discussed, but that there is no doubt
as to the existence of such a sense in man. Some attempt
to throw doubt over it by pointing to its perversions, maintaining that it is a mere creature of circumstances, varying
almost endlessly in different parts of the world. But it
would be just as rational to attempt to show that there is no
such thing as a sense of the beautiful in man, by appealing
to the evidences of perversions of taste, which ignorance,
bad education, and foolish and novelty-loving fashion have
induced.
417.. NVone in Anizimals.-In those cases in animals
in which this moral sense has been supposed to exist, it is
nothing but slavish fear. It has been said by some one that
man is the god of the dog; but it is trifling with wbhat is sacred
to compare the attachment of an animal to its master and
its fear of his displeasure, with the intelligent regard of man
for his Creator as a holy and benevolent being. We ordinarily recognize the distinction between man and animals, as
to the existence of a conscience, in the language we use.
We never attach the idea of moral character to the acts of
an animal except by the force of association, and then only
slightly and loosely. We are not apt to speak of punishing
a dog, for this word implies a moral fault as the occasion of
the infliction. We whip him, sometimes, simply to associate
in his mind the smart with the act done, so as to prevent
him from doing it again, and sometimes to vent our ill feeling for the harm done us on the poor dog that has so innocently done it.




MAIN  AND THE INFERIOR ANIMALS.       309
It is related of Sir Isaac Newton that he had a favorite
little dog called Diamond, who being left in his study,
overset a candle among his papers, and thus burnt up the
almost finished labors of many years, and yet the philosopher
only said, "0 Diamond! Diamond! thou little knowest the
mischief thou hast done." Newton was a wise and good
man, and while he saw that whipping the dog would do no
good in preventing any similar accident in the future, he
had no ill feeling to vent on poor Diamond, who certainly
had a better and more rational master than most dogs have.
418. Sumtrnary of Mental Distinction.-The
mental distinction between man and animals may be thus
summed up. The animal is governed by instinct, and in
the higher orders by a kind of reasoning which is based
upon mental association. Man has, in addition to instinct
and this lower order of reasoning, the power of abstract
reasoning. In the lower orders of animals probably instinct
rules alone. In them there is none even of the limited
reasoning which we see in the higher animals. They have
a nervous system with certain central organs, but have really
no one great central organ that we can call the brain. As
we trace the animal kingdom upward, we soon find that a
brain appears, that is, such an organ as may be considered
the chief center of the nervous system. When we come to
man the brain is much larger than in any other animal, and
his intelligence is not only greater, but it is of a different
character. Not only is the amount of his reasoning by
association greater than in other animals, but there is also
superadded, as his grand distinguishing mark, the power of
abstract reasoning.




310           PHYSIOLOGY AND HYGIENE.
CHAPTER XIX.
VARIETIES OF THE HUMAN RACE,
419. 1Jankind all the Same Species, but Presenting very mnarked Farieties.-Although, as we
look at men of different nations, we find that there is a
general agreement in form and organization, there are many
points in which they strikingly differ from each other.
"With those forms, proportions and colors," says Mr. Lawrence, "which we consider so beautiful in the fine figures
of Greece, contrast the woolly hair, fiat nose, thick lips, retreating forehead, advancing jaws, and black skin of the
negro; or the broad square face, narrow  oblique eyes,
beardless chin, coarse straight hair, and olive color of the
Calmuck.
Compare the ruddy and sanguine European with the jetblack African, the red man of America, the yellow Mongolian, or the brown South Sea Islander; the gigantic
Patagonian to the dwarfish Laplander; the highly civilized
nations of Europe, so conspicuous in arts, science, literature,
in all that can strengthen and adorn society, or exalt and
dignify human nature, to a troop of naked, shivering, and
starved New Hollanders, a horde of filthy Hottentots, or
the whole of the more or less barbarous tribes that cover
nearly the entire continent of Africa;-and although we
must refer them all to the same species, they differ so remarkably. from each other as to admit of being classed into
a certain number of great varieties; but with regard to the
precise number, naturalists have differed materially."
Cuvier admitted but three varieties, the  Caucasian,
Negro, and Mongolian.  The more commonly received
classification, however, is that of Blumenbach, who makes
five varieties, viz., the Caucasian, Ethiopian, Mongolian,
American, and Malay.




VARIETIES OF THE HUMAN RACE.           311
420. Caucasian.-The chief characteristic of the
Caucasian variety is the fine form of the head, it being
nearly oval, as you view it from the front. It is also characterized by a great range of variations of the color both of
the skin and the hair. There has been more of civilization
and improvement of every kind in this race than in any of
the others.  It is mentally superior to the other races.
It is called Caucasian from  Mount Caucasus,'from  the
vicinity of which, it is supposed, it originated. Even at the
present day it is said that the characteristics of this race are
most perfectly developed in the Georgians and Circassians,
who live in the neighborhood of this range of mountains,
and who are considered the handsomest people in the world.
421. Thle Ethiopian Variety.-The organization
has not the perfection and elegance which the Caucasian
presents, and it shows an approximation to the higher
orders of the inferior animals. The skull is small. The
forehead is retreating, while the face below is projecting,
the cheek bones being prominent, and the nose broad. The
apparatus of the senses is thus fully developed, while the
brain is less than in the Caucasian. The hair is black, oily,
and frizzled. It is commonly said to be woolly, but it is
really not so. Dr. Carpenter says that " microscopic examination clearly demonstrates'that the hair of the negro has
exactly the same structure with that of the European, and
that it does not bear any resemblance to wool save in its
crispiness and its tendency to curl." The skin is generally
black; but not so in all the race, for the Caffirs and the
Hottentots are yellow.
422. The Mongolian Variety.-The Chinese race
forms the largest family and is characterized by prominent
broad cheek bones, fiat square face, small oblique eyes,
straight black hair, scanty beard, and olive skin.
423. The American  Variety.-Characterized by
high cheek bones, a narrow low forehead, features large and
bold, except the eyes, which are deeply sunken in large
sockets, hair generally black, stiff and straight, and complexion varying from a crimson brown to a deep copper.




312           PHYSIOLOGY AND HYGIENE.
424. The Mialay Variety.-This variety occupies
the Islands south of Asia, in the Indian and Pacific oceans,
and has not so well marked characteristics as the other varieties. The complexion is brown, varying from a light tawny
to almost black, the hair is black and thick, the forehead
is low and round, the nose is full and broad, the nostrils
wide, and the mouth large.
425. -Differences in Individuals, Fanilies
and Nations-produced by Similar Causes. —
The national differences are evidently produced by causes of
very much the same character with those which produce
differences in individuals and families. And the question
arises whether such differences as those which Blumenbach
describes as marking the races, are not produced in a similar
manner. This question has been much discussed, and there
is great difference of opinion in regard to it. The great
majority of naturalists believe in the unity of the origin
of the human race, and hold that its varieties are the results
of the various circumstances by which man has been surrounded.
But some suppose that the different varieties come from
separate pairs created by God in different localities, and
hold that the history in Genesis is a history of the origin
of only one of the varieties of the race. Those who advocate this doctrine are few in number; but it has acquired
greater currency of late, because one of the most eminent
naturalists, Professor Agassiz, espoused it.
426. Views of Prof. Agassiz.-All animals, he
asserts, like plants, have particular localities, for which they
are fitted, and to which they belong. The zoological provinces, as he terms them, are of unequal extent, some animals having a wider range than others. From this general
law of distribution, which he illustrates with many facts, he
infers that the various animals on the face of the earth were
not created in one part of the earth and distributed from
this to other parts, but were created in the provinces to
which they belong.
This view of the subject forces itself upon the mind of




VARIETIES OF THE HUMIAN RACE.           313
the naturalist, as he observes the arrangement of the various
tribes of animals on the earth's surface. And besides,
there are apparently insurmountable difficulties in the way
of a diffusion of animals over the globe by means of migration. For example, we can not conceive how the polar
animals could have migrated over the warmer tracts of
land, which they would have to cross according to this supposition, for, with the greatest precautions, if is impossible
now to keep them alive in such circumstances.
And farther, some animals of the same species, sometimes presenting varieties and sometimes not,.are found in
different localities, which are so cut off from all communication with each other that it is impossible that these
animals could migrate from some one locality to all the
rest. "To assume," he remarks, "that the geographical
distribution of such animals, inhabiting zoological districts
entirely disconnected from one another, is to be ascribed to
physical causes, that these animals have been transported,
and, especially, that the fishes which live in fresh water
basins have been transported, from place to place-to suppose that perch, pickerel, trout, and so many other species
found in almost every brook and every river in the temperate zone, have been transported from one basin into
another by freshets or by water-birds-is to assume very
inadequate and accidental causes for general phenomena."
Not only then were different species of animals created
originally in different localities, but it is also true, to a considerable extent, that animals of the same species occupying different localities were created in those localities.
All this he claims to be consistent with scripture, and
with very good reason. The account of the preservation
of animals in the ark, interpreted according to the common
license of language, indicates really only such a preservation as would be necessary for the stocking of that part
of the world where Noah and his family were, after the
waters should subside. The number and the variety of
the animals preserved for this purpose would of course
be very great, and would, according to the common usage
14




314            PHYSIOLOGY AND HYGIENE.
of language in narration, be spoken of in the terms
used in the Bible.  This  interpretation holds equally,
whether the deluge be considered as having been partial or
universal.
The case being thus quite clearly made out in relation to
animals generally, he proceeds to trace an analogy between
them  and the races of man in this respect.  He supposes
that there are certain zoological provinces for the different
human races, as there are for the different species- and
varieties of animals; and that these races were separately
created in these provinces with organizations suited to their
peculiar localities. While he allows that climate and other
influences affect the varieties of the human race, he claims
that they alone are not competent to produce them, and he
infers, therefore, that there must have been, as in the case of
animals, different original creations in the different zoological districts. He accordingly claims that the history given
in Genesis is a history of the origin of only one branch of
the human family. He does not suppose that the different
branches constitute different species, but are made varieties
of one species.*
He characterizes mankind as being every where essentially
the same in mental character, and alike the accountable
subjects of God's kingdom, notwithstanding their multiple
origin. It is in this respect that he considers them as being
of one brotherhood, and he looks upon the expression in
* The difference between species and varieties is this: The distinction of specics rests upon specific characteristics, that can not be
changed by those influences which tend to produce the differences that
make varieties. The characteristics of a species are original, while
those of a variety are acquired. " The term species," says Prichard,
"includes only the following conditions, namely, separate origin and
distinctness of race, evinced by the constant transmission of some
characteristic peculiarity of organization. A race of animals or of
plants marked by any peculiarity which it has ever constantly displayed, if termed a species; and two races are considered specifically
different, if they are distinguished from each other by some characteristic which the one cannot be supposed to have acquired, or the
other to have lost, through any known operation of physical causes."




VARIETIES OF THE HUMAN RACE.           315
the Bible, "made of one blood," as being entirely figurative, and as referring to "the higher unity of mankind, and not to their supposed connection by natural descent."
We will not go into a thorough discussion of this question, as it is not possible in the narrow limits of a chapter.
Only a general view of the chief facts and arguments that
bear upon the point at issue will be presented. Let us look
at this subject first in the light of physiology and natural
history.
The great majority of physiologists and naturalists, as
has been remarked, have thus far been of the opinion
that the human race came from one origin, and that the
varieties of it have been produced by the various influences
to which man has been subjected. These are commonly
included in the general expression, climatic and other infuences. To be more particular, they are-climate, situation,
food, clothing, customs, habits, state of civilization.
Too great prominence has been undoubtedly given to the
influence of climate. Lawrence very justly remarks in his
general conclusions in regard to the production of the
varieties in man and animals, "that of the circumstances
which favor this disposition to the production of the varieties in the animal kingdom, the most powerful is the state
of domestication."  This word, as he uses it, includes all
those social influences, which as manifestly affect the animals which man domesticates as they do man himself.
The analogy between man and animals in relation to the
results of the influences referred to, will be spoken of more
particularly.
That climatic and other influences do have a very great
agency in producing the varieties, both individual and general, that we see on looking over the human family, no one
doubts. The only question is, whether they have produced
all these differences -whether, for example, they have
occasioned that, very wide difference that we see between
the Caucasian and the Ethiopian. These limits will not
allow us to go into a full examination of the influence of




316          PHYSIOLOGY AND HYGIENE.
these causes, and only a few points will be noticed in a
very general way.
42r. Color Affected by Clirnate.-That climate
has a great influence upon the color of the race is proved
by many clearly observed facts. Tropical heat always has
a tendency to produce a black skin. This is shown very decidedly in the case of the Jews, who have preserved their
characteristic features amid varieties of climate, and yet
have their color altered.
Thus, while the Jew of the interior of Europe has a fair
complexion and light hair, under the scorching sun of
India his hair is crisped, and his skin is black. The evidence of the influence of climate is the stronger in this
case, because the change from the original color has been
twofold. For the original Jew in Palestine had undoubtedly a dusky skin and dark hair, upon which the temperate
climate of the interior of Europe and the tropical climate
of India have produced two opposite effects.
428. Circumstances Affecting the Fornm.But in the varieties of the human race there are differences
of form as well as of color. That the various influences to
which man is subjected have a marked effect upon his
physical form is universally acknowledged. We see this
alike in individuals, families, and nations. Intellectual and
moral influences manifestly have some agency in moulding
the shape of the head in the individual. The differences
which we so commonly see in the shape of the head between
the intellectual and the ignorant, are not owing altogether
to original difference of capacity, but in part to education.
The brain, like all other organs in the body, is influenced
in its development by the degree of activity to which it is
stimulated. It is not made an exception to this general law
of development. Accordingly we find that depressing influences tend to make the top of the head, the cerebral
part, small, and the forehead retreating, while the face,
from the predominance of the sensual over the intellectual,
is rendered relatively too prominent.  The tendency of
elevating influences is of an opposite character. And




VARIETIES OF THE HUMAN RACE.          317
such influences, thus operating in the individual, when
repeated and accumulated from generation to generation,
produce great and lasting results. It is thus that a race
becomes either degraded or elevated. By a continuance and
accumulation of influences it acquires either a good or a
bad fixed character.
One class of causes effecting changes in the physical
form has been mentioned, the influence of which is manifest. But there are changes seen, the causes of which we
cannot clearly make out; and yet we know that they are
occasioned by the varying circumstances in which man is
placed. By the compound influence of many causes combined we continually see introduced differences in the
shapes of various parts of the body. Family and national
peculiarities are thus occasioned. The influences to which
we have thus referred, some of which are little understood,
are all those which Mr. Lawrence includes in the term
domestication, which, as before said, he applies to man as
well as to animals.
429. ilarked Tendencies to Three Differentt
-Forms of the Hlead.-Dr. Prichard has pointed out
three different types of form in the head, occasioned by three
distinct classes of influences. One he terms the prognathous
(a word derived from two Greek words meaning before and
the jaw), in which the jaws project very prominently forward. This formation is characterized by the predominance of the sensual over the intellectual, the apparatus of
the senses being largely developed, while the cerebrum is
small, making the forehead retreating.
The tendency to assume this type is always in proportion
to the action of the degrading influences. " Want, squalor,
and ignorance," says Carpenter, "have a special tendency
to induce the diminution of the cranial portion of the
skull, and that increase of the facial, which characterize
the prognathous type." It is seen most strongly marked
in the negroes of the Gold Coast.
In the pyramidal type, as it is termed, the cheek bones
are very broad, and the bones above are so shaped as to




318          PHYSIOLOGY AND HYGIENE.
give the top of the head a sort of pyramidal form. This
type we see in those tribes that lead a wandering life-the
nomadic races, as they are called.
The oval or elliptical form, which is seen so well marked
in the Caucasian variety, is manifestly the result of elevating influences.  These types are convertible into each
other. Thus, the oval may be degraded into the prognathous, or the prognathous may be elevated into the oval.
The latter change is seen in the Ethiopian, when in successive generations he is subjected to elevating influences,
in his intercourse with the Caucasian. And it is interesting to observe that the form of the head is more readily
chanced than the color.
"Thus," says Carpenter, "in some of the older West
Indian colonies, it is not uncommon to meet with negroes,
the descendants of those first introduced there, who exhibit a very European physiognomy; and it has even been
asserted that a negro belonging to the Dutch portion of
Guinea may be distinguished from another belonging to
the British settlements, by the similarity of the features
and expression in each to those which peculiarly characterized his master's. The effect could not have been produeed by the mixture of bloods, since this would be made
apparent by alteration of color." In the same way is the
pyramidal type convertible with the others. The pyramidal
and the prognathous are often mingled together, by the
influence of vagabond habits and degrading causes.
430. Insensible Gradations in  Diversity.The view thus given of the operation of influences in producing the varieties of mankind is strengthened by the
fact that, as Humboldt says in his Cosmos, there are
"many intermediate gradations in the color of the skin
and in the form  of the skull."  If we look alone at the
extremes in varieties of color and form, we are of course
disposed to regard such great differences as marking a distinction of species. But when we see these varieties passing into each other by such insensible gradations, and at
the same time observe the manifest influence of causes




VARIETIES OF THE HUMAN RACE.            319
upon these gradations, as in the cases referred to in the last
paragraph, the evidence is clear to us that the varied influences brought to bear upon man are competent to produce
the varieties of the race.
431. Fixedeness of the  Varieties.-But it is
objected that, although climatic and other influences have
a great effect, yet, so far as we can see, they only produce
changes that approximate to those differences that mark
the grand divisions of the race. They cannot, for example,
be shown, from actual observation, to have effected the
entire change in any length of time of any portion of the
Caucasian race into the Ethiopian, and, on the other hand,
of the Ethiopian into the Caucasian. It is objected, farther,
that the peculiarities of the principal varieties of man
existed in the early history of the race. This appears in
relation to the Ethiopian variety in the figures found on
Egyptian monuments. These show that the peculiarities
of the negro race were as strongly marked nearly 5,000
years ago as they are now. This fixedness of character
under such a variety of influences continued so long, it is
claimed, indicates that the peculiarities were original, and
not acquired.
In reply to both of these objections, your attention is
called to a general fact, which is deemed very significant in
its bearing upon the great point at issue. It is the fact
that when a variety is formed by any influences, either
among plants or animals, it is apt to remain in spite of
opposing i9fluences. It seems to be easier by far to produce
a variety, than to bring it back to the character of the
original from which it came.
432. Influence  of DIomestication  both  in
-iIMan  and  in  Aniintals.-Domestication  has been
continually producing varieties in the animals that man
has so largely appropriated to his service, and the varieties
once produced commonly remain. And the same thing is
seen in the varieties resulting so continually in the human
race from the same class of influences. It is matter of
common observation that family and national peculiarities




