COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX64070263 R K53 . F73 1916 Mouth hygiene : a co !':!' i •,.;i: ■J. il:' 'I] i'''r] Xm aniiM«Mra liii. !:nil 'I ■'' r II l! m ■j f^irSS F75 Columbia ^nibcri^itp intljcCitPof J^etjj^orfe College of ^Jjpgicians anb burgeons Reference Itifararp DR. WILLIAM J. OILS J"^' fo enrich the [ihra.ry resources available to holders of the GlES FELLOWSHIP in Biolosica.1 Chemistry Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/mouthhygienecourOOfone CONTBIBUTOES ANDERSON, WILLIAM G., M.D., Dr.P.H. CHITTENDEN, RUSSELL H., Ph.D., LL.D., Sc.D. CRAMPTON, C. WARD, M.D. FISHER, IRVING, Professor FONES, ALFRED C., D.D.S. HUTCHINSON, R. G., Jr., D.D.S. HYATT, THADDEUS P., D.D.S. KEYES, FREDERICK A., D.M.D. KIRK, EDWARD C, Sc.D., D.D.S., LL.D. MacKEE, GEORGE M., M.D. MINER, LeROY M. S., M.D., D.M.D. O'NEILL, CORDELIA L. OSBURN, RAYMOND C, Ph.D. OTTOLENGUI, RODRIGUES, M.D.S., D.D.S., LL.D. PRINCE, ALEXANDER M., M.D. RETTGER. L. F., Ph.D. RHEIN, M. L., M.D.. D.D.S., D.R.C., U.S.N. STRANG, ROBERT H. W., M.D., D.D.S. TURNER, CHARLES R., M.D., D.D.S. MOUTH HYGIENE A COURSE OF INSTRUCTION FOR DENTAL HYGIENISTS A TEXT-BOOK CONTAINING THE FUNDAMENTALS FOR PKOPHYLACTIC OPERATORS COMPILED BY ALFRED C. FONES, D.D.S. BRIDGEPORT, CONNECTICUT EDITED BY EDWARD C. KIRK, Sc.D., D.D.S., LL.D. ROBERT H. W. STRANG, M.D., D.D.S. ALFRED C. FONES, D.D.S. TKIlitb 278 llllustrationg anJ) 7 IPlatea LEA & FEBIGER PHILADELPHIA AND NEW YORK 1916 Entered according to the Act of Congress, in the j^ear 1916, by LEA & FEBIGER, In the Office of the Librarian of Congress. All rights reserved. PEEFACE. Dentistry is in a position today where the problem of mouth hygiene must be solved in a practical manner. The medical profession now realizes that unsanitary mouths with diseased teeth are a very potent factor for ill health and systemic infection. Although many of the leading investigators and writers of the dental profession have repeatedly called attention to the rnouth as a cause for systemic disease, the cry has not been heard by the mother profes- sion until a comparatively recent period. Now that we know that this gateway to the body must be kept clean, the teeth sound and the gum tissue maintained in a healthy condition, the question arises how such an enormous work as that which is before our profession can be suc- cessfully accomplished. Surely the dentists alone cannot cope with it. Judging from the condition of the mouths of the children in om* public schools, fully 90 per cent, of the population of this country has decayed teeth. If all the dentists in the United States devoted all of their time to reparative work alone, they could not take care of one-eighth of the people. But operative dentistry is expensive. It is beyond the means of the great working class who need sound teeth and good health. There must be some cheaper and better solution than merely to follow the endless chain of repair. We must get at the source of this universal disease and try to check it by educational and preventive means. The source is the children in our public schools. We know that with extreme cleanliness, the elimination of improper foods and with surface treatments of the teeth at regular intervals, fully 90 per cent, of dental decay can be eliminated. If this knowledge and service is to be given to the children as well as to those adults who are patients in private practice, who is to give it? Apparently the only solution is the woman who is educated and trained as a dental hygienist. This is woman's work and there is an immense field open for thou- sands of women in dental offices and public institutions. Such a course of education and instruction should also be annexed to the training of the medical nurse, as her services for mouth hygiene in the hospitals and sanitariums would soon prove to be invaluable. These questions have repeatedly been asked, " Where are we going to secure such women, educated and trained as dental hygienists ? Where are they to secin-e such an education? What should constitute such a course for lectures vi PREFACE and practical training? Are there text-books that they may study to comprehend and perfect themselves in this preventive work?" The main object of this publication is to present a definite answer to these questions and introduce an educational course for dental hygienists that will prove to be something definite and tangible at tiie start. In the fall of 1913 the gentlemen whose names appear as contrib- utors to this work were approached and asked if they would aid in such a cause, if they would come to Bridgeport and deliver their lectures to a class of thirty -two women, the lectures to be taken in shorthand, sent to them for correction and condensation so that the pith of the subject might be published in a text-book for the education of women assistants in prophylaxis. Without exception these gentlemen agreed to come. The lectures were held in the evenings on Mondays, Wednesdays and Fridays, and with the exception of a vacation at Christmas time, ran from November 17 until March 30. The class assembled at 7.30 p.m. and a review of previous lectures was taken up by one of the quiz masters. At 8 p.m. the lecturer of the evening commenced, and lectured until 9.30 p.m. or there- abouts. Eleven ^\Titten examinations were held and out of a class of thirty-two, all but six passed with an average above 70 per cent., and nine passed above 90 per cent. It is our earnest desire that educational institutions, such as dental colleges, will take up this work and establish a course of education and training for women as dental hygienists. We believe that the title, dental nurse, is a misnomer, as these M^omen are not to perform any service that resembles the work of the medical nurse. They are pro- phylactic operators and, although they have a knowledge of dental dis- eases, their service is limited by law to prophylactic work. When the value of a service such as theirs is fully appreciated by the dental and medical professions, there will be a great demand for these practical workers for mouth hygiene, not only in i)rivate offices but in the public schools. It is our hope that this educational course will help to sjK'cd the day. A full description of the methoils emi)loyed for the practical train- ing will be found in the ii,])i)(n(lix. Aside from our obligation to the lecturers, quiz masters, a loyal office force and a numl^er of kind friends who are influential in the den- tal profession and whose aid proved so valuable, we are also grateful to the S. S. White Dental ^Manufacturing Company for their display of generosity in loaning us sixteen new Diamond chairs for our course in ])ractical training. A. C. F. BitiDGEPouT, Conn., 1010. LIST OF CONTRIBUTORS. WILLIAM G. ANDERSON, Dr.P.H., M.D., Professor and Director of Yale Universitj' Gymnasium. RUSSELL H. CHITTENDEN, Ph.D., LL.D., Sc.D., Director of Sheffield Scientific School of Yale University. C. WARD CRAMPTON, M.D., Hygienist and Director of Physical Training, Public School System, New York City. PROFESSOR IRVING FISHER, Chairman of Committee of One Hundred on National Hygiene, of Yale L'niversitj', New Haven, Conn. ALFRED C. FONES, D.D.S., Bridgeport, Conn. R. G. HUTCHINSON, Jr., D.D.S., Specialist in Treatment of Pyorrhea Alveolaris, New York City. THADDEUS P. HYATT, D.D.S., New York City. FREDERICK A. IiI]YES, D.M.D., New York City. EDWARD C. KIRK, Sc.D., D.D.S., LL.D., Dean of Dental Department of the University of Pennsylvania, Philadelphia. GEORGE M. :MacKEE, M.D., Instructor in Dermatology in the College of Physicians and Surgeons, New York City. Editor of Journal of Cutaneous Diseases. LEROY M. S. MINER, M.D., D.M.D., Assistant Professor in Surgery in the Harvard Dental School, Boston, Mass. MISS CORDELIA L. O'NEILL, Principal of Clarion School, Cleveland, Ohio. RAYMOND C. OSBURN, Ph.D., Professor of Biology, Connecticut College for Women, New London, Conn. RODRIGUES OTTOLENGUI, M.D.S., D.D.S., LL.D., Editor of Items of Interest, New York City. viii LIST OF CONTRIBUTORS ALEXANDER M. PRINCE, M.D., Instructor in Medicine and Physiology, Medical Department of Yale Uni- versity, New Haven, Conn. L. F. RETTGER, Ph.D., Assistant Professor of Bacteriologj'- in the Sheffield Scientific School of Yale University, New Haven, Conn. M. L. RHEIN, M.D., D.D.S., Lecturer on Dental Pathology in the Dental Department of the University of Pennsylvania (Philadelphia), New York City. ROBERT H. W. STRANG, M.D., D.D.S., Specialist in Orthodoatia, Bridgeport, Conn. CHARLES R. TURNER, M.D., D.D.S., Professor of Prosthetic Dentistry and Metallurgy in the Dental Department of the University of Pennsylvania, Philadelphia. CONTENTS. CHAPTER I. ANATOMY 17 By Raymond C. Osburx, Ph.D. CHAPTER II. SPECIAL ANATOMY ^ 57 By Robert H. W. Strang, M.D., D.D.S. CHAPTER III. PHYSIOLOGY 104 By Alexander M. Prince, M.D. CHAPTER IV. BACTERIOLOGY AND STERILIZATION 130 By L. F. Rettger, Ph.D. CHAPTER V. INFLAMMATION 158 By LeRoy M. S. Miner, M.D., D.M.D. CHAPTER VL DEPOSITS AND ACCRETIONS UPON THE TEETH 170 By Edward C. Kirk," Sc.D., D.D.S., LL.D. CHAPTER VII. DENTAL CARIES • 187 By Edward C. Kirk, Sc.D., D.D.S., LL.D. CHAPTER VIII. THE TEETH AS A MASTICATING MACHINE 205 By Charles R. Turner, M.D., D.D.S. X CONTENTS^ CHAPTER IX. MALOCCLUSION OF THE TEETH 237 By Rodrigues Ottolengui, M.D.S., D.D.S., LL.D. CHAPTER X. PYORRHEA ALVEOLARIS 261 By R. G. Hutchinson, Jr., D.D.S. CHAPTER XI. ODONTALGIA AND ALVEOLAR ABSCESS 266 By M. L. Rhein, M.D., D.D.S., D.R.C., U.S.N. CHAPTER XII. DENTAL PROPHYLAXIS 288 By Alfred C. Fones, D.D.S. CHAPTER XIII. CHEMISTRY OF FOOD AND NUTRITION 367 By Russell H. Chittenden, Ph.D., LL.D., Sc.D. CHAPTER XIV. DERMATOLOGY 401 By George M. MacKee, M.D. CHAPTER XV. FACTORS IN PERSONAL HYGIENE 429 By C. Ward Crampton, M.D. CHAPTER XVI. FRESH AIR AND CORRECT POSTURE IN THEIR RELATION TO HYGIENE 440 By Professor Irving Fisher. CHAPTER XVII. LENGTHENING THE LIFE OF THE RESISTIVE FORCES OF THE BODY 449 By Willia.m G. Anderson, M.D., Dr.P.H. CONTENTS xi CHAPTER XVIII. THE TEACHING OF MOUTH HYGIENE TO SCHOOL CHILDREN 459 By Thaddeus P. Hyatt, D.D.S. CHAPTER XIX. INSTITUTIONAL DENTISTRY 463 By a. C. Fones, D.D.S., Frederick A. Keyes, D.M.D., AND Cordelia L. O'Neill. APPENDIX 505 INDEX 521 MOUTH HYGIENE. CHAPTER I. ANATOMY. By RAYMOND C. OSBURN, Ph.D. ANALYSIS OF THE ORGANISM. .[naiomy is the science which treats of the structure of organ i.wis or hving beings. The different parts of an organism, called organs, are each fitted for the performance of one or more kinds of work. Any particular kind of work, or special part of the vital process, is known as a function. Organs are said to be specialized or differentiated for the perform- ance of their various functions. Structural differentiation enables an organ to perform its particular duty more readily, hence we say that it is adapted to its function. Thus in the human body the liver, kidney, ear and eye have certain definite kinds of work to do, and so on throughout the long list of organs. This setting aside of special parts for particular uses, termed biological divisio7i of labor, has come about gradually during the course of evolution. Anatomy is not only interesting in itself, but it is necessary to the study of physiology and the phenomena of life generally. One would not expect to understand how a watch keeps time until he knew the parts concerned, as the main spring, the hair spring, the balance wheel, etc., and the relationship which these parts bear to each other. So one need not expect to understand how the human body does its work without knowing the parts that enter into its formation and how these are related in the body complex. Furthermore, in this course of study, in preparation for work upon an important part of the body, anatomy has an intensely practical interest. SYSTEM OF ORGANS. One of the first things we observe when we examine the organs of any higher animal is that they are often related to each other in a definite way for the purpose of carrying on some work too complicated to be handled satisfactorily by a single organ. Such arrangements of 2 18 ANATOMY organs are called systems. In the alimentary system, for example, the mouth, the pharynx, gullet, stomach, small intestine, and large intes- tine are all distinct organs having different functions to perform, but all operate in series to handle, digest and absorb the food. Similarly, in the circulatory system, the heart, arteries, capillaries, veins, and lymphatics all have different things to do, but all work together toward the one end of circulating the fluids of the body. Classification of Systems: -^ Individual. ^-r/^^^.^^-i^'*^' Nutritional Relational Alimentary Respiratory Circulatory Excretory Motor Supporting Nervous Reproductive Racial. The nutritional systems are those which supply food and oxygen, circulate or distribute them, and collect wastes and eliminate them from the body; in other words they work in harmony toward the nutrition of the body. The relational systems relate or coordinate the various parts of the body with each other and the organism as a whole with the outside world. All of these are concerned primarily with the welfare of the individual, so may all be classed together as the indi- vidual systems. On the other hand, the rejiroductive system has to do with the propagation of the species and is therefore of racial importance. The various systems and their organs will be considered separately later. STRUCTURE OF ORGANS; HISTOLOGY. Anatomy does not stop with the analysis of the organism into organs but considers also the structure of the organs themselves. Here again we find both structural differentiation and division of labor, for these always go hand-in-hand, and each part of every organ is developed in its particular position and is structurally suited to its special duty. The study of the organs and systems is commonly called r//o.s-.s- anatomy. The finer parts of which the organs are made up must be studied with the aid of a microscope, and this field of work is therefore known as mlcrosropir auatonii/ or histdldfu/. Tissues. — The organs of the human body, in s])itc of their manifold duties, are made up of a very limited number of common building stuffs. These we call tissues. An organ consists of several kinds of tissues intimately l)ound together. The hanfl, for example, though one organ, consists of the .skin, muscles, bones, cartilages, nerves, blood, fat and fibrous connec- tive tissues. The tongue consists of epithelial tissue on the outside, STRUCTURE OF ORGANS— HISTOLOGY 19 while within are several sets of muscles, the nerves, blood and con- nective tissues. And so in any organ various sorts of tissues are blended, according to the work for which it has been specialized. Furthermore, the same tissue may be found in difi'erent organs. Thus, no organ is without nervous tissue for sensation and for coordi- nating and regulating the parts; muscular tissue is distributed in all the organs of the body, and connective tissues occur everywhere to bind the other parts together. Classification of Tissues: I. Epithelial. 11. Supporting. III. Circulatory. IV. Glandular. V. Motor. VI. Nervous. VII. Reproductive. These may be taken up in order for further discussion. I. Epithelial tissues are those which cover surfaces on or within the body, such as the epidermis forming the outer skin; mucous membranes which line the alimentary tract, the lungs, the air passages, and the nasal cavities; and serous membranes (sometimes called endo- thelial) which line the closed cavities of the body, as the peritoneum of the general abdominal cavity, the pleurae lining the space about the lungs, the lining of the heart and bloodvessels, etc. II. Supjjorting tissues are of many kinds and serve variously to give form and rigidity, to connect organs and to bind other tissues together that they may be held in their proper place. Bone forms the general skeletal framework and is the firmest of all the tissues. Cartilage, or gristle, serves to support parts that need more or less flexibility, such as the external ear and the tip of the nose, as well as to connect the ribs with the breast-bone or sternum, and it is usually found also between the bones at the joints w^here it prevents shock. Tendons are found chiefly as the cords which connect the muscles with the bones to which they are attached. Ligamenis bind the bones together at the joints and hold certain other organs in place. White fibrous tissue, in the form of minute crinkly fibers, is distributed every- where among the other tissues (except in epithelia which it underlies) and forms the common binding substance which holds other tissues in place. Yellow elastic tissue is made up of delicate, straight, branched fibers that are like so many little rubber bands. It serves to pull back into place any tissue that has been temporarily distorted. III. The circulatory tissues consist of the blood and lymph cells, together with the fluids in w^hich they are carried. IV. Glandular tissues are those which have the power of picking up minute quantities of substances from the blood and concentrating them, or of elaborating substances into the forms in which they are again given out in secretion and excretion. 20 ANATOMY V. Motor tissves consist of muscle cells of three different kinds; the iinstriped or involimtary, such as those in the wall of the intestine; the cardiac, which form the muscular walls of the heart; and the striped or so-called voluntary muscle cells, which form the great mass of the body wall and limb muscles. VI. Nervous tissues are made up of the nerve cells with their fibers and the end-organs of the special senses. The brain and spinal cord are merely aggregations of nerve cells and fibers bound together by connective tissue. VII. Reproductive tissues are differentiated in the two sexes. In the female they are the ovarian tissues which give rise to the ova or egg cells and in the male they are the spermatic tissues which give rise to the male cells or spermatozoa. Tissues can perform only the particular kinds of work for which they are adapted, and each cell of any tissue performs the same func- tion as all the other cells of that tissue. This is true no matter in what part of the body they may be located. Thus, muscle cells contract, though found in the hand, heart, eye, or stomach; nervous tissues are capable of stimulation and conduct impulses wherever they may be, etc. A tissue may be best defined as consisting of similar cells all of which do the same kind of work. •The Cell. — Cells are the fundamental structures of the organism. They are the physical units, out of w^hich all the tissues, therefore all the organs, and the organism itself, are constructed. Cells differ greatly among themselves in size, form, internal structure and in function. They are classified according to the tissues in which they occur. Thus in epithelial tissue we find epithelial cells, bony tissue contains bone cells, glandular tissue contains gland cells, and so on through the list. Structure of the Cell (Fig. 1). — ^The all-important substance in the cell is that to which we apply the name protoplasm . It was originally applied to the living matter of minute one-celled organisms, and meant, therefore, the simplest living substance. But later chemical and microscopic studies have shown that this substance has the same general properties as the living matter of all cells of all organisms, both plant and animal. Protoplasm, in all jjrobability, is a mixture of substances, chemically speaking, but the one thing that distinguishes it at once from any other material is the fact that it is alive. All the functions of the body, no matter what they are, originate directly in the protoplasm. It should })e evident that it varies somewhat in the different cells, since these are capable of doing different kinds of work. However, in all cases the work is performed by lixing matter and there is no living substance but protoplasm. Under the microscoijc the protoplasm appears as a rather thickish, STRUCTURE OF ORGANS—HISTOLOGY 21 nearly clear fluid, which is usually slightly granular, but may appear quite homogeneous when alive. The protoplasm in a cell is divided into two portions. The larger part forms the general cell fluid, known as the cytoplasm. Within this, usually near the center of the cell, is the nucleus. This consists of a denser fluid which does not mix with the cytoi)lasm. Occasionally more than one nucleus is present. Both the cytoi)lasm and the nucleus are alive, and both take part in the activities of the cell. Usually there is also j)resent a limiting membrane about the proto- plasm, forming the cell wall or cell membrane. This structure is not li\ing and therefore is not protoplasm, but it is formed by the proto- plasm as a secretion. Fig. 1. — Diagram of a cell. (F. H. Gerrish.) Intercellular Substances. — In addition to the living matter of the body, forming the cells, there is present a great deal of very essential non-living matter which is known as intercellular substance , because it is found between the cells. This substance varies in extent and character according to the tissue of which it forms a part. One would not expect to find the same kind of intercellular substance between the cells of the brain as in muscle, nor the same in bone as in cartilage, and so on. It is secreted by the cells which are embedded in it. It may be very scanty, as in the epidermis, or abundant, as in the connective tissues. If we examine cartilage (Fig. 2) we find that the cells are imbedded in a mass of translucent, rubbery material, which is present in such quantity that the cells are often widely separated. It is this substance which gives cartilage or gristle its peculiar toughness and elasticity. Tendons are composed of parallel fibers between which the cells are imbedded. These tough, inelastic fibers, which form the larger part of the tendon, give it its special character as the connecting structure between muscle and bone. In the bones and teeth the intercellular substance is impregnated with lime salts to give great hardness and rigidity. The supporting and connecting tissues in general contain great quantities of intercellular matter. To summarize: cells, consisting of protoplasm, together with the intercellular substance, make up the tissues. Tissues are intimately 22 ANATOMY blended to form organs. Organs may function alone or in connection with others in systems. The whole complex of organs and systems makes up the organism or living body. Fig. 2. — Articular hyaline cartilage from the femur of an ox: s, intercellular substance; p, protoplasmic cell; n, nucleus. (Ranvier.) THE NUTRITIVE SYSTEMS. Organs have alreadj^ been defined as parts of the body which per- form different kinds of work, and systems as series or groups of organs which work together toward some greater end than can be attained by a single organ. It is axiomatic, of course, that no organ or system is entirely independent of the others. This conception is at least as old as J^sop's fable of "The Belly and the INIembers." However, for the purpose of analysis they may be considered separately. The alimentary, respiratory, circulatory, and excretory systems have already been mentioned as forming the nutritional group. All of these systems are concerned with supplying nutritive substances to the body or its various parts, or with the removal of wastes that have accumulated in the process of nutrition and work. The real chahi of events in nutrition is as follows: 1. Alimentation, the mechanical handling of the food. 2. Digestion, the chemical breaking up of the food. 3. Absorption of food and water by the alimentary system. 4. Absorption cjf oxygen by the resjjiratory system. 5. Circulation, to jjass these substances to the cells where they are used. THE ALIMENTARY SYSTEM 23 6. Metabolism. (a) Anabolism, the l)iiil»'^' Internal ili;ic Temper"! external carotid Common carotid Subclavian Aorta ■\xilbry Urachial The Principal Arteries and Veins of the Body. (Morrow. tup: CIRCl'LATOIiY SYSTKM 'Afi descend i II (/ aorta. From the arch are given oil' the iitnoiiiuiaic artery which divides at once into the right common carotid and right sub- clavian. The left common carotid and left subclavian arteries are given ofi' separately from the arch of the aorta. The suhclavians supply the arms. The common carotids divide to form the internal carotids, distributed to the brain and eyes, and the external carotids which divide to supply with blood, the structures of the oral cavity, tongue, throat, face, and the outer ])art of the head. The descending aorta gives oti" many branches, one of which goes to the lungs to supply them with food and oxygen. The important abdominal arteries are the celiac axis supplying the stomach, liver, spleen, and pancreas; the superior mesenteric supplying the small intestine and half of the large intestine; the inferior mesenteric supplying the lower half of the large intestine, and the renals supplying the kidneys. The abdomi- nal aorta divides at its lower end into the right and left iliac arteries which go to the legs. The Capillaries. — The arteries divide into smaller branches, the arterioles, and these continue to divide until the smallest divisions, the capillaries, are formed. These consist of a single, flattened layer of cells, continuous with the lining of the heart and other vessels. They form an exceedingly fine network among the tissues and the only tissues lacking them are the e])ithelia, the cartilages, and the cornea of the eye. The Veins. — The capillaries unite to form small venules which again unite to form larger and larger veins. Veins differ from arteries in their thinner walls, though the same tissues are present, and in the fact that valves are usually present which prevent any return flow of blood, allowing it to flow only toward the heart. In general the veins are nearer the surface than the arteries but have a similar distribution. Thus the jugular veins return the blood from the head, the pulmonaries from the lungs, etc. One notable exception is found in the portal vein (see Plate V), already mentioned under the liver, which collects the blood that has passed through the capillaries of the intestinal tract, carries it to the liver, and there again breaks up into capillaries among the lobules of the liver. The hepatic vein then collects the blood from both the portal vein and the hepatic artery to return it to the heart. The Blood. — The blood may be considered a tissue in which the inter- cellular substance is fluid. This fluid is called the plasma and consists chiefly of water containing in solution the various foods and wastes as well as the peculiar <.uh<,t'c\nve , fibri nogen , which forms the clot when it escapes from the vessels. The cells are of three sorts, the red cor- puscles, the white corpuscles and the platelets. The red corpuscles (see Plate VI) are circular, biconcave disks of protoplasm, without nuclei or cell walls, but which have the red coloring matter known as hemoglobin for the transportation of oxygen. These cells are very minute, 3^21x0^ of an inch in diameter, but are so numerous that four and a half millions (in woman) to fi\'e millions (in man) are contained in a 36 ANATOMY single cubic millimeter of blood. These corpuscles are continually being formed in the red marrow of the bones. The white corpuscles, or leukocytes (Plate VI), are of several different kinds, but all agree in being slightly granular, in having nuclei and in possessing indepenc^ent motion and ability to change their form (ameboid movement). They occur in the lymph and other fluids of the body as well as in the blood. They measure on an average about 2X0 0" of an inch and are much less numerous than the red corpuscles. Fig. 11. — Lactcals mid lymphatics duriiiy digestion. The hlood jjlatrlds arc not well known. They are irregular in form, smaller than the red corpuscles and somewhat less junncroiis. The Lymphatics (l^'ig. 11).