320           PHYSIOLOGY AND HYGIENE.
are apt to be perpetuated. And it is not merely from a
continuance of the causes from which they result, for they
are apt to remain even when strong counteracting influences are brought to bear upon them.
Now the causes which tend to produce varieties in the
human race acted of course at the first, and during the
first ages of the race were competent to produce the most
prominent varieties. And the tendency to fixedness, which
we see exemplified in so many ways in the varieties of both
plants and animals, is sufficient to account for the perpetuation of such marked characteristics as those of the
Ethiopian and the Caucasian.
The analogy then which is thus observed between man
and the domesticated animals is a much  clearer and
stronger one than that which Professor Agassiz has attempted to make out between man and animals generally
in regard to zoological districts. And the inference is a
legitimate one, that the same influences that we see produce varieties in domesticated animals, are competent to
produce the varieties in the human race, which are even
less marked than some of those which we see in animals.
Varieties are produced more readily and in greater numbers
in animals than in man, probably because they have less
power of resisting influences that act upon them. The varieties of some of the domesticated animals are very numerous.
The analogy drawn between man and animals in regard
to zoological districts is weakened by the consideration
that there was no necessity for man's being created in different localities, because he can migrate so easily from one
country to another. The necessity existed in regard to
plants and animals, but not to the same extent in all. Migration is easier in the case of some than in the case of
others. And this difference seems to have been acted upon
by the Creator.
Accordingly, the evidence is quite conclusive, that those
animals which have been so universally appropriated by
man to his service, have been diffused from central points
and have gone with man, instead of being created in many




VARIETIES OF THE HUMAN RACE.           321
localities. This being the case, it is hardly to be supposed
that man, who is capable, through his ingenuity, and skill,
and daring, of going every where, would be unnecessarily
created in different pairs at different points on the earth's
surface.
433. Netv Causes Occasionally Introduced
by the Creator.-But suppose that, in view of all the
evidence, we should come to the conclusion that the climatic and other influences are not the sole causes of the differences in the races, are we of course driven to the admission
that, as Agassiz and others teach, there must have been created at the first, several, we know not how many, different
pairs in different localities? By no means. We are not to
forget that the Creator, besides using influences of which
we have no knowledge (which he is continually doing), can
effect new combinations of the causes already existing, or
introduce into operation entirely new causes. That he is
from time to time evolving new results in one or the
other of these ways, or both of them, is manifest.
The very common notion, that at the creation all the
causes which have produced all the phenomena that have
been observed to the present time were then set in operation, and have been left to work out their results, seems to
be contradicted by many facts. Most of the causes then set
in operation, it is true, have been at work ever since.
Unless this were so, nature would not exhibit the regularity
which it now does, and calculations could not be made with
such definiteness as to its processes from knowledge gained
by experience. But changes and irregularities sometimes
occur which must have been the result of new causes. A
few examples only will be given.
The age of man before the flood was much greater than
it has been since. A change was effected at that period.
It was not a mere arbitrary change, but such a change in
the very character of the human system, that its capability
of resisting the tendency to decline was greatly reduced in
the period of its continuance. It was not a change resulting from the influence of deteriorating causes, for in that




322           PHYSIOLOGY AND HYGIENE.
case it would have been less suddenly induced. To effect
this change some new causes must clearly have been
brought to bear upon the system, making it in the postdiluvian a different system in some important respects from
what it was in the ante-diluvian.
Take a fact of a different kind, indicating a similar change
of agency. New diseases from time to time appear. This
could not occur without either entirely new causes, or new
combinations of elements heretofore existing. That very
definitely marked disease, the small-pox, we have the best
of evidence, was not known to the ancients, but is comparatively a modern disease. It is impossible to conceive of its
being introduced without some new cause of a very definite
character.
Take now another fact of a widely different kind from
either of those noticed. The earth is marked all over with
signs of great convulsions that have occurred since its
creation.  It has been supposed till recently that these
signs all refer to that great event described in the Bible,
the Deluge of Noah; but geological researches have demonstrated pretty clearly that they point in part at least to
other previous convulsions. Now these convulsions are not
to be reckoned as a part of the regular order of nature.
They could not have resulted from the ordinary causes that
act continuously. New causes must have been introduced
at the time, to produce these unwonted results.
It matters not to the argument above indicated, whether
the new results that are occasionally developed, come from
a direct agency at the time, or come from a chain of causes
set in operation a long time before. The results are new
results, and come from causes or combinations of causes
which differ from those that have produced the ordinary
and regular results which we witness from day to day or
from year to year.
Now in like manner can we suppose, if it be necessary,
that the Creator produced the varieties of the human race
by adding other and new causes to the ordinary influences
to which man is subjected. This is a much more probable




VARIETIES OF THE HUMAN RACE.                323
supposition than that of the advocates of the multiple origin
of the race.
For besides accounting satisfactorily for the facts, and at
the same time being consistent with the record in Genesis,
it is more clearly supported by analogical facts than the
supposition (for it is mere supposition) that the human
race was created in different localities. And farther, this
supposition avoids difficulties which attend the other. For,
if we suppose that the race came from different pairs, it
would be difficult to decide how many pairs there were.
Such are the variations of the race in different localities that
there would be much disagreement as to the number of the
represen tative pairs, and their distinguishing characteristics.
But it may perhaps be said in objection, that we are supposing a miraculous interposition. Whether it may rightly
be termed such will not be considered; but it is just such
an interposition, or rather, direct agency, as is affirmed by
the advocates of a multiple creation, differing from it only
in the time of its occurrence.
They suppose the direct agency of God to be put forth
in creation at different points, whether at different times
they do not say, and this is really quite immaterial; and we
suppose the same direct agency to be put forth, but in a
less marked manner, to produce a change in what has
been already created. In supposing the direct agency of
the Deity at all, we go beyond mere physics; and he surely
has the power to put forth this agency at such times as he
pleases.*
* There seems to be in the minds of some naturalists a great reluctance to admit at all the direct agency of the Creator, whether it be
exerted in consonance with the order of nature which he has established, or miraculously in opposition to it. And they would smile
skeptically at what they would deem the simplicity or superstition of
Hugh Miller, in referring some narrow escapes which he has had, in
pursuing his geological researches, to a particular Providence. The
relation of the agency of the great First Cause to second causes, it is
true, is a mysterious subject; but it implies no disposition to fathom
what is unfathomable if we assert that the facts are far from warranting us in the belief that this agency has not been exerted since the
period of the creation, but confined itself to that time.




324           PHYSIOLOGY AND HYGIENE.
But the supposition made above is not needed. The
regular, continuous, natural causes, which have ever operated upon man, have been competent to produce all the varieties of the race. And this supposition was only suggested
as a consideration for those who fail to see that these causes
have been thus competent; it is a more probable supposition than the one offered by Agassiz and others to meet
the difficulty in the minds of such persons.
434. The Testimony of the Bible to be Received as Evidence.-Thus far this subject has been
treated chiefly as one of natural history and physiology.
But is the testimony of the Bible not to be received as a
part of the evidence? Is the question to be decided wholly
on considerations and facts drawn from natural history and
physiology? This seems to be the view of some naturalists,
though the great majority of them are disposed to admit
the statements of Scripture as evidence.
It is true that the Bible does not purport to be a philosophical book. Its language is based on the principles of
common and not scientific usage, and is so to be interpreted.
And it should be thus interpreted in relation to the subject
before us. its statbments on this subject are of the most
explicit character. It purports to give an account of the
origin of the race, and portions of its history. It ascribes
the corrupt character of the race to a fallen parentage.
This connection of the general corruption of the race with
the fall of its original pair, however divines and philosophers may differ in accounting for it, is recognized as a fact
throughout the whole book of revelation. The testimony
is definite, and is not to be mistaken.
The question is, whether it be valid testimony. And if
the Scriptural record be established, as it is abundantly, by
both internal and coincident evidence, its testimony in
regard to the origin of the race is to be received by scientific men. It can not be set aside by any mere presumptive and analogical evidence drawn from physiology and
natural history. If actual facts be proved inconsistent with
the Mosaic history, as properly interpreted, they will of




LIFE AND DEATH.                 325
course bring discredit upon that history. No immunity
against a strict investigation is to be claimed for the Bible.
But there is no fear of such an issue; and it is to be
remembered that mere analogies are not facts, and are not to
be deemed as having much force, especially when there is a
question in regard to their value in comparison with other
analogies that point to an opposite conclusion.
CHAPTER XX.
LIFE AND DEATH.
435. Life, though  Various in its Manifestations, in some Senses always the Same.-Life
is very commonly spoken of as being one thing, although
its manifestations are exceedingly various in their character. In the simplest growths that we see, both in the
vegetable and in the animal kingdoms, the operations of
life are in some respects very different from the complicated
processes that we witness in the human structure, which
has been the subject of your study in this book. And yet,
as you have seen in the Chapter on Cell-Life, life in these
apparently opposite cases is essentially the same. It is the
same in its origin. It begins always in a single cell,
whether the living being is to be great or small, simple
or complex, a plant or an animal, a creature of a day, or
a being destined to immortality.
Why it is that from a simple cell the vital force, as it is
termed, can evolve such a range of diversified results as we
see in all animated nature, is one of the great mysteries of
the Creator. As we see in the springtime a bud upon a
tree unfold itself gradually, and develop to us successively
leaves and flowers and fruit, it fills us with wonder when
we reflect how much has come from that little bud; but
when we go farther, and think of the whole tree as having
come from a single cell, so small that it can be seen only




326          PHYSIOLOGY AND HYGIENE.
by the microscope, the mystery appears passing wonderful.
And it is a still greater mystery, when a complicated animal organization is looked at as having been developed by
the vital force, alike with all other living things, through
a single cell as its origin.
Not only is life always the same in its origin, but it continues essentially the same in its processes. All the various
forms which it produces, both in the vegetable and in the
animal world, are built and kept in repair by cells. All the
functions, too, are carried on through the same agency.
The secretions and excretions are effected by constant successive creations of numberless cells. Even the intellectual
operations in the mind of man are dependent upon cells
so long as the mind is connected with the body. In thinking, as well as in muscular motion, cells are worn out, and
must be replaced by other cells, which are continually supplied by the vital force.
436. Difference between the Vital Force, and
Meat, Light, and  Electricity.-Life being thus
wonderful in its operations, the inquiry arises, what can
this mysterious agent be? With curious eye we watch its
workings, but although we can learn some of its laws, its
nature eludes our search. Then pressing the microscope
into our service, we trace it back to its hiding-place in a
minute round cell containing a fluid; but simple as this
prison is in which it is confined, it is more of a mystery
than ever. The vital force, which begins here, and, enlarging more and more the sphere of its operations, develops
gradually the simple or the complicated living form, as the
case may be, has been classed by some with other forces,
the nature of which we do not understand, as heat, light,
and electricity. But it differs from them entirely in some
important points. While they act in connection with matter generally, both organized and unorganized, vital force
is seen acting only in organized substances. While they
diffuse themselves through all kinds of matter with more
or less rapidity, the vital force has no power of diffusion,
but is confined within certain limits. These limits differ




LIFE AND DEATH.                  327
in the different living substances. The vital force has the
power of appropriating matter to itself within these limits.
It does this by assimilation. It has then the power of extension to a limited degree; while the other forces mentioned
have the power of diffusion, in some respects limitless.
Another difference is this. While these forces, light,
heat, and electricity, are lessened in power by being diffused, vital force is not lessened by extension. Heat. for
example, if diffused is lessened at the point of its diffusion;
but life is as energetic at its starting-point after its extension as before, and even more so. It is, so to speak, selfgenerating, while the other forces are mere products. The
vital force stands peculiarly alone in this respect.  The
effects, too, which this force produces, as it lays common
matter under contribution, and fashions it in such diversified forms, have an infinitely wider range of variety than
the effects of the other forces.
437. Life in Blood.-We can thus trace the differences between the vital force or principle and other forces,
but we can not, as before said, discern its nature. We know
not whether it be one thing. It is convenient to speak of
it as being so. But we know not but that it may be a
compound of endowments, or tendencies imparted to matter, and varying with the various forms of living substances.
Some have supposed that the vital principle resides chiefly
in the blood, and that this is the meaning of the passage
in the Bible, " the life of the flesh is the blood." That the
blood has some vital properties is certainly true. These
properties are communicated to it as it is made from the
food, and fit it to be the material for the construction and
repair of the organization. And it is simply the fact, that
the blood is the common material out of which all the diversified parts of the living structure are made, that is recognized in the language of Scripture on this subject. The
same fact is embodied in another form in the remark of
the French physiologist, that the blood is chair coulante, or
running flesh.
438. —Vital Laws Control the Chemnical and




328          PHYSIOLOGY AND HYGIENE.
2Mechanical. — When the vital force appropriates to
itself common matter in assimilation, it takes it away in
part from the operation of certain forces which have had
entire control over it. As long as it is common dead matter, it is wholly subject to the laws of mechanics, and of
chemical action. But when it becomes organized living
matter, the laws of life take possession of it.
The laws of chemistry and mechanics are not, it is true,
annulled in relation to it. They still exert their influence,
but under the control of vital laws. The force of gravity
acts continually upon the body; but the living muscles are
much of the time acting in direct opposition to it. The
blood circulates on hydraulic principles; but the vital
force furnishes the motive power, and keeps the blood
from becoming solid and stopping up its channels. Chemical changes are going on in the stomach, the lungs, and
at every point in the capillary circulation; but they are
modified, controlled, by the vital principle, and are properly
termed chemico-vital processes.
The human body is made of materials that are exceedingly prone to chemical decomposition, and the degree of
heat which is maintained is such as to favor this result;
but the vital force not only holds the chemistry of the
system in abeyance, but even presses it into its service.
When life is destroyed, the laws of chemistry assume their
full sway, and the process of decay begins.
The very agencies which served, while under the control
of the vital principle, to maintain the living organization,
now acting alone, run riot, and work its destruction. Thus,
that powerful agent, heat, existing in the body at the point
of 98~, is necessary to the carrying on of the processes of
life; but let life be destroyed, and the maintenance of this
degree of heat would ensure a very rapid putrefaction. So,
too, a degree of heat which would rapidly putrefy a dead
egg by quickening the chemical changes, would actively
stimulate in a living egg those curious vital processes that
produce at length the bird. During incubation the egg of
the hen is kept for three weeks at a heat of 105~, and yet




LIFE AND DEATH.                329
when the chicken is hatched all of the yolk that is left is
unchanged. A dead egg would soon putrefy under such a
temperature.
439. Change always attends Life in Action.
— The vital force exhibits its controlling power in an
extraordinary manner in connection with that great force of
nature to which reference has just been made. Heat is
very diffusive, and is exceedingly liable to change from
varying circumstances. And yet the vital force maintains
the heat of the body quite uniformly at one point, although
the agencies which tend to vary it are very numerous and
effective.  The production of heat in the system  is a
chemical operation, but the vital principle regulates the
quantity in the body very accurately, by providing for its
escape in various ways, and perhaps by curtailing in some
measure its production.
Continual changes are effected by the vital force in every
part of the body. In one sense death may be said to be
taking place constantly, while life is as constantly generated, as the useless particles are separated and taken away,
and the new ones are deposited in their place. While these
changes are going on the vital force so operates as to maintain the peculiar shape and plan of every part, even during
its growth. And as we look abroad over all the diversified
forms of animated nature, the accuracy with which this
force works in the prescribed mould of each is very wonderful.
440. Life  Sometimes Dormant.-While the
vital force is in action there is constant change; but sometimes it is dormant. A seed in its quiescent state has life
in it, ready to be waked into action by the proper excitants,
air, warmth, and moisture. Seeds that were found in the
excavations of Pompeii have shown that they retained
their life during all this time, by shooting forth their
germs as soon as they were exposed to these natural excitants of their growth.
One of the most interesting cases of this kind is related
by Dr. Lindley. "I have now before me," he says, "three




330           PHYSIOLOGY AND HYGIENE.
plants of Raspberries, which have been raised in the gardens of the Horticultural Society, from seeds taken from
the stomach of a man whose skeleton was found thirty
feet below the surface of the earth, at the bottom of a
burrow which was opened near Dorchester. He had been
buried with some coin of the Emperor Hadrian, and it is
probable, therefore, that the seeds were sixteen or seventeen
hundred years old."
A similar dormant condition of the vital force exists in a
greater or less degree in the state of hibernation. So, also,
in cold climates, life is throughout almost the whole vegetable world dormant during the period of winter, to wake
to greater energy from the stimulating warmth of spring.
In the human body, with the exception of some few very
rare cases, life is always in an active state. Some portions,
however, of the system are a part of the time dormant for
the purpose of rest and repair.
The brain and the muscles sleep; but during their sleep
life is busy in the formative vessels, repairing their energies,
and we may say, their textures also, which have been wasted
by their labor. It is a very wonderful attribute of the vital
force that it can, as in the case of the hibernating warmblooded animals, stop all its active operations, without damage to the machinery of life, and with such facility resign
itself to a state of temporary inactivity.
441. Mysterious Connection of Life Bwith the
Soul.-The most mysterious of all the circumstances in
regard to the vital force is its connection in man with the
immortal soul. The life and the soul are so intimately connected that some have considered them to be the same.
But they are two distinct forces. They are in some measure
indeed antagonistic to each other. For the soul, in using
the machinery of the nerves and muscles, occasions a wear
and tear of the structure, which it is the office of life with
its numberless cell-laboratories to repair.
The soul and the vital principle are both present in all
parts of the system, but not in the same sense. The vital
principle is seen equally at work every where. It has no great




LIFE AND DEATH.                 331
central organ from which it sends forth its influence. But
the soul is especially connected with the brain, and by means
of the complicated nervous connections of this organ, it
affects and is affected by all parts of the system. Its influence is thus an all-pervading one.  Every point of the
living organization has thus a sort of telegraphic communication with the immaterial soul.
But there is another view of this connection of the soul
and the vital principle. The soul is developed in and with
the living structure. It is not created by itself and put
into the body as a tenant. Its powers are developed while
the vital force develops the powers of the physical organization. The two processes go on together. Nay more, the
development of the soul is in a measure dependent upon the
development of the body. The vital force exerts a manifest
influence upon the soul's growth. As it prepares the organs
for the use of the soul —those organs by which it acquires
knowledge from without, and thus procures the stimulus
and even the material for its growth-whenever the vital
force fails to construct these organs properly, the powers
of the soul are not well developed. This we see exemplified
in the idiot.
In this intimate connection of the soul with life we find
a great mystery. Life, a force belonging to mere matter,
an endowment of it, or a compound of its endowments-life,
that builds up all organized substances, the humblest and
simplest vegetable growth as well as that most complex of
all living structures, man-life, that so soon perishes in the
noblest of its works that it is likened to the dissolving vapor
— is made by the Creator an agent in developing an immaterial principle or being, that is to survive the dissolution
of the'structure in which it is generated, and is to live forever. Strange that the immortal should be thus produced
in the mortal-that the unchangeable and imperishable soul
should be thus developed in such intimate connection with
the changeable and perishable body. It is a mystery which
we can not fathom.
442. Natural Limits of Life Decay.-The vital




332           PHYSIOLOGY AND HYGIENE.
force, that is so busy in building and repairing so long as it
lasts, has in all cases its natural limit; and in the case of the
human system it seldom fully reaches this limit. The diversitied, and complicated, and beautiful structures which it
evolves, if saved from accident till the natural period of decline comes, lose their vigor and beauty, and at length die
and are given up to the action of the common laws of chemistry, which the vital force has so long resisted and controlled. The structures then decay, and the particles are
dissipated, perhaps to be united again to other structures.
443. Systeumic  and  Molecular Death.-The
death of the body is not ordinarily complete at the moment
when what we term death occurs. Though as a whole, as a
system of organs, the operations of life are at an end, yet there
is some degree of life in some parts, and there may be in all
parts of the body. The beard and nails even, may grow.
Some of the organs may secrete their fluids-the liver its
bile, and the stomach its gastric juice. Some of the properties
of life, too manifestly, still remain. The irritability of the
muscles, which is strictly a vital property, as it never belongs
to common dead matter, still appears on the application of
excitants. It was the contraction of the muscles in the leg
of a dead frog on the accidental application of a stimulus,
that led Galvani to his grand discovery. And it is through
this vital property that the culprit who has been hung can
be galvanized into apparent life.
Death, then, may be said to be of two kinds-systemic,
that is, the death of the body as a whole, a system of organs
-and molecular, that is, the death of the individual molecules or particles which compose the body. Death can be
said to be complete only when the laws of life have resigned
their power over these molecules, and the laws of purely
chemical action have taken their place. When this change
occurs, the process of decay, which is strictly a chemical
process, begins.
444., Death beginnin+ g in the tHearit and in
the Lutn/s.-If a large quantity of blood be lost, so large
as to result fatally, death in this case obviously begins in the




LIFE AND DEATH.                 333
circulation.  The heart not being supplied with the quantity
of blood that usually flows through it, becomes more and
more feeble in its action, till it at length ceases to beat.
When a large aneurism bursts, it is the sudden drain from
the circulation that destroys life.
Any thing which to any great extent prevents the air
from entering the lungs may cause death to begin in the
respiratory system. This may be done by three classes of
causes.  1st. Causes that act upon the large air-passages.
Examples of this class of causes are strangling, smothering,
drowning, &c. In croup the principal cause of death is
the prevention of the free passage of air through the windpipe into the lungs.
2d. Causes which act upon the walls of the chest. If a
bank of earth fall upon a man, though it leave his head
clear, so that the air-passages are unobstructed, he can not
breathe, because his'hest is held as if in a vise. A man
came near dying from this cause who was having a cast
taken of the upper part of his body. If the muscles of respiration were to be paralyzed, death would ensue, just as it
does when they are prevented from acting by other causes.
3d. Causes acting upon the lungs. Disease may occasion
an amount of obstruction in the very substance of the lungs
sufficient to cause death. It does so by preventing the introduction of the air into the minute air-vessels, where the
air revivifies the blood. The obstruction is just as effectual
in this case as it is where it occurs in the large air-passages.
445. Death begiyning in, the Nervous Systemn.-When death occurs from a blow upon the head as the
immediate result of the shock, we have an example of death
beginning in the nervous system. But the cause may act
upon this system in some other quarter. A blow at the pit
of the stomach, for example, may so shock the whole nervous system as to stop at once the operations of life. Some
poisons, too, as opium, destroy life by their influence upon
this system. Very extensive burns give a shock to the
nerves from which they do not rally. The same can be
said of other injuries when there is no recovery from the




334           PHYSIOLOGY AND HYGIENE.
first shock. Powerful medicines, improperly given in cases
of disease disposed to prostration, may depress the nervous
system to a point from which it may never revive. Cold
destroys life mostly by the benumbing, paralyzing influence
which it exerts upon the nerves.
Though we thus classify the modes of death, in the great
majority of cases death is a complex event, resulting from
a concurrence of causes. It is so even when the disease is
not of a complicated character. Take, for example, a case
of pure uncomplicated consumption, in which all the organs
but the lungs are in a healthy state to the end. The whole
system becomes at length exhausted by the disease. If this
exhaustion alone be the cause of death, then we may say
that it is an example of death beginning in the nervous system. But if the obstruction in the lungs to the admission of
air in the air-cells be the cause, it is a. case of death beginning in the respiratory system. Generally in such cases
death results from the two causes combined, and it is often
difficult to determine which is the more prominent cause.
446. The Si.gns of Death.-The signs of death are
so clear that there is, with very few exceptions, no mistake
in regard to the occurrence of the event. The stories that
are related about burying alive are most of them unfounded.
The apprehensions created by them in the minds of some
persons have led them to insist that no body ought to be
committed to the grave till the most infallible sign of death,
putrefaction, has appeared. We should wait for the appearance of this sign in all cases in which there is a shadow of
doubt. But the cases are exceedingly rare in which we
cannot determine the reality of death long before this sign
shows itself. Our decision is not made up, it must be observed, merely from the signs of death.
All the circumstances of the case are taken into viewthe disease, its progress, its symptoms, and the events of the
last hours of the patient. With this evidence before us,
we absolutely know, in all ordinary cases, that death has
occurred when the respiration and the circulation have
ceased. And in the exceedingly few cases in which there is




LIFE AND DEATH.                 335
any reason to doubt on that point, there is always something which will attract the attention and excite the curiosity of some one, unless there be stolid indifference and
the most absolute lack of intelligence.
In such cases there is always something strange-the circumstances attending the cessation of the respiration and
circulation are singular, and the signs of death are not
complete and in their proper order of succession. Whenever there is for these reasons any doubt as to the reality
of the apparent death, the strictest watch should be maintained till the signs of commencing putrefaction appear.
With this simple rule of prevention burying alive need
never occur.
The investigations of physiology, as you have seen, end
with the death of the body. It can give us no light on the
question as to what may be beyond this life. Although the
physiologist studies the human structure not merely as an
organization instinct with life, but also as the wonderful
machinery through which a reasoning soul acts and is
acted upon in this state of being, yet, as a physiologist, he
knows not that the soul survives the death of the body.
He knows not but that it is a mere endowment of matter,
as life probably is, and so perishes in the hour of dissolution.
He may indeed conjecture that the exalted faculties which
are in this world susceptible of such high cultivation, instead of being destroyed with the body, are destined to still
farther development in another state of existence. But
what is mere conjecture to him as a Physiologist, is made
fact to him as a Christian. The eye of his faith sees an
immortal spirit rise from the dying body, and he realizes
the truth of the sublime declaration, that death is swallowed
up in victory.




336                      QUESTIONS.
QUESTIONS.
CHAPTER I.
1. In what respect are a crystal and a plant alike? How do the3
differ in the modes of their formations What different offices do the
organs in a plant perform? What is meant when we call the plani
an organized substance, and the crystal an unorganized substance? Dc
the organs in the plant act wholly on mechanical principles?
2. Or on chemical? What principles control the mechanical and
the chemical? What two classes are there of organized living beings,
How do they differ as to the complex character of their organization ]
Under what two grand divisions do you class all the substances of the
material world? How do plants and animals differ from minerals as
to the parts of which they are composed?
3. What is assimilation? Explain it as it takes place:-First, in
the plant, and secondly, in the animal.
4. How do organized and unorganized substances differ as to permanency? Point out the mode and the extent of the change that occurs
in the organized. Why is there more change in animals than in
plants? How can minerals be changed? Are they productive, as animals and plants are?
5. Contrast organized and unorganized substances in regard to
change in the phenomena that you see in the world around you. How
do organized and unorganized substances differ as to regularity in
form?
6. What does irregularity in the unorganized arise from?  How
does the law of regularity operate in organized substances? In which
is the regularity the most wonderful, the organized or the unorganized, and why?
7. Give the four reasons assigned: —First, as to change; secondly,
as to variety of form; thirdly, as to its continuance from age to age;
and fourthly, as to its preservation in the midst of a certain range of
irregularity. Exemplify the last point by reference to the human
countenance. How is the law of regularity exemplified in the two
halves of the body? Mention some organs which are destitute of this
symmetry; mention also some animals that do not exhibit it. What




QUESTIONS.                       337
is the distinction between organized and unorganized substances as to
limit of size?
8. How do organized and unorganized substances differ as to their
structure? How do they differ as to the number of elements of which
they are composed? What are the four principal elements of organized bcdies? Which one of these is solid? In what form are the other
three? How many elementary substances are there in the material
world? How many of these are found in plants and animals?
CHAPTER II.
9. Point out the difference between the plant and the animal as to
locomotion. How does this difference make it necessary that the animal should have a stomach?
10. Trace the analogy between the stomach in the animal and the
roots in the plant. What is the difference between most animals and
plants as to central organs? What is their difference as to the effect
of mutilation upon them? What is the distinction between animals
and vegetables as to sensation and spontaneous motion? Have all animals consciousness and thought? Name some exceptions to the distinction as to locomotion. What is the difference between the motions of such plants as the sensitive-plant and catch-fly, and those of
animals?
1 1. Make the comparison in relation to the hydra, which describe.
What part of the structure of animals is peculiar to them. Has this
structure ever been discovered in any plant? Why ought we to be
able to discover it in the sensitive-plant and catch-fly, if it were the
cause of their motions?
1 2. Is the nervous system necessary to the carrying on of nutrition?
What are the functions of organic life? What of animal life? What is
the order of action in the nervous system? In what respect is this
order not observed in some cases?
13. What is the distinction between animals and plants as to their
chemical composition? In which is carbon the characteristic element,
and in which is it nitrogen? From what organs in animals is carbon
thrown off? In what organs in plants is it absorbed?
CHAPTER III.
13. How is man commonly classed in the animal kingdom? On
what ground can the classification be claimed to be correct? Does this
classification recognize at all the essential distinctions between man
and other animals.
15




338                      QUESTIONS.
14. What are those distinctions? What bearing has man's immortality on this subject? Is the difference between man and other animals like that which we see between different animals?
15. Is it a mere difference of degree? What notice should the
naturalist take of the difference? What is the distinction made in the
common classification between man and such animals as apes and
monkeys?  Can these animals be properly said to have four hands?
How do the hands which they are said to have resemble the hand of
man, and how do they differ from it?
16. State some particulars in which the structure of man differs
from that of the inferior animals.
1 7. What relation have the peculiarities of man's organization to
his mental peculiarities? Why is it important that the essential distinctions between man and animals should be prominently taught?
CHAPTER IV.
17. Of what two parts is bone composed? What are the proportions of these parts in childhood-in adult age-and in old age? How
can you obtain these parts separate from each other?
18. What is the animal part of bone? What relation does this
sustain to the mineral part? What is the arrangement of the two
parts of bone in the very young child? What is true of the skeleton
of many fishes? Of what are cartilages constituted? What two different purposes do the bones fulfil?
19. In what two forms is bony substance deposited? How are
these arranged in the flat bones? How in the long? How are both
lightness and strength secured in a long bone-first, in the body of the
bone, and then in its ends?
20. Why are the ends not made like the shaft? What is the marrow of the bone? How is a bone nourished? What is the periosteum?
Do arteries enter the solid substance of the bone? Describe the manner in which circulation is carried on in every point, as shown by the
microscope. What fluid circulates in the minute channels in bone,
shown to us by the microscope?
21. What is said of the sensibility of bone?
22. Give a general description of the skeleton, noticing the variety
of shape in the bones, and the purposes which they answer. How
many bones are there in the head? How many of these belong to the
face? How many to the cranium? Describe the latter, as represented
in Fig. 6.
25. Why is the box (as the cranium may be called) holding the
brain, composed of so many bones?
26. Describe the' structure of the principal bones of the cranium.




QUESTIONS.                        339
What is the difference between the joinings of the outer and those of
the inner tables of these bones? What is the reason of this differ.
ence?
27. How are the principles seen in the construction of domes illustrated in the cranium? Of what bones is the dome of the cranium
made up? Describe the different ways in which strength is secured
around the base of this dome.
28. Describe especially the arrangement between the parietal and
temporal bones. When violence is inflicted upon the head, what is
the direct cause of the injurious effects felt by the brain? On what
principle do the guards of the brain defend against this cause of injury?
29. Mention now in their order the different textures through
which the vibration of a blow must pass before it reaches the brain,
pointing out their agency in lessening the vibration. What arrangement is there of the lower part of the frontal bone as a special guard
against injury at that point?
3:0. How is the side of the head, so peculiarly exposed to violence,
especially guarded? What other organs, beside the brain, are protected by the cranium? Describe the arrangement of some of the
bones of the face.
31. Describe the cavities of the nostrils, and the sinuses connected
with them. What is the object of the great extent of surface iu these
cavities? Describe the lower jaw.
32. How many distinct structures are there in the teeth? What
is their arrangement? How does a tooth differ from a bone?
33. What is the reason for this difference? What is the necessity
for having a second set of teeth? Describe the hyoid bone, its position, and its connections.
34. Mention other bones which, like this, are not directly connected with the bones of the skeleton. Of how many bones is the
spinal column composed? Acting as the great pillar of the body, what
does it support? What is the pedestal on which it stands, and in what
manner is this pedestal made firm? While this column is thus firm,
it needs to be flexible —how is this accomplished?  Notice its different degrees of flexibility in different portions of it. Why is there so
little motion in that portion that supports the framework of the
chest?
35. Besides serving as a firm pillar and a flexible chain, what other
purpose does the spinal column fulfil? Describe a vertebra.
36. By what are the vertebra bound together? Describe the canal
in this column for the spinal marrow. What is the arrangement for
the nerves that pass from it? How are the cartilages arranged?
37. What two purposes do they subserve? What is there in the
shape of the spinal column that acts as a safeguard against shocks to




340                      QUESTIONS.
the brain? What are now the three objects secured in the structure
of the spine?
38. Describe the contrivance at the top of it, as represented in
Figs. 14, 15 and 16. Compare this with the mounting of a telescope.
XWhat is the difference in the two cases?
39. By what arrangement is the freeness of motion in the neck of
birds made consistent with the security of the spinal marrow?
40. What is there peculiar in the spinal column of quadrupeds?
What is the paxy-waxy? How are the vertebrae of fishes constructed
and arranged?
41. How is the great flexibility of the spine in reptiles secured?
How in the neck of the giraffe?
42. Describe the arrangement of the breast-bone, the collar-bone,
and the shoulder-blades. What is the use of the collar-bone, and what
are its variations in different animals? How does the shoulder-blade
differ from all other bones in the body?
44. Why is the socket of the shoulder-joint so shallow? Describe
the arrangement of the radius and ulna, and the manner in which
such free and varied motion is given to the arm. Describe the three
parts of the hand?
45. Describe the ligaments that bind the bones of the hand together.
46. WVhat is the principal object aimed at in the construction of the
lower extremity? What in the upper? Describe the thigh-bone.
47'. What is the patella?  What purposes does it answer?  What
part of the foot is formed by the tarsus? What part by the metatarsus? How many bones are there in the toes? How many in the
whole foot? What object is secured by having so many bones in the
foot? Why is the foot arched?
48. Describe its movement in walking. With what are the ends
of the bones tipped, and why? What is the arrangement of the membrane that lines the ends of the bones?
~0. What contrivance is there in the knee-joint, and in the articulation of the lower jaw?
CHAPTER V.
50iO. Give the summary in regard to the action of the muscles, and
their nervous connections.
51. What are the tendons? What is said of the relation they
bear to the muscles-their shape-their mode of union with muscles
and with bones-their strength-and their size?
42. How are the muscles and tendons arranged in reference to con



QUESTIONS.                        341
venience and beauty?  Illustrate by the arm and the hand. Illustrate
the application of the first kind of lever in the action of muscles.
53. So also of the second kind.
54. And of the third kind. Which kind is most frequently used in
the body?
55. What two different objects are aimed at in the application of
these two levers? Illustrate by examples of the second kind of lever.
56. Illustrate the same by examples of the third kind.. What is
the difference between the motion of the forearm on the arm, and the
motion of the lower jaw, in the application of the principles alluded to?
5'7. Show how quickness is secured at the sacrifice of power in the
case of the biceps muscle, as illustrated in Fig. 33. Under what mechanical disadvantage do most of the muscles act, as represented in
Fig. 34.
59. Show by this figure how quickness of movement is gained in
this case. Why is the muscle, the deltoid, whose action is represented
in this diagram, so large?
60. How is the mechanical disadvantage, which thus results from
the oblique action of the muscles, in part obviated? Illustrate by Figs.
35 and 36. Describe the agency of the patella in this respect.
61. To what extent is the pulley used in the arrangement of muscles? Show the application of the pulley, as seen in the ankle.
62. Describe the pulley arrangement of the digastric muscle. What
is the necessity for such an arrangement?
63. What other office does this muscle perform, besides drawing
down the lower jaw, and how does it do it? Describe the muscles that
move the ball of the eye.
64. What is said of the actions of opponent muscles?
65. Give some examples of the tonic contraction of muscles.  What
is the cause of wry neck, and of squinting? Illustrate the compound
action of muscles by Fig. 32. How does variation in the degree of the
contraction of muscles affect the variety of motion? What organ
peculiarly exemplifies variety in muscular action?
66. Give a general description of the muscles of the body as exhibited in Figs. 41 and 42.
70. What other parts besides the bones are moved by muscles?
How are the muscles arranged in reference to convenience and symmetry? Describe a peculiar arrangement of tendons and muscles in
the sole of the foot. Describe the arrangement of tendons represented
in Fig. 43.
71. Describe the operation of the toggle-joint. Give examples of
the application of this operation in the action of muscles.
72. How many muscles are there in the hand and arm? What
is said of the extent of the variety of their action? What is the muscular sense? Illustrate the operation of it in various ways.