- — These vessels in a general way follow the .same cour.se as the veins. They carry back to the general circula- tion the fluid part of the blood which has escaped through the thin PLATE V Portal System of Veins. The liver is turned upward and backward, and the transverse colon and niost of the small intestines are removed. (Gerrish. PLA.TE VI ^.■^ eg) D 1) 0' i'^ Ik ^.- % ^ (>^^!■ 'i^ Normal Blood, showing Rouleaux and Leukocytes. (Musser.) (Oe. 4, ob. 1-12 inimersion ) Dravv-n l^v J. D. Z. Cliase. THE EXCRETORY SYSTEM 37 walls of the capillaries to bathe the cells of the various tissues. As the pressure is greater in the capillaries the fluid, once escaped, cannot return to the blood directly, but is carried back by another set of vessels. These differ but little from the veins except that they are thinner walled. The lymph itself differs but little from the plasma of the blood, except that it contains less food and oxygen and more carbon dioxide and other waste matter. There are two large lymphatic vessels which pour the lymph back into the blood by way of the jugular veins just under the collar-bones. The right vessel is small because it collects only the lymph from the right arm and shoulder and the right side of the head. The left vessel collects the lymph from the corresponding areas and also from all the lower part of the body. A large vessel, known as the thoracic duct, brings up to the left jugular vein all the lymph from the abdominal region and the lower limbs. The lymphatics of the intestinal region have a special function in absorbing the fatty portions of the digested food. This passes into these vessels in the form of an emulsion of a milky color, and this fact has given to the particular lymphatics carrying this fluid the name of lacteals. Along the line of the lymphatic vessels are found the lymph nodes or glands, in which the white corpuscles are formed. They are very numerous and widely distributed. THE EXCRETORY SYSTEM. The elimination of wastes formed in the body is carried on to some extent by the lungs, which remove practically all the carbon dioxide, the skin, the liver, and the intestinal epithelium, but the special S3'stem evolved for the remo^'al of the non-volatile wastes is that known as the excretory system. The essential organs of this system are the kidneys, and the accessory organs are the ureters, bladder, and urethra. The Kidneys (Fig. 12). — The kidneys are compound tubular glands, somewhat bean-shaped, situated on either side of the midline behind the peritoneum with the concave side (hilum) toward the midline, and the middle of each kidney is a little above the waist line. The right kidney is a little lower than the left, to make room for the liver. Each kidney is about four inches long by two broad and one in thickness, and averages about five ounces in weight. On the outside of the kidney is a tough capsule of connective tissue. Inside of this is a thick layer known as the cortex which is the chief secreting portion. Toward the center from this there is still another layer, the medulla, which is thrown up into a number of pyramidal projections, the pyramids of Malpighi. There remains a central cavity, the j^ehis (basin) of the kidney. This chamber serves to collect the urine which is poured into it from the countless tubules. From the pelvis the urine is passed out into the ureter to be carried to the bladder. The essential structures of the kidneys are the uriniferous tubules which are estimated to number about 500,000. On examination 38 ANATOMY under the microscope the tubule (Fig. 13) is found to consist of an irreguhirly coiled portion, one part of Avhich is a straight loop and of an inflated terminal portion, the Bowman capsule. This capsule contains a knot of capillary bloodvessels known as the glomerulus. The capsule and glomerulus together constitute the Malpighian corpuscle. The cavity of the capsule is continuous with that of the tubule. This latter structiu'e is formed of glandular cells for the purpose of secretion and the cells vary somewhat in different portions of the tubule. Each tubule terminates in a collecting tubule which gathers the secretions from a number of the uriniferous tubules. The collecting tubules open upon the surface of the pyramids and pour the urine into the pelvis of the kidney. Fig. 12. — Vertical section of kidney. (Gray.) The kidneys are abundantly sui)i)H('d with blood from the renal arteries. After the blood has passed through the cai)illaries of the glomeruli and about the secreting tubules it is returned to the circula- tory system by way of the renal veins. The Ureters. — The ureters are the ducts of the kidneys. They are about the diameter of a goose-quill and a foot or more in length. Their walls are muscular for the purpose of forcing the urine into the bladder. The Bladder. — The bladder is merely a reservoir for the urine. It is lined witli a mucous membrane which is continuous with that of the THE EXCRETORY SYSTEM 39 ureters and urethra. The wall is chiefly made up of muscle and con- nective tissues. Oil the outside it is covered by the peritoneum. The Fig. 13. — Diagram of three uriniferous tubules and their relation to a collecting tubule: A, beginning of a tubule, the Malpighian corpuscle of which is situated in the lowermost portion of the cortex; B, about the middle of the cortex; C, in the outer portion of the cortex; m, Malpighian corpuscle; v, vessel porta; n, neck; pc, proximal convoluted portion; es, end segment; dl, descending limb; al, ascending limb of the loop of Henle; dc, distal convoluted portion; j, junctional tubule; c, collecting tubule. (Huber.) 40 ANATOMY ureters enter the bladder near its base by a very diagonal course. At the neck of the bladder is a sphincter muscle which is normally closed and opens only in the act of micturition. The duct of the bladder is the urethra. EPIDERMIS PAPILLA OF DERMIS SUBCUTANEOUS AREOLAR TISSUE MALPIGHIAN LAYER DUCT OF SEBA- CEOUS GLAND SEBACEOUS GLAND ROOT OF HAIR HAIR FOLLICLF. ADIPOSE TISSUE GLOMERULUS OF SWEAT GLAN D BULB OF HAIR PAPILLA OF HAIR Iarrector pili Fig. 14. — Vertir-al section of the skin. (Tcstut.) THE SKIN. This organ is by no means a simple structure, but consists of the following parts (Fig. 14): 1. Cuticle or epidermis. 2. Cutis or dermis. 3. Sweat glands. 4. Oil glands. o. Hairs and nails, appendages of the skin. 1. The epidermal tissue or cuticle forming the outer or scarf skin consists of layers of cells that are dead on the outside and fall oil' continually in great numbers. These are replaced by others which are constantly being formed in the lower layer next to the cutis. The epiflcrmis has no nerves and receives no blood, but obtains its nour- ishment from bloodvessels which come very close to it in the cutis and the l\'mph j;enetrates it to nourish the living cells. DUCTLESS GLANDS 41 2. The Cutis. — The cutis or inner or true skin (derma) is composed chiefly of white fibrous and yellow elastic connective tissues closely interwoven to form an extremely tough and ])lial)le layer. In this are embedded the bloodvessels, nerves, and muscles of the skin. 3. Bloodvessels. — These are very numerous in the cutis. They not only serve to nourish the skin, but are of the greatest importance in aiding in controlling the temperature of the body. 4. Nerves. — Xerxes of several classes penetrate the cutis and have their endings in the walls of the bloodvessels, in the muscles and glands, or end as sensory papilla? of touch and temperature. 5. Muscles. — There is not a great quantity of muscle tissue in the skin, but at the base of 'every hair (and even though the human body seems to be naked over the greater part of its surface there are minute hairs thickly imbedded in the skin) there is a little muscle which is able to contract and set the hair on end. In cold weather these muscles contract the skin, which is roughened on the outside as a result of the reaction of the muscles on the vestigial hairs, the phenomenon being known as "goose flesh." 6. Sweat Glands. — The minute glands which secrete the perspira- tion arise from the epidermis, but they are deeply imbedded in the cutis. They open as the microscopic pores of the skin, below which they have the form of spiral tubules and end near the lower part of the cutis in a coiled knot. 7. Oil Glands. — These also belong to the epidermis, though imbedded in the cutis. They are found in connection with the hair follicles. Even though the hairs are microscopic the glands are present and secrete the sebaceous matter which keeps the skin soft. 8. Areolar Tissue. — This tissue is composed of connective tissues similar to those which make up the cutis, but the fibers are loosely woven. This layer lies below the cutis, which it attaches more or less loosely to the organs beneath. 9. Adipose Tissue. — This is fatty tissue, some of which is nearlj^ always present in the areolar tissue just below the cutis. In reality it is composed of areolar tissue, in the cells of which fat globules are stored. It occurs frequently in other parts of the body in connection with areolar connective tissue. DUCTLESS GLANDS. A number of glands are without ducts and deliver their secretions to the blood (ductless glands or glands of internal secretion) . Although these work together to some extent in controlling the metabolism of the body, they are not usually considered as forming a system, because they are scattered about the body and usually have no connection with each other. Their secretions, called hormones, are chemical regulators of the body and are of such great importance that the removal of the glands is often foUow^ed by death or at least by grave disturbances in the metabolism of the body. 42 ANATOMY 1. Thyroid Gland. — This gland lies in the neck on either side of the trachea, just at the lower end of the larynx. It is deep red in color and weighs about one ounce. Enlargement of this gland is known as goitre. 2. Parathyroid Glands. — These are two small masses of cells, about a quarter of an inch in diameter, imbedded in the surface of the thyroid. On accoiuit of their small size and their position they were not known until comparati\'ely recently. Functionally they have nothing to do with the th\Toid, but are quite separate organs. 3. Thymus Gland. — This organ is situated within the chest cavity, above the heart and in front of the trachea. It appears very early in fetal life, functions during childhood, but has almost entirely disap- peared at puberty. iVt its largest it weighs about three-quarters of an ounce. 4. The Adrenal or Suprarenal Glands. — The adrenal or suprarenal glands are two bodies, each weighing about an eighth of an ounce, lying one above each kidney (Fig. 12). In addition to gland cells they contain much nervous tissue. 5. The Hypophysis or Pituitary Body. — The hypophysis is lodged within the skull beneath the midbrain, to which it is attached. 6. The Spleen. — The spleen is the largest of the ductless glands. It is situated behind the stomach on the left side of the body. It has a dark red color and weighs from five to eight ounces. This gland also varies according to age, being larger in youth. It is well supplied with blood and contains a large amount of lymphoid tissue. After prolonged attacks of malaria the spleen becomes permanently enlarged, forming the condition known as "ague cake." Other ductless glands, which are minute and which are little known as far as their functions are concerned, are the pineal hudy arising from the roof of the midbrain, the coccygeal gland near the tip of the coccyx and the carotid glands situated at the upper ends of the common carotid arteries. While the above glands apparently function only as ductless glands, there are other structures in the body, which, in addition to other functions, secrete hormones to the blood. Among these are the liver, the pancreas (islands of Langerhans), the reproductive organs, the lymph glands, and the mucous membrane of the intestinal wall. THE SKELETAL OR SUPPORTING SYSTEM. h\ the broadest sense this includes all the sui)])()rting structures of the body, which fall into the following classes: 1. P'ibrous connective tissues. 2. Tendons. 3. Ligaments. 4. Cartilages. 5. Bones. THE SKELETAL OR SUPPORTING SYSTEM 43 The skeleton proper consists of the bones and the cartilages con- nected with them, hut the connective-tissue fibers that bind together the soft cells of other tissues are just as truly supi)orting in their function and form for those tissues a skeletal structure that is just as real as is the bony framework for the body as a whole. 1. The Connective Tissues. — The connective tissues have already been described as consisting of white inelastic and yellow elastic fibers which are interlaced among the cells of other tissues all over the body except in the epithelium, and even in this case we find that the cells are underlaid by a structure, known as the basement membrane, formed by connective tissue. 2. Tendons. — Tendons have already been mentioned as forming the connection between muscles and the structures which they move. 3. Ligaments. — Ligaments consist of bundles of inelastic fibers and serve to bind the bones together at the joints and to hold other organs, as the liver and ovaries, in place. 4. Cartilages. — Cartilages or gristles as they are more commonly called, are characterized by their tough, elastic nature. They are known as (1) hyaline, when pure; (2) fibrocartilage, when mixed with white fibrous tissue; and (3) yellow elastic cartilage, when mixed with yellow elastic fibers. As a rule the cartilages are disposed in certain definite relations to the bones, either between the joints to absorb shock, which is the usual arrangement, or as in the attachment of the ribs to the sternum to per- mit the expansion of the thorax in inspiration. They are also found in the external ear and the tip of the nose, and the sternum is pieced out at its lower end by the xiphoid cartilage. Rings of cartilage are present in the trachea and bronchi, as already stated, to keep these passages open. Skeleton (Fig. 15).^ — The skeleton or bony framework consists of about 200 to 208 bones. The number varies within narrow limits because certain small bones may be present or absent without making any apparent difference in the efficiency of the structure. Bony tissue is made up of bone cells, between which there is an intercellular substance of organic matter impregnated with lime salts for the sake of rigidity. In young children the bones are somewhat pliable, but in older persons they become very rigid, owing to the increasing deposition of lime. Bone tissue is permeated by blood- vessels, just as other tissues are, for nourishing the cells. Around the outside, except in the joints, there is a tough connective- tissue layer called the periosteum. Bony tissue may be compact or it may be spongy (cancellous) . Com- pact bone is found in the shanks of the long bones, such as those of the arms and legs, and in the outer layer of all other bones. vSpongy bone forms the mass of the heads of the long bones, the vertebrae and ribs, the middle layers of the skull, and so on. The cavities in the middle of the long bones are filled with yellow marrow, a fatty deposit, while 44 ANATOMY the small spaces in spongy bone are filled with red marroic within which the red blood corpuscles are manufactured. • 5. Bones. — The bones fall naturalh' into two classes, the axial skeleton and the appendicular skeleton. The former class includes the bones of the head, spinal column, ribs and sternum, while the latter class consists of the bones of the limbs. FRONTAL ORBIT- . PARIETAL -TEMPORAL .CARPUS METACARPUS Fig. 15. — The human skeleton. (Morrow.) The bones of the head include those of the cranium or })raiii-case, 8 in number, occipital, parietal (2), frontal, temporal (2), sphenoid and ethmoid; those of the face, 14 in number, nasal (2), lacrimal (2), vomer, malar (2), palate (2), turbinated (2), maxilla or upper jaw (2), and THE SKELETAL OR SUPPORTING SYSTEM 45 mandible or lower jaw; the ear bones, three pairs in number, malleus (2), incus (2), and stapes (2) ; and the hyoid at the base of the tongue. Most of these are more or less immovably locked together, the only movable ones being the mandible, the hyoid, and the ear bones. The bones of the spinal column are 31 in number, arranged as follows: 7 cervical or neck vertebra?; 12 dorsals in the thoracic region; 7 lumbars in the lumbar region; 5 sacrals in the pelvic region; and 4 coccj/geals forming the coccyx or rudimentary tail. The first two cer\'ical vertebra? are specially modified, the first or atlas to form the connection with the base of the skull and the second or axis to form a special kind of joint with the first to allow the head to be turned. The dorsal vertebrae all bear ribs attached to their transverse processes. The lumbar vertebrae are free from ribs or other special modification. They are the largest of the vertebrae and their processes are well developed for the attacJiment of muscles. The sacral vertebrae are fused into a single mass to afford better attachment for the other bones of the pelvis to which the legs are joined. The cocygeal bones are more or less vestigial vertebrae, varying somewhat in number, but usually four. The bones of the spinal column are all capable of being moved except those of the sacrum and, to some extent, the coccyx. The sternum or breast-bone protects the main organs of circulation and respiration. It consists of three parts which are slightly movable. To the upper portion, which is short, are attached the collar bones and the first pair of ribs. The body of the sternum has the cartilagin- ous portions of other ribs attached to it down to and including the seventh rib. The xiphisternum, xiphoid process, or ensiform process, as it is variously called, is the free portion of the sternum projecting downward over the stomach. In younger years it is cartilaginous, but becomes more or less ossified in later life. The ribs are bony arches, 12 in number, which support the thoracic wall and protect the organs of circulation, respiration, and to some extent the upper abdominal organs. The first seven pairs, called true ribs, are attached directly to the sternum by continuations of hyaline cartilage. The next three, called false ribs, are attached in front, each to the cartilage of the next rib above. The last two pairs, the floating ribs, are not attached at their anterior ends. The ribs are all attached to the vertebrae by movable joints, so that in respiration they can be rotated outward and upward, and the costal cartilages, by which they are attached to the sternum, permits the expansion of the anterior thoracic wall. In the appendicular skeleton the framew^ork of the upper extremity consists of 32 bones: the shoulder-blade or scapida, the collar-bone or clavicle, the humerus in the upper arm, the radius aufl ulna in the fore- arm, 8 carpal bones in the wrist, 5 metacarpals in the hand, and 14 phalanges in the fingers. In the lower extremity the bones have much the same arrangement. On either side is one large irregular shaped 46 ANATOMY bone', the innoimnate, to form the sides of the pelvis. These are firmly united behind to the sacrum and to each other in front. In the leg are 30 bones: the femur or thigh bone, the pateUa or knee-cap, the tibia and fihuhi or large and small shin bones, 7 tarsal bones in the ankle, one of which is the heel-bone, 5 metatarsals in the instep, and 14 phalanges in the toes. Joints. — Bones are attached to each other by joints which we may classify' in the following manner: 1. Immovable joints. 2. Slightly movable joints. 3. Freely movable joints. Of the immovable joints there are two chief types. Sutures, such as are found between the bones of the skull, are formed by the inter- locking of irregular edges of adjoining bones, and symphyses, or joints in which the bones are closely united by connective tissue, as between the innominate bones in the front of the pelvis. Both sutures and symphyses often become completely ossified in adult life, but in younger years they allow the parts to yield slightly. Slightly movable joints are found between most of the vertebrae of the spinal column. Here pads of fibrocartilage, the intervertebral cartilages, are inserted between the vertebrae and allow the column to bend in any direction by the compression of the cartilages. Movable joints are those in which the bones slip or rotate past each other in motion. The articular surfaces of the bones forming such joints are covered with hyaline cartilage and between the bones is found a closed sac, the synovial membrane, which secretes a slippery fluid to prevent friction. There are a number of classes of these. 1. Gliding joints, in which the articular surfaces are nearly flat and the bones slip past each other slightly, as in the articular processes of the vertebrae and the bones of the wrist and ankle. 2. Hinge joints are those which permit of motion in only one plane as in a hinge. Examples are found in the elbow, knee, and between the phalanges of the fingers and toes. 3. Ball-and-socket joints, in which the rounded head of one bone is received into a cup-shaped cavity, as in the attachment of the humerus at the shoulder and that of the femur to the pelvis. This i)ermits of motion in any plane. 4. Torsional or pivot joints, which permit one bone to rotate against another. One such joint occurs between the first and second cervical vertebne to permit the turning of the head. Another is found in the forearm where the radius twists about the ulna in turning the hand over. The ulna is unable to twist on account of its mode of attach- ment to the humerus, and the hand is attached to the radius which twists around the ulna. 5. Saddle joints are formed by bones whose articular surfaces are concave in one direction and convex in the other. Such bones fit together like a man in a saddle and allow free movement in any direc- THE MOTOR OR MUSCULAR SYSTEM 47 tion, as in the attachment of the metacarpal bone of tlie thumb to the wrist. 6. Sliding hinge. — There is only one pair of these in the body, at the articulation of the mandible to the temporal bone. In opening the mouth the lower jaw not only acts like a hinge, but the head or con- dyle of tlie mandil)le slides forward in its fossa or socket. The jaw can be shoved forward, backward, and sidewise. Levers. — The levers formed by the movable bones of the body are for the operation of the joints by muscular stress. According to the principles of physics they fall into the groups, known as levers of the first, second, and third classes, according to the position of the weight to be moved and the point of application of the power which moves it. Arches. — The skeleton as a whole consists of a series of curves and arches. These give greater elasticity to the framework and help to absorb shock. So elaborate is this arrangement that no bone is with- out its curved surfaces and the plan is carried out even in the internal structure of the bone. The greater curves of the body are found in the arches of the feet which are of the greatest importance in preventing shock in walking, in the structure of the pelvis which consists of a series of arches, and in the curves of the spinal column. Any shock in walking which might be carried upward through the body tends to be shunted ofl' by every one of these larger cur^'es as well as by the innumerable smaller ones, before it can be communicated to the skull and the brain. Since there are twenty-two of the intervertebral pads in the spinal column, in addition to the curves, it is evident that here is a splendid structure for preventing the transmission of shock. THE MOTOR OR MUSCULAR SYSTEM. The cells of the body which are specialized for contraction make up the muscle tissue. The function of these cells is to bring about motion by shortening their length. This motion may be concerned with the internal affairs of the body, as of the heart in circulation, the intestinal wall in peristalsis, the arterioles in controlling the flow of blood, etc., or it may be related to outside matters, as in the move- ments of the eyeballs, or the hands, or it may take the form of locomo- tion. As these movements are not all of the same character, some differentiation of the contractile tissues is to be expected. In the evolution of the higher animal three distinct kinds of muscle cells have arisen for particular uses. -K^y!!:^ 1. Non-striated, or smooth muscle, not under control of the will. ^" 2. Cardiac or heart muscle, a special kind found only in the heart and also in^'oluntary. 