342                      QUESTIONS.
CHAPTER VI.
74. By what alone are thought and feeling expressed? By what
mode of muscular action are thought and feeling mostly communicated? What relation has writing to this mode of communication?
Describe the muscles of the face with the action of each as exhibited
in Fig. 45.' 6. Describe the muscles about the mouth, as shown in Fig. 46.
7 7. In what way is the expression of the face made the same in its
two halves?
78. Explain the agency of various muscles-the frontal-the corrugator supercilii —the superbus. What is the action of the muscles in
quiet sorrow?
79. Is there commonly any one. muscle devoted to the expression
of any one emotion or passion? Does the same muscle often take a
part in the expression of various emotions? What is their state in the
expression of a calm pleasure? Illustrate the agency of the muscles of
the eyeball in expression. What is said of the action of the oblique
muscles?  Why is the intoxicated man apt to squint and see double?
Why does he raise his eyebrows in the effort to keep his eyes open?
What other parts besides the face are brought into action in the lan
guage of the muscles.
80. What is said of the action of the rest of the body in expression?
What muscles of the body sympathize most with those of the face in
expression? Give examples in illustration. Explain the expression
of the countenance, as seen after death.
CHAPTER VII.
81. Give a summary of the processes of digestion.
82. Of what substances is the body of a tooth composed, and how
are they arranged? What are the different shapes of teeth, and for
what different purposes are they fitted? How do the teeth of carnivorous animals differ from those of the herbivorous? How does the
motion of the lower jaw differ in the two classes? What is the shape
of the teeth in the insectivorous? What in the frugivorous?
83. What is the peculiar arrangement of the enamel in the teeth
of the herbivorous, and for what purpose? What can be inferred
about an animal from an examination of his teeth? Why is man said
to be an omnivorous animal?
84. Why are his tearing teeth less in length and in power than
those of carnivorous animals? What has the common whale instead
of teeth? What is the purpose of the arrangement?




QUESTIONS.                       343
85. What supplies the place of teeth in birds? What is the use of
the saliva? Describe the situation and arrangement of the glands that
supply this fluid.
86. How much saliva is secreted by the salivary glands during a
meal?  Why is more saliva than usual needed when one is speaking?
What effect does motion of the mouth have on the secretion? How
are these salivary glands affected by tobacco-chewing? Explain the
influence of sympathy in the secretion of saliva. What are the two
kinds of fluid secreted by the salivary glands, and what is the purpose
of each kind?
87. Describe the various parts engaged in the act of swallowing, as
represented in Figs. 54 and 55.
88. Describe the arrangement of muscular fibres in the aesophagus.
89. What is the character of the gastric juice? By what is it
formed?
90. Describe the appearance of the mucous membrane of the stomach, as seen by Dr. Beaumont, in the case of Alexis St. Martin. To
what is the amount of gustric juice proportioned? What is the effect
of stimulating the stomach to too large a secretion of it from day to
day? What is the nature of its action on the food? How is the application of it to all portions of the food secured? Describe the arrangement of the muscular fibres of the stomach, and the manner of
their action.
91. What is the chyme?  What is the arrangement of the valve
called the pyloruss? When is the pylorus especially in action? If
there be difficulty in digesting the food, what is the effect on the action
of this valve? What is the true character of the process?
93. What is the consequence if fresh food be introduced into the
stomach while the process is going on? Why is the practice of eating
between meals a bad one? Why does eating fast, do harm? What
effect has great variety in food? How does exercise affect digestion?
Relate the experiment with the two dogs, and state what it proves.
94. What shows that hunger does not arise from emptiness?
What that it does not arise from the irritation of the gastric juice?
What is the cause of hunger?  What is the seat of the sensation?
Upon what does the degree of hunger depend? What must be the
state of the stomach to have this sensation exist?
95. How do mental impressions sometimes destroy the sensation
of hunger? What is the cause of thirst? Where is its seat? Describe the arrangement of the digestive organs as seen in Fig. 60.
96. W'hat are the uses of the mesenterv?
97. Where are the bile and the fluid secreted by the pancreas
mingled with the chyme?
98. What is one of the offices which they execute? What is the
chyle? What are the lacteals? What glands do they enter? After




344                      QUESTIONS.
passing on from these glands, into what duct do they empty the chyle?
What is the size of this duct, and where does it pour its contents?
99. Describe the operation of the suction power at the mouth of
the thoracic duct. What becomes of the chyle thus forced into the
blood? What is the general rule by which the variation in the digestive apparatus in different animals is governed? Exemplify by a comparison between herbivorous and carnivorous animals. What is the
length of the alimentary canal in the lion?  What in the sheep?
What in man? In what animals is the stomach most complicated?
100. Describe the apparatus of digestion in the sheep, and its successive processes. Which of the four cavities in the sheep's stomach is
the real stomach? Into which cavity does fluid matter always go?
What is the arrangement when the animal is suckling?
102. Describe the digestive apparatus of birds as exemplified in
the turkey. What circumstances govern the variation of the digestive
organs in different animals? What is true of the stomach in the lower
orders of animals? What peculiarity is there in the Hydra in regard
to its stomach?
CHAPTER VIII.
105. What are the different parts of the apparatus of the circulation? Describe the agency of each in circulating the blood.
106. What relation does the heart bear to the rest of the circulating apparatus? Wheat is the difference between the arteries and the
veins in their structure? What two reasons are there for this difference?  What is the pulse? How do the arteries and veins differ in
the mode of their division?
107. How does the venous system differ from the arterial in capacity? How in regard to rapidity of flow of the blood? Describe the
valves in the veins.
108. Why are these valves needed? Why is it more dangerous
to wound an artery than a vein? Give some examples, showing how
on this account the arteries are seated more deeply than the veins.
Where are the arteries superficially situated?
109. What is the proper way to stop bleeding from an artery?
110. What is an aneurism? When a ligature is tied around the
artery above the aneurism in a limb, how is the limb to be supplied
with blood? What is the chief agent in the circulation of the blood?
How can you illustrate the contraction and the dilatation of the heart?
111. What phenomena show that the blood-vessels exert an active
agency in circulating the blood? How does the circulation through
the liver show that the capillaries are active agents in circulating the
blood?




QUESTIONS.                       345
113. Why are the veins generally full of blood after death, while
the arteries are nearly empty? What is the origin of the term artery?
Why do we not in common language speak of the blood as running in
the arteries as well as in the veins?
114. What is the color of the blood in the arteries?  What color
has it in the veins? Where is it changed from red to purple? What
other changes besides that of color take place? What would be the
consequence if the dark venous blood should be sent to the brain?
Where is the change in the blood from purple to red effected? How
is the apparatus arranged so as to send the purple blood to the lungs
to be changed? Explain the diagram showing the plan of the two
circulations?
115. What is the difference in the two circulations as to the color
of the blood in the veins and the arteries?  What is the difference
between the change of the blood in the capillaries of the lungs and
that which takes place in the capillaries of the general system?
116. Describe the parts of the right half of the, heart as represented in Fig. 70. Describe the manner in which the auricle and
ventricle, with the valves, act. Give the illustration as represented in
Fig. 71. What is the difference in size and strength, between the
auricle and ventricle? What is the size of the heart?
1 18. Describe the arrangement of the valves of the aorta. Describe
the special provision to prevent leaking in these valves. How are the
walls of the heart supplied with blood?
120. Describe the valves between the auricles and the ventricles.
Why are they regulated by muscles? Why are there no valves where
the blood pours into the auricle from the venae cave? Describe the
parts of the heart as represented in Fig. 74.
122. Describe the circulation as given in the map of the heart in
Fig. 75.
123. Describe the situation of the heart and its blood-vessels, as
represented in Fig. 76.
124. What is the difference between the two sounds of the heart?
What is the cause of the first sound? What of the second? How is
the pulse produced? Explain the impulse of the heart against the
chest.
125. Explain the plan of the pericardium.
126. Has the heart any repose? Give some calculations as to the
amount of work it does in a lifetime.
CHAPTER IX.
127. What two objects are effected by the respiration? Of what
are the lungs composed? To what is their spongy lightness owing'?




346                       QUESTIONS.
How minute are the air-cells or vesicles? In what way is the change
produced by the air in them upon the blood?
128. Describe the arrangement of the larynx, the trachea, the
bronchi, and the lungs, as exhibited in Fig. 79. How are the heart and
the lungs arranged in the chest?
129. What is the pleura? Why are the lungs not fastened to the
walls of the chest?
130. Describe the manner in which the air is made to enter the
chest in breathing. Describe the framework of the chest, as represented in Fig. 80. How are both iightness and strength secured in
this structure'! Why are the ribs joined to the breastbone by means
of cartilages?
131. What is the chief connecting material of this framework?
What is the diaphragm, and how is it arranged?
1 32. How does the diaphragm act? Describe inspiration and expiration as illustrated by Figs. 81 and 82.
134. In what way do other muscles, besides the diaphragm, act
in respiration? Describe their arrangement and action, as represented
in Fig. 83.
135. What is the arrangement of the muscular fibres between the
ribs, and their mode of action? In what directions are the ribs moved
by the muscles in the neck and between the ribs? Do these muscles
act much, if at all, in ordinary easy respiration? Under what circumstances do they act strongly? If air were admitted to the outside of
the lungs by openings in the walls of the chest, what would be the
result?
136. How are the blood and the air kept from mingling in the
lungs, while they are brought so near together that the air changes
the blood? What experiment shows that blood can be acted upon by
air through pores?  How important is the office of the air-cells?
What provisions are made for securing to them sufficient room under
all circumstances? Illustrate by reference to the state of things in
violent exercise.
137. If the expansion of the chest be restrained in any way, what
influence is exerted upon the air-cells? In what two ways does violent
exercise injure the lungs when the chest can not be well expanded?
138. What is said of the influence of compression of the chest in
the production of disease in the female sex? What is said of the extent to which compression of the chest is often carried? What is said
of the gradual moulding of the chest by continued compression during
its growth?
140. How is death produced in drowning? How is water prevented
from getting into the lungs in any quantity? If arterial blood could be
supplied to all the organs while the breathing is stopped, what would
be the result? What contrivance has the whale for this purpose?




QUESTIONS.                      347
141. What is the arrangement of the gills of a fish? By what
experiment can you prove that it is the air in the water that acts on
the blood in the gills, and thus keeps the fish alive? Why can not
the fish use air that is not mingled with water? What provision in
the land-crab enables him to live in air as well as in water? Describe
the arrangement of the gills in the lob-worm, and the larva of the
May-fly.
142. How are the respiratory organs arranged in insects? What
is the effect of covering their stigmata with varnish? For what two
purposes is the apparatus of respiration largely developed in birds?
What special arrangement is there for securing lightness?
144. By what experiment can you show that carbonic acid is
thrown off from the lungs? What are the components of the air, and
what is their proportion? Which of these is essential to life? Why
would it not be- well to breathe pure oxygen alone? Where has it
been supposed till recently that the oxygen of the air unites with carbon to make carbonic acid? Where does this union take place?
What facts settle the last question?
146. Does the change effected by the air upon the blood in the
lungs take place to some extent, when blood drawn from a vein is exposed to air? What experiment illustrates the manner in which the
air acts on the blood in the lungs?
147. How much carbon is contained in the carbonic acid thrown
off from the lungs in twenty-four hours? What effect does this. gas
produce upon the health if ventilation be imperfect?
148. What becomes of the carbonic acid thrown off from the
lungs of animals? How is the air replenished with oxygen? How is
the equilibrium preserved in different climates? What effect has
light upon the discharge of oxygen from the leaves of plants?
149. By what process is the heat of the body maintained? Trace
its analogy to ordinary combustion. What was formerly supposed in
regard to the place of the production of animal heat? What objection
was made to this supposition? Where was it at length discovered
that the heat is made?
150. What are the three sources of fuel for keeping up the animal
heat? Why is so large a quantity of oily food eaten in cold climates?
How do cold and tropical climates differ in the provisions of nature in
this respect? How is the use of fat in maintaining heat exemplified in
hibernating animals? Whence comes the heat produced by exercise?
Why is heat in different animals proportioned to their degree of activity?
15i1. Contrast the warm and cold-blooded animals in this respect?
152. Whlat is the ordinary temperature of the human body?
What is essential to comfort as to temperature in man? Detail experiments which show how high a degree of temperature can be borne.




348                      QUESTIONS.
How are the evil effects of excessive heat in such cases chiefly prevented?
153. How much does the state of torpidity vary in different animals? On what does the degree to which a deprivation of air can be
borne depend?
154. How far are the chemical changes described in this chapter
dependent on nervous action?
CHAPTER X.
155. By what is the building and repairing of the body done?
Have the Vessels by which this is done, the power of selecting their
material from the blood? Give examples of the co-operation of the
formative vessels in their work. How is the concert of action in these
vessels illustrated in the definite but various shapes of the structures
which thev make?
156. Illustrate the agreement necessary between different neighboring sets of formative vessels in the process of growth. Illustrate the
wonderfulness of the concert of action in the formative vessels, when
there is a change of action. How is this exemplified in certain animals,
as the frog?
158. Describe the agreement of action seen in the successive
changes that take place in the formation, discharge, and healing of an
abscess.
i59. How many kinds of waste particles are there? By what absorbents are those particles taken up that can be used again?
160. What organs probably fit them to be used again as a part of
the building material?  Where is the lymph, which they compose,
mingled with the blood? By what are the particles that are wholly
useless absorbed? By what organs are they excreted or thrown off
from the body? Do these various organs excrete different parts of this
waste?
16~1. Give some examples in which other functions besides excretion are performed by the same organ. What are the various functions of the skin? Describe its structure to show how well it is fitted
for. these functions.
162. How extensive is the tubing of the sweat-glands?
163. What is the difference between insensible and sensible perspiration? What are the sebaceous glands? What purpose do they
serve?  Where are they most abundant?  Upon what does the
rapidity of the change constantly going on in the body chiefly depend?
Which has the most influence on this change, mental or bodily
labor?
16'4. Illustrate the influence of activity on this change by a com



QUESTIONS.                       349
parison between the frog and the canary bird. Illustrate the same
influence by a comparison between different parts of the body.
165. What is said of the mingling of life and death in the changes
of the particles?
CHAPTER XI.
165. By what are all the minute operations of the system performed?  How do the cells differ from the cells in the cellular
tissue? What do these cells contain? WVhat is to be said of their form?
166. Describe them as seen in the blood. Of what are the solid
parts of the body composed?
167. How do the cells appear as seen in the Hydra? Upon what
does the character of many of the textures of the body depend? What
is the chief difference between the various glands of the body? Upon
what do the colors of various parts depend? Illustrate the selecting
power of the cells.
168. WVhat is said of the changes that take place in the contents
of the cells? How many kinds of cells are there in the blood? What
gives the red color to the blood? What are two of the offices of the
colored cells?
169. How does their amount vary in different animals, and in
different individuals of the human race? Describe by the figure the
manner in which absorption is performed on the surface of the mucous
membrane in the bowels.
170. Describe in like manner secretion by Fig. 102.
1 71. How many fibrillce are there in a muscular fibre? What is
each one of these fibrilla? What takes place in them when the muscle contracts? What is the cause then of the swelling out of a
muscle when it acts? How minute are the cells in muscles?
172. What solid animal deposits are made by cells? Describe the
arrangement in the enamel of the teeth.
173. Of what are the nerves composed? What has been found in
regard to combinations between the tubuli of the nerves? How are
these tubuli made from cells? What is the extent of the agency of
the cells? In the formation of every animal what precedes the appearance of any diversity of parts
1 74. Describe the arrangement of the contents of an egg.
175. Describe the succession of processes that take place in the
yolk preparatory to the formation of the bird.
176. From what material are all the parts of the bird made?
What is the grand distinction between organized and unorganized
substances? What comparison is made between gravitation and celllife? Compare the exhibition of the Creator's power in the minute