3. Cross-striated or striped muscle, often known as voluntary muscle, although there are certain of these muscles such as the dia- phragm and intercostals, used in breathing, which are only partially 48 ANATOMY under the control of the will, and any of them, under certain condi- tions, may become involuntary in action. The smooth nmscle is the most primitive tj^pe in man and occurs commonly in lower forms, many of which have no other kind. The cells of this tissue (Fig. 16) are small and spindle-shaped, with the nucleus at the center, without cell walls, and the cytoplasm is faintly striped in a lengthwise direction, a characteristic of all contractile tissues. Cells of this type occur in the intestinal w^all, in the ducts of glands, the ureters, the blood and lymph vessels, the iris of the eye, the skin, etc. The}' are very slow in movement in comparison with other types of muscle tissue. There are no tendons in connection with this sort of muscle, since it usually lies in the walls of tubes, the sizes of which can be controlled by their contraction. The cells are intermingled with connective tissues. The heart or cardiac muscle cells differ in being block-like in form, often branched, with a central nucleus and a faint cross-striation. They also have no cell walls. In some respects this type is intermediate between the other two, yet with special characters of its own. There are some tendons in connection with the heart muscle, particularly the chordoB tendonce which hold the valves of the heart in place during contraction. The heart muscle has the special property of automatic action. Cross-striated muscle (Fig. 17) is highly spe- cialized for rapidity of contraction. The cells are in the form of long threads, sometimes several inches in length, which end rather bluntly. There is a definite cell wall known as the sarco- lemma. The nuclei are very numerous and are scattered over the cytoplasm immediately under the sarcolemma. The cytoplasm is much more highly differentiated than in either of the other kinds, and wc find not only the lengthwise striation much more definite, but there is also a very definite cross-banding of the con- tractile substance. This character seems to be connected with rapidity of action. When such a muscle fiber is subjected for a time to the action of alcohol, it tends to split lengthwise into much more delicate threads called fihriUce. When treated with acid the cell substance readily breaks crosswise, forming what are known as Bowman's disks. Contractile tissues are very widely distributed throughout the body, though we are not aware of the action of many of them when they contract, for example, those in the skin, bloodvessels, intestirtal^ tract, etc. When these tissues are aggregated into definite masses Fig. 16.— Fiber cells of plain muscular tis- sue (highly magnified). (Kimber.) THE MOTOR OH MUSCULAR SYSTEM 49 they are referred to as muscles. But muscular tissue is not always so distributed; in fact the non-striated type is generally distributed in the form of sheets or layers, such as those we find in the walls of the bloodvessels and the intestine where they form continuous layers throughout these structures. Even in the heart, though there are four chambers, the muscles which govern these are more or less continuous. The great mass of striated muscle tissue, which makes up so large a part of the limbs and of the body wall and which is usually to a greater or less extent untler the control of the will, is characteristically divided into definite muscles. In size these aggregations range from -'^OlOlliumminn- i3aR)innnmMiifHimnni«»-'~-,_<« '^^^m'&mmimmmm^ Fig. 17. — Wave of contraction passing; over a muscular fiber of dyticu.s. (Very highly magnified.) R, R, portions of the fiber at rest; C, contracted part; /, /, intermediate condition. (Schaefer.) the almost microscopic muscles which move the tiny ear ossicles, to the large muscles of the limbs. In form they are extremeh' variable, in adaptation to the spaces they occupy and the functions they per- form. As a rule muscles show the parts known as the belly, origin, and insertion. The belly is the swollen portion such as is seen in a long muscle like the biceps, for example, though it is usually not so well marked as in this case. At each end such a muscle tapers off into the tendons by which it is attached. The attachment at the stationary end is known as the origin of the muscle, and that upon the part to be moved as the insertion. Such muscles are usually arranged in pairs on opposite sides of the parts the}^ are concerned in moving. Thus the biceps lies on the front 4 50 ANATOMY of the arm and the triceps on the back of it and they are inserted into the bones of the forearm which they move. There are numerous departures from this rule, however, and certain muscles even lie free without any relation to the skeleton, such as the diaphragm, the cheek muscles, and those of the lips and eyelids. Altogether there are about five hundred separate voluntary muscles. If we examine a cross-section of a muscle we will find on the outside a connective-tissue layer forming a -binding membrane called the fascia or perimysium. Strands of similar tissue run inward from this, di^•iding the muscle into large portions which are again subdivided until the muscle bundles, consisting of a number of muscle fibers, are formed. The tendons originate among the connective tissue between the muscle cells. THE NERVOUS SYSTEM. This system has the function of correlating the activities of all the other systems of the body, as well as of relating the body to the outside world by means of the special senses. Therefore we naturally expect to find nervous tissues widely distributed throughout the body. The essential structure of the nervous system consists of the nerve cells or neurons (Fig. 18). Each neuron is made up of a cell body with at least two processes or nerve fibers which are merely extensions of the cell. As a rule one of these nerve fibers is longer than the other and is known as an axon. The cell bodies are aggregated into masses called ganglia. The "gray matter" of the brain and spinal cord con- sists of large numbers of these nerve cells, while the "white matter" consists of the nerve fibers. The fibers are often collected into bundles for convenience of distribution, such bundles of fibers being called nerves. Xerve cells originate impulses and also receive them from the sensory endings or from other nerve cells. The nerve fibers are highly specialized for the purpose of transmission of the impulses. The apparatus is often compared with a telegraph system in which the ganglia represent the offices where messages are received and sent out and the nerve fibers represent the wires which can only carry the messages sent over them. Neurons communicate with each other by having their processes in close contact, though they do not form a continuous network, as was formerly supposed. One nerve fiber at its end is divided into braric-hcs called terminal arborizations, and these are closely associated with the endings of branches or dendrites of other cells. An impulse travels in only one direction along any one nerve fiber in the body, and in passing from one cell to another it goes outward through the axon, over the terminal arlxtrizations, to the dendrites of the other cell and on to the cell body. This process is not reversible. Xerve fibers are classified according to the direction in which they carry impulses. THE NERVOUS SYSTEM 51 1. Afferent fibers are those which conduct inii)ulses from without toward their respective cell bodies. A fiber carrying impulses from Fig. 18. — Scheme of central motor neuron. (I. type of Golgi.) The motor cell body, together with all its protoplasmic processes, its axis-cylinder process, collaterals, and end-ramifications, represent parts of a single cell or neuron, a.h., axon-hillock devoid of Nissl bodies, and showing fibrillation; c, cytoplasm showing Nissl bodies and lighter ground substance; n', nucleolus. (Barker.) the skin to the central nervous system would be an afferent fiber. The nerves of special sense all belong to this class. 52 ANATOMY 2. Efferent fibers are those which conduct impulses away from the cell bodies, such as those going to the muscles or glands to govern their action. 3. Commissural fibers are those which run from one nerve cell to another. A nerve usually consists of both afferent and efferent axons or fibers, which are bound together in one bundle for convenience in distri- FiG. 19. — Diagram illustrating the general arrangement of the eerebrospinal system. (Kimber.) bution, since every ])urt of the body requires both afferent and efferent coriiicftions. \Vhcn nerve fibers ])hss out to any distance from the ganglion they usually have a special coat or sheath called thevirdvllary sheath. Such nerve fibers are said to be medidlated to distinguish them from the non-vied iillatcci which lack the sheath. The longest nerves in the body are tho.se which go to the extremities. The fibers THE NERVOUS SYSTEM 53 which are distributed to the fingers and toes have their cell bodies in the spinal cord. The nervous system consists of two chief parts: 1. The central or cerebrospinal system. 2. The sytit pathetic system. The Central System. — ^The central system is made up of the gangli- onic or cellular masses of the brain and spinal cord (Fig. 19), together with the axons or fibers belonging to these cells. The principal parts of this system are the brain, the spinal cord, the cranial nerves and the spinal nerves. r> untul lobe. Occipital lobe. Fig. 20. — Base of brain, showing superficial origin of cranial nerves. (Little.) The Brain (Fig. 20).— The brain consists essentially of great masses of cells or ganglia (the gray matter) with their commissural fibers and the fibers connected with the cranial nerves and spinal cord. It is protected within the skull and is further surrounded by three con- nective-tissue membranes. These are known as the dura mater, lining the bones of the cranial cavity; the pia mater, a delicate mem- brane closely covering the surface of the brain and richly supplied with bloodvessels; and the arachnoid which is between the other two. The largest part of the brain is the cerebrum or forebrain, which 54 ANATOMY fills the whole upper part of the skull. Its surface is deeply and irregularly convoluted and it is nearly separated into right and left honispJicres by a deep furrow, the median fissure. At the bottom of the fissure, however, there is a broad band of commissural fibers called the corpus callosum. The next largest portion is the cerebellum or little brain situated behind and beneath the cerebrum. It is only about one-seventh as large as the cerebrum. Its surface is regularly convoluted and it is divided into a median and two lateral lobes. A broad band of com- missural fibers crosses below to place the two lateral lobes in connec- tion. This band is known as the pons Varolii (bridge of Varolus). The medulla oblongata is that portion of the brain which is contin- uous with the spinal cord. It is situated beneath the cerebellum immediately behind the pons Varolii. The cavities within the brain, known as ventricles, are expansions of the minute canal which runs all the length of the spinal cord. There are twelve pairs of nerves, the cranial nerves, connected with the brain. Three of these are devoted entirely to special senses. The first pair, the olfactory nerves, have to do with the sense of smell; the second pair are the optic nerves or nerves of sight; and the eighth pair are the auditory nerves or nerves of hearing. The third, fourth, sixth, seventh, eleventh, and twelfth pairs are motor nerves distributed to certain muscles of the head. The fifth, ninth, and tenth are mixed. All these are distributed to the head, except the tenth (vagus or pneu- mogastric nerve), which sends fibers to the esophagus, heart, and stomach as well. The cranial nerves emerge from the skull through openings called foramina. The Spinal Cord. — This is the portion of the central nervous system lodged witliiu the spinal column and it is in direct continuation with the brain. It is not as long as the column, but tapers oflF and ceases at the le\'el of the second lumbar vertebra. The same three protect- ing membranes which surround the brain are continued down around the cord. The cord is deeply grooved in front and behind and so is nearly separated into right and left halves, and the middle is pene- trated by a tiny canal, the central spinal canal, which is continuous with the ventricles of the brain. The spinal nerves number 31 pairs arranged as follows: 8 cervical nerves in the neck region. 12 dorsal nerves, corresponding to the dorsal vertebrae. 5 lumbar nerves, corresponding to the lumbar vertebrae. 5 sacral nerves, corresjjonding to the sacral vertebrae. 1 coccygeal nerve, corresixdiding to the first coccygeal vertebra. The spinal nerves pass out through/om?/rirmoroj)enings between the vertebra, but the lower ones run for some distance down the vertebral canal before they emerge. Each spinal nerve has two roots, a dorsal anrl a \(Mitral, which merge into one nerve before ])assing out of the vertebral canal. The dorsal root is made uj) of afferent (sensory) fibers THE NERVOUS SYSTEM 55 only and bears a ganjjr()ximal side which are V>uilt into its cementum. These, as they pass across the space, are closely interwoven, forming a basket-work structure that supports the overlying gum in a most perfect manner. The third (jrovp. A little more rootward to the second group is another set of fibers that soon after passing from their attachment in the cementum are inclined aj)ically. These form a very strong bundle of fibers. On the labial and lingual sides they ])ass to the outer sur- THE PERIDENTAL MEMBRANE 97 face of the alveolar process and are attached to the i)eriosteLim cover- ing the bone here. On the proximal side they either pass to the Fig. 39. — Diagram of the fibers of the perickiital membrane: G, gingival portion; AL, alveolar portion; Ap., apical portion. (From a photograph of a section from incisor of sheep.) (Noyes.) cementiim of the adjoining tooth or are built into the upper surface and sides of the bone that intervenes between the teeth. These fibers 7 98 SPECIAL ANATOMY resist any force that tends to pull the tooth from its socket. They form what is known as the dental ligament. The fourth grovp are arranged like a constrictor muscle around the gingival margin and keep the gum tissue in close contact with the neck of the tooth. Arrangement in the Alveolar Portion. — Here are found three areas of variation in direction of the fibers. First: The fibers coming off from the cementum at the level of the top of the alveolar process pass at right angles across the intervening space to be inserted into the bony walls of the process. This arrangement is continued down the root of the tooth nearly one-third of the distance to the apex. These fibers arise from the cementum in strong bundles and then break up into fan-like forms as they cross the space to be inserted into the bone. In transverse sections of the root at this level it is noted that the fibers that come oft' from the angles of the roots do not pass immediately across the space but are deflected to right and left. These are the fibers that resist any force that tends to rotate the tooth in its socket. Second: As the lower portion of the previously considered area is approached the fibers, after leaving the cementum, begin to pass occlusally and are inserted somewhat higher up on the wall of the alveolus. This arrangement is continued until the apical end of the tooth is reached. This area is large and the fibers are strong because they have to resist the greatest force exerted in mastication, /. e., the thrust force as the jaws are closed. By these fibers the tooth is actually suspended in its alveolus. Third: At the lower portion of the apical third of the root the fibers again begin to take a more direct course from the cementum to the bone until they are passing directly across, as noted in the upper third. The Arrangement in the Apical Portion. — Here the fibers after passing horn the cementum radiate in all directions before being inserted into the bone. In this way the apical space is filled with a mass of fibrous tissue. The Cells. — Fibroblasts. — These are the cells that ha^•e formed the fibers and are looking after their welfare. They are scattered throughout the entire membrane. Cementoblasts. — These are the cementum-forming cells and lie in contact with this tissue between the points of origin of the fibers. As they form the cementum some of the cells surround themselves with it and then take the name of cement cells or corpuscles. They also build into the cementum the fibers of the membrane. OsteoblasU. — These are the bone-forming cells and have their station on the bony walls of the alveolus. They are active in forming the bone of the alveolar process that is in juxtaposition to the roots of the teeth. They too become bone cells when they have surrouiided themselves with this tissue. The attachment of the fibers of the membrane into the bone is performed by these elements. THE PERIDENTAL MEMBRANE 99 Osteocla.sf.s. — These are the cells that eat away the bone or cemen- tiini when there is a demaiul for this j)r()eess. Through their action the fibers of the membrane are detached at any o;iven area. This occurs during the absorption of the roots of the deciduous teeth and it is these cells that are responsible for this process. They are also used when nature believes that the l)one in any given place is too thick and heavy for the strain brought to bear upon it. If so, these cells are brought into activity and d(>stroy the thick bone by forming marrow spaces within it. This occurs in the formation of the alveolar ])rocess and accounts for its cancellous or spongy character. Bloodvessels. — The peridental membrane has a very rich supply of blood. The arteries enter the apical space from the bone beneath. They then give off branches which pass into the pulp cavity to supply the organ therein. The main branches pass occlusally in all directions through the peridental membrane. They lie nearer the wall of the alveolus than the. cementum. As they pass upward they receive from and gi\'e off })ranches to the bone of the alveolar wall. They end by anastomosing with the bloodvessels of the gum tissue and help supply this area. From this it is noted that the blood supply of the gums and peridental membrane is intimately related so that stimulation of gum tissue by massage and brushing will in turn stimu- late the peridental membrane — a fact that is of the greatest impor- tance in the treatment of lesions of this latter structure. The Nerves. — These have the same point of entrance and the same distribution as the bloodvessels that have just been described. It is important to note that these nerves give to the peridental membrane the sense of touch. This sense is well developed, for the lightest con- tact is immediately recognized. Epithelial Elements. — As the function of these structures is still a mystery it is sufficient in this text to note that such tissues are present but that their real significance still remains unknown. The function of the peridental membrane. (a) A physical function, i. e., the maintaining of the tooth in the socket. (6) A vital function, manifested through the agency of its cells in the formation of cementum and bone. (c) A sensory function in that it supplies the sense of touch to the tooth . Changes in the Membrane with Agie. — ^^'hen the tooth first erupts the sj)ace between the root and wall of the alveolus is relatively wide. Each year finds this becoming smaller and smaller because of the formation of new^ lamellae of cementum on the one side and of bone on the other. The peridental membrane grows proportionately thinner as it is thus encroached upon. However, there is always membrane present no matter what the age of the individual may be. In other words, the bone and cementum never come in immediate contact with each other. This thinning of the membrane makes it less resistant to irritations and so predisposes inflammatory conditions. Hence 100 SPECIAL ANATOMY diseases of the peridental membrane are more frequently found after adolescence. The Alveolar Process. — As has been perviously emphasized, the bone of this process is built secondary to the formation of the teeth or rather coincident to their eruption. It is a product of function and is arranged as to its structure in a way that will best resist the forces that are brought to bear upon it. In the upper jaw we find a dense, hard layer of bone about the necks of the teeth labially and buccally. In the incisor and cuspid region where much force is exerted upon the whole length of the roots the bone is quite thickened over their entire labial surfaces. This is well demonstrated in those lower animals that use these teeth for seizing and tearing their prey. 0^'er the buccal roots of the bicuspids and molars it is very thin. Lingually, all the teeth of the upper arch are well supported. In the lower arch again is found the compact bone about the necks of the teeth and their roots well supported buccally, as most of the strain is in this direction. The great mass of bone of both the maxilla and. the mandible is made up of the cancellated variety about the periphery of which is a layer of thick, dense bone. The wall of each alveolus joins this thick- ened layer at its upper border. Below this point of union the wall of the alveolus is surrounded with cancellated bone so that the alveolar process as a whole is quite elastic and springy. In connection with our reference to bony tissue it is well to mention the fact that this is living tissue, a specialization of the connective tissues, adapted for perfect support and that it is ever throughout life undergoing constant change as a result of the mechanical forces brought to bear upon it. By virtue of the ability to make such changes, nature is able to meet any requirement that is demanded, even though it be far different from the original condition for which the bone was built. So in examining a specimen of bony tissue under the microscope various forms of bone cell activity are seen going on, representing different stages of bone formation and absf)rption. Tooth Formation. — The first sign of the formation of teeth is seen in the embryo at about two and a half months. Along the top of each arch (upper and lower) there is seen a heaj:)ing up of the cells of the outer layer of tissue. If a cross-section is made of the arch, it will be noted tliat these cells are also di])])ing down into the underlying tissue. This formation is known as the dental rl(l(/e. From the lingual side of this ridge a shelf-like growth is formed called the lainina. At intervals along the lamina corresponding to location of each tooth little buds grow down from it. The under surface of these buds becomes indented, taking on the ap])earance of an inverted cuj). This structure is now known as the enamel organ (Fig. 40), and will soon begin to lay down enamel along its inner surface. The cells lining this surface are the enamel cells and are active in the formation of this substance. The enamel organ is of epithelial tissue origin. TOO TH FORMA TION 101 As the enamel organ is forming, the cells of the tissue into which it grows begin to take on activities. As fast as the infolding of the base of the enamel organ takes place the indentation is filled in with these active underlying tissues until a papilla is formed. This is known as the dental papilla (Fig. 40). This structure is of connective-tissue origin and will become active in the formation of the dentin. Growth of the papilla continues until it has assumed the shape of the crowni of the tooth to be formed. To this structure formed l^y the enamel organ and dental papilla is given the name of tooth germ. Fig. 40. — The enamel (irjiuii. The outer tunic connected i'^ ili.- lamina l)y the dental iiaiiilla gro\vin<; up into the cap. The spaces are shrinkage spaces. t he cord ; (Noyes.) After the dental papilla has been formed the cells at its base develop fibrous tissue which grows up and around the outer side of the enamel organ and over its top so that the tooth germ is enclosed in a fibrous sac. This combination of structures, /. e., the fibrous wall, the papilla and the enamel organ constitutes the dental follicle. This is completed by the end of the twelfth week. Just before the enclosure takes place a secondary bud is given off from the enamel organ, usually near its point of origin from the lamina, 102 SPECIAL ANATOMY which wpows downward to become the enamel organ of the permanent tooth (Fig. 41). Soon after the formation of the dental follicle the bone of the jaw below this structure sends up processes which pass to the lingual and labial side of the follicle. Later bony growth appears on the proximal sides and finally the top is covered over. This bony structure is what Fig. 41. — The tooth Korni showiiiK the Imd for tlu; pcrmiiiiciit tooth ;it P. Calci- fimtion is just bcKiniiiiiK: /'', folliflc wiill; J), dental papilhi; T, inner tunic; 7", outer tunic; .S, stellatxj rcticuhitn; O, odontol)lasts; yl, amelohlasts; B, bone. (Noyes.) is known as the deiifdl rri/pt and simply serves as a protection to the forming tooth. This formation ])ersists until the entire crown is developed and the tooth ready to. erupt when the top is absorbed and the t(K)th passes into the mouth. At about the sixteenth week the dentin and the enamel begin to form, the former on the outer edge of tlie dental pajjilla and the latter on top of this dentin. THE DEVELOPMENT OF THE JAWH 103 Tlie roots of the teeth (h) not appear until the tooth l)egins to take on the process of eruption. At this time also the first of the cementum is seen. This is formed by cells in that fibrous tissue that grew up and around the enamel organ to complete the follicle. This fibrous tissue now may be considered as the peridental membrane. Coincident with the formation of cementum by the cells on the inner side of this membrane there is a deposit of bone laid down by the osteoblasts on the other side of the membrane. This is the beginning of the alveolar process . The first permanent molars are the only permanent teeth for which the enamel organ arises directly from the lamina. The enamel organs for the second and third permanent molars arise from the buds of the first and second permanent molars respectively. THE DEVELOPMENT OF THE JAWS. While it is impossible in the space alloted this subject to go into detail regarding the growth of the jaws, yet it is quite necessary that the dental hygienist should know briefly the plan upon which nature builds under normal conditions. For an exhaustive study of this subject the student is referred to Dr. Noyes's text-book, Dental Histology and Embryology. In a comparison of the skull of an infant at birth with that of an adult it is noted that as growth proceeds there is practically twice as much development below the nasal spine of the frontal bone as above it. Passing in our study to this region of greatest change it is seen that in the adult it can be divided into thirds, the upper of which is occupied by the nasal cavity and the lower two-thirds by the organ of mastication. When, however, an attempt is made to study the child's head from this point of view it is foinid that it is impos- sible to so divide the head for there is a fusion, as it were, of the upper two-thirds, and that territory that is entirely nasal in the adult, is here more than half given over to the developing tissues of the organ of mastication. To be more specific, all that part of the nasal cavity which lies below the lower border of the orbits is literally lined with tooth germs. From this study it may be deducted that the great (loioncard growth in the lower half of the head is due primarily to the formation and subsequent eruption of the teeth, and secondarily to a continued growth of bone thrown out to act as a supporting structure for these organs. This downward growth begins with the eruption of the deciduous denture and continues until all the permanent teeth anterior to the first molars are in position. After the completion of the deciduous denture two new directions of growth manifest them- selves, a lateral or expanding grt)wth to allow for the difference in size between the teeth of the decidiibus and permanent dentures, and a forward one to make room for the developing permanent molars. This development continues until all the teeth are in position and occlusion is established. CHAPTER III. PHYSIOLOGY. By ALEXANDER M. PRINCE, M.D. Definition. — General physiology, a branch of the biological sciences, is concerned with the study of function in all living organisms. Ilumcm physiology, one of its subdivisions, deals with the functions of the body of man. The term function is applied to all the activities or life processes of the various parts of the body, and in a broader sense includes the interrelations of these activities in the economy of the individual as a whole. As all the reactions of the body are dependent on physical and chemical phenomena, function may be further defined as the chemistry and physics of the living body. From the study of anatomy it has been found that the structural unit of every living thing is the cell and that cells of the same type enter into the formation of tissues which in turn constitute the different organs. Likewise, the nnit of function is the cell, as the behavior of any tissue or organ depends upon the characteristics of its cells. The Cell. — The typical cell consists of a semifluid, jelly-like substance called protoplasm. This substance is a complex chemical combination of the following elements: nitrogen, carbon, oxygen, hydrogen, sulphur and a trace of phosphorus. The protoplasm is divided into the cytoplasm which forms the body proper of the cell and a spherical or oval body, usually found in the center of the cell, called the nucleus. The maj(jrity of cells contain but one nucleus, although not infre- quentl\' two or more are present. In the higher organisms an excep- tion to this rule is found in the red blood cell, the nucleus of which is lost in the ])rocess of development. The nucleus is an essential constituent of tlic cell, for if a cell is divided })y section into a luicleated and non-nucleated ])orti()n, the first regenerates to a complete cell, whereas the non-nucleated portion soon dies. The formation of certain substances in the cytoplasm are prevented by removal of the nucleus and furthermore, reproduction cannot take ])lace in its absence. On the other liand, tiie nucleus is dependent on a certain amount of cyt()])lasm, for if completely isolated, it also perishes. It is therefore evident that both the nucleus and cytoplasm are essential to the life processes of the cell. Properties of Protoplasm. — Protoplasm is not only very complex, })ut also \(Ty uiisljiblc. In the presence of oxygen, ])r<)toplasm undergoes THE AMEBA 105 chemical changes with the formation of simpler substances. This process is known as o.vidaiion and is essentially a burning uj) of proto- plasmic material. The result of this combustion is the production of energy which manifests itself as heat, motion, etc. The end-products of oxidation, which are known as waste material.^, exert a poisonous influence on the cell if allowed to accumulate, but means are available for their removal by the function of excretion. On the other hand, the waste resulting from the evolution of energy must be constantly replaced, otherwise death of the cell would eventually follow. This waste can only be repaired by the absorption of new material and it is for this reason that food is required. The process of breaking down in the cell which accompanies the liberation of energy is known as vdtdhoJism; the repair and growth of the cell is known as anabolism; and these two processes considered together are included under the term metabolism. Most foods as found in nature are not in a condition to be absorbed and assimilated by the cell until especially prepared by chemical processes. This function of food preparation is present in certain cells and is known as dic/estion. An important function foimd in animal life is motiJiiy or the ability to perform movements which result from changes in the shape of the cell. This form of cellular activity is associated with the functif)n of irritability, by which the organism is enabled to perceive and react to external changes. As all beings originate from a preexisting cell, the function of reproduction, which permits such perpetuation of species, must be considered. To recapitulate then, it is noted that there are certain fundamental properties or functions common to all forms of living matter: metab- olism, motility, irritability, and reproduction. These activities are found in a very primitive form in single-celled organisms and so may be advantageously studied in one of these, for example, the ameba. The Ameba. — The amel)a is an example of the simplest form of animal life and consists of a single cell. It is found in stagnant bodies of water and moves about slowly by the extension of finger-like pro- cesses resulting from the flow of its protoplasm. This form of motility is known as ameboid motion. This organism also presents evidence of irritability, for it will respond to external influences, moving toward food particles and away from harmful substances. This ameboid motion also serves as a means of capturing particles of animal and vegetable matter upon which it feeds, two protoplasmic processes encircling the food particle and forcing it into the semifluid interior of the animal. The food is then slowly digested by juices formed in the protoplasm and is distributed to all parts of the cell where it is utilized for repair and the storage of energy while the undigestible portions of the food are finally extruded from the cell body. These reactions represent the functions of digestion, assimilation and excretion. The ameba absorbs the oxj'gen necessary for energy production from the water in which 106 PHYSIOLOGY it lives and gives off carbon dioxide. This function is known as res- piration. In this animal, reproduction is very simple, taking place by division of the nucleus and cell body. It is noted from the ameba that all functions may be present in one cell, but as the scale of evolution is ascended animal forms consisting of many cells are met with. In these it is found that all functions are not possessed alike by all the cells, but that there is a dicision of labor, certain groups of cells becoming better adapted along particular functional lines. This specialization of cellular function cannot be better observed than in man, for the human body is essen- tially a large colony of cells the individuals of which have special duties to perform. The first physiological process that demands attention is that of nutrition or alimentation, as it is called. This is studied under four divisions, /. e., digestion, absorption, assimilation, and elimination or excretion. PHYSIOLOGY OF DIGESTION. The human body in the performance of its functions is constantly losing material. Every form of activity, whether the contraction of a muscle, the transmission of an impulse through a nerve or the secretory processes of gland cells, is accompanied by catabolic or breaking down changes in the cell protoplasm. These changes result mainly from the com- bination of oxygen, carried in the blood, with complex chemical sub- stances in the cell. The simple products arising from the destruction of the cell substance, being no longer of value to the cell, are removed by the process of excretion. In order to maintain the activity of the tissues, this waste of substance must be constantly replaced by suit- able new materials, wliich are called foods. Classification of Foods. — Foodstuffs are divided into two general classes: (I) nitrogenous and (II) non-nitrogenous. I. The nitrogenous foodstuffs include the yroteins and the alhn- minoids. The proteins are found in the protoplasm of all forms of vegetable and animal life and are chemical combinations of nitrogen, carbon, oxygen, hydrogen, sulphur and phosphorus. Protein has been called the "essential" foodstuff, as it contains the necessary elements for the repair of the body cells. The albuminoids, chemically allied to the proteins, are derived from ccMinective tissues (bones, tendons, etc.), but are unimportant as foods, owing to the difficulty with which thej' are absorbed from the alimen- tary tract. II. The non-nitrogenous foodstuff's, as the name implies, do not contain nitrogen and include the r.drbdlij/drdtrs, the /a/.v, the nrineral salts and vater. The carbohydrates consist of carbon, oxygen and hydrogen in com- PHYSIOLOGY OF DIGESTION 107 bination ami are mainly derived from the vegetable world. This division inclndes the starches and sugars. These substances are readily oxidized in the body and for that reason have great energy- producing ])o\ver. The fat.s- consist of the same elements found in carl)ohydrates and include the oils and fats derived from animal and plant life. The most important mineral salts- required for the needs of the body are the chlorides, phosphates, sulphates and carbonates of sodium and potassium and the phosphates and carbonates of lime and mag- nesium. Of these substances the chloride of sodium (common salt) is the most essential. Iron and iodin are also necessary in small quantities. ]]'(iter is a chemical compound of hydrogen and oxygen and next to air is the most important substance required for the maintenance of life. Water constitutes 70 per cent, of the body weight and is found in all the tissues and fluids of the body. It also acts as a solvent for many substances which could not be otherwise absorbed or excreted. TABLE I.— FOODSTUFFS. 1. Nitrogenous Proteins Albuminoids Albumin Casein Myosin Syntonin Vitellin Gluten / Choiidrin \ Gelatin Occurrence. white of eggs, milk, blood, etc. milk and cheese. muscle tissue (meat). yolk of eggs, cereals (flour). cartilage. in bones and other con- nective tissue. 2. Non-nitrogenous ■ Starches Carbohydrates { Sugars 1 Sucrose Glucose Maltose Lactose Fats Salts [ Water. in all cereals, potatoes, unripe fruits, sugar cane, fruits, malt, milk. Stearin 1 Palmitin I found combined in animal Margarin f and vegetable fats and oil. Olein J Lecithin in yolk of egg and nervous tissue, in vegetable and animal tissues and directly from mineral world. Most of the foodstuffs as they occur in nature are not in a condition to be utilized by the body cells until especially prepared by chemical processes. This food preparation or digestion is accomplished by specialized cells associated with the organs of the alimentary .system. lOS PHYSIOLOGY Of all the materials used as foods, water and the majority of the salts are diffusible and therefore readily absorbed by the cells lining the alimentary canal. On the other hand, the proteids, carbohydrates and fats are not diffusible, that is, they will not pass through an animal membrane until their chemical nature has been changed. This process of making indiffusible substances suitable for absorption is brought about by the action of enzymes secreted by the cells of glands which empty into the alimentary canal. Properties of Enzymes. — Although little is known of the chemical composition of enzymes, these substances may be recognized by the folhnving facts: 1. They are manufactured and secreted by living cells. 2. A very small quantity of an enzyme, without undergoing any special change in itself, will act upon enormous amounts of foodstuffs. 3. Their action is selective, that is, they will only act upon special substances, i. e., ptyalin only digests starches and has no effect on protein or fats. 4. Their action depends on the reaction of the medium, i. e., ptyalin only exerts its effects in alkaline solutions, its chemical action being arrested immediately in the presence of acids. Pepsin, on the other hand, acts in an acid medium. 5. Their activity depends on the temperature, being most effective at body temperature, ceasing to act in the cold, and being per- manently stopped at high temperatures, such as would result from boiling. Alimentation. — The alimentary system consists of a long tubular channel running through the body. Emptying into it at different levels are the ducts of the digestive glands, the cells of which secrete digestive fluids of specific qualities, some acting on proteins, others on fats and carbohydrates. Through the motility of this alimentary tube the food is propelled and progressively brought in contact with these fluids. Chemical transformations take place whereby the food is prepared for absorption, the undigestible portions remaining in the digestive tract from which they are later expelled. Mastication . — The first process of alimentation is mastication or the chewing of food. The food introduced into the mouth is ground by the teeth and mixed with the secretion of the salivari/ (/lands. During the process of mastication the food is finely reduced so that it will oiler a greater surface for the action of the digestive juices and is at the same time moistened with saliva so that it can be more readily swallowed. Furthermore, if any starches are present, they are in part transformed into (iilVusible sugars by the actioji of the salivary enzymes. The Salivary Glands. — The digestive (/lands of the month occur in pairs and are named from their location, the parotid, the sub- maxillary and the sublingual. The secretion of these three groups rtf glands, mixed with the mucus of microscopic glands which arc scattered throughout the mouth, is called salicd. PHYSIOLOGY OF DIGESTION 109 P^ach gland is made up of secreting cells arranged in the form of small sacs which communicate l)y fine ducts or tubules. These tubules join to form the larger ducts which open into the mouth. These glands are supplied with a rich network of bloodvessels and nerves. Their nervous control is beautifully shown by the marked secretion which occurs at the sight or smell of pleasing foods. The mixed saliva of the glands of the mouth consists in great part of water and is of an alkaline reaction. Among its constituents are mucin, the substance which gives the saliva its slimy character and an enzyme known as yiyalin to which the partial digestion of starches is due. The food after being thoroughly masticated and mixed with saliva is forcetl into the yharyn.v, a funnel-shaped muscular bag, by the act of deglutition. By the contraction of the pharynx the food is then pressed into the esophagus. The latter structure is a tube which conveys the food from the pharynx to the stomach by a pro- gressive wave-like contraction of its muscular coats. This type of muscular action which occurs also in the stomach and intestines is known as peristalsis. (kistric Digestion. — The stomach, continuous above with the esophagus and below with the small intestines, is a muscular bag having a capac- ity of about three pints. Its internal surface is lined with secreting glands the cells of which are arranged in the form of simple tubular structures. The cells forming these tubules are of three types; those lying near the opening of the glands secrete mucin, the other two varieties secrete hydrochloric acid and the enzymes pepsin and rennin. At the point of junction with the small intestines the stomach is furnished with a muscular ring continuous with its muscular coats. This ring acts as a valve and is called the pyloric sphincter. The junc- tion of this structure is to prevent the further progression of the food until sufficiently digested in the stomach. The Gastric Juice. — The secretion of the stomach, known as the gastric juice, is a clear, acid fluid consisting of water, hydrochloric acid, to which the acidity of this secretion is due, and two important enzymes, pepsin and rennin. These two enzymes, unlike ptyalin, produce their effects only in an acid medium. Pepsin transforms the indiffusible protein foodstuff's into pep- tone. Peptone differs from undigested protein by its great solubility and the ease with which it passes through animal membranes. In this way peptones are readily absorbed by the cells lining the alimen- tary canal and can be then transferred to the blood and carried away to supply the needs of nearby and distant cells. Rennin is an enzyme which acts on milk by precipitating the milk protein. This protein, known as casein, is indift'usible. After being precipitated it is then converted into peptone by the pepsin. The gastric juice does not digest fats or carbohydrates, and the no PHYSIOLOGY digestion of starches previously begun in the mouth is soon arrested by the acid reaction of the gastric secretion. The stomach by the contraction of its muscular walls, churns the food so that it is thoroughly mixed with the secretions, thus hastening the process of digestion. The food, when gastric digestion is com- pleted, is reduced to a grayish liquid material known as chyme. At this stage the pyloric sphincter relaxes and allows the gradual passage of the stomach contents into the small intestines. Although the stomach is richly supplied with bloodvessels, only a very small portion of the digested foods are absorbed into the blood from this organ, so that the stomach, like the mouth, is concerned principally with the preliminary preparation of food. The Squall Intestine. — Th esmall intestine, where final digestion and absorption take place, is a muscular tube, the mucous membrane of which is thrown into folds so as to offer a greater surface for absorp- tion. This mucous membrane consists largely of finger-like projections called I'iUi, between which lie tubular glands (glands of Lieberkiihn) which produce a secretion known as the succus entericus. This secre- tion contains water, mucin and some enzymes concerned with the digestion of protein and the transformation of indiffusible carbo- hydrates into dextrose. In the upper part of the small intestine (the duodenum) open the ducts of two large glands, the liver and the ixincreas. The Liver. — The liver is a large gland which secretes an alkaline, golden-yellow fluid known as hile. The principal junction of the bile is to neutralize by its alkalinity the acid chyme derived from gastric digestion, and thus prepare it for the action of the pancreatic enzymes which are effective only in an alkaline medium. The bile t:'ontains pigments and salts. The hile salts are especially important, as they aid in the digestion and absorption of fats in the presence of the pancreatic secretion. The Pancreas. — The pancreas is a gland much larger but similar in structure to the salivary glands. Its cells secrete an alkaline fluid which contains three important enzymes, trypsin, amylopsin and steapsin. Trypsin has an action similar to pepsin, as it transforms proteins into peptones, but in this case only in an alkaline medium. Amylopsin is similar in its action to ptyalin, transforming starches into sugar. Steapsin is the enzyme concerned with the digestion of fats. Under its influence fats are broken up into glycerin and fatty acids. Glycerin is readily absorbed by the intestinal cells and the fatty acids combine with the alkali of the pancreatic juice and bile to form soaps which are very diffusible. The rest of the fats which are not changed in this manner are emulsified or reduced to fine division by the action of the soaps. The fat emulsioi) and soaps arc then in a form which can be absorbed bv the vilH. I'llYSIOUmV OF ABSORPTION 111 As ill the stomach, the food is kept in motion 1)\' the peristalsis of the intestines so that finally the food is distril)nted throvij^hout the small intestine for (ihsorj/tion. The contents of the small intestine when digestion is complete are known as chyle and have a creamy color owing to the presence of finely divided fat. The original food which was taken into the mouth as nnabsorbable proteins, carbohydrates, and fats is now converted into peptone, sugar, glycerin, soaps and emulsified fats, any one of which can readily be absorbed. TABLE II.— DIGESTION IN THE ALIMENTARY CANAL. Place. Secretion. Source. Enzyme. Reaction of medium. Foods acted upon. Final products. A. Mouth Saliva li. Stomach Gastric juice C. Small intestines Secreting cells Ptyalin of salivary glands Peptic glands Pepsin Rennin Pancreatic juice Bile Succus en- entericus Pancreatic cells Liver cells Intestinal gland cells Alkaline Acid Trypsin Amylopsin Steapsin None Maltase Acid Alkaline Alkaline Alkaline Alkaline Alkaline Starches Proteins Milk Proteins Starches, sugars Fats, oils Aids pan- creas in fat digestion. IndSfusible sugars Dextrin, mal- tose. Peptones. Casein precipi- tated (milk curds) which pepsin trans- forms into peptone. Peptones. Maltose. Fatty acids, glycerin (emulsified fats, soaps). Dextrose. PHYSIOLOGY OF ABSORPTION. Practically all ah.sorpfioti takes place in the small intestine. This proceeds in two different ways. (1) Absorption into the lymphatics by means of the villi, and (2) direct absorption into bloodvessels, tributaries of the portal circulation. Fats are absorbed by the lymphatics; sugars, peptones, salts, etc., by the bloodvessels. The villi are small finger-like structures containing a lymphatic channel surrounded by a network of fine bloodvessels, the whole being covered by a single layer of columnar shaped cells. These lym- phatic channels or lacteals of the villi connect with larger lymphatic vessels which eventually empty into the general circulation by means of a large lymphatic vessel known as the thoracic duct. Fats are absorbed by the cells lining the villi and passed into the central lymphatic channels. They are then carried through this system of vessels and thrown directly into the blood stream to be distributed to all parts of the body. The intestinal tract is furnished with a rich network of fine blood- vessels which lies directly under the cells lining the intestines. The 112 PHYSIOLOGY bloodvessels or capillaries forming this network fuse into larger vessels which empty into the liver by means of a large vein called the portal. Peptones, sugars, salts and icater pass into these bloodvessels and hence are taken through the liver before their final distribution to the body cells. PHYSIOLOGY OF ASSIMILATION. Peptones, after undergoing further changes in- the liver, are dis- tributed to all the cells by the general circulation and there are used for the repair of the cell protoplasm. The sugar (dextrose) in excess of the immediate requirements of the body, is stored in the liver cells as glycogen. This substance is an insoluble sugar formed from dextrose by the liver cells with the aid of an internal secretion furnished by the pancreas. This glycogen is retained in the liver until called for by the tissues when it is reconverted into dextrose and carried away by the blood stream. If carbohydrates are taken in excess, so that the limit of storage is reached in the liver, sugar is converted by connective-tissue cells into fat which is stored in various parts of the body, under the skin, about the mesenterj^ etc. Fats are utilized like sugar in the production of energy, work, animal heat, etc., and if in excess are also stored as fats for future use. The Removal of Waste Products. — By the peristalsis of the small intestine the undigestible portions of the food are gradually carried to the large intestine. The contents of the latter structure are practically free from absorbable substances. This undigested food undergoes bacterial changes, becoming acid in the process, while the large amount of water present is removed by absorption. It is then known as the feces and as such is finally expelled from the body. The physiology of elimmation or excretion is considered in detail on page 122. THE PHYSIOLOGY OF RESPIRATION. Chemical Changes. — When oxygen combines chemically with carbon a gaseous compound is formed known as carbon dioxide. This chemical reacticni (oxidation) is always accompanied by the liberation of energy which appears as heat. By suitable means heat may be converted into some other form of energy, for instance, mechanical work. These changes are well illustrated by the steam engine in which coal, a substance rich in carbon, coml)iiics with the atmospheric oxygen to form carbon dioxide, the result of this oxidation being to liberate energy in the form of heat. This heat applied to the boiler converts the water it contains into steam, and the pressure of the latter is then transferred to the functionating parts: piston, piston rod, wheel, etc., THE PHYSIOLOGY OF RESPIRATION 113 so that the energy derived from a chemical process, the l)uniing of coal, is transformed into mechanical work. In the living cell are fonnd similar processes occurring in a modified form. In fact every cell is a minute chemical engine, burning fuel and liberating energy. In the cell the fuel consists of carbonaceous materials in the protoplasm which have been derived from the carbo- hydrate, fat and protein foodstuffs. This carbon-rich material combines with oxygen absorbed from the surrounding medium of the cell and carbon dioxide is formed. This chemical reaction, as in the steam engine, is associated with the evolu- tion of energy which appears as heat (animal heat) and work, the latter manifesting itself in different forms of activity according to the structure and the functional capacity of the cell. Although many other chemical activities occur in living cells, oxidation is by far the most important of these. Deprived of oxygen, cells soon lose their functionating powers, and as life is absolutely dependent on the proper maintenance of functions, it is evident that oxygen must be constantly supplied to all the body cells. Carbon dioxide, the final product of oxidation, is no longer of value to the cell, and like all excretory products acts as a poison if allowed to accumulate in the medium in which cells live. Therefore some means must also be available to remove carbon dioxide as rapidly as it is formed. The function through which oxygen is supplied to the tissues and carbon dioxide removed is known as respiration. In a single-celled organism, such as the ameba, no special organs are required for this interchange of gases. Oxygen is derived from the water in which this animal lives by direct absori)tion into the cell and carbon dioxide is excreted into the same medium. In higher animals the same processes take place, for the body cells, like the ameba, live in a fluid medium which is represented by the blood and l>Tnph. Each cell obtains its oxygen from the circulating blood and the carbon dioxide is excreted in these body fluids. But the blood must carry a constant supply of oxygen and at the same time some provision must be made to remove the carbon dioxide which would otherwise accumulate and exert a noxious influence on the tissues. This is accomplished in higher forms of life through the agency of the lungs. The air is a mixture of three gases, oxygen, nitrogen and carbon dioxide. During the process of respiration this air is drawn into the lungs where, owing to the structure of these organs, the gases are brought into intimate contact with the circulating