350                      QUESTIONS.
and in the large operations of nature. What comparison can you
make between the beauty of nature as seen by the naked eye, and its
inner beauty revealed by the microscope?
CHAPTER XII.
178. How far are the functions of nutrition alike in animals and
plants?
179.  Through what system are the uses for which the body is constructed secured? Why are the functions that are performed through
the nervous system, called functions of animal life? Why are they
also called functions of relation? Through what intermediate instrument does this system perform its functions?
180. How does this system vary in complication in different animals'? How much is learned through the nerves and their subordinate organs, the organs of the senses? What are the three parts into
which the nervous system may be divided?
18 1. What three things are necessary to sensation? Illustrate the
necessity of each. What three things are necessary to voluntary motion? Describe the arrangement of the parts of the nervous system as
represented in Fig. 110.
183. Describe the arrangement and structure of the brain as represented in Fig. 111.
184. What part of the nervous system is most immediately essential to the continuance of life? And why? Illustrate by facts. What
are the convolutions of the brain?
185. Describe the membranes of the brain-the pia mater-the
dura mater-the arachnoid. What is the arrangement of the gray and
the white substance? Does the arrangement of the convolutions favor
the idea of the phrenologist? Of what is the white substance of the
brain composed? What function is performed by it?
187. What tubuli transmit impressions from the brain? What
transmit to it? What is said of the size of the tubuli? What is the
function of the gray substance? In proportion to what does its amount
vary in different animals? Is there gray matter at the extremities of
the nerves?  With what are the cells in the gray substance mingled?
What is said of the necessity of a supply of arterial blood to this substance?
188. How does the arrangement of the gray and the white substance differ in the brain, in the spinal marrow, and in the ganglions?
What are ganglions? What are plexuses? Why is the gray matter
so largely supplied with blood?
189. What is said of the manner in which the nerves terminate in




QUESTIONS.                       351
the organs of the body? Where are the Pacinian corpuscles mostly
found? Describe their structure. What do we know of their use?
190. What is there that is wonderful in the healing of a divided
nerve? What do the observations of M. Sequard show?  What fact
was proved by the experiments of Dr. Haighton? What nervous
changes occur when a union takes place between parts that do not
belong together?
192. Do the same nerves answer for sensation and for motion? In
what part of the body are nerves of different kinds kept separate?
How is it in all other parts? What is the arrangement of the nerves
that branch out from the spinal marrow? What two purposes do the
two roots of each nerve serve? How is this ascertained?
193. Are there different nerves for different kinds of sensation?
How is it in the eye? How in the nose? What is a nerve of common
sensation? What is a nerve of special sensation? Is each nerve fitted
for its own peculiar office? Illustrate by reference to the nerves of the
eye. Notice particularly the effects produced, if the nerve of common
sensation in the eye be paralyzed.
194. Why are different parts of the body endowed with different
degrees of sensibility? What organ is more sensitive than any other?
How much sensibility have the muscles? How much have the bones?
What fact is related to show the use of the sensibility of the skin in
preventing injury? What change takes place in the sensibility of internal parts when they become inflamed? What benevolent purpose
is there in this?
195. Does a nerve, as a matter of course, have sensibility? What
is true of the brain in relation to sensibility? What of the heart? Is
the heart well endowed with nerves? With what nerves is it endowed? What is said of the nerves of motion in the face? What are
the appearances when the nerve of expression in the face is paralyzed?
Why is this nerve called the respiratory nerve of the face? How are
the motions of expression in the face connected with the motions of
respiration? Describe the results when this connection is broken by a
paralysis of the respiratory nerve of the face.
197. How many. different nerves are devoted to the eye? What
are their different offices? Of nerves going to the same part may one
be palsied while another is not? Give some illustrations. Give the
case related by Sir C. Bell.
198. Are the nerves of different kinds all alike in their structure
and composition? Why can not the impression producing sensation
be transmitted by the same nerve with the impression producing
motion? In what direction is nervous action in sensation? In what
direction is voluntary motion?
199. Does voluntary motion occur sometimes in consequence of
sensation, and sometimes not? Illustrate this. Give the resemblance




352                      QUESTIONS.
of the nervous system to a telegraphic apparatus. What is true of
motion caused by mental emotions? Give some examples of muscles
that are wholly involuntary, and of muscles that are partially so.
200. What is the difference between an excitor and a motor nerve?
Illustrate by reference to the respiration-and the action of the muscular
coat of the stomach. Why is the action of these two classes of nerves
called a reflex action?  Do we know what is transmitted through the
trunk of a nerve? Does reflex action ordinarily occur without positive sensation? Under what circumstances is sensation connected with
it? Illustrate by reference to the action of the respiratory muscles.
201. State the two separate functions of the spinal marrow. By
what arrangement are they performed? Illustrate the modes of effecting sensation-motion-and reflex action.
202. How does the brain differ from the spinal marrow as to intervals of rest? Illustrate the continuous action of the spinal marrow, as
seen in the operations that go on in the system when the brain is
asleep, or is torpid with disease. Besides these operations, mention
some of the motions that can be excited through the agency of the
spinal marrow independent of the brain. Cite some of the facts to
show that voluntary muscles act involuntarily more often than is
commonly supposed.
203. Explain the involuntary action of muscles. in walking and
other like acts. What was formerly supposed in relation to the importance of the brain as a central organ of the nervous system? How
do we know that the brain is not directly essential to the maintenance
of life?
204. What are the functions most essential to life? Upon what
part of the spinal marrow do these depend? Illustrate the extent to
which the different parts of the spinal marrow are independent of each
other. Is there any sensation independent of the brain?
205. Why is the system of nerves, of which I have treated in this
chapter, called the cerebro-spinal system? What other system is
there? What are its purposes?
CHAPTER XIII.
205. What principles apply to the construction of the apparatus
of the voice?
206. Into what two kinds are wind-instruments divided? Explain
the manner in which the variation of note is produced in those of the
first kind, by reference to the flute and the trombone.
207. Illustrate the same point in the operation of the flute-stop of
the organ. What influence does the width of the vibrating column of




QUESTIONS.                        353
air have upon the note? How is the note varied in those wind-instruments in which the length of the column of air can not be altered?
What are some of the wind-instruments of the second class? How is
the sound produced in these? How is the note varied? Illustrate by
reference to the reed-stops of the organ. How are the various notes
produced in the clarionet?
208. Trace the analogy, in the application of the principles of
musical sounds, between the vibrating column of air, the reed, and the
strings in such instruments as the piano and violin. Explain the relation of the tube of the reed-instrument to the reed.
209. What is the trachea, and of what is it composed? What is
the larynx?
210. Describe the parts of the larynx as represented in Fig. 122.
Describe particularly the arrangement of the arytenoid cartilages and
the vocal ligaments, as represented in Figs. 123 and 124.
211. Describe, by means of Fig. 123, the manner in which the
different notes of the voice are produced.
212. How do we know that the lower ligaments are the true vocal
chords? Apply now the principles regulating the variation of note in
common musical instruments to the vocal apparatus. Give Magendie's experiment.
213. What is the tube of the vocal apparatus, which answers to
the tube of a reed-instrument?  How many outlets has it?  From
which does the voice generally issue? How is it in humming? What
influence do the cavities of the nose have on the voice?
214. In what two ways is the size of the vibrating column of air
in the tube of the vocal instrument varied? What influence does this
tube have on the character of the voice? How would the voice sound
if it should come directly from the larynx, instead of passing through
the tube attached to it?
215. What is said of the variety and precision of the action of the
muscles in the modulation and articulation of the voice? How much
do the ligaments vary in length in producing all the variety of notes
of which the voice is capable? Give the calculation in regard to the
minuteness of the muscular action in passing from one note to another.
What is said of skill in managing the muscles of the chest in speaking
and singing? Give the illustration of the bag-pipe.
21 6. What is one of the chief causes of " throat disease" in public
speakers?  What circumstances tend to produce this disease? In the
articulation of how many letters is the tongue the chief agent? State
some facts to show that the tongue is not so essential to the power of
speech as is commonly supposed.
2.17. What letters are chiefly formed by the teeth? What is lisping? What letters are chiefly formed by the lips? Why do children
use labials so early and so freely? Of what are there terms of endear



354                      QUESTIONS.
ment composed in most languages? Illustrate the agency of the nasal
cavities in articulation.
218. Explain the difficulty called speaking through the nose.
What is said of articulation in whispering? How is the variation of
note in whispering caused? Mention some of the attempts that have
been made to imitate the articulation of the voice by mechanism.
CHAPTER XIV.
219. How is sound produced? When is sound musical, and when
discordant? What is said of the transmission of sound? What of its
reflection?
220. Illustrate the influence of the reflection of sound in accumulating it.
221. What is true of the facility of the transmission of sound
through solids and fluids as compared with air? Illustrate it by facts.
How is the fact that sonorous vibration does not readily pass from one
medium to another, illustrated? Upon what does the degree to which
the vibration is lessened in passing from one substance to another,
depend?
222. In what cases is the intervention of a membrane of essential
service, and why? Give a general description of the process of hearing. Describe the apparatus of hearing, as represented in Fig. 132.
223. What is the object of the external ear? What is the use of
its ridges and prominences? What is said of the external ear of animals in comparison with man?
224. Describe the tube of the ear. By what two means is it
guarded against intruders? Describe the drum of the ear and the
little bones. What is the arrangement of these bones? What are
their connections, and how do their muscles act upon them?
225. How does the cavity of the tympanum communicate with the
mnouth, and why? What part of the ear is the essential part of the apparatus? How much of the apparatus may be destroyed without
entire loss of hearing?
226. Describe the parts of the labyrinth. WVhy is it better that
the vibrating substance in the labyrinth be a fluid than a solid or a
gaseous substance.
29T. Describe now, step by step, the process of hearing. Is all our
hearing done in this way?
228. What is said of the two ends of the apparatus of hearing?




QUESTIONS.                       355
CHAPTER XV.
228. Into what two parts may the process of seeing be divided?
What principles govern the construction of the mechanical part of the
apparatus? What is the object of its arrangements? How is the
second part of the process executed? How does the transmission of
light resemble that of sound?
229. What is the refraction of light? Illustrate by Fig. 136. How
are the rays bent in relation to a perpendicular when they pass from a
denser into a rarer medium'? How, when they pass from a rarer into
a denser?
230. How are the rays refracted when they pass through a medium which has a concave surface?
231. How many coats has the eye? Describe the arrangement of
the parts of the eye, as represented in Fig. 139. What is the use of
the sclerotic coat? How is the cornea fitted into it?
232. What is the color of the choroid coat, and to what is it owing?
Of what is the retina chiefly composed? What are the three humors
of the eye? Describe the chamber in which the aqueous humor is
What is the consistence of the crystalline humor or lens? Describe
the vitreous humor. Why is it called vitreous? Describe the various
parts as they are more minutely delineated in Fig. 140. How is the
aqueous humor formed? How is it continually changed?
233. Describe the membrane called the conjunctiva. What are
the ciliary processes? Describe their arrangement. What is their use?
2.34. How are images of objects formed upon the retina?  How
can the fact that such images are formed, be proved?
235. Why are these images inverted? On what does the color of
the iris depend? What is the principal office of the iris? By what
arrangement of its muscular fibres are its motions effected? What is
the office of the crystalline lens? What is its shape? Its structure?
236. What two purposes does the choroid coat serve?  What is
the state of the choroid coat in the albino? What gives the bright
red or pinky hue to the iris in his case? How does the color of the
choroid coat vary in different animals? What is the character of the
retina, and its office? Trace the analogy between the optic nerve and
the other nerves of sense? What resemblance is there to the nerve of
touch in its termination?
237. What is the defect in the operation of optical instruments,
called spherical aberration, and how is it obviated in the eye?
238. WVhat is the difficulty in the operation of a common lens,
called chromatic aberration? How in the eye? Contrast the eye with
the telescope in regard to the facility with which the eye accommo



356                     QUESTIONS.
dates itself to objects at different distances. In what two ways is this
accommodation effected?
239. By what defects in the structure of the eye in the nearsighted is this power of adjustment counteracted? How is this difficulty obviated? What is the difficulty in the far-sighted? How is it
obviated?
240. What is necessary to single vision in regard to the two
images formed in the two eyes? When are the two images in the
eyes alike.
241. In what cases are they unlike? Relate the experiment given
in explanation. How is it that in such a case, while there are two
images, and therefore two impressions sent along the two optic nerves,
vet the impression on the mind is single? Explain Professor Wheatstone's stereoscope.
242. What is the visual angle? Can we get a correct idea of magnitude by the visual angle alone? Illustrate by the Figure.
243. What circumstance must be known in regard to an object, in
order to have our estimate by the visual angle correct?
244. Illustrate the manner in which we get ideas of the magnitude
of objects by comparison. Show how we sometimes are made aware
of our dependence on this sort of evidence. Explain the use of the
muscular sense in acquiring an idea of the size and distance of objects.
Do all the images formed on the retina transmit impressions to the
mind? Illustrate in reference to ordinary vision by an experiment.
245. What is the "Blind Spot "?
246. How is the eye situated so as to protect against injury? How
does the cushion of fat on which it rests serve to protect it? In what two
ways does the muscle that closes the eyelids serve as a protection to
the eye. How is it protected by the eyelashes?  How by the eyebrows? How are the eyelids constructed in reference to the protection of the eye?
247. How do the tears serve as a protection? Why do fishes have
no tear-apparatus? Describe the arrangement of the tear-apparatus.
248. Why do the tears overflow the edges of the eyelids when
they are abundant? What arrangement of glands is there on the eyelids? What two purposes does the oily substance formed by them
serve? How. are the tears conducted into the mouth of the ducts
when the eyelids are closed? Describe the nictitating membrane in the
eyes of birds.
CHAPTER XVI.
249. From what two sources are the rules of hygiene to be learned? How far is a knowledge of physiology necessary to a proper
understanding of these rules?




QUESTIONS.                       357
250. What division of topics should be made in the subject of
hygiene?
251. What points in the hygiene of digestion have been before
noticed? VVhat is said in regard to the amount of food needed by the
body? How can we know what this amount is? What errors are
committed in regard to quantity of food?
25 2. From what causes is too little food sometimes taken? WVhat
is said of the intervals between our meals? What is said of eating
regularly?
253. What of the different kinds of food? What of fruits?
What influence has the mind on digestion?
254. What is the general statement in regard to the hygiene of
respiration? In what two ways is the free access of the air to the
lungs interfered with? What general rule is given as to dress in
regard to the chest? In what ways does compression of the chest
occasion disease?
255. Why ordinarily is the influence of defective aeration (or airing) of the blood not appreciated? What is the office of the organs
of the circulation? Is the action of these organs ever violent and
tumultuous?
2,56. What influence has muscular exercise on the development of
the organs of the body? How is it a preservative against disease?
What is said of violent exercise?
25Z. What is the change going on continually in all parts of the
body? What two conditions are necessary to the proper performance
of this change?  What is said of the discharge of waste matter from
the system? What organs effect this discharge?
258. How much matter is discharged from the skin? How is the
animal heat produced? How does exercise increase it? What influence has the quality of the blood upon it?
259. What is essential to a comfortable temperature of the body?
When one is too much heated how is the extra heat disposed of?
What is the object in covering the body with clothing and in surrounding it with heated air? What is said of cold as a cause of disease? What are our means of guarding against cold?
260. How should we regulate the amount of clothing? What is
said of guarding against cold when the body is in a state of rest?
What is said of the weak suffering from  exposure to cold? How
should the shoes of delicate females be made?
261. Under what circumstances does cold act as a stimulant?
What circumstances are necessary to this result? What are the conditions on which reaction depends?
262. What rules should be observed in the use of cold bathing?
What are the best times for using it? What occasions the wear and
tear of the system? When is most of the repairing in the system done?




358                      QUESTIONS.
263. What is said of the relation of exercise to health?  What
effect has it on the muscles themselves? What on the other textures?
How does it prevent deformity?
264. What are the two causes of the common deformity of the
spine? Explain their action. Why is this deformity found so much
more often in females than in males?
265. How much influence has posture in producing it?  What
especially debilitates the muscles of the back in the female? Illustrate the necessity of having exercise varied-also of having it general.
266. What is said of gymnastics and calisthenics? What is said
of having the exercise habitual?  How does too much exercise do
harm? What is said of having the exercise agreeable?
267'. What is said of the hygiene of the senses? What is said of
the necessity of seasons of rest for the brain? What significant fact
in regard to insanity shows this? What is said of the conditions
under which the mind can perform much labor without harm?
26(8. What is said of overworking the brain during its growth?
What of the manner in which the child's mind is ordinarily exercised?
What two mental causes acting together injure the health and sometimes produce insanity?
269. What influence has the regulation of the passions on the
health? On what portions of the system do alcohol and tobacco
chiefly act? What is said of alcoholic stimulants?
270. Show how tobacco may act indirectly as a stimulant. What
are its effects on the system? To what class of persons is it especially
injurious? What is the evidence in regard to the influence of tea and
coffee?
27 1. What is said of emanations from filth as producing disease?
Give a summary of the chief causes of disease. Is disease commonly
produced by any one of these causes alone?
2,2. What is said of our control over these causes? What other
causes of disease are there? To what extent do they act compared
with those mentioned? How may we often escape their influence?
What is said of the comparative value of preventive and curative
measures? Illustrate the prevalent error on this point by reference to
consumption. From what does the common neglect of preventive
measures arise, and how can this be obviated?
CHAPTER XVII.
273. What is said of the brain as the organ of the mind? What
facts show that motion and sensation are dependent on the brain?
How does it appear that the mind thinks only by means of the brain?
How is life continued when sensation, motion, and thought are stopped




QUEST0ONS.                       359
by compression of the brain? How does the variation of the degree of
compression vary the effect on the mental functions?
27J. Of what is insanity always the result? How do moral causes
produce it? If the mind were separate from the body, could insanity
be produced in it? Can the disease in the organization in insanity, be
always discovered in an examination after death? Describe the situation of the brain and its immediate connections. What is said of the
face?
276. Illustrate the rapidity of the communication between the
mind and the different parts of the body. How does a child learn to
use its muscles?
2'7. What is said of the amount of knowledge acquired by the
child in the first year of his life? What is said of skill in the use of
the muscles? What is said of the training of the senses?
278. Illustrate the fact that the senses and muscles are mutual
teachers in their training. How does the dependence of the muscles
on the senses differ from that of the senses on the muscles? TWhat
fact illustrates the absolute dependence of the muscles on the senses?
In the education of the muscles and the senses, what is, strictly speaking, educated or trained? Illustrate by reference to the idiot and the
deaf-mute. Why does not the education of the muscles extend to
those that are involuntary?
279. What difference is there in the different stages of the train.
ing of the muscles in the degree of cognizance which the mind takes
of their action? Illustrate by reference to learning to walk, to read
and to sing. What part of the brain has an especial connection with
the mind?  What is the chief office of the cerebellum? Give the
evidence from comparative anatomy on which this point is settled?
281. What experiments lead to the same conclusion?  What is
said of the comparative amounts of the white and the gray substance in
the brain?
282. In what portion of the brain is the process of thinking carried
on? What is the facial angle? What is the difference in regard to
this between the skull of the European and that of the African?
What between the skull of animals and that of man?  What is the
common measure of this angle in ancient statues of deities and heroes?
283. What is said of the rule that the amount of intelligence, both
in man and in animals, is proportioned to the amount of the cerebrum?
284. What facts show that size is far from being the only measure
of power in case of the brain? In studying the comparative physiology
of the brain, what significant fact do we find when we come to pass
from the higher animals to man? Of what character is the mental
difference between them and man? What is said of the definiteness
of the distinction between man and animals? What note ought to be
made of this distinction by the comparative physiologist? What are




360                      QUESTIONS.
the three sources of our knowledge in relation to the connection of the
mind and the body? What is the consequence if we rely upon any
one of these alone?
285. What is the alternative to which one is driven, if he confine
himself to the evidence which physiology furnishes? What course
is commonly pursued by those who take this narrow view of the subject?  What is said of the distinction between organized and unorganized matter? What are the common suppositions in regard to the
endowment of organized or living matter? What is said of those
endowments of living matter that are connected with the nervous
system?
286. What question now arises in relation to intelligence in its
connection with matter? What does physiology show us in regard to
this connection? Point out the deficiencies of its teaching in relation
to the nature of this connection. What is the tendency of its presumptive evidence?
28". Looking at the subject solely in the light of physiology, what
would be the conclusion in regard to the dependence of mind on organization, when we observe the origin and growth of a thinking animal?
What bearing on this point has the fact, that the intellect grows with
the brain and appears at last to perish with it? What fact in comparative physiology is strongly adverse to materialism? In which direction, however, on the whole, does the evidence from physiology,
taken alone, preponderate?
288. State the ground of the great need which the physiologist
has of the evidence from other sources besides his physiology.
289. What is the testimony of consciousness in relation to the
independence of the soul in its action? What in regard to its responsibility for its acts? How far is this testimony acted upon by all, when
physiological speculations are left out of view? What does the evidence from consciousness show us in relation to the connection of the
mind with the material organization? To what alternative does it
drive us?
290. How is this testimony of consciousness treated by the
Bible?
291. Illustrate our dependence on the Bible for the proof of the
soul's immortality? How may the decrepancies in the evidence from
physiology in regard to the connection of the mind and the body be
cleared up?
292. What is said of the character of the evidence drawn from consciousness and Revelation? What is said of the presumptive evidence
from physiology in comparison with it? What is said of the present
moral tendencies of physiological investigations?




QUESTIONS.                       361
CHAPTER XVIII.
293. What was Lord Monboddo's idea of the development of man?
What recent theory has an analogy to this'? What is true of man and
animals in relation to instinct and reason?
2.g. Do we know what the nature of instinct is?  Which can be
understood best, the actions of instinct or those of reason? Illustrate
this point. What seems to produce the actions of instinct? What
influence does the intelligence of the animal exert upon them? What
is said of the invariableness of the actions of instinct.
295. Describe the nests of the Baya and the Tailor Bird. What is
said of the perfection of the actions of instinct? Why are the cells of
the honeycomb made hexagonal? Describe the arrangement of the
ends of these cells.
29r7. Give the fact stated in regard to the angle made by the surfaces at their ends. How is the perfection of the actions of instinct
seen in animals that live in communities? Describe the structure of a
wasp's nest.
298. Give the description of the habits of the beaver.
300. In what respect may instinct be said to be blind? Illustrate
by reference to animals that provide for a progeny which they are
never to see.
301. Why is it often difficult to distinguish between the results
of reason and those of instinct? What would be true of instinct if it
were at all rational? Under what circumstances is there perfection in
the actions of instinct? Under what circumstances does it fail? Contrast instinct and reason in this respect. Give some illustrations of the
characteristics of instinct alluded to. Give Mr. Broderip's account of
the beaver. If the beaver in this case had been guided by reason,
what would he have done?
302. How far is the care that animals take of their progeny governed by a blind instinct? What is said of the temporary character
of parental affection in their case? In what case is there no affection
at all?
303. What degree of intelligence is shown in the power of imitation in animals? How do animals show that they reason? How far
did the beaver, whose story is given in ~ 409, reason? How does the
character of the inferences made by animals differ from that of those
made by man? Illustrate by reference to Newton and his dog.
304. Of what are the inferences made by animals the results?
When the processes of thought in animals are extended and complicated, what is true of them? Illustrate by examples the extent to
which mental association may be carried in the animal.
306. How do animals learn the relation of cause and effect? Illus16




362                      QUESTIONS.
trate by examples. How does this knowledge of cause and effect differ
in man and in animals? Is the mental difference between man and
animals one of degree only?
307. What attribute constitutes the great superiority of the human
mind? Show how this attribute is the origin of language in man.
What is the character of the language of animals? Why can not they
have a language of arbitrary signs? What is the source of man's belief in a Creator? Illustrate this point. Is this belief implanted in the
mind?
308. What two suppositions have been offered in relation to conscience? What is said of the doubts which some entertain as to the
existence of conscience? What is true of those cases in which animals
seem to some to have a moral sense? Illustrate the fact that in common language we recognize the difference between man and animals as
to the possession of a conscience.
309. Give a summary of the mental differences between man and
animals. Give the gradations which we find in the nervous system as
we trace the animal kingdom upward.
CH IAPT ER XIX.
310. Mention some of the contrasts which we find on looking over
the human race. How many varieties of the race are commonly reckoned?
311. What are the characteristics of the Caucasian variety? What
are the characteristics of the Ethiopian varieties —the Mongolian-the
American?
312. What are the characteristics of the Malay variety? What is
said of the extent to which the race may be divided into varieties?
What is said of the way in which national differences are produced?
What is the opinion of most naturalists in regard to the production of
the races? What is the doctrine of Professor Agassiz and others?
State the grounds on which he bases his doctrine. What is his opinion
in regard to climatic and other influences? What is his opinion of the
history given in Genesis? Are the different branches of the race in
his view different species, or mere varieties? What is the distinction
between a species and a variety?
315. Mention the influences included in the expression, climatic and
other influences. What is said of the influence of climate? What is
the circumstance which has most influence in producing varieties in
man and in animals? What is included in the term domestication?
What is the precise question in regard to climatic and other influences?
316. Mention some facts that show that climate has a great influence on the color of the race. What influence do intellectual and
moral causes exert upon the shape of the head?




QUESTIONS.                       363
317. What is said of certain changes in form produced by causes
the operation of which we do not understand? What are the three
different types of form in the head stated by Dr. Pritchard, and by
what causes are they produced? State in regard to each:-the prognathous-the pyramidal-the oval.
318. Give some facts showing that these types are convertible into
each other. What is said of the insensible gradations by which the
varieties of the race pass into each other?
319. What effect has the influence of domestication on both man
and animals? What two objections are brought against the alleged
competency of climatic and other influences to produce the varieties
of the race? What great fact is a sufficient reply to these objections?
320. Apply this fact in explanation of the production of the varieties of the human race. What is said of the analogy thus drawn between man and animals, in comparison with that which Professor
Agassiz has tried to establish? What consideration weakens his analogy? If the climatic and other influences appear to any one incompetent to produce the varieties of the race, is he driven necessarily to
admit its multiple origin?
321. What is said of the occasional introduction of new causes by
the Creator? Upon what do our calculations upon the regularity of
nature depend? What is said of the change in the age of man effected
at the time of the flood?
3S22. What is said of the occasional appearance of new diseases?
What is said of the convulsions which have evidently taken place in
the earth? Does it make any difference to the argument, whether the
results came directly from causes, or from a chain of causes?
323. Apply the argument to the production of the varieties of the
race. What is said of the objection to the argument, that it is supposing a miraculous interposition?
324. Is the supposition thus made needed? What is said of it in
comparison with the supposition of Agassiz? On what principles is
the testimony of the Bible as to the origin of the race to be interpreted?
What are the main facts which it gives in relation to it? How is the
truth of its testimony confirmed? Of what force is analogical and
presumptive evidence in opposition to it? Is any fear to be entertained
in regard to bringing the Bible to the test of ascertained facts?
CHAPTER XX.
325. What is said of the diversity in the manifestations of life?
How is life always the same in relation to its origin? Remark on the
wonderful variety of results worked out by the vital force beginning
in a simple cell.




364                      QUESTIONS.
326. How is life always essentially the same in its processes as well
as in its origin? Do we know what life is? How does the vital force
differ from such forces as light, heat, and electricity, in regard to its
power of diffusion? How in regard to self-generation? How in regard
to the variety of its cffects?
327. Do we know whether life is one thing? What is said of the
supposition that the principle of life resides chiefly in the blood?
What are the relations that exist in living bodies between the laws
of chemistry and mechanics and those of life? Illustrate this point?
328. What is said of the materials of which the human body is
composed, and of the degree of heat in which they are kept? Show
the difference in the operation of heat on dead and on living matter,
as seen in the egg.
329. How is the power of the vital force exhibited in the uniformity of the heat of the body? What is said of the changes going on by
the operation of the vital force? Remark on the dormant condition of
this force in the case of seeds.
330. Remark on the analogy between the hibernation of animals
and the state of most of the vegetable world in winter. What portions
of the human system are some of the time dormant, and why? What
is the most mysterious circumstance in regard to the vital force? Show
how the soul and the vital force are two distinct, and, in some measure,
opposing forces. In what different senses are they both present everywhere in the system?
331. What is said of the development of the soul in the body?
What of the mystery of this connection? What is said of the limit of
the vital force? Has the vital force a natural limit?
332. What is the distinction between systemic and molecular
death? How may death begin in the circulating system?
333. Give the three classes of causes by which death may begin in
the respiratory system. Give examples of death beginning in the
nervous system.
334. Illustrate the fact that death is commonly a complex event.
What is said of the signs of death? What is said of the clearness of
the evidence in all ordinary cases in regard to the fact of death?
335. In the very few cases in which there is any doubt, what
course should be pursued? What light can physiology give us in relation to what is beyond this life? What is said of the conjectures on
this subject which its investigations may prompt?




GLOSSARY.
Ab-do'nen, (Latin abdere, to conceal.) The largest cavity of the
body, containing the liver, stomach, intestines, etc.; the belly.
Ab-duc'tor, (L. abducere, to lead away.) A muscle which moves
certain parts, by separating them from the axis of the body.
Ab-sor'bents, (L. ab, and sorbere, to suck up.) The vessels which
take part in the process of absorption.
Ab-sorp'tion. The process of sucking up fluids by means of an ailimal membrane.
A-ce-tab'u-lunr, (L. acetum, vinegar.)  The socket for the head
of the thigh-bone; an ancient vessel for holding vinegar.
Ac'id, Ac'etic, (L. acetumn, vinegar.)  Relating to acetic acid.
This is always composed of oxygen, hydrogen, and carbon, in the
same proportion.
Ac'id, Lactic, (L. lac, milk.) The acid ingredient of sour milk;
the gastric juice also contains it.
A-chil'les. A term applied to the tendon of two large muscles of
the leg.
A-cro'mi-on, (Gr. aKpoC, akros, highest, and duos, omos, shoulder.)
A process of the scapula that joins to the clavicle.
Ad-duc'tor, (L. adducere, to lead to.) A muscle which draws one
part of the body toward another.
Al-bu'men or Albumin, (L. albus, white.) An animal substance resembling white of egg.
At-bu'mi-nose, (from  albumen.)  A  soluble animal substance
produced in the stomach by the digestion of the albuminoid substances.
Al-bu'miun-oid substances. A class of proximate principles resembling albumen; they may be derived from either the animal or
vegetable kingdoms.
Al'i-ment, (L. alere, to nourish.) That which affords nourishment;
food.
Al-i-ment'a-ry Ca-nal, (from aliment.) The tube in which the
food is digested, or prepared for reception into the system.
Al've-o-lar, (L. alveolus, a socket.) Pertaining to the sockets of the
teeth.




366 6GLOSSARY.
An-oes-thet'ics, (Greek av, an, without: ataO7ata, isthesia, feeling.)
Those medicinal agents which prevent the feeling of pain, such as
chloroform, laughing-gas, etc.
A-nas'to-mnose, ((Or. ava, ana, through, and atoya, 8toma, mouth.)
The communication of arteries and veins with each other.
A-nat'o-tly, (Gr. ava, ana, through, and Troy, tome, a cutting.)
The description of the structure of animals. The word anatomy
properly signifies dissection.
An-i-mat'cule, (L. animal'culum, a small animal.) Applied to
animals which can only be seen with the aid of the microscope.
Animalculum (plural, aninmalcula) is used with the same meaning.
A-or'ta, (Gr. doprij, from adepetv. aeirein, to lift, to be lifted up.)
The largest artery of the body, and main trunk of all the arteries.
It arises from the left ventricle of the heart.
Ap-o-netu-ro'sis, (Gr. alto, apo, from, and vevpov, neuron, a nerve.)
The membranous expansions of muscles and tendons. The ancients called every white tendon neurovo, a nerve.
A'que-ous Hutntmor, (L. aqua, water.)  The watery colorless fluid
occupying the space between the cornea and crystalline lens.
A-rach'lnoid Mern'brante, (Gr. dipiXvr, arachne, a cobweb, and
etdoc, eidos, like,) An extremely thin covering of the brain and
spinal cord. It lies between the dura mater and the pia mater.
Ar'bor Vi'tae, (L. the tree of life.) A name given to the peculiar
appearance presented by a section of the cerebellum.
Ar'ter-y, (Gr. Cdp, aer, air, and rpeZtv, terein, to contain.)  A
vessel by which blood is conveyed from the heart. It was supposed by the ancients to contain air; hence the name.
Ar-tic-u-la'tion, (L. articulare, to form a joint.) The more or less
movable union of bones, etc.; a joint.
A-ryt-e'noid, (Gr. apvratva, arutaina, a ewer, and etuor, eidos,
form.) The name of a cartilage of the larynx.
As-phyxc'i-a, (Or. a, a, not, and abovSt, sphyxis, pulse.) Originally,
want of pulse; now used for suspended respiration, or apparent
death.
As-trag'a-lus, (Gr.) The name of a bone of the foot. One of the
tarsal bones.
As-sizn-i-la'tion, (L. ad, to, and similis, like.) The conversion of
food into living tissue.
Au-di'tion, (L. audire, to hear.) The act of hearing sounds.
Au'dti-to-ry Nerve. The special nerve of hearing.
Au'ri-cle, (L. auris, the ear.) A cavity of the heart.
Ax-il'la, (L.) The arm-pit.
A-zote', (Gr. a, a, not, and woa, zoe, life.) Nitrogen. One of the constituent elements of the atmosphere. So named because it will
not sustain life..




GLOSSARY.                         367
Bel-la-don/na, (It. beautifll lady.) A vegetable narcotic poison.
It has the property of enlarging the pupil, and thus increasing
the brilliancy of the eye.
Bi-cus'puid, (L. bis, two, and cuspis, prominence.) The name of the
fourth and fifth teeth on each side of the jaw.
Bile, (L. bills.) A yellow viscid fluid secreted by the liver.
Bronch'i, (Gr. ppoyxoc, bronkos, the windpipe.) The two great divisions or branches of the trachea.
Bronch/i-al Tubes. The smaller branches of the trachea within
the substance of the lungs, terminating in the air-cells.
Bronch-i'tis, (from bronchia, and itis, an affix.) An inflammation
of the larger bronchial tubes.
Bur'sae Mu-co'sa, (L. bursa, a purse, and mucosa, viscous.) Small
sacs, containing a viscid fluid, situated about the joints, under
tendons.
Cal-ca-re'ous, (L. calx, lime.) Containing lime.
Ca-nine', (L. canis, a dog.) Name given to the third tooth on each
side of the jaw; in the upper jaw it is also known as the eye-tooth.
Cap'it-la-ry, (L. capil'lus, a hair, capilla'ris, hair-like.) The name
of the extremely minute blood-vessels connecting the veins.
Car-bon'ic Ac-id, or Car'bon Diox-ide, (C02.) The gas
which is expired from the lungs.
Car'di-ac, (G(r. Kapcta, kardia, the heart.) The upper orifice of the
stomach near the heart; hence its name.
Car-niv'o-rous, (L. ca'ro, flesh, and vora're, to devour.) Subsisting upon flesh.
Ca-rot'id, ((r. Kapoc, karos, lethargy.) The great arteries of the
neck that convey blood to the heart. The ancients supposed
drowsiness to be seated in these arteries.
Ca'se-ine, (L. cdseus, cheese.) The albuminoid substance of milk;
it forms the basis of cheese.
Car'ti-lage, (L. cartilago.) Gristle. A smooth, elastic substance,
softer than bone.
Ca'va, (L.) Hollow.  Vena cava. A name given to the two great
veins of the body.
Cer-e-bet'lum, (diminutive of cer'ebrum, the brain.) The little
brain, situated beneath the cerebrum.
Cer'e-brum,, (L) The brain proper, occupying the entire upper
portion of the skull.
Cere-bro-Spi'nal. Relating to the brain and spine.
Chor'da-ae, (L.) A cord. An assemblage of fibers.
~Cho'roid, (Gr. x6ptov, ehorion, a membrane or covering.) The middle tunic or coat of the eyeball.
Chyle, (Gr. Xv26r, cAulos, juice.) The milk-like fluid formed in the
intestines by the digestion of fatty articles of food.