blood. It will be seen under the pliA'siology of the circulation that the blood, after having been in contact with the tissues, is carried to the lungs. There the carbon dioxide formed by oxidation in the cells is thrown off and a new supply of oxygen is absorbed by the blood to replace that part of the oxygen which has been utilized by the body 114 PHYSIOLOGY cells. After this interchange the now purified blood. leaves the lungs to be redistributed throughout the body. The air in the lungs must also be changed at frequent intervals, otherwise there would be an insufficient supply of oxygen for the blood to absorb while the carbon dioxide in the blood could not be eliminated. It is for this purpose that nature provides the respiratory act, which is simply an alternate inflation and deflation of the lungs, by virtue of which the air in these organs is constantly renewed. Respiration is therefore divided into two phases: inspiration, during which the external air is drawn into the lungs; and expiration, during which air, now deficient in oxygen and laden with carbon dioxide, is expelled. The Respiratory System. — In man the organs of respiration are classi- fied for description as follows: (1) The respiratory passages, a system of cavities and tubes through w^hich the atmospheric air gains access to the lungs and through which the impure air is expelled. (2) The lungs, where the interchange of gases of the air and blood takes place. (3) The thorax, which by its expansion fills the lungs with a fresh supply of air and which by its relaxation aids in the expulsion of the impure air. (The latter function is effected principally through the collapse of the lungs by virtue of their elasticity.) (4) Nervous structures, which control the rate and depth of respiration. Air may pass into the respiratory passages by way of the nose or mouth. Of these two the nasal passages are especially adapted for breathing, for the ca\ity of the nose is lined with mucous membrane richly supplied with bloodvessels which aid in warming the inspired air; furthermore, this membrane is thrown into intricate folds so that much of the dust and other impurities of the air which would other- wise enter the respiratory passages do not pass beyond the nasal cavity. The mouth and nose communicate with the pharynx and the latter with the larynx. • The larynx is a cartilaginous box, triangular on cross-section above and circular below where it is continuous with the trachea. Like all the respiratory passages, it is lined with mucous membrane. In the triangular portion of the larynx, the vocal cords are situated. These structures are bands of elastic tissue, lying directly under the mucous membrane, which by their vibration, under the influence -of a blast of air, produce sounds known as the voice. At the upper extremity of the larynx and lying just behind the tongue is a leaf-shaped structure, the epiglottis, consisting of cartilages. Although not directly associated with the respiratory act, the epi- glottis is of great importance, as by its lid-like action it closes the larynx during swallowing and thus prevents the passage of food into the respiratory tract. The trachea is continuous above with the larynx. The mucous mem- brane of this tube anrl its subdivisions is of special interest, as the uppermost layer of this incmljraiic consists of ciliated cells. These cells are furnished with cilia, or hair-like processes which l)y their THE I'ilY Slower OF UESl'l RATION 115 motility swcej) dust i)artides toward the external world and thus prevent theii" entrance into the lungs. The sul)di^•isions of the trachea, the bronchi and bronchioles, are generally included with the lungs. The two bronchi, into which the trachea divides, enter the right and left lungs respectively, where they subdivide into numerous smaller tubes known as the bronchioles. (The l)r()nchi and the larger bronchioles are similar to the trachea in structure, but the smaller bronchioles, those which terminate in the air chambers of the lungs, have much thinner walls and are not sup- plied with cartilaginous rings.) The bronchioles further subdivide and finally terminate in dilated cavities, the infundibula. The walls of each infundibulum are closely beset with still smaller chambers, the alveoli, where the actual exchange of gases takes place. The alveoli consist of a single layer of flat cells supported by delicate elastic tissue under which lie a close network of capillaries (small bloodvessels).^ The lungs therefore consist of myriads of these air chambers, fur- nished with passages (bronchioles and bronchi) leading to the external air. The lungs are enclosed in a conical shaped, air-tight chamber known as the thorax. Each lung is tucked into a sac, the pleura, one layer of which invests the surface of the lung, the other being attached to the inner surface of the thorax. This sac is lined with a single layer of flat cells which secrete a thin fluid. The purpose of this secre- tion is to reduce the friction between the limgs and the thorax during respiration. The bones of the thorax are the sternum in front, the twelve ribs on each side and the thoracic vertebrae behind. Owing to the convexity of the ribs and the peculiar manner in which they articulate with the vertebrae, the capacity of the chest is greatly increased when the ribs are elevated by the contraction of muscles during inspiration. Run- ning obliquely between the adjacent ribs are tw^o sets of muscles, the internal and external intercostals. The base of the thorax is shut oft' from the abdominal cavity by the diaphragm, a dome-shaped muscle with its convexity upward. The structures at the root of the neck complete the thorax above. The muscles concerned in respiration are activated by impulses transmitted through nerves, which in turn are controlled by a central station known as the respiratory center. The respiratory center is composed of nerve cells situated in the medulla (a portion of the central nervous system lying between the upper part of the spinal cord and the brain). These cells are sur- rounded by bloodvessels and react to changes in the gaseous contents of the blood, being especially susceptible to increases in carbon dioxide. ^ It will be noted that the air contained in the alveoli is separated from the circulating blood, by only two layers of flat cells, one layer forming the wall of the alveolus, the other the wall of the capillarJ^ Through this double membrane oxygen and carbon dioxide can diffuse with great facility. 116 PHYSIOLOGY The Mechanics of Respiration. — During inspiration the muscles of the thorax contract under the influence of impulses sent through nerves from the respiratory center. The int-ercostal muscles (the external and internal) by their contraction lift the ribs and increase the lateral and anteroposterior diameters of the chest. At the same time the diaphragm contracts and thus becomes flatter, its central portion moving downward, so that by the simultaneous contraction of these muscles the capacity of the thorax is increased in all dimensions. This enlargement of the thorax must be followed by an expansion of the lungs as the pressure exerted through the respiratory passages (atmospheric pressure) upon the interior of the alveoli is always greater than the counter-pressure exerted by the elasticity of the lungs. As the lungs expand the pressure in the alveoli necessarily becomes less than that of the external air so that the latter rushes into the alveoli until an equilibrium is established. It is during this phase, known as inspiration, that a fresh supply of oxygen is brought in contact with the blood circulating in the lung. The lung tissue is also supplied with nerves and the expansion of the lungs gives rise to nervous impulses, which reaching the respiratory center, arrest the impulses to the respiratory muscles, so that the latter relax. With this relaxation expiration sets in. The ribs are brought back to their position of rest by gravitation and by virtue of the elasticity of the thoracic cage. Furthermore, the return to the expiratory position is aided by the traction exerted upon the chest walls by the elasticity of the lungs. As the capacity of the thorax and consequently the volume of the lungs diminish the pressure in the alveoli becomes greater than that of the external air, so that the lung air, deficient in oxygen and rich in carbon dioxide, is expelled through the respiratory passages. Changes in the Air. — Atrnospheric air contains 21 per cent, of oxygen, 79 per cent, of nitrogen and a small fraction of carbon dioxide (3 parts in 10,000). The expired air, on the other hand, contains about 17 per cent, of oxygen, 79 per cent, of nitrogen and 4 per cent, of carbon di(jxide. This, of course, indicates that during respiration about 4 per cent, of oxygen is absorbed by the blood and 4 per cent, of carbon dioxide excreted from the blocxl into the alveoli. The nitrogen percentage remains the same, for it l)ehaves as a neutral gas and is not absorbed in the lungs. It should also be mentioned that the blood in passing through the lungs gives oft' a small amount of its water, about one pint being excreted daily. The raie and dejjfli of respiration vary with the age and the degree of activity in the iiirlivi(hial. In the adult the normal rate during re.st is about Ki to 20 jjcr miimte and the amount of air taken in each inspiration is about 1 pint. Both the rate and depth of respiration increase markedly during exercise, the total capacity of the lungs under forced breathing being about seven pints. PHYSIOLOGY OF THE CIRCULATION 117 Nervous Mechanism. — At first sight the respiratory act appears to l)e under control of tlic will, hut this is true only to a slight degree. Resi)iration is actually an involuntary function under the constant regulation of the respiratory center. As has been seen, the irritability of this center is influenced by the carbon dioxide contents of the blood. Durimj exercise when the activity of the muscles gives rise to an in- crease of carbon dioxide in the circulating blood, the respiratory center, which is sensitive to slight changes of carbon dioxide, is stimulated to greater activity. This stimulation of the center is followed by a cor- responding increase of activity in the respiratory muscles, so that respiration during exercise is deeper and more rapid. Conversely, during sleep less carbon dioxide is formed in the tissues, the respira- tory center is not so strongly stimulated and consequently respiration is consideral)ly slower. '^rhere is, therefore, in the respiratory function, not only a means of supplying the tissues with oxygen and removing carbon dioxide, but also an automatic mechanism whereby the supply and removal is controlled according to the constantly changing requirements of the body. PHYSIOLOGY OF THE CIRCULATION. The Circulatory System, — The circulatory organs consist essentially of a closed, continuous system of tubes through which blood, the common nutritive fluid of the body, is kept in constant circulation b}' the pump-like action of the heart. The circulating blood serves two 'purposes: to convey food and oxygen to the body cells and to carry to the organs of excretion the waste products resulting from cellular activity. The Blood. — The blood is a red, opaque fluid and makes up about one-thirteenth of the body weight. On microscopic examination this fluid is found to consist of several varieties of cells suspended in a clear yellowish fluid known as plasma. The cellular elements of the blood are of three types: the red blood cells or erythrocytes, the white blood cells or leukoc^'tes and the blood platelets. The red blood cells are thin, biconcave, non-nucleated, circular disks, about one thirty-five hundredths of an inch in diameter. These cells are composed of protoplasm in which is found an iron-containing sub- stance called hemoglobin. It is to this substance that the red color of the blood is due. Hemoglobin has a great affinity for oxygen, and owing to this property the red blood cells are able to absorb oxygen during their passage through the lungs. The white blood cells or leukocytes, less numerous and somewhat larger than the red blood cells, are more or less irregular in shape, colorless, and have a well-defined nucleus. By a form of motility similar to that of the ameba (ameboid motion) these cells are able to engulf foreign particles. This function, known as phagocytosis, is 118 PHYSIOLOGY especially important in disease, the invading germs being destroyed in great numbers by the leukocytes. Another property of the white blood cells is the production of a ferment which assists in the clotting of blood. The bJood platelets are very small cells probably concerned only with the process of clotting. The fluid portion of the blood or plasma is a yellowish, alkaline fluid consisting of 90 parts of water holding in solution albumin, sugar, mineral salts, and other substances which are constantly replenished by the intake of food. The plasma therefore represents the nutritive element of the blood from which the cells derive their needs. Owing to the alkalinity of the plasma, carbon dioxide is readily dissolved in this fluid, and in this manner is carried from the cells to the lungs where this gas is excreted. The plasma also acts as a solvent for other excretor}' products of the cells which can be then conveyed to the excretory organs and there finally expelled from the body. The blood when removed from the body is soon transformed into a semisolid mass. This transformation, known as coagulation or clotting, takes place through the agency of a ferment derived from the blood platelets and leukocytes. This ferment precipitates part of the albumin of the plasma in the form of delicate fibrils which form an interlacing network. In this network the cellular elements become entangled, the whole mass form- ing the clot. The purpose of coagulation is to prevent the excessive loss of blood after injury to the tissues, the coagulated mass occluding the mouths of the bleeding vessels. The blood is kept in constant circulation throughout the body by the pumping action of the heart. The Heart. — The heart is a hollow muscular organ, conical in shape. It is situated in the thorax, lying between the two lungs just above the diaphragm and behind the breast-bone or sternum. It is placed obliquely so that its apex reaches to a point just inside and a little below the left nipple. The heart is surrounded by the pericardium, a connective-tissue pouch made up of two layers, one of which is closely adherent to the heart wall, the other being attached to the surround- ing structures. The interior of this pouch is lined with a single layer of flat cells which secrete a thin fluid. This fluid serves to diminish the friction between the heart and the adjacent organs. The interior of the heart is divided by a longitudinal muscular wall into two distinct cavities, each of these cavities being subdivided by valves into two compartments, a lower and an upper, which com- municate with each other. The heart is thus divided into four chambers. "^I'he two upi)er chambers are called the right and left auricles, the two lower, the right and left ventricles. The outlets of these cham})ers are guarded by valves which prevent the back flow of l)lood after its expulsion from any one fhamber and keeps the })lood circulating in the same direction. PHYSIOLOGY OF THE CIRCULATION 119 The heart walls consist of muscle cells, roughly columnar in shape and striated. These cells have the peculiar property of contracting and relaxing at fairly definite intervals. This rythmical action gives rise to the heart heat. The nuiscular walls of the different chambers of the heart vary in thickness, according to the amount of work per- formed by these parts. The walls of the auricles are thin as the press- ure in these chambers is always comparatively low; the walls of the left ventricle, on the other hand, are very thick, as it must propel the blood against the high pressure in the systemic vessels. The right ventricular walls are thinner than the left, as the pressure in the lung vessels, into which the right ventricle pumps its contents, is much lower than the pressure in the systemic vessels. The internal surface of the the heart is lined with a single layer of cells, this layer is con- tinuous throughout the whole circulatory system and reduces fric- tion by offering a smooth surface to the rapidly flowing blood. The movements of the heart consist of the alternate contraction and relaxa- tion of the heart walls. Each heart heat is divided into three stages: (1) The contraction of the auricles; this is rapidly followed by (2) the contraction of the ventricles during which the auricles relax; and (3) a pause during which both auricles and ventricles "are relaxed. The heart is so designed that two streams of blood are pumped simultaneously. The right side of the heart receives the blood on its return from the tissues and pumps it into the lung vessels where a fresh supply of oxygen is absorbed and carbon dioxide given off. The left side of the heart receives the blood after its transit through the lungs and discharges the now aerated blood into the systemic vessels to be distributed throughout the body. The Bloodvessels. — The tubes or vessels through which the blood circulates are divided according to their structure and function into arteries, arterioles, capillaries, venules, and veins. The arteri&s, vessels which conduct the blood away from the heart, are made up of three layers, an internal layer of flat cells, a middle muscular layer containing numerous elastic fibers and an outer layer of tough connective tissue. To this structure the arteries owe their great elasticity and strength. Strength is essential to resist the great pressure in these vessels, and the elasticity permits the arteries to distend at each heart beat and thus to accommodate the three or four ounces of blood suddenly expelled into their lumen by the con- traction of the ventricles. The arteries branch repeatedly, each suc- cessive division giving rise to smaller and smaller vessels until the arterioles are reached. The latter differ from the arteries in that their external and middle layers are much thinner and contain very little elastic tissue. These vessels, being under control of the nervous system, are able to contract or dilate under stimulation. By this mechanism the amount of blood circulating through any organ is regulated. The arterioles subdivide like the arteries and terminate in minute vessels known as capillaries. The capillaries, consisting only of a 120 PHYSIOLOGY single layer of flat cells, form a network of microscopic tubes the meshes of which are occupied by the cells. Owing to the thinness of the capil- lary walls, plasvia diffuses readily into the spaces of this capillary net- work and in this way the albumin, sugar, and other foods contained in the plasma are brought into immediate contact with each cell of the body. Oxygen diffuses likewise from the red blood cells into the intercapillary spaces where it is absorbed by cells. The carbon dioxide and oilier excretory products of the cells passing in the opposite direc- tion, enter the blood through the capillary walls and are carried away by the circulation to be excreted from the body. The network of capillaries formed by the division of each arteriole unite again to form vessels known as venules; the later in turn join to form larger vessels, called veins, w^hich return the blood to the heart. The veins, like the arteries, are composed of three coats. In the veins, however, the outer coats are much thinner, as the pressure in the veins is considerably' lower than that in the arteries. The veins are furnished with valves which permit the passage of blood only in the direction of the heart. As has been seen, the heart is composed of two distinct halves — the right side of the heart pumping blood into the lungs, the left side forcing blood throughout the body. There are therefore two systems of bloodvessels, one between the right ventricle and left auricle, the other between the left ventricle and the right auricle. The first is known as the pnJinonary circulation, the second as the systemic cir- culation. The Pulmonary Circulation. — The blood returning to the heart after its circulation through -the tissues, enters the right auricle through two large \'eins, the inferior and superior vena cava. It then passes into the relaxed right ventricle. The right auricle contracts and thus com- pletes the filling of the ventricle. The auricles now relax and the ventricles contract. As the pressure in this chamber increases, the blood i)rcssing against the under surface of the tricuspid vcdve (between right auricle and \'entricle) brings about its closure. When the pressure in the right ventricle exceeds that in the pul- monary artery, the semihinar valve, situated at the outlet of the ven- tricle, opens so that the blood is forced into this vessel. After ven- tricular contraction has reached its height relaxation commences, and the pressure in the pulmonary artery closes the semilunar valve. The pulmonary artery di\'ides into branches which enter the substance of the lungs. Within the hings, these branches sul)divide into arte- rioles and the latter into ca])illaries which form a network about the respiratory chambers (alveoli). The blood during its passage through the lung capillaries throws off carbon dioxide and absorbs a fresh suj)])ly of oxygen. The lung capillaries empty into venules, the veiniles unite to form veins which finally emj^ty the oxygenated blood into the left auricle by way of four large vessels, the pnhnonary veins. PHYSIOLOGY OF THE CIRCULATION 121 The Systemic Circulation. — The blood returning from tlie lungs passes from the left auricle into the left ventricle, the filling of this chamber is aided by the contraction of the auricle. The left ventricle then contracts, and the auricle relaxes. The rising pressure in the ventricle closes the mitral valve (between the left auricle and ventricle), and opens the aortic semilunar valve, so that the contents of the ven- tricle are forced into the aorta, a large artery which through its branches carries the aerated blood to all parts of the body. As the ventricle relaxes the pressure in the aorta closes the aortic valve. The blood passes successively through arteries, arterioles and capillaries. In the capillaries the oxygen and food is distributed to the cells and carbon dioxide and other excretory products removed. The blood then passes from the capillaries into venules, next into veins, and finally returns to the right auricle by way of the two large veins, the iuferior and superior vena cava. The Portal Circulation. — Associated with the organs of alimentation and of special importance during digestion is a third system of vessels known as the portal circulation. The veins of the abdominal alimen- tary organs do not pass directly into the vena cava but unite to form a large vessel, the portal vein, which enters the liver. In the liver the portal vein subdivides into capillaries which form a close network about the liver cells. From this capillary network arise veins, which unite to form the hepatic vein, which in turn empties into the inferior vena cava. The alimentary organs receive their blood supply from branches of the aorta. In the mucous membrane of the stomach and intestines these branches subdivide in capillaries. Here the capillaries serve a twofold purpose, they carry aerated blood to the cells of these organs, and during digestion convey the absorbed peptones and sugars to the liver by way of the portal vein. In the liver the capillaries arising from the portal vein bring these peptones and sugars in close contact with the liver cells. The excess of sucjar is converted into glycogen which is stored in the liver for future use and the peptones are modified and carried away in the blood plasma to be distributed to all cells of the body. The Lymphatic System. — ^Related to the circulation of the blood is another system of vessels known as lymphatics. The lymphatics begin as exceedingly minute vessels which arise from the spaces between the cells. These intercellular spaces contain fluid derived from the plasma of the blood which has diffused through the capillary walls. The small lymphatics, therefore, drain off this fluid after the food originally contained in it has been absorbed by the cells. The excre- tory products are not entirely removed by the blood so that the fluid carried away by the lymphatics contains part of the excretions of the cells. The lymphatics unite to form large vessels which empty at intervals into the lymphatic glands. In these glands wdiite blood cor- puscles are formed and are eventually carried into the blood stream by the lymphatic channels. From the lymphatic glands the lymph 122 PHYSIOLOGY passes into larger vessels which unite to form the right and Jeff thoracic ducts. The right thoracic duct is a short vessel which drains the lymph from the right side of the head, the right arm and the corresponding half of the thorax. It empties into veins situated at the root of the neck. The left thoracic duct is a long vessel which drains the remaining lymphatics of the body including those of the intestines. The lymph capillaries in the villi of the small intestines are concerned principally with the absorption of fats during digestion. The absorbed fats are thus thrown directly into the blood stream by way of the left thoracic duct which also empties in veins at the root of the neck. The lymphatic vessels, like the veins, are supplied with valves which allow the Ij^mph to flow only in the direction described. PHYSIOLOGY OF EXCRETION. The maintenance of health in any organism depends upon the constant removal of the excretory products arising from the metabolism of its cells. The most important excretory products are carbon dioxide, urea, uric acid, sulphates, phosphates, chlorides, and water. Carbon dioxide, as we have seen, results principally from oxidative processes in the cells. Urea and uric acid are the final products in the breaking down of protoplasmic material and represent not only cellular wastes, but also the decomposition of protein foodstuffs after their absorption from the alimentary tract. The sulphates, p)hosphates, chlorides, and water are derived partly from cellular changes, and partly from the amount of these substances absorbed during digestion in excess of the needs of the cells. These products, constantly excreted into the blood and lymph, are conveyed by the circulation to the excretory organs where means are pro\'ided for their removal. Excretory Organs. — The organs concerned in the removal of these products are the lungs, the skin, and the kidneys, accordingly the.y are known as the organs of excretion. The lungs, the function of which has already l)een considered, excrete practically all the carbon dioxide formed in the body and in addition about a pint of water daily. "The sJci7i, besides its excretory function, plays other important parts in the economy of the body. The skin is di\ided into an external layer, the epidermis, or scarf skin, and an internal layer, the dermis, or true skin. The epidermis consi.sts of numerous superimposed cells, the uppermost of which are dead, and constantly dro])j)ing off. The cells thus lost are replaced by the inulti])Hcation of cells at the bottom of this layer. The epi- dermis has no bloodvessels and dcrixcs its nourishment from the PHYSIOLOGY OF EXCRETION 123 lymph which escapes thn)uji;h the walls of capillaries in the true skin, and this accounts for the death of the externally situated cells which are unable to obtain a sufficient supply of food. The junction of the epidermis is a protective one. It covers the entire surface of the body, and by its horny texture prevents injury to the underlying tissues. The internal layer of the skin or dermis, upon which the epidermis lies, is made up of numerous interlaced connective-tissue fibers richly supplied with bloodvessels and nerves. The dermis at its point of contact with the epidermis is studded with papillae, minute finger-like elevations, which contain loeps of capillary vessels. Many of the papilke contain in addition sensory end-organs through which external impressions are received. The function of the skin as a sensory organ will be again mentioned under the nervous system. Two important sets of structures situated in the dermis are the sebaceous and sweat glands. The sebaceous glands consist of minute sacs lined with a single layer of cells, each sac emptying into a common channel which opens into a hair follicle. The cells of these glands have the property of manu- facturing, from substances derived from the blood, an oily secretion which passes to the skin surface through the hair follicles. The purpose of this secretion is to keep the skin soft and pliant and prevent the drying of the hair. The sweat glands are composed of a single tube also lined with a single layer of cells. This tube is coiled several times upon itself and opens externally by a straight duct which passes through the epidermis. The openings of these ducts are called pores. The coiled portion of the gland is surrounded by a network of capillaries, so that the blood is brought in close contact with the gland cells. The latter by their selective action remove certain materials from the blood which are then excreted through the pores. This excretion, know^n as sweat, consists of water, carrying in solution salts and a small amount of urea, carbon dioxide, and fatty acids. To the latter the peculiar odor of this excretion is due. The arterioles of the dermis, in conjunction with the excretion of sweat, play an important part in the heat regulation of the body. During exercise when an enormous amount of heat is generated by the activity of the muscle cells, the bloodvessels of the skin dilate and the secretion of sweat increases. The dilatation of the skin vessels brings the overheated blood to the surface in great quantities, where it loses heat by radiation, the external air being cooler than the blood. The sweat, on the other hand, evaporates rapidly and in this way causes a marked loss of heat. If the skin is exposed to cold the reverse occurs, the bloodvessels of the skin become constricted and the secretion of sweat diminishes. In this way heat loss is prevented. The kidneys are, with the lungs, the most important organs of excre- tion. The lungs are concerned principally with the excretion of carbon 124 PHYSIOLOGY dioxide and the kidneys with the greater part of the soHd excretory products as only a small portion of these products are excreted through the skin. The urine, the fluid resulting from the activity of the kidneys, con- sists of an aqueous solution of urea, uric acid, phosphates, sulphates, chlorides, a very small quantity of carbon dioxide and pigment. To the latter the characteristic color of the urine is due. The kidneys, two in number, are situated in the upper part of the abdominal cavity on either side of the spinal column. These organs are bean-shaped with their concavity facing the spine. From the stand-point of function the essential parts of the Jcidney are : (1) The tubules, the cells of which by their selective action remove solid excretory products and water from the blood. (2) The bloodvessels which convey the blood to the tubules. (3) The pelvis of the kidney into which the tubules empty their contents. The tubules of the kidneys with their related bloodvessels form little systems, which are exceedingly numerous, but as these systems are all alike in structure and function, the description of a single one will suffice. The tubules, little tubes consisting of a single layer of cells, begin as minute blind pouches near the external surface of the kidney. These pouches may be compared to the inverted tip of the finger of a glove. The blind extremity of the tubules is thus composed of two layers of flat cells, an internal layer forming a dilated cavity and an external layer continuous below with the walls of the tubules. Into this dilated cavity an arteriole enters which immediately divides into a network of capillaries. This portion of the tubule with its capillary tuft is called a Malpighian corpuscle. Soon after leaving its blind, pouched extrem- itj^ the tubule, from now on lined with a single layer of cubical cells, is coiled spirally for a few turns (proximal convolution) and then dips down in a straight line for a short distance toward the concavity of the kidney; it then bends back upon itself and returns to a position near its point of origin, where it forms a second series of coils (the distal convolution). Both the first and second coils of the tubule are surrounded by netAvorks of capillaries. The tubule after leaving the distal convolution enters collecting tubules, which, joining with tubules of other similar systems, run in a straight course toward the concavity of the kidney and empty by small openings into the i)elvis of this organ. The secretion of vrinc takes ])lace in the following maimer. The blood which contains the excretory prcxlucts reaches the kidney by way of the renal artery, a branch of the aorta. The renal artery subdivides into brunches, which on entering the concave side of the kidney, divide into mmierous arterioles. These arterioles pass between the collecting tubules and near the external surface of the kidney give off branches which enter the blind pouches formed by the infolding of the extremities of the tubules (the Malpighian corpuscle). Each PHYSIOLOGY OF THE NERVOUS SYSTEM 125 pouch receives an arteriole which (Hvides into a tuft of capiUaries. At this point a process of selective filtration takes {)lace. The icater and salts to be excreted from the blood filter through the capillary walls and then through the single layer of cells forming the wall of the tubule and thus collect in the interior of the latter. From the capillary tuft just described a small vein arises which carries the blood along to the proximal and distal convolutions of the urinary tubules. There the vein again divides into a second network of capillaries. The cells of the tubules at this point have the power of sch'cfiiif/ certain substances from the blood, such as urea and uric acid, and at the same time of reabsorbing the excess of the waiter which has passed into the tubule from the first system of capillaries. The blood, now relieved of excretory products, is collected by veins which, joining with other similar vessels, empty into the renal vein, a tributary of the inferior vena cava. The urine after its passage through the course of the tubules enters the pelvis of the kidney. F'rom this dilated sac the m-ine passes through the ureter into the bladder, where it collects until voided by the act of micturition. PHYSIOLOGY OF THE NERVOUS SYSTEM. The function of the nervous system is purely correlative. Through the activity of its units, the nerve cells, it brings organs into intimate relation and thus harmonizes their vital processes, and through recep- tive organs, those of the special senses, it relates the body as a whole to its external surroundings. The Nerve Cell. — The functional unit of the nervous system is the nerve cell or neuron. The neuron consists of a nucleated cell body from which issue two or more protoplasmic processes, the nerve fibers. When a nerve cell is stimulated either by chemical or physical causes, a current arises which is known as a nervous iuipnlse. This impulse, which may be aroused from changes at the periphery of the fiber or in the nerve cell body, is transmitted by the nerve fiber in a way comparable to a current of electricity travelling through a ware. Nerve Fibers. — The nervous impulse in its course through the nerve fiber, always travels in a definite direction, accordingly all neurons are divided into three large classes: (1) The afferent neurons , the fihevs of which convey impulses from all parts of the body to central stations in the nervous system. (2) The efferent neurons which conduct impulses from, these central stations to the cells of all the organs. (3) The neurons which transmit impulses from one nerve cell to the other. Receptive Organs. — The afferent nerves are supplied at their point of origin with specialized structures known as receptive organs. These receptors are part of the nei-ve fiber and are adapted to receive impres- sions arising from changes in the surroundings of the organisms or from changes in its tissues. These receptive organs and the afferent 126 PHYSIOLOGY ne^^■es to which they are attached are speciaHzed in function and so respond best to one particuhir form of stimnhition. To illustrate: Tlie receptive organs of the skin receive impressions of pain, heat, cold, touch, and pressure. When an object is brought in contact with the skin, the receptive organs of touch are stimulated. They originate an impulse which is conducted through the fiber to the central nervous system where our consciousness translates this impulse into the sensation of touch. If the skin is pricked with a pin, receptive organs of pain are stimu- lated and a sensation of pain is aroused. In this w^ay the organism is acquainted with immediate external changes and can respond accord- ingly. Situated in the joints, tendons, and muscles are receptive organs which give us what is known as the muscle sense. This sense enables us even with our eyes closed, to determine the exact position assumed by our limbs, trunk, and head. The receptive organs of sight are located in the retina of the eye. Light waves entering through the pupil stimulate- afferent nerves, the impulse is conveyed to the brain and gives rise to the perception of color and shape. In the upper part of the nasal cavity, lying in the mucous membrane are the receptive organs of smell. Volatile substances coming in contact with these endings, give rise to olfactory sensations. The internal ear contains two sets of receptive organs, one sensitive to air vibrations and through which w^e perceive sound, the other trans- mitting the impulses which regulate the equilibrium of the body. The sense of taste arises from the stimulation of endings in the mucous membranes at the posterior part of the tongue. All the internal organs are also supplied with afferent fibers which conduct impulses centrally. The efferent nerve fibers which con\'ey impulses peripherally' to the cells of the body are divided into three classes: (1) The motor nerves. (2) The secretory nerves. (3) The inhibitory nerves. The motor nerves carry impulses to the muscle cells and thus bring about their contraction. The voluntary muscles are supplied by motor neurons arising from the central nervous system. The smooth muscles of the bloodvessels and the internal organs are supplied by motor fibers from the sympathetic system. The secretory nerves are deriy'cd from the sympathetic system and terminate in gland cells throughout the body. It is the stimulation of such nerves that activates the fiow of secretions, i. e., the saliva, the gastric juice, etc. The inhibitory nerves, also branches of the sympathetic system, supply the muscle cells of the heart and bloodvessels. Their function is to suppress or diminish the activity of these structures. P^.xamples of these are the vagus nerve, wliich slows tiic heart rate, and the vaso- dilator nerves, which bring about the relaxation of bloodvessels. PHYSIOLOGY OF THE NERVOUS SYSTEM 127 In the central and symi)athetic nervous system the afferent and efferent nerves are brought into relation with each other in such a way that any afferent ini])ulse arising from the periphery is always followed by a suitable cflVrent response. The Central Nervous System. — The central nervous system includes from below upward, the spinal cord, the medulla, the cerebellum, and the cerebrum. The spinal cord presents on cross-section a butterfly-shaped area, grayish in color, and made up of numerous nerve-cell Ixxlies anfl their fibers. Situated anteriorly in this gray matter are the cell bodies of the spinal motor neurons, the fibers of which supply the voluntary muscles. The gray matter is surrounded by bundles of nerve fibers (white matter) which run u]) and down the cord, their cell bodies lying at higher or lower levels. From the anterior portion of the cord at the level of each \ertebra two large nerve trunks arise, one on either side. These trunks are known as the anterior roots and contain the fibers of the spinal motor neurons. From the posterior aspect of the cord and at corresponding levels arise similarly the posterior roots. These two trunks consist of afferent or sensory fibers which conduct impulses from the periphery to the spinal cord. A short distance away from the spinal cord the anterior and pos- terior roots on each side join to form a single bundle, known as a spinal nerve. Just before "joining with the anterior root, the posterior root presents an enlargement, the spinal ganglion, which contains the cell bodies of the afferent or sensory nerve fibers. The spinal nerves, of which there are thirty-one pairs, pass out per- ipherally and by their subdivisions bring afferent and efferent fibers in contact with the tissues supplied by each spinal nerve. Reflex Nervous Action.— The most primitive fimction of the nervous system is a simple refle.x action. The simple reflex involves only two neurons, an afferent and an efferent. The path taken by the impulse is as follows: From the stimulation of a receptive organ an impulse arises which passes through the afferent neuron and enters the spinal cord through the posterior root. In the cord the afferent fiber sub- divides into fibrils (terminal arborizations) which are in contact with motor neurons. The impulse passing through this point of contact is, so to speak, transferred to the motor neurons which pass out of the cord through the anterior roots and convey the impulse to the muscles they supplv. The result is a muscular response not controlled by the will. Reflex action always involves an afferent path, which may be repre- sented by any afferent nerve, and efferent paths through motor, secre- tory or inhibitory nerves. Not only in the spinal cord, but throughout the entire nervous sys- tem, we find reflex paths, some more complicated than others, through 128 PHYSIOLOGY which important functions of the body are regulated. As an example of these ^egulati^'e reflexes may be mentioned the profuse reflex flow of saliva and gastric juice which follows the stimulations of the nerves of taste. The white matier of the spinal cord contains bundles of fibers which act as connecting paths between the peripheral afferent and efferent neurons and the higher iterve centers of the cerebrum and the cerebellum. The Higher Motor Paths. — Among these higher nerve centers are the voluntary }itotur neurons which are situated in the cortex or gray matter of the cerebrum, on its lateral aspect. In this area arise motor impulses originated by the will. The fibers of these neurons pass into the medulla (the first part of the cord) where the greater part of them cross over to the opposite side from which they originated, and then, passing on through the medulla, run down the spinal cord. At dif- ferent levels individual fibers leave this motor bundle or tract as it is called and by their terminations come in contact with the spinal motor neurons of corresponding levels. Owing to the crossing of the fibers in the medulla, each half of the brain controls voluntary motion on the opposite side of the body. Therefore when a part of the body is voluntarily moved as, for example, the left index finger, the impulse arises in the brain cortex on the right side and travels to the medulla where it crosses to the left side; it then continues its course down the spinal cord and at the level of the arms passes over to the spinal motor neurons which then convey the impulse to the muscles concerned in moving the part. The Higher Sensory Paths. ^ — Thus far only the peripheral afferent neuron has been considered and the part it plays in reflex activity. But as the ability to perceive sensations resides in the brain, path- ways are required to transmit impulses from these afferent nerves to this organ. The sensory nerve fibers after their entrance into the cord, divide into tico parts: one, as already mentioned, comes in contact with adjoining motor neurons; the other ascends the posterior portion of the spinal cord and ends in the medulla. At this point are located other cell bodies which through their fibers complete the path to the brain. These fibers, like the motor fibers, cross to the opposite side and end in the cortex just behind the cell bodies of the voluntary motor neurons. The Cerebellum. — The spinal cord contains other nerve paths which relate afferent anfl efferent nerves with the cerebellum, and this organ is in turn related to the cerebrum by nerve paths. The function of the rcrebrllum is to coordinate muscular movement. The Medulla. — The medulla is the continuation of the upper part of the spinal cord and gives origin to some of the cranial nerves. Through it course the afferent and efferent nerve i)aths which bring into relation the spinal cord with the cerebrum and cerebellum. The medulla is of great importance, for it is the seat of nerve centers which PHYSIOLOGY OF THE NERVOUS SYSTEM 129 control the vital fuitction.s. In it are located the respiratory, the cardiac and the vasomotor centers. The rcspiratori/ coder contains cell bodies the fil)ers of which run down the spinal cord where they connnunicate with the motor neurons supplying the muscles involved in the respiratory act. The function of this center has been considered under Respiration. The cardiac centers regulate the heart rate through two important nerves, the vagti.s' and the acceleratur. The vagus decreases the heart rate and the accelerator increases it. The vasomotor center contains cell bodies which carry impulses to the muscle of the bloodvessel walls through the vasoconstrictor and vasodilator nerves. The former constrict the bloodvessels, thus raising the blood-pressure, while the latter have exactly the opposite effect and lower blood-pressure. The Cerebrum. — The cerebrum is composed of gray and white matter. The gray matter, made up of numerous cell bodies and their fibers, is distributed into two groups, the cortex and the l)asal ganglia. The cortex, the surface of which is greatly increased by numerous folds or convolutions, is divided into three functional areas: the motor, the sensory and the higher psychic. The motor areas control voluntary motor activity. The sensory areas are locatefl in various regions of the cortex, each area recei\'ing the final nervous paths of one particular special-sense organ. All these regions of the cortex are in turn intimately related by nervous connections with the psychic areas from which the higher mental processes originate. The basal ganglia are series of nerve cell masses, at the base of the brain. The white matter consists of the motor and sensory paths already mentioned and nerve fibers connecting the different areas of the brain. The Sympathetic Nervous System, — ^This system consists of ganglia and numerous communicating and distributing nerve fibers. The ganglia form two principal groups, (a) those of the ganglionated cord on either side of the spinal column, and (6) the more peripherally situated ganglia of the plexuses of the thoracic, abdominal, and pelvic cavities. Collections of sympathetic neurons are also found in the wall of the visceral organs, /. e., the heart, intestines, etc. The important efferent branches of the sympathetic system are the following. The pupil-dilating fibers which bring about the dilatation of the pupil; the vasomotor nerves (vasoconstrictors and dilators) con- trolled by the vasomotor center in the medulla; the motor fibers to the smooth muscle cells of the alimentary tract; the secretory nerves supplying all the gland cells of the body; and the nerves regulating the rate of the heart. The afferent sympathetic nerves convey impulses from the visceral organs to reflex centers in the central nervous system. 9 CHAPTER IV. BACTERIOLOGY AND STERILIZATION. By L. F. RETTGER, Ph.D. For many years it was thought that insofar as the body was con- cerned bacteria were necessary to its welfare; that they helped it in some way. It was even thought, by many at least, that life was maintained h)y the very existence of bacteria within the body. For example, it was taught that some of the intestinal bacteria were necessary for certain processes that go on in the intestine; that intestinal digestion was not complete without bacteria. The problem was argued pro and con for years but it has been well demonstrated that the old view was an erroneous one. Yet, while the bacteria that are present in the body are not neces- sarily helpful, there are organisms in nature which do aid in an eco- nomic way, such as those which are of special importance in connection with the growing of plants. Some farm products depend in a large measure on bacteria. So that, in spite of what is said as to the prob- ability that bacteria are useless within the body, we owe much to them because of this external cooperation. Ordinarily the bacteria within the body are harmless. Normally they are unable to overcome its natural resistance. Fortunately it is against only a few kinds of bacteria that the body is compelled constantly to protect itself. The fight against these of course consti- tutes one phase of hygiene and a most interesting and important one. The practice of this phase of hygiene falls within the modern con- ception of medicine; to prevent bacteria or other harmful agencies from getting a foothold and working mischief, rather than to try to eliminate them after they once establish themselves should be the chief aim of science. A few years ago ex-president Eliot of Harvard said that the real medical school of the future was the school of pre- ventive medicine. Modern dentistry, like medical science, is likewise moving in that direction. This is due to the fact that men who are active in the practice of these professi(jns now realize that they will accomplish the greatest good if they direct their energies toward the prevention rather than the cure of disease. There are many diseases that are now known to be caused by bacteria, such as typhoid fever, tuberculosis, diphtheria, and a large number of others, the specific causes of which are well recognized. (Combating typhoid fever means, in reality, keeping out of the way of the bacterium which causes it. In the present-day fight against Fig. 42. — Tuberculous sputum stained by Gabbett's method. Tubercle bacteria seen as red rods; all else is stained blue. (Abbott.) CLASSIFICATION OF BACTERIA 131 tuberculosis au outleavor is made to keep out of the way of the tubercle bacillus. Since there are so many chances of getting into trouble with foreign harmful agencies like bacteria, it is important to know some- thing about them. Description of Bacteria. — Some of the largest bacteria measure ^o^^^a of an inch in thickness, or, in other words, it takes 25,000 of them packed closely side l)y side to cover an inch. This gives a vague con- ception of the minuteness of these organisms. In order that they may be examined it is necessary to use the best and most ]K)werful micro- scope to bring them to view. From this it can readily be understood that years of scientific study have been required to glean any real knowledge concerning them. Bacteria are vegetable organisms, not animal. Therefore it is wrong to call them bugs, worms, or anything inferring a close relationship to that kingdom. A bacterium is essentially a minute mass of protoplasm surrounded by a delicate envelope. This protoplasm is the same in bacteria as in all other living cells, and is peculiar to living matter. Bacteria are single-celled organisms. They may often occur in bunches or chains, but their unit is the single cell; so that each individual bacterium is able to reproduce its kind. CLASSIFICATION OF BACTERIA. The protoplasm of the bacterial cells is held in shape by a delicate envelope, or defining wall; consecj[uently bacteria can be regarded as being definite in size and in shape. Fig. 43. — Staphylococcus. X 1100 diameters. (Park.) In a large measure, the size, shape, internal structure and grouping of the different organisms are used as means of recognizing and classifying them. The tubercle bacillus is spoken of as being a long, slender bacillus (very long as compared with its thickness), and this fact is depended upon, to a large extent for diagnostic purposes, that is, for the detection of the tubercle bacillus in any part of the body 132 BACTERIOLOGY AND STERILIZATION that may possibly be infected with tuberculosis (Fig. 42). The same thing is true insofar as the typhoid bacillus is concerned. The com- mon pus organisms that occur so frequently in the mouth, especially in abscesses of the gums and in a])scesses in other parts of the body represent a different type. They are organisms which are round or almost globular (Fig. 43). ■j^riS.tfc Fig. 44. — Spirillum obermeieri blood-smear. Fuchsin. X 1000 diameters. (From Itzerott and Niemann.) There is a third type of organism which is often present in the mouth. It is also frequently found in stagnant water, and in infusions of hay, straw, etc. These are rod-shaped like the typhoid bacillus, but the rods are decidedly curved and longer; they resemble a spiral (Fig. 44). We have then, first, the simple, straight, rod-shaped organism called the bacillus (Fig. 42) ; second, the globular type, known as coccus, or micrococcus (plural cocci, Fig. 43) ; and third, the long, slender, curved rod, known as the spirillum (Fig. 44, plural spirilla). PROPAGATION OF BACTERIA. How do these organisms propagate their own kind? In brief, bac- teria multiply by a process of transverse division. A large bacillus, for example, when it has reached full maturity, divides into halves. The process is simply one of equatorial fission, or of separation of the halves by a little dividing wall which becomes more and more apparent until the constriction becomes complete, and instead of one parent cell two slaughter cells appear. '^I'his is in reality the only method of multiplication. Spore formation^ which is referred to later, does not constitute a state or stage of reproduction in the real sense of the word. 