368                         GLOSSARY.
Chysme, (Gr. xvylo, chumos, juice.) A kind of grayish pulp formed
from the food in the stomach.
Cil'i-a, (pl. of cil'i-um, an eyelash.) Minute hair-like processes found
upon the cells of the air-passages, and other parts that are habitually moist.
Cin-e-ri'tiou.', (L. cinis, ashes.) Having the color of ashes.
Cir-cu-la'tiou, (L. circulare, to move in a circle.) The circuit or
course of the blood through the blood-vessels.
Clav'i-cle, (L. clavicula, from clavis, a key.) The collar-bone; so
called from its resemblance in shape to an ancient key.
Co-ag-u-la'tion, (L. coagulere, to curdle.)  Applied to the process
by which the blood clots or solidifies.
Coch'le-a, (Gr. Kox.dA, kochlo, to twist; or L. cochlea, a screw.) A
cavity of the ear resembling in form a snail shell.
Co'lon, (Gr.) A portion of the large intestine.
Col-um'na, ee, (L.) A column or pillar.
Con'dyle, (Gr. KovdVuoc, kondulos, a knuckle, a protuberance.)  A
prominence on the end of a bone.
Con-junc-ti'va, (L. con, together, and jungare, to join.) The membrane that covers the anterior part of the globe of the eye.
Con-trac-til'i-ty, (L. con, and trahere, to draw together.)  The
property of a muscle which enables it to contract, or draw its extremities closer together.
Con-vo-lu'tions, (L. con and voluvre, to roll together.) The tortu.
ous foldings of the external surface of the brain.
Cor'ne-a, (L. cor'nu, a horn.) The transparent membrane which
covers the anterior fifth of the eyeball.
Cor'pus-cles, Blood, (L. dim. of cor'pus, a body.) The small biconcave disks which give to the blood its red color; the white corpuscles are globular and larger.
Cos'ta, (L. costa, a coast, side, or rib.) A rib.
Cra'ni-al, (L. cra'nium, the skull.) Pertaining to the skull. As
the cranial nerves.
Cri'coid, (Gr. KpKOc, krikos, a ring.) A cartilage of the larynx, resembling in shape a seal ring.
Crys'tal-line  Lens, (L. crystal'lum, a crystal.)  One of the
humors of the eye; a double convex body situated in the front
part of the eyeball.
Cu'ti-cle, (L. dim. of cu'tis, the skin. The scarf-skin; also called the
epider'mis.
Cuz'tis  (Gr. aKcvro, skutos, the skin or hide.) The true skin, lying
beneath the cuticle; also called the der'ma.
De-cus-sa'tion, (L. decus'sis, the Roman numeral ten, X.) A reciprocal crossing of fibres from side to side.
Di'a-phragm, (Gr. dtaopayfua, diaphragma, a partition.)  The




GLOSSARY.                           369
midriff; a muscle separating the cavity of the chest from the
abdomen.
Di-as'to-le, (Gr. dtaarteAetv, diastellein, to put asunder.) The dilatation of the heart and arteries when the blood enters them.
Dor'sat, (L. dorsum, the back.) Pertaining to the back.
D1t-o-de'numin, (L. duode'ni, twelve.) The first division of the
small intestines.
Dit'ra Matter, (L. durus, hard, and mater, mother.) The outermost membrane of the brain.
E-mul'sion, (L. emulgere, to milk.) Oil in a finely divided state
suspended in water.
En-am''el, (Fr. email.) The smooth hard material which covers the
crown or visible part of the tooth.
Ep-i-glot'tis, (Gr. Ert, epi, upon, and y-Trra, gl3tta, the tongue.)
One of the cartilages of the glottis.  I
Eu-sta'chi-an Tube. A channel from the fauces to the middle
ear, named from Eustachius, who first described it.
Ex-pi-ra'tion, (L. exspird're, to breathe out.) The act of forcing
air out of the lungs.
Ex-ten'sion, (L. ex, out, and tendere, to stretch.) The act of restoring a limb, etc., to its natural position after it has been flexed,
or bent; the opposite of Flexion.
Fas'ci-a, (L. fascia, a band.) A tendinous expansion or aponeurosis.
Fe-nes'tra, (L.) Literally, a window; the opening between the
middle and internal ear.
Fi'brin.  A peculiar organic substance found in animals and vegetables; it is solid, tough, elastic, and composed of thready fibers.
Flex'ion, (L. flectere, to bend.) The act of bending.
PFib'u-la, (L. a clasp.) The outer and lesser bone of the leg.
Fol'li-cle, (L. folliculus, a small bag.) A gland; a little bag in animal bodies.
Gan'gli-on, (Gr. yayywtov, ganglion, a knot.) A knot-like swelling
in the course of a nerve; a smaller nerve-center.
Gas'tric, (Gr. yaar7p, gastir, stomach.) Pertaining to the stomach.
Gland, (L. glans, an acorn.) An organ consisting of follicles and
ducts, with numerous blood-vessels interwoven; it separates some
particular fluid from the blood.
Glos'so-phar-iyn-ge'al Nerve, (Gr. yXcaua, glossa, the tongue,
and 0pipvvS, pharunx, the throat.) The nerve of taste supplying
the posterior third of the tongue; it also supplies the throat.
Glot'tis, (Gr.) The narrow opening at the upper part of the larynx.
Gus'ta-to-ry Nerve. The nerve of taste supplying the front
part of the tongue; a branch of the " fifth" pair.
IIem'or-rhage, (Gr. aLta, hai'ma, blood, and Aiyvvyt, regnumi, to
burst.) Bleeding, or the loss of blood,




370                      GLOSSARY.
Ie-pat'ic, (Gr. 7ra.p, hepar, the liver.) Pertaining to the liver.
Hy'gi-ene, (Gr. vyieta, huygieia, health.)  The art of preserving
health and preventing disease.
In-cis'wor, (L. incidere, to cut.) Applied to the four front teeth of
both jaws, which have sharp cutting edges.
Ilte-utw, (Gr. eiXeLv, eilein, to wind.) A portion of the small intestines.
In-sat-i-va'tion, (L. in, and sali'va, the fluid of the mouth.) The
mingling of the saliva with the food during the act of chewing.
ln-spi-ra'tion, (L. in, and spird're, to breathe.) The act of drawing in the breath.
In-teg'u-ment, (L. in, and tegere, to cover.) The skin, or outer
covering of the body.
IFris, (L. i'ris, the rainbow.)  The thin muscular ring which lies
between the cornea and crystalline lens, and which gives the eye
its brown, blue, or other color.
In-ter-cost'al, (L. inter, between, and costa, a rib.) Between the
ribs.
Je-ju'num, (L. empty.) A portion of the small intestine.
Jfu'gu-lar, (L. jugulum, the neck.) Relating to the throat. The
great veins of the neck.
Lab'y-rinth, (G(r.) The internal ear, so named from its many
windings.
Lach'ry-mal, (L. lachryma, a tear.) Pertaining to tears.
Lac'te-al, (L. lac, milk.) A small vessel or tube of animal bodies
for conveying chyle from the intestine to the thoracic duct.
Lar'ynx, (Gr.) The cartilaginous tube situated at the top of the
windpipe, or trachea; the organ of the voice.
Lens, (L.) Literally, a lentil; any transparent substance so shaped
as either to converge or disperse the rays of light.
Lig'a-ment, (L. ligdre, to bind.) A strong fibrous material binding
bones or other solid parts together.
Lynmph, (L. lympha, spring-water.) The colorless, watery fluid conveyed by the lymphatic vessels.
Mar'row, (Sax.) The soft, fatty substance contained in the central
cavities of the bones. (The spinal marrow, however, is composed
of nervous tissue.)
Mas-ti-ca'tion, (L. mastica're, to chew.) The act of cutting and
grinding the food to pieces by means of the teeth.
Me-dl'tl a Ob-lon-gatta. The " oblong marrow," or nervous cord,
which is continuous with the spinal cord within the skull.
Mem-bra'na Tymrpan-i, (L.) Literally, the membrane of the
drum; a delicate partition separating the outer from the middle ear.
Mem'brane. A thin layer of tissue serving to cover some part of
the body.




GLOSSARY.                         371
liit'tral, (L. mitra, a mitre.) The name of the valves in the left
side of the heart.
l.lo'lar, (L. mola, a mill.) The name of some of the large teeth.
31lo'tor, (L. movere, to move.) Causing motion; the name of those
nerves which conduct to the muscles the stimulus which causes
them to contract.
JItu'cous Memn'brane. The thin layer of tissue which covers those
internal cavities or passages which communicate with the external
air.
Mut'cus. A viscid fluid secreted by the mucous membrane, which it
serves to moisten and defend.
Na'sal, (L. na'sus, the nose.) Pertaining to the nose; the nasal cavities contain the distribution of the special nerve of smell.
Nerive, (Gr. vewpov, neuron, a cord or string.) A glistening, white
cord of cylindrical shape, connecting the brain or spinal cord with
some other organ of the body.
Nu-tri'tion, (L, nutrire, to nourish.) The processes by which the
nourishment of the body is accomplished.
Oc'ci-put, (L. ob and caput, the head.) The hinder part of the
head..E-soph'a-gus, (Gr.) Literally, that which carries food. The tube
leading from the throat to the stomach.
0l-f ac'to-ry, (L. olfacere, to smell.) Pertaining to the sense of
smell.
Op'tic, (Gr. 67rwcor, from the root ow, future 6bo/uat, opsomai, to see.)
Pertaining to the sense of sight.
Or'bit, (L. or'bis, the socket.) The bony socket or cavity in which
the eyeball is situated.
Os'mose, (Gr. oaofc, osmos, a thrusting or impulsion.) The process
by which liquids are impelled through a moist membrane.
Os'se-ous, (L. os, a bone.) Consisting of, or resembling bone.
Palate, (L. pala'tum, the palate.) The roof of the mouth, consisting of the hard and soft palate.
Pal'mar. Relating to the palm of the hand.
Pan'cre-as, (Gr. rus, pas, all, and Kpea~, kreas, flesh.) A long, flat
gland situated near the stomach.
Pa-pilZ'la, s, (L.) Small conical prominences.
Pa-ren'chy-ma, (Gr. 7apeyXecv, parengchein, to pour through.)
The substance contained between the blood-vessels of an organ.
Pa-rot'id, (Gr. 7rapa,para, near, and b0row, otos, the ear.) The name
of the largest salivary gland.
Pa-tel'la, (L. dim. of patina, a pan.) The knee-pan; a small
bone.
Pel'vis, (L.) Literally, a basin; the bony cavity at the lower part
of the trunk.




372                        GLOSSARY.
Pep'sin, (Gr. irreLv, peptin, to digest.) The proximate organic
element of the gastric juice.
Per-i-car'di-unt, (Gr. n ept, peri, around, and Kapdta, kardia, the
heart.) A membrane that incloses the heart.
Per-i-crfLZt'i-urn, (Gr. irept, and Kpavtov, kranion, the cranium.) A
membrane that invests the skull.
Per-i-to-ne'uln,, (Gr. 7reptretvetv, periteinein, to stretch around.)
The investing membrane of the stomach, intestines, and other abdominal organs.
Per-spi-ra'tion, (L. perspirdre, to breathe through.) The sweat,
or watery exhalation of the skin; when visible, it is called sensible
perspiration, when invisible, it is called insensible perspiration.
Phar'yinx, (Gr. Papvy, pharunx, the throat.) The cavity between
the back of the mouth and aesophagus.
Phys-i-ol'o-gy, (Gr. ivatc, phusis, nature, and 7?oyoc, logos, a discourse.)  The  science of the functions of living, organized
beings.
Pi'a Ma'ter, (L.) Literally, the tender mother; the innermost of
the three coverings of the brain.
Pleu'ra, ac, (Gr. 7rXevpa, pleura, the side.) A thin membrane that
covers the inside of the thorax, and also forms the exterior coat
of the lungs.
Pneu-mno-gas'tric, (Gr. rverli&v, pneumon, the lungs, and yaCrb7ip,
gaster, the stomach.) The name of a nerve distributed to the
lungs and stomach; it is the principal nerve of respiration.
Proc'ess, (L. procedure, to proceed, to go forth.) Any projection
from a surface. Also, a method of performance; a procedure.
Pty'la-lin, (Gr. 7r7va2ov, ptualon, saliva.) The peculiar organic ingredient of the saliva.
Pul'mo-na-ry, (L. pul'mo, pulmo'nis, the lungs.) Pertaining to
the lungs.
Py-lo'rus, (Gr. irvwop6r, pultros, a gate-keeper.) The lower opening of the stomach, at the beginning of the small intestine.
Res-pi-ra'tion, (L. re, again, and spirdre, to breathe.) The act of
breathing. Inspiring air into the lungs and expelling it again.
Ret'i-na, (L. re'te, a net.) The innermost of the tunics or coats of
the eyeball, being an expansion of the optic nerve.
Sa'crumn (L. sacred.) The bone which forms the posterior part of
the pelvis, and is a continuation of the spinal column.
Sa-li'va, (L.) The fluid which is secreted by the salivary glands.
Scle-rot'ic, (Gr. aK~Xp6f, skljros, hard.) The tough, fibrous outer
tunic of the eyeball.
Se-cre'tion, (L. secer'no, secre'tum, to separate.) The process of
separating from the blood some essential important fluid; which
fluid is also called a secretion.




GLOSSARY.                         373
Se'rnum, (L.) The watery constituent of the blood, which separates
from the clot during the process of coagulation.
Sta'pes, (L.) Literally, a stirrup; one of the small bones of the
tympanum, or middle ear, resembling somewhat a stirrup in shape.
Skel'e-ton, (Gr. aehe6Xw, skell&, to dry.)  The aggregate of the hard
parts of the body; the bones.
Sub-lit'gual, (L. sub, under, and lingua, the tongue.)  Situated
under the tongue.
Sub-mnax'il-la-ry, (L. sub, under, and maxilla, the jaw-bone.) Located under the jaw.
SynL-o-vi-a, (GOr. o6v, soin, o6v, oon, resembling an egg.) The lubricating fluid of joints, so called because it resembles the white of egg.
Sys'to-le, ((r. avarGi70), sustello, to contract.) The contraction of
the heart, by which the blood is expelled from that organ.
Ta ctile, (L. tac'tus, touch.)  Relating to the sense of touch.
Tent'don, ((r. TE&LEtV, teinein, to stretch.) A hard, insensible cord,
or bundle of fibers, by which a muscle is attached to a bone.
Thto'ra.x, (Glr. i)paS, thorax, a breastplate.)  The upper cavity of
the trunk of the body, containing the lungs, heart, etc.; the chest.
Thy'roid, ((Gr. 9vpe6f, thureos, a shield.) The largest of the cartilages of the larynx; its angular projection in the front of the
neck is called "Adam's apple."
Tra'che-a, (OCr. TpaXv~, trachus, rough.) The windpipe.
Tym'pa-num, (O(r. ruvwavov, tumpanon, a drum.) The cavity of
the middle ear, resembling a drum in being closed by two membranes, and in having communication with the atmosphere.
UT'vu-la, (L. uva, a grape.) The small pendulous body attached to
the back part of the palate.
Vas'cu-lar, (L. vas'culum, a little vessel.) Pertaining to, or containing blood-vessels.
Ve'nous, (L. ve'na, a vein.) Pertaining to, or contained within a vein.
Yer'te-bral Column, (L. ver'tebra, a joint.) The back-bone, consisting of twenty-four separate bones, called vertebra, firmly jointed
together; also called the spinal column and spine.
Ves'ti-bule.  A portion of the internal ear, communicating with the
semicircular canals and the cochlea; so called from its fancied resemblance to the vestibule or porch of a house. -
Vil'li, (L. vil'lus, the nap of cloth.) Minute thread-like projections
found upon the internal surface of the small intestine, giving it a
velvety appearance.
Vit're-ou0s, (L. vi'tru'm, glass.) Having the appearance of glass;
applied to the humor occupying the largest part of the cavity of
the eyeball.
JViv-i-sec'tion, (L. vi'vus, alive, and seedre, to cut.) The practice of
operating upon living animals, for the purpose of studying physiological processes.