'J'he abo\e method is also sj)oken of as the economic process because of the grc;it raj)idity with which multiplication takes ])lace. A bottle of milk will sour in the course of a few hours if ke])t at a moderately warm temperature. The milk spoils because it is such a good food SPORE FORMATION 133 for certain bacteria, known as the lactic acid organisms, that multij^ly rapidly. Milk sDtir.s. Other foods, like meats, do not sour; they decay, and by an entirely difi'crent process; the decay of meat is ordinarily spoken of as piitrcfartio)!. But in either case the food is there, the bacteria are there, deconij)()siti()n occurs, and in the process of this decomposi- tion the bacteria have l)een multiplying rapidly. It can be determined readily how rapidly these organisms reproduce themselves. Start with one organism, allow it to go on reproducing its kind at the rate of one reproduction an hour, that is, the doubling of the original bacillus and the doubling of each of its progeny once every hour, and there will be in twenty-four hours over 1 (5,000,000 of them. If the reproduction occurs once in thirty minutes, it will be necessary to use higher mathematics to compute the number at the end of twenty-four hours, and frequently in a new mediimi like milk or beef broth which is prepared for such a purpose, reproduction does occur as often as once in thirty minutes. In some cases complete division may occur in twenty minutes. Thus it may be seen how the term rcononn'r rnefhod of multiplication applies. Spore Formation. — There are many kinds of bacteria that have the property of being able to fortify themselves against destructive agents. This is accomplished by virtue of their ability to take on a form that is much more resistant to injury than the normal state of the organ- ism. They can change themselves into what are termed spores. The tetanus or lockjaw bacillus has this propertv, for example. (Fig. 45.) Fk;. 45. — Tetanus bacilli with spores in distended ends. X 1100 diameters. (Park.) A spore then is a transition form that certain bacteria can assume for purposes of defense. Spores possess a thick wall, which is more or less impervious to heat, poisons, etc., and therefore protects the contents against fatal injury. In this way spore-producing organisms can fortify themselves against destructive influences which ordinary bacteria may be unable to resist. Spores remain dormant as long as conditions for growth 134 BACTERIOLOGY AND STERILIZATION and development are unfavorable. When, however, new food is sup- plied, and harmful influences have been removed, they develop into the original types of bacteria which gave rise to them by a simple process which may be called germination. The importance oj the spore, or spore-production by bacteria, cannot be overestimated. If it were not for the spore it would be very easy to sterilize objects. Fortunately, however, comparatively few disease- producing bacteria have the property of producing spores. ARTIFICIAL CULTIVATION OF BACTERIA. There are various ways of growing bacteria. Some favorable nutrient medium must be employed like milk, beef broth, and nutrient gelatin or jelly. The examination of a specimen of milk or water is accomplished by putting a drop or several drops in a tube of jelly that has been warmed enough to liquefy it, mixing the contents well and then pouring it into little glass plates made for this purpose (Petri xlishes). By this procedure it is possible to get the bacteria away from the milk or Fici. 40. — Anthrax bardlli. water and start them growing in the new medium. The jelly hardens just as ordinary table jelly does. After one, two or three days quite a change will have taken place in the jelly; the same sort of change that frccpiently takes place on a slice of bread that is put into the bread-box when dajnp; the same sort of change that takes place on a bit of cooked potato that is kept long enough. Families of bacteria have grown here and there, forming various sized masses. These families are the offspring of the individual })a('teria that were in the drop of milk or water which was placed in the liquefied jelly. Such ARTIFICIAL CULTIVATION OF BACTERIA 135 families or "jroiips may frequently be distinguished from eaeh other by their famil\' traits. These families are known as cohmics. Frequently the mieroscope is used to examine the colonies as well as the individual organisms. As a rule each colony is the product of one original bacillus, spirillum, or micrococcus. Fig. 47. — Typhoid Ijafilli from mitiient gelatin. X 1100 diameters. (Park.) In studying a plate containing a number of colonies of different bacteria a great variation in their character will be noted. Some are large, others small; some are colored, others colorless, etc. In other words, they show dift'erent family traits. The differentiation of family characteristics plays an important part in the process of identification and is used for diagnostic purposes. Fig. 48. — Streptococci in peritoneal fluid, partly enclosed in leukocj'tes. X 1000 diameters. (Parlv.) Often the investigation is carried still further by various methods. For instance, one -or more of these colonies may be further isolated; some of the individual bacteria may be removed from these colonies and placed in a tube of sterile jelly, milk or broth. The tube is then closed with an ordinary cotton plug, and put away for development. The organisms are now isolated or imprisoned, and may be held indefinitely under these conditions. Why is all this necessary? Just 136 BACTERIOLOGY AND STERILIZATION as soon as one bacterium is isolated from another and studied, the danger of confusion is avoided. It is impossible to study any par- ticular kind of organism to the best advantage when another organism is present. Different organisms produce, as a rule, different kinds of growth on the surface of sloped jelly or agar. In some instances the growth is scanty, in others, luxuriant. Some growths are raised, rough or irregular; others are smooth, flat and regular. The common organism known as Bacillus prodigiosus produces a blood-red color; another, the most common pus organism, a golden-yellow pigment; some, like the typhoid bacillus, produce no color at all. ¥u:. 49. — Piieumococc!. A microscopic examination of the bacteria present in a colony furnishes additional information. This is accomplished by removing a small portion of the growth and spreading it on a microscopic slide in a dro]j of water. Some kinds of bacteria will be seen to swim about of their own accord. The property of moving about independently in a liquid, which some bacteria possess, is termed motility. They have moving organs known as 'flaf/eUa. A large number of bacteria can mo\'e about iiidejx'iidently. On the other hand, a large grou]) lack this i)roi)erty; they are iion-iiioiilc; they do not have flagella. In addition to motility, the si'/e, shape and other iiiicn)sc()])ic characters are studied. While organisms are grouped under the three types previously men- tioned, members of each gronj) \vd\v (listingnishing characteristics of their own, differing in appearance as individuals, and so permitting flefinite recognition or diagnosis under the eye of the microscope. To BACTERIA IN THEIR RELATION TO DISEASE 137 make this clear it is but necessary to study the accompan\iii,r()perty of some of the lower animals, like the salamander, of restoring lost members. These tissues, when they lose a side chain, immediately replace it. If they lose two side chains, they replace them. If they lose a thousand, they will replace a thousand, and soon they acquire the habit of reproducing not only the lost rcc('i)tors, })ut more than the number sacrificed, and so where one side chain has been lost there will STERILIZATION AND DISINFECTION 153 be dozens to take its ])lace. The cells have prothiced these side chains in such large numbers that the toxin is insufficient in amount to com- bine with all of the newly formed receptors. Furthermore, the side chains are produced in such large numbers that the tissue cells cannot hold on to them any longer. The body fluids become filled with these free receptors which are now known as the immune bodies or cmti- toxins. The antitoxins are the side chains that have been produced in such large numbers that the very tissues from which they were generated can no longer retain them, and they are shot oft* into the circulation and remain there as safeguards against any other toxins that may invade the tissue. If toxins present themselves, they will combine with these free antitoxins and thus no injury will be wrought on the tissues. The antitoxins are in the blood floating about freely, and combine with the individual toxins, neutralizing them, and preventing the toxins from getting at the living sensitive tissues themselves. This is one of the most ingenious and at the same time one of the most satisfactory theories of immunity. STERILIZATION AND DISINFECTION. There are three important phases of this subject that have received a great deal of attention: (1) asepsis; (2) antisepsis; and (3) disin- fection. The actual distinctions are important. In asepsis there is what the term implies, absence of infection, or absence of sepsis; that is, in asepsis living bacteria are excluded, and where microorganisms do not exist there can be no such thing as antisepsis or disinfection. The idea of asepsis is coming to the front more and more in surgery, and, to a large degree, actually supplanting disinfectants and antiseptics. The second phase, that of antisepsis, has its own significance. Various food substances are preserved by means of chemicals. The salting or curing of pork is an instance. If a thorough bacteriological examination of cured pork were made, it would not be found sterile but would, in all probability, be found to contain any number of bacteria. But there is an antiseptic condition, and the bacteria that are present are unable to multiply appreciably under such conditions. An antiseptic is an agent which prevents growth and multiplication of bacteria but does not destroy them. The third phase, disinfection, deals with agents that destroy or remove bacteria, and therefore is entirely different from either one of the other two phases. Asepsis means no bacteria. Antisepsis means the holding in check of bacteria that are present. Disinfection means the destruction or complete removal of all bacteria. On entering a modern surgical operating room one is impressed with its appearance. The most up-to-date surgical ward now depends more on asepsis in ordinary surgical operations than on the other 154 BACTERIOLOGY AND STERILIZATION two phases of the subject. The instruments must be steriUzed. The hands of the surgeon and his assistants are thoroughly cleaned and disinfected. In some of the best hospitals they do not even depend on washing and sterilization of the hands, but use gloves that have been sterilized and kept in an antiseptic solution. The air should be perfectly still. There are operating rooms where per- sons are prevented from coming into the room or anywhere near the patient operated upon, until they put on long, sterilized coats. Furthermore, those who perform surgical operations frequently have a mask over their mouth, so. as to prevent infection of the patient by mouth spray. No mouth is ever found to be sterile, and it is doubtful if it ever will be possible to sterilize the mouth, so there is no such thing as asepsis in dentistry in the pure sense of the word. But asepsis is an important factor insofar as the hands and the instruments are concerned. It may be said that disinfection involves the absolute destruction of all forms of life. The term is often misused, as for example, in connection with the pasteurization of milk. Sterilization of milk means the destruction of all microbic life, including spores. Steriliza- tion of milk, or sterilization of water, is real sterilization only when all organic life is destroyed. There are different degrees of purification by heat or chemicals. Pasteurizatio?i of milk is an important example of ijicoinyilete steriliza- tion. It is neither antisepsis nor disinfection nor sterilization. It is the destruction of the comparatively non-resistant types of bacteria in the milk. Spores and a small number of resistant vegetative forms are not killed. In pasteurization the heat used is far below the real temperature for sterilization. In the ordinary pasteurizer the milk is heated at a temperature of 140° to 145° F., for a period of twenty to thirty minutes. Milk that is pasteurized at such a temperature will keep much longer, and is less apt to cause disease than the unpasteur- ized. If disease-producing bacteria, like the typhoid and the tubercle bacillus, were present, they have been destroyed in the process, and the milk has been made safe. But that does not mean that this milk, when it is put in the ice-box or allowed to stand on the kitchen table, is not undergoing an}' further chemical or bacterial change. Pasteuri- zation simply holds in check. It corresponds to antisepsis, but is not antisepsis, because the pasteurization is temporary. In antisepsis the antiseptic influence is permanent. Methods of Sterilization. — In disinfection or sterilization various agencies may be employed to bring about the desired result. One of the most efficacious, and one of the most practical and reliable means of sterilizing objects is heat. Heat is perhaps the most important of all sterilizing agents, and, of course, in many professions it is indispensable as such. Sterilization by dry heat is a method that is commonly used in labora- tories anfi hospitals. Glass plates or Petri dishes are sterilized, before STERILIZATION AND DISINFECTION 155 they are used, by the hot-air method of steriHzation. Test-tubes are often sterihzed, before filling, in the same way. There are many occasions on which the dry-heat method cannot be used and another method of sterilization must be resorted to, namely, moist heat. Dry heat may be applied only to certain objects that will stand it. It is not safe to sterilize ordinary fabrics with dry heat, as they are apt to become discolored and charred. Steam heat will often take the place of dry heat, and is an important means of sterilization. The sterilization of towels, of dressings, of media that are used in the ordinary laboratory work, and a large number of other objects that cannot be subjected to dry heat are advantageously sterilized in this way. A word may be said about the comparative efficacy of dry and moist heat. While dry heat may char or discolor cotton and woolen fabrics, it is not nearly as effective in its destructive action on bacteria as moist heat at the same temperature. This fact should always be borne in mind. An illustration may be given. Some bacteria, like the diphtheria bacillus, will stand a temperature as high as that of boiling water for a short time when in a dry condition, whereas a moist temperature of 150° F. applied for the same length of time is fatal. In other words, moist heat is effective at relatively low temperatures, whereas dry heat is often ineffective at even relatively high temperatures. Spores are unusually resistant to heat and other sterilizing agents. They will often withstand a moist temperature of 212° F. for an hour. When dry heat is applied it is necessary to raise the temperature to at least 300° F. and maintain it for an hour. Frequently it it not necessary to destroy all spores, but only such organisms as possess disease-producing powers. In such instances, boiling for fifteen to twenty minutes, with a small amount of potash or soda may be sufficient. Since in the use of surgical and dental instruments there is always some danger of lockjaw infection (caused by the lockjaw bacillus or its spore), thorough disinfection should always be made. Some things are sterilized under pressure. The ordinary barber-shop sterilizer, a big globe-shaped apparatus, is a valuable instrument for sterilizing towels, brushes, etc. The objects to be sterilized are put in, the door is placed in position, and steam is generated by means of a gas lamp, or is introduced tlu"ough a steam pipe. The increase in the pressure of the steam becomes such that the temperature can be raised considerably above that of boiling water. Thus, within certain limits, any temperature may be obtained. Ordinary boiling is not sufficient for absolute sterilization. Wherever complete sterilization by moist heat is required, it is imperative to use a sterilizer that will heat under extra pressure, or to use some chemical agent which lowers the sterilization temperature. When instruments are boiled in water it is advisable to add a small amount of a solution 156 BACTERIOLOGY AND STERILIZATION of soda or potash, for the purpose of lowering the steriHzation tempera- ture, and of pre^'enting the instruments from rusting. Chemicals. — There is another method of disinfection, that is by means of chemicals. A great deal is being done today in the disinfection of water supplies, of all sorts of surgical instruments, clothing, etc. Also in aerial disinfection of rooms, as with formaldehyde. The disinfection of the interior of rooms, including the hangings, and all sorts of articles that may have become infected by some occupant who has had some infectious disease, has been practised for many years. In the purifica- tion of water supplies one of the best disinfecting agents employed is chloride of lime. A disinfectant that is being extensively used in surface disinfection 6i the body is iodine in the form of tincture of iodine. This may be applied externally only. The choice of a disinfectant depends upon the specific object to be disinfected, and in many cases, upon the bacteria and spores that it is intended to destroy. Corrosive sublimate and carbolic acid have been used for years as general disinfectants for the hands and for different portions of the body and body wastes. The bichloride, usually in 1 to 1000 dilution, and the carbolic acid in the proportion of 1 to 35 to 1 to 50. In fact, mercury bichloride, or what is known as corrosive sublimate, has been used in past years to a very large extent in connection with surgical operations. Today there is a growing sentiment against corrosive sublimate, especially as an internal disinfectant. It contains mercury, and for that reason it is useless in the disinfection of metallic objects because it attacks the metal, forming an alloy with it. Then there are other facts that make corrosive sublimate and carbolic acid as well more or less worthless. Both, and particularly the former, will combine with various chemical substances, like protein, and lose their disinfectant properties. Another disinfectant that has been used a great deal is formalin, or formaldehyde. In house disinfection it is used as a spray, or asformalin vapor. Permanganate of potash and formalin are now used in com- bination for the evolution of the disinfectant vapor, the permanganate serving simply to generate heat by its action on the formalin. A certain amount of moisture is always necessary, to obtain a high disin- fectant efficiency. Sulphur also has been used a great deal for aerial disinfection of the interior of houses, but it is useless unless there is an abunrlance (jf mf)isture, which combines with the suli)hurous gas, to produce sulphurous acid. While this product is a jjowerful disinfectant, it is also destructive to furniture, hangings, wallpaper, etc. It is impossible as yet to name a completely satisfactory chemical disinfectant, although in recent years many new ones have been put on the market. How often does the dentist take his instruments, dip them into carbolic acid, take them right out again, and assume that they are sterile and ready for further use. That is not disinfection. If STERILIZATION AND DISINFECTION 157 a chemical is to be used as a disinfectant, it must either be extremely powerful, or the time that is allowed for the disinfectant to act on the subject to be disinfected must be considerable. It is for that reason too, largely, that boiling with a little alkali is taking the place of chemical disinfection of one sort or another, as for example with car- bolic acid, carbolized vaseline, etc. In determining the value of a duinfectant several points are taken into consideration. The time during which the agent is allowed to act is an important factor as well as the temperature. In many cases the effi- ciency increases with increase in temperature. Then the conditions imder which disinfection takes place are of much significance. A good disinfectant will not lose its power by contact with proteins, carbonates and other chemicals. Finally, it must be efficient as a disinfectant, but harmless to man or animal. Alcohol in a dilution of 40 to 80 per cent, serves as a valuable dis- infectant, under certain conditions. Recently ether has been strongly advocated as a disinfectant in certain abdominal operations and treatment. There are many disinfectants which are powerful enough under certain favorable conditions, or when thoroughly adapted. Soap is one of the most valuable agents in the elimination of bacteria. It is a cleanser, and surgeons are coming more and more to the idea that cleansing is of extreme importance, as well as disinfection. If cleansing can be done at the same time as disinfecting, or just before, then disinfection will be doubly effective. But if the disinfectant is put on over a coating of dirt or grease, it is of little value. Soap, hot water and a nail brush will do a great deal toward absolute disinfection of the hands. Soap alone has some disinfectant properties but its chief value lies in its cleansing action. CHAPTER V. INFLAMMATIOxX. By LeROY M. S. MINER, M.D., D.M.D. IxFLAiMiMATioN may well be called the cornerstone of Pathology, for an accurate conception of the principles involved in the phenomena of inflammation is necessary in order to have a foundation upon which to build a knowledge of general pathology. Inflammation in its various forms is so exceedingly common that without a knowledge of the changes that take place one cannot hope to understand the manifestations which occur in diseased conditions. Definition. — Inflammation may be described, in a word, as a response or reaction to an irritation or injury. Its ijurpose is twofold: 1. To counteract or neutralize the agent causing the injury. 2. To repair the injury produced. Thus it is seen that inflammation is intended to be a building up pro- cess; a beneficial effort of nature to repair damage. Unfortunately it not infrequently happens that under unfavorable conditions it becomes rlistinctly destructive instead of reparative. Classification. — The many types of inflammation have been classi- fied in \arious w^ays. The terms most frequently used, however, are (1) acute and (2) chronic. It may also be classified according to the location. Catarrhal wflammatiov. affects the epithelial structures, especially the mucous membranes; inflammation is said to be Interstitial, when the connec- tive or supporting tissues are involved; or Parenchymatous, when the functionating cells of an organ are attacked. Inflammation has also been described as Ulcerative, when there is l(xss of tissue by necrosis or gangrene; Exudative, when the process is characterized by unusual exudates as in pleuritic effusion; Swp- jmrative, when the inflammation ends in suppuration or the formation of pus. While these classifications help to describe the location or the type of inflammation, and while the clinical aspects may vary somewhat, it must be firmly borne in mind that the i)henomena of the reactions which take ])lace are essentially the same in all forms. The location of the injury will determine to a considerable extent the effect, but the reacti(;n is fundamentally the same. Inasmuch as the cinmlation of both blood and lymph plays a very important role in the phenomena of inflaniniution, it is neces- sary to have some knowledge of the normal circulation and also some THE CONSTITUENTS OF THE NORMAL BLOOD 159 idea of tlie simpler tissues wliicli may be affected before studying the process itself. The Normal Circulation. — The circulation of blood differs in each of the three types of vessels. In the arteries, which carry the fresh red blood, the flow is inter- mittent, the red blood corpuscles flow in the center of the vessel (axial core), while between them and the vessel wall is a colorless zone called the plasma zone. The white blood corpuscles travel in this zone and travel much more slowly than the red corpuscles. In the capillaries, or the intermediate vessels, the blood flow is slow and continuous. There is no plasma zone. The flow in the mins is continuous and slower than in the arteries. The plasma zone is present, but less sharply defined than in the arteries. The Constituents of the Normal Blood.