INDEX.
PAGE                                         PAGE
ABERRATION, spherical......... 238  CARPUS............................  19
chromatic........................ 29  CARTILAGE.........................  18
ABSORPTION.......................   2  CELLS, the true formative vessels... 168
by lacteals........................ 98    their shape........................ 167
AERATION Of the Blood, how done... 144    their contents................... 167
AGAssIZ, his doctrine of the multiple          their selecting power............ 167
origin of the human race........ 312    two kinds in the blood.........  163
AIR, composition of and changes in             cells perform absorption.......... 170
it by respiration............... 145    and secretion.....................   171
agency of plants in keeping it pure 148    fibres of muscles made up of cells. 171
AIr-CELLS of the lungs.............. 128    cells make teeth, nails, &c........ 173
Am-sAcs in birds............... 144    how they make nerves.                       173
ALCOHOLIC Stimulants, their influ-             ali living things built by cells...... 173
ence on health.................. 269    operation of cells in the egg durALIMENTARY Canal..............          96      ing incubation.................. 174
of different lengths in  different         CEMENTUM........                         32
animals.........................   99  CEREBELLUM, functions of.......... 03
ANEURIsmu........................ 106  CHEMICAL laws controlled by vital... 328
ANIMALS, distinctions between them           CHIN, possessed only by man....... 16
and plants......................  10  CHOROID coat of the eye............ 233
intelligence of...................   303  CYLE............................            91
AORTA, valves of............... 118  CHYME..............................  91
AnR, bones of...................... 43  CILIARY processes.................. 234
ARTERIES.........................     106  CIRCULATION, its apparatus......... 105
how to stop their bleeding........ 109    double............................ 115
ARTICULATION of the voice..........  217  CLIMATE, influence of in causing the
ARYTENOID Cartilages.............      211      varieties of the race............. 316
COFFEE, influence of on health...... 270
BATHING, how it should be practiced. 262  COLD, depressing influence of....... 261
BAYA'S nest......................... 295    sometimes a stimulant........... 261
BEAVER, habits of.................. 301  COLD-BLOODED animals....                  153
BIRDS, respiration of................ 144  COLLAR bone........................ 43
spinal column of..................  40  CONvOLUTIONS of the brain......... 200
BLOOD, its changes................ 114  CRANIUM, bones of.................. 27
its course......................... 115  CRICOID Cartilage................... 212
variety of textures made from it.. 159  CRYSTALLINE lens.................. 236
cells in i     t.......................... 168  CUTICLE............................ 162
BONES, composition of........... 17
uses of......................... 17  DEATH................... 335
insensibility of...................  21  DEFORMITY, how produced......... 316
very sensible when inflamed......  21  DEGLUTITION................   87
BRAIN...............                   180 DENTINE.32
how guarded from violence........ 185  DIAPHRAGM......................... 132
its situation and connections.....   275  DIGESTION............                   81
hygiene of....................  267    hygiene of...................... 251
DISEASE, summary of its causes..... 271
CALISTHENICS....................... 266    prevention of.................  272
CAPILLARIES........................         DOMESTICATION, influence of........ 319
their agency in keeping up the cir-        DROWNING explained................ 140
culation......................... 111
CARNIVOROUS Animals.............  83  EAR............................ 220
CARBONIC Acid Gas, thrown off from           Eea, section of..................... 224
the lungs......................... 147  ELEMENTARY substances in animals
where formed.............     148    and vegetables.13
quantity of it discharged from the         ENAMEL, structure of............... 32
lungs............................ 147  EPIGLOTTIS.......................... 211
absorbed by plants..............   148  ERECT posture of man............  16




INDE X.                                       375
PAGE                                           PAGE
ETHIOPIAN variety of the race....... 311  IL.............................. 
EXCRETION, by  what organs per-                INSPIRATION, mode of performing.   132>
formed.........................  161  INSTINCT more mysterious than reaEXERCISE, influence of on digestion. 265            son........................... 301
on the circulation................. 105    uniformity of its action........... 301
EXPIRATION, mode of performing... 132    its perfection...................... 301
EXPREssION effected by muscles.....  74    exhibited in communities of aniEYE, optical instrument............ 229         mals............................ 301
its defences.................. 246    blindness of it.................... 302
INVOLUNTARY muscles..............    81
FACE, muscles of...................  57  IRIS................................ 335
FAcIAL angle........................ 283
FAR-SIGHTEDNESS..................        240  JAW, lower........................        31
FINGERS, arrangements of tendons in  45    its digastric muscle..............  62
FISHES, respiration of.............. 141  JOINTS, lining of....................  49
spinal column in.................  40
FOOD, quantity needed............. 251  KNOWLEDGE, communicated only by
FOOT, bones of......                       47      muscles......................  74
FORDYCE, his experiments on heat.. 153
FORMATION and repair, by what done 155  LACTELS..........................   98
FORMATIVE vessels, selecting power             LARYNX............................ 211
of............................... 158  LEVER, the three kinds of exemplitheir concert of action illustrated            fled in the muscles...............      52
in various ways................. 158  LInE, its origin and processes....... 326
FROG, changes  from   the  tadpole               its nature unknown............... 327
state............................ 157    differs from  other forces......... 327
FRONTAL sinus..........                   29    controls chemical forces........... 328
FUNCTIONS, distinctions between nu-              sometimes dormant............... 330
tritive and animal.............  12  LIGHT, refraction of................. 230
LOBWORM, respiration of............ 141
GANGLIONS...................... 184  LOCOMOTION, distinguishing animals
GASTRIC juice.....................  89            from plants.............10
GILLS, truly lungs............. 141  LUNGS, structure of................. 129
GIZZARD, in birds................ 102  LYMPHATIC absorbents..............    98
GRAY substance of brain..                204
amount of compared with the white            MAN, distinctions between him and
substance...................... 282           animals.........................  13
dependence of mind on............ 285  MASTICATION........................            81
GYMNASTICS........................ 266  MECHANICAL   disadvantage   under
which muscles act.........              54
HAND...............................       15  MESENTERY, plan of................        98
HEAD, bones of...................25, 27  METACARPUS......................  45
HEART, a forcing and suction pump. 106 METATARSUS.46
double.................... 115  MIND, influence of on digestion..... 253
valves in......................... 115  MONBODDO'S notion............... 293
its auricles and ventricles........ 116  MOTION, involuntary................    81
front view of..................... 121  MUSCLES......................... 49
map of.        1........ 122    their structure...................  49
situation of...................... 123    mode of action................  51
sounds of................. 124    of arm....................... 54
its sac............................. 125    of face and neck.................  57
its number of beats.............. 126    of the eye........................  64
HEAT of the body, how maintained. 149    combined motions................  65
where made...................... 149    all knowledge communicated by..  74
sources of the fuel for it.......... 150    their associated action...........  79
its uniformity in man............. 152
HIERBIVOROUS animals..............  83  NAILs, made by cells................ 172
HIBERNATION.................... 153  NEAR-SIGHTEDNESS................. 240
HONEYCOMB, the perfection of it as a           NERVES made from cells........... 173
structure.......................... 298    terminations of..............   181
HUMAN race, varieties of............ 310    different sets of for different purHUMERUS.....................              43      poses..................... 206
HUNGER, cause of and seat......... 94    nerves of the eye................ 245
HYDRA..                                   11    of the ear...................... 223
cells in........................... 11  NERVOUS system, distinguishing aniHYGIENE, how  its  principles  are                 mals from vegetables............  11
learned..................... 249    its different parts.................. 180
HYOID bone......................... 211  NICTITATING membrane............ 249




376                                    INDEX.
PAGE                                         PAGE
NOSE, bones of......................  31  SPECIES, how it differs from variety. 310
SPINAL column.............            36
(EsoPHAGUS described..............  89    of birds...........................  40
ORGANIC  life, distinguished  from             of fishes and reptiles.............. 41
animal life................. 12    deformity of, how caused......... 264
ORGANIZED  and  unorganized  sub-            SPINAL cord or marrow............. 181
stances..................  8    its functions..................... 181
difference between in permanency.  9  STEREOSCOPE...................... 242
in regularity.9  STOMACH, uses in two senses.......                                9
OSTRICH, respiratory apparatus of... 144    distinguishing    animals   from
OXYGEN absorbed by the lungs ex-                 plants.10
haled by plants.................. 148    its three coats..................... 91
difference of this organ in different
PATELLA.................... 50       animals.........................  96
action of the muscles on..........  60  SUTURES of the skull................ 27
PELVIS...                               24  SWEAT glands...................... 161
PERSPIRATION  influence of in ena-           SYMPATETIC system of nerves....  206
bling the'body to bear very hot
air............................. 163  TARsUS.............................       23
PETROUS (rock-like) bone...........    30  TAILR-BIRD'S nest................. 296
PHARYNX........................... 88  TEA, influence of on health......... 270
PLANTS, distinctions between them            TEAR-APPARATUS                          247
and animals...................    10  TEETH, different kinds..............      32
PLEURA......:.................. 129    structure of....................  32
PLEXUSES of nerves............... 181    nerves in.................... 32
PYLORUS............................ 92    why second set needed............  33
TENDONS............................   51
RADIUS........................... 94  TEPORAL bone....................  25
REACTION  against cold, how  pro-            THIGH bone.46.............. 4
duced........................... 261  THoRACIC duct...................... 83
REASON of a lower order in animals. 304  THYROID cartilage.................. 211
REASONING abstract, peculiar to man 309  ToBAcco, its influence on health.... 270
REED instruments................... 215  TOGGLE-JOINT,  exemplified  in the
RESPIRATION, its apparatus......... 127         joints of the body...........  71
mechanism of..................... 127  TONGUE, its variety of motion...... 65
hygiene of....s.. e............. 255
RESPIRATORY apparatus of fishes... 141  ULNA............................... 43
of insects......................... 143
of birds....................... 144  VALVES of the heart............ 120
RETINA, structure of................ 234  VEINS, structure and situation of.... 107
RIBS, arrangement of............... 131  VENTILATION, effects of, defective... 254
movement of in respiration....... 131  VERTEBRAE described..         35
VISUAL angle....................... 243
SACRUM............................ 36  VITREOUS table of the bones of the
SALIVARY glands.................... 85  skull......................         27...  27
SCAPULA............................  43  VOCAL ligaments.............. 213
SEBACEOUS glands................. 163  VOICE.................... 206
SEMICIRCULAR canals............... 227
SENSATION,  distinguishes  animals           WASTE of the system, by what orfrom  plants.10                             gans thrown off............. 161
SKELETON, description of.......... 22, 23    influence of its retention.......... 257
SKIN, structure and functions of..... 162  WAsP's nest................. 298
hygiene of........................  257  WATER-SCORPION, respiration of.... 143
SOUND, how  produced  and  trans-            WHALE, arrangement for catching
mitted.... 2......220, 222       its food..................... 84
difference in transmission through           its reservoirs for containing artesolids, liquids and gases......... 222      rial blood...............   140
musical, how it differs from noise. 220  WHISPERING, how done........... 219
how in the vocal instrument......  213  WHITE substance of the brain....... 184




Sheldon & Company's flext-Books.
OLNEY'S HIGHER MATHEMATICS.
Olney's Complete School Algebra.............. $1 50
Olney's Key to    do.  with extra examples...1 50
Olneyg's Book of Test Examples in Algebra....  75
Olney's University Algebra...................... 2 00
Olney's Key to        do........................ 2 00
Olney's Elements Goom. &  Trigonom. (Sch. Ed.) 2 50
Olitey's Elements of Geometry.  Separate........ 1 50
Olney's' Elements of Trigoaonoetry. Separate.. 1 50
Olney's Elements of Geometry and Trigonometry.  (Univ. Ed., with Tables of Logarithms)...... 3 00
Olneyy's Elements of Geometry and Trigononmetry. (University Edition, without Tables.)......... 2 50
Olney's Tables of Logarithmns. (Flexible covers.).   75
Olney's General Geomlietry and Calcutlus......  2 50
The universal favor with which these books have been received
by educators in all parts of the country, leads the publishers to
think that they have supplied a felt want in our educational appliances.
There is one feature which characterizes this series, so unique,
and yet so eminently practical, that we feel desirous of calling
special attention to it. It is
The facility with which the books can be used for classes of
all grades, and in schools of the widest
diversity of purpose.
Each volume in the series is so constructed that it may be used
with equal ease by the youngest and least disciplined who should
be pursuing its theme, and by those who in more mature years
and with more ample preparation enter upon the study.
Any of the above sent by mail, post-paid, on receipt of price.




8heldon & Compnany's 7ext- 7ooks.
HISTORIES OF THE UNITED STATES.
By BENSON J. LOSSING, author of " Field Book of the Revolution," " Illust.rated Family History of the United States," &c.
These books are designed for different grades of pupils and adapted to the
time usually allowed for the study of this important subject. Each embraces
the history of our country from its discovery to its present administration.
The entire series is characterized by chasteness and clearness of style, accuracy
of statement, beauty of typography, and fullness of illustration. It is admirably suited to class recitations by copious marginal notes and questions, which
greatly assist the teacher, while its views, portraits, maps, and diagrams, have
the utility and attractiveness of object lessons, aiding the comprehension of
the learner. The author has spent the greater part of his life in collecting
materials for, and in writing history, and his ability and reputation are a sufficient guarantee that the work has been thoroughly done, and a series of
histories produced that will be invaluable in training and educating the youth
of our country.
Lossing's Primary  History.  238 pages.  Price $1.00.
Lossing's Grammar School History.  288 pages. Price
$1.25. Containing the Constitution of the U.S., with Review
Questions.
The facts of this book have been drawn chiefly from original sources of
information, and errors in the history of our country have been corrected.
This book also contains a large number of views of places, things, and events
which greatly assist the memory of the pupil.
Lossing's Common School History.  383 pages.  Price
$1.75. Containing the National Constitution, Declaration of
Independence, biographies of the Presidents, and Questions.
This work is arranged in six chapters, each containing the record of an important period. The First exhibits a general view of the Aboriginal race who
occupied the continent when the Europeans came. The Second is a record'of
all the Discoveries and preparations for settlement made by individuals and
governments. The Third delineates the progress of all the Settlements until
colonial governments were formed.  The Fourth tells the story of these
Colonies from their infancy to maturity, and illustrates the continual development of democratic ideas and republican tendencies which finally resulted in
a political confederation. The Fifth has a full account of the important events
of the War for Independence; and the Sixth gives a concise History of the
-Republic from its formation to the present time.
Lossiwng's Pictorial History of the  United  States.
428 pages. Price $2.00. For High Schools and Families.
Any of the above sent by mail, post-paid, on receipt of price.




Sheldon &  Comnpany's Yext-~/ooks.
COLTON'S NEW GEOGRAPHIES..The whole subject in Lwo Books.
These books are the most simple, the most practical, and best
adapted to the wants of the school-room of any yet published.
I. Colton's New Introductory Geography.
With entirely new Maps made especially for this book, on
the most improved plan; and elegantly Illustrated. Price 90 cts.
II.  Colton's Common School Geography.
With Thirty-six new Maps, made especially for this book,
and drawn on a uniform system of scales.
Elegantly Illustrated.  Price $2.00.
This book is the best adapted to teaching the subject of Geography of any yet published. It is simple and comprehensive,
and embraces just what the child should be taught, and nothing
more. It also embraces the general principles of Physical Geography so far as they can be taught to advantage in Common
Schools.
For those desiring to pursue the study of Physical Geography,
we have prepared
Colton's Physical Geography.
One VoL 2to. Price $1.50.
A very valuable book and fully illustrated. The Maps are
compiled with the greatest care by GEO. W. COLTON, and represent the most remarkable and interesting features of Physical
Geography clearly to the eye.
The plan of Colton's Geography is the best I have ever seen. It meets the
exact wants of our Grammar Schools. The Review is unsurpassed in its
tendency to make thorough and reliable scholars. I have learned more Geography that is practical and available during the short time we have used this
work, than in all my life before, including ten years teaching by Mitchell's
plan.-A. B. HEvwooD, Prin. Franklin Gram. School, Lowell, Mass.
So well satisfied have I been with these Geographies that I adopted them,
and have procured their introduction into most of the schools in this county.
Jgnas W. THOXPsoN, A.M., Prin. of Centreville Academy, Maryland.
Any of the above sent by mail, post-paid, on receipt of price.




SileZdon d& Company's.rext- 1ooks.
SCHOOL AND COLLEGE CLASSICS, Etc.
Long's Classical Atlas.  Constructed by WILLIAM HUGHES,
and edited by GEORGE LONG, formerly Professor of Ancient
Languages in the  University of Virginia.  With  a Sketch
of Ancient Geography, and other Additions, by the American Editor. Containing Fifty-two Colored Maps and Plans
on Twenty-two large imperial quarto Plates, beautifully engraved on steel in the clearest and most finished style. With an
index of Places. Handsomely half-bound, with cloth sides, in
one large volume. Price $4.50.
"Now that we are so well supplied with classical dictionaries, it is highly
desirable that we should also have an atlas worthy to accompany them. In
the volume before us is to be found all that can be desired. The names of
those who have been concerned in its preparation speak for themselves. On
examination. we find it adapted to the present state of classical scholarship,
and distinguished by a superior style of execution. The wants of the classical
student have been carefully consulted throughout; all places of peculiar interest, such as Rome, Athens, and its harbors, Syracuse, &c., being given upon
an enlarged scale, and the relative positions of the public buildings, roads, &c.,
clearly exhibited. We notice, also, that places which have more than one
name in the classics, such as Dyrrachium and Epidamnus, Carchedon and Carthage, appear with both in the Atlas."-Athenzaeum.
The Classical Manual: an Epitome of Ancient Geography,
Greek and Roman Mythology, Antiquities, and Chronology.
Chiefly intended for the use of Schools and Colleges.  Compiled
by JAMES S. S. BAIRD, T. C. D., &c. In one handsome 18mo
volume, of about 175 pages. Price 90 cents.
The want has long been felt and acknowledged of an epitome, presenting, in a moderate space and a low price, such information as is necessary
for the proper comprehension and appreciation of the classical authors most
commonly read in our schools. The object of the present volume is to supply
this want, by affording, in the most condensed form, and in such a manner as
to admit of its being thoroughly mastered and retained, all the information
respecting classical antiquity which is requisite for the earlier stages of study.
Schmitz  d} Zumpt's   irgqil.   Eclogues, Georgics, and 12
Books of ZEneid. 1 vol. 16mo. Price $1.
Horace.  Odes and Satires.  $1.
Ovid. Select Poems. $1.
Livy. Books I., II., XXI., and XXII. $1.
Cooper's Virgil.  With valuable English Notes.  $2.50.
Kaltschmidt's  La tin  Dictionary  for Schools.   A
School Dictionary of the Latin Language, in two parts, LatinEnglish and English-Latin. By Dr. KALTSCHMIDT. Forming
one large royal 18mo volume of 850 pages, closely printed in
double columns, and strongly bound. Price $2.50.
Any of the above sent by mail, post-paid, on receipt of price.