— The chief constituents of the normal blood are eight in number, as follows: I. Red blood corpuscles, erythrocytes. J^^ • II. Blood platelets. -^sJ.us is filled in gradually by granulation tissue and coiniectix'c tissue in much the same way as in healing by first inten- tion; but there is much more tissue to be restored, and the healing process may be slow, jjarticularly if the cavity is large. It is often IKjssiblc, after the pus has sjK-nt itself and the acute symi)toms have subsided, to bring the edges of a wound together and have it heal by first intenti(jn, but that is not customary. If instead, in this type of wound the opening is packed with gauze, and allowed to fill in, as we say, from the bottom, the granulation tissue fills up gradually, and each day less gauze is used in the ])acking until the cavity is filled in solidly with this connective tissue. I'his healing by granulation HEALING BY SECOND INTENTION 169 becomes very important under some conditions, })ecaiise the contrac- tion is sometimes excessive. If there is a bad inflammation or a bad abscess of the cheek, for instance, or the cheek muscle and the wound has to be repaired by second intention, or by granulation healing, after a while this contraction of the cicatricial tissue may be so great that the person is unable to extend the lower jaw, or open the mouth as wide as desirable, and it becomes a very serious condition under some circumstances. Fortunately, this state of affairs is not very common. Repair then in general is the effort of nature to restore the tissues to the normal after an inflammation; and when the repair is complete, especially if it is by first intention, the parts have been restored to function and the tissue cells resume their normal relations. Note: — In this discussion, liberal use has been made of the masterly exposition of the subject by Prof. F. B. Mallory, to whom the author is deeply indebted. CHAPTER VI. DEPOSITS AND ACCRETIONS UPON THE TEETH. By EDWARD C. KIRK, Sc.D., D.D.S., LL.D. The factors involved in the composition and mode of production of deposits and accretions upon the teeth are those which are intimately connected with the chemistry, physiology and pathology of the saliva, the study of which is perhaps one of the most important considerations both in its scientific and practical aspects, that is engaging the atten- tion of the dental profession, for it is through the study of saliva that we hope to ultimately solve some of the most important problems with which we have to deal in dental practice. It has been mainly through the study of the saliva that we have arrived at some very definite ideas as to the causation of dental caries, that one disorder, the prevalence of which has really created the den- tal profession; and through the study of saliva we have also learned something of various other diseases to which the teeth and soft tissues of the mouth are subject, and further, we hope to learn something through the study of the saliva about the deposits or accretions that are commonly spoken of as tartar and about their mode of formation. After all, there is no phase of dental practice that is of more immediate importance to those who are pursuing this course than the causes which lead to the formation of these deposits upon the teeth. As for the word "tartar," some years ago in one of the popular magazines there appeared an article by a physician who stated that the tartar on the teeth was called "tartar" because it consisted of tartrate of lime. An eminent professor of chemistry once said to his class during a lecture that he never had understood why the sulphate of iron was popularly called copperas. He said he imagined it must have been called copper by the Dutch, because it had no copper in it. By the same mode of reasoning, it is probable that this medical man called these deposits tartar because there is no tartaric acid in them. The term tartar was applied by the alchemist Basil Valentine to the deposits called argols in wine casks consisting essentially of potas- sium tartrate, and the acid derived therefrom was called tartaric acid or the acid of tartaros. Paracelsus applied the term much more widely to include earthy deposits from animal fluids such as calculus from the saliva. Tartar consists essentially of calcium pliosphatc or phosphate of lime and some carbonate of lime and corresponding magnesia salts held together by a binding material that we call mucin, a substance derived from the mucus of the saliva; that and some organic matter DEPOSITS AND ACCRETIONS UPON THE TEETH 171 such as food particles, the bo(hes of dead or dying bacteria, make up the bulk of what we call "tartar." In order to understand the formation and deposition of tartar we must first know something about the saliva. By saliva we mean that mucoid fluid which we find in our mouths from time to time. It is not always flowing, but our mouths and our food are lubricated and mois- tened by it. This saliva is manufactured by three i)airs of glandular structures situated in the region of the mouth which pour their secre- tions into the oral cavity. The secretions of these several pairs of glands, which we speak of as the salivary glands, differ in their composition. Neither do all of these glands pour their secretion into the mouth at the same time, but under different circumstances and in response to different kinds of stimuli, namely, the stimulus of food or the stimulus of the thought of food or the stimulus of pain. You are all familiar with the common expression that if we think of this or that kind of food it makes our "mouths water." This is literally true. I'nder the psychic stimulus of the thought of food, espe- cially of food which is sapid or tasty, the salivary glands are encouraged to pour their secretions into the mouth, but it is interesting to note that different kinds of foods excite the secretion of different glands. For example, the physiological chemist Pavlow, of St. Petersburg, found that when a piece of fresh meat was offered to a dog the flow of saliva from the sublingual and submaxillary glands was stimulated, but not that from the parotid, which is a large gland situated in front of the ear. When dry food, like powdered meat, was offered to the dog, the parotid salivary secretion was stimulated. So under different stimuli we find a response from different glands, and the response seems to stand in very close relationship to the character of the food that exerts the stimulus. This is an important relationship too, because dry foods, for example, need a great deal of moisture for two reasons: first, for converting the food into a bolus so that it may be swallowed; second, for furnishing sufficient water to the food in order to dissolve its soluble elements and to give taste to it. Tasty things stimulate the flow of saliva, and the watery secretion of the parotid gland is necessary in order to dissolve what is soluble in the food in order to bring out its taste. We cannot taste anything unless it is soluble, no more can we smell something unless it gives oil" a vapor of some sort. So that gratification of the sense of taste is secured by the solvent action of the parotid saliva, mainly, upon the foods that we take into the mouth. Besides the secretion of the salivary glands, the secretion of innumer- able mucous glands that are imbedded throughout the whole oral or buccal mucous membrane, the lining membrane of the mouth, is added to the mixed saliva, and it is the secretion of these mucous glands that give to the saliva its slimy or slippery quality, owing to the sub- stance mucin contained therein. 172 DEPOSITS AND ACCRETIONS UPON THE TEETH Mucin is a very important constituent of the saliva, and among other things has a very direct bearing upon tartar formation, but its main function seems to be that of a hibricant. Perhaps you all know of the peculiar technic of reptiles when they feed. A boa constrictor for instance, kills its prey, which may be a half-grown 4)ig, and covers it with a slimy coating so as to lubricate this relatively enormous mouthful, and to render its passage into his interior as easy as possible. In a minor degree, the same function is performed by the lubricating exudate of the mucous glands of the mouth upon the bolus of food in the mouth of the human being. Beside this important substance, mucin, the saHva contains also a peculiar ferment known as ptyalin, the function of which is to begin the digestion of starchy substances in the mouth. Starch as such is not utilizable as food by the body, therefore the ptyalin acts upon it, con- verting it by degrees into a kind of sugar, maltose. This predigestion of starch, or preparation for intestinal digestion, takes place in the mouth, hence the very great importance of thorough mastication of starches, which is doubtless the main justification for the fad of super-chewing that has spread over the country under the name of Fletcherism. Another constituent of the saliva, though perhaps it is not of very great importance, has been exciting a great deal of comment in the past four or five years; that substance is known as potassium sulpho- cyanate, ordinarily spoken of as sulphocyanate. It may be ques- tioned that it is a potassium sulphocyanate, but some kind of sulpho- cyanate is present which is possibly a sodium or ammonium sulpho- cyanate. It has the peculiar property that when to a small quantity of sali\'a a drop or two of a test solution of perchloride of iron is added, if the sulphocyanate is present it causes a red or reddish colora- tion of the saliva. This is rather a striking reaction which can be made very easily by simply taking a few drops of saliva, a half-thimbleful, adding to it a drop or two drops of the ordinary tincture of chloride of iron, and if sulphocyanate is present in the saliva, a red color will result. This reaction is rather dramatic, and has caused a great deal of discussion and debate as to its significance which thus far appears to be unimportant. Sulphocyanate was at one time supposed to have a very im- portant bearing upon caries causation, or of the prevention of carious action in the mouth, but recently it has been pretty definitely shown that sulphocyanate is an incidental constituent of the saliva, and that it has iio very important significance exccj)t as a waste ])roduct of rmtrition related to some other chemical activities in the body. In arldition to the constituents mentioned, saliva collected in a receptacle will show certain sediments, solid matter, if it stands for a short tiiiK!. The salivary scflimciit consists mainly of tlic desquamated or peeled-off external epithelial cells. Just as the scarf-skin, or outer layer of the cuticle, separates from time to time, so does the mucous DEPOSITS AND ACCRETIONS UPON THE TEETH 173 nuMiibnine of the mouth sliecl its ei)ithelial coatiiij^ into the saliva, and we find mixed with the saliva these epitheilial seales from the buccal m.ucous membrane which when a specimen of sali\'a is allowed to stand for a time separate as sediment. We find also as corpuscular elements, the leukocytes, or white blood C()ri)uscles, which s; it varies in the rapidity with which it forms, it varies in the position in which it is dei)()sited, and above all it varies in its density, the tenacitx' with which it adheres to the tooth surface and its toughness. Certain classes of tartar undergo very raj)id formation and enormous development. Masses of tartar weighing as nnich as from two hundred and fifty to three hundred grains are reported. It seems incredible that any human being could tolerate in his mouth a mass of tartar larger than a pigeon's egg attached to the buccal surface of the molar teeth, yet such instances are by Jio means infrequent. Tartar which is formed rapidly and in large masses is usually relatively soft and friable and can be readily removed by proper instrumentation. DEPOSITS AND ACCRETIONS UPON THE TEETH 179 Every dentist has had patients with the idea in their minds that tartar was j^rotective to the teeth and for that reason they objected Fig. 52. — Sublingual tartar on a lower incisor. Fig. 53. — Sublingual tartar on a lower canine. to having it removed. It is true to a great extent that teeth upon which that kind of tartar is deposited rarely decay, not because the tartar is protective, but because conditions that cause the deposition of the tartar are precisely the opposite of those that favor caries of the teeth Fig. 54. — Partial denture clasped to first and second molars, which have been lost by deposition of parotid tartar. When such enormous accumulations are removed from the teeth the patients are often surprised that the teeth do not come out. 180 DEPOSITS AND ACCRETIONS UPON THE TEETH This kind of tartar will form upon artificial dentures just as readily as upon the surfaces of the natural teeth, and it is usually found at positions opposite the orifices of the ducts of the salivary glands. For the same reason we find these enormous masses ordinarily upon the buccal surfaces of the molars and upon the lingual surfaces of the lower teeth occupying positions almost opposite the openings of the salivary ducts. (See Fig. 54.) The question of why this is so is the chemical problem that we are confronting. This is what we know : that calcium phosphate as it exists in tartar is not the same kind of calcium phosphate that exists in solution in the saliva; that is to say, after it reaches the mouth it undergoes some chemical change, the nature of which may be illus- trated as follows: One of the popular drinks advertised at the soda fountains is "Acid Phosphate." Calcium phosphate or lime phos- phate, chemically speaking, is a term applied to a group of compounds of which there are two distinct kinds. One contains more lime in pro- portion to the phosphoric acid than does the other. The one which contains less lime in proportion to the phosphoric acid is designated as acid phosphate, which is soluble in water, and has acid properties; whereas the other phosphate which is designated as basic phosphate contains a larger proportion of lime and is insoluble in water. If we add to the acid phosphate a little more lime, we convert it into basic phosphate; and because of its relative insolubility it would fall out of solution as a sediment or precipitate. A similar process occurs in the deposition of this phosphate as tartar in the mouth. It is in a state of acid combination in the saliva. Possibly it is the content of carbonic acid in the saliva which holds the phos- phate in solution, and when the carbonic acid escapes in the saliva, the phosphate, having nothing to hold it in solution, falls down as a precipitate. Mucin acts as a glue-like binding material to the small earthy particles of phosphate and fastens them together and when the pro- portion of mucin to the calcium phosphate is in certain ratio the mass- may be so dense and adhesive that it is almost impossible to cut it with a steel instrument or scrape it from the tooth surface. The escape of carbonic acid is one of the means by which we think the earth\' materials of the sali\a are precipitated. If we take any alkaline substance into the mouth, thereby adding free alkali to the saliva, we are likely to cause a precipitation of the lime salts. There is always a certain amount of ammonia, produced by the chem- istry of nutrition, that issues from the lungs with the expired air, and if there is enough ammonia produced in a given case to im])art a definite free alkalinity to the saliva, then precipitation of the lime salts takes place or ammonia may be produced in the mouth by putrefaction, decomposition of aniinjij substances causing tartar formation in unclean months. There is another suggested mode of tartar formation. Dr. II. II. DEPOSITS AND ACCRETIONS UPON THE TEETH 181 Burchanl t'oiiiid that when fermentation is going on in the mouth with production of hictic acid in small quantities the mucin is j^recipitated and the coagulated mass of mucin tends to gather within itself these earthy salts, just as a net going through a stream would gather up fish; this mass is deposited upon the teeth, and coiulenses more and more, forming tartar. Tartar has l)een thus produced artificially out of the mouth, by taking saliva rich in calcium salts and adding small quantities of dilute lactic acid, causing precipitation wlien a hard material of a dark green- ish shade is produced, physically similar to the deposits that we find upon the teeth. One of the most interesting examples of tartar formation is that observed upon the teeth of the natives of Indo-China and the Malay Archipelago. They are habituated to the chewing of the betel nut. This use of the betel nut as a masticatory is very prevalent throughout Indo-China and the Malay Archipelago. Habitual chewing of the betel nut, in the course of a short time, causes the teeth to become stained to a very dark reddish brown of about the color of the exterior of a chestnut, and enormous deposits of tartar quickly aggregate, so that the teeth become distorted in appear- ance and position and are very quickly lost from their sockets. It is not infrequent that young people not over twenty-five years of age are rendered completely toothless by the habit of betel- nut-chewing. The shavings of betel nut are wrapped up in pieces of the leaf of a certain kind of plant called Penang pepper, along with some aromatic spices such as catechu or cloves, or cardamom seed, according to the taste of the betel-nut-chewer, to give it an aromatic flavor. Then about the quantity of half a small spoonful of lime, made by burning oyster shells, is sprinkled all over this mass to develop the flavor. This morsel, rolled up in the green pepper leaf, is very carefully tucked away in the cheek. It causes a free flow of saliva tinged with a red color. The addition of the lime, which develops the flavor, is what causes the trouble. The acid or soluble phosphate of lime in the saliva upon the addition of this extra lime, is converted into the insoluble form of phosphate and precipitated on the teeth. (Figs. 55, 56, and 57.) The foregoing is an example of the formation of tartar due to change in the chemical composition of the lime salts of the saliva from a soluble form into an insoluble form. The hardness of the tartar depends upon the amoimt of its lime con- stituent as related to the mucin constituent. The hardest formations of tartar contain more of the glue-like or mucinous element than do the more friable and easily broken-down forms. The hardest tartar formed is found just under the gum margin. The large masses that are attached to the free surfaces of the teeth opposite the ducts of the glands are usually soft and easily removed regardless of size, but the rings of tartar underneath the gum margin, the hard scales of tartar, are the most difficult of removal. It is this kind of tartar that contains 1S2 DEPOSITS AND ACCRETIONS UPON THE TEETH the largest proportion of organic binding material, because the deposit of tartar at that point sets up an irritation of the gum tissue and causes the weeping out from the gum tissue of the albuminous, serous portion i Fig. 55. — Lower incisor almost completely encrusted with betel tartar. Fig. 56. — Lower canine covered with betel tartar. Fig. 57. — Upper and lower inci.sors lost from deposit of betel t;ut;ir. As they grad- ually loosened from the eiifroiichment of the tartar they were bcjuiid together with fine brass wire by a native dentist, to give them firmness by mutual support. DEPOSITS AND ACCRETIONS UPON THE TEETH 183 of tlie blood which (•()inl)iiies with this deposit and forms a very hard, tenacious mass. Fartlier down ui)on the roots of the teeth we frecjuently find deposits of another form of tartar, which is probably not salivary in origin. It is sjjoken of'as serumal tartar and is derived from the serum of the blood. From a chemical stan(li)()int it is i)ractically a formation of the same character but it originates difi'erently. So far as we know, this serumal tartar which is situated deep down upon the roots of the teeth and not connected with saliva in its origin, is the result of some primary infianunatory condition upon the tooth root. It is not neces- sary to go into the causes of such preceding inflammatory conditions which, instead of breaking out as abscesses, have healed spontaneously by what w^e call the process of resolution, by which is meant that the bacteria which set up the inflammation have died. They have been killed by the resisting forces of the body itself and the inflammatory process has stopped, and the tissues have undergone repair, but the dead bacteria and the broken-down tissue constituting pus has grad- ually- become dehydrated, and there is left a cheesy mass which later on has become saturated with lime salts derived from the blood stream itself. These lime salts combine with this cheesy mass resulting in a tartar-like formation in which the cheesy mass of colloidal organic matter takes the place of the mucin in saliva as the binding material. Tartar formed in that way is a mechanical irritant to the surround- ing tissues, making them subject to subsequent infections. The tartar acts as a foreign bod\' in the tissue setting up irritation, infection fol- lows and the process is repeated with continued growth of tartar, or the abscess may break at the gum margin and a pyorrheal pocket may thus be formed. The pus pockets in pyorrhea may be formed from the root to the gum margin or from the gum margin rootward. Two other phases of this subject are of importance; one is the color of the tartar, the other is the solubility of the tartar. Tartar we find to be of different colors. The tartar which forms rapidly is soft and friable, sali^'ary in origin and more nearly colorless than any of the other varieties. It is nearer in chemical composition to a simple pre- cipitation of phosphate of lime. But when it forms slowly and under the margin of the gum we usually find it highly colored. It must always be remembered that tartar precipitated around the necks of the teeth is a mechanical irritant to the soft tissues of the gum region. This irri- tation predisposes to bacterial infection, which leads to an inflamma- tory process and, as the inflammation proceeds, more or less blood weeps out from the irritated tissue in contact with the tartar. The tartar is then colored by what we call the hemoglobin or the coloring matter of the red blood corpuscles. In other words, the color of the darker varieties of tartar is derived from the coloring matter of the blood which undergoes a variety of changes in color when it is sub- jected to the preocesses that lead to its decomposition. It is a familiar fact that a black eye, or any black-and-blue pigmen- 184 DEPOSITS AND ACCRETIONS UPON THE TEETH tation of the skin surface due to a bruise is at first red, then grows a Httle darker because the coloring matter from the blood has weeped out into the surrounding tissues; then it undergoes chemical decompo- sition, with a variety of color changes, until it becomes very dark. In the same way when blood oozes out from the gum margin and comes in contact with the tartar this coloring matter is absorbed by the tartar, becomes part of its binding material and undergoes color changes which are quite analogous to those observed in a bruise, that is, from a reddish or brown tint through a variety of color changes down through brown and blue to a final grayish or greenish, almost black, appearance. Tartar may be pigmented from other causes. It may be pigmented through the activities of certain bacteria that are color-producing, or it may be pigmented by the character of the food or other material that is taken into the mouth as in the case of the betel-nut-chewer, or as in the case of tobacco-chewers or smokers. The solubility of tartar is an important consideration from a prac- tical point of view. We have had to depend thus far almost altogether upon mechanical instrumentation for the removal of these deposits, for the reason that we have had no proper solvent for this material, something that will disintegrate it without endangering the texture of the teeth. The enamel of the teeth is composed of the same mineral ingredients as tartar, namely, calcium phosphate and a little carbonate. Therefore, generally speaking, a solvent of tartar will necessarily also be a solvent of enamel, and it is a very difficult proposition to apply a solvent to the tartar without damaging the teeth. There are instances, of course, where the importance of the removal of tartar in certain positions may warrant that risk, if the solvent is applied intelligently and quickly neutralized if it tends to affect the teeth detrimentally. But, broadly speaking, the chemical problem is to find something that will dissolve tartar, but will not dissolve the tooth structure. We would be safer if we could find some chemical solvent that would dissolve, not the calcium phosphate, but the binding mate- rial that holds the calcium phosphate together, i. e., the mucin; but the calcium phosphate is soluble in acid, while the mucin is not. Mucin is soluble in alkali while calcium phosphate is not soluble in alkali, at least in an\' such strength as can be borne in the mouth. So we are confronting a very delicate problem. It is like trying to use a germi- cide strong enough to kill bacteria without killing the individual that is infected by them; to find an agent selective in its action, so that it will damage the germ and not damage the host of the germ. Certain substances have been used as tartar solvents with a fair degree of success. Lactic acid has the property of dissolving the cal- cium phosphate and of forming soluble salts of calcium phosphate and may be a])i)lied as a tartar solvent. It is not a vicious acid in attack- ing the tooth structure, and may be ai)i)lied to remove the last par- ticles of tartar after tlic bulk has been removed mechanically by instru- DEPOSITS AND ACCRETIONS UPON THE TEETH 1S5 mentation. Solvents shonid not l)e used for the removal of the bulk of tartar deposits; they are indieated only for tiie removal of the last remnants. It should never he forji^otten that all the other pieces of tartar are of minor, even negligible importance as compared with the last piece. A man may walk one hundred miles aufl take many thous- and of steps through storm and weather to reach his home, but if he does not take the last step over the doorway, he is not home yet. He may die before he lifts the latch. He has not reached his destination. All his previous steps coinit for nothing. It is quite the same with reference to the removal of deposits. It is not all those that have been taken ofi' which count. It is the last one that counts, and when that is removed the work is done. The last fragment of tartar sometimes even the most delicate tactile sense may fail to detect, especially if it is situated down toward the end of the root of a tooth, or in a pocket which has been thoroughly gone over with the instrument, yet one is not sure whether a small particle has not been left. It is in such a place that we may have recourse to the use of a solvent such as lactic acid. Dr. Joseph Head, of Philadelphia, has promulgated a preparation known as " Tartasol," which is said to be a solution of a certain percent- age of acid ammonium fluorid. I have had no personal experience with it, but it is said by its inventor to have the desirable selective property which we have referred to, that it will dissolve tartar, but not tooth structure. If this is so, it should be a very useful agent, excepting in certain cases in which it is reported to have had a decidedly irritant effect upon the soft tissues aliout the teeth; therefore it should be used with discretion. A word should also be said about the solubility of the bacterial plaque. As this plaque is produced mainly by precipitation of mucin by acids, it is perfectly soluble in alkalies. The alkali that is a natural solvent of mucin precipitated by acid is calcium hydroxide, the solution of which we ordinarily speak of as lime water. A solution of three parts of lime water with one part of hydrogen dioxid has greater efficiency than lime water as a means of removing the bac- •terial plaque. The lime water renders the mucin soluble so that it can be washed off the teeth, and the hydrogen dioxid disintegrates the placjue, so that this solution has a doubly favorable action. It should be used habitually as a dentifrice by all patients who are known to be constitutionally susceptible to caries. The sources of the discoloration of tartar to which I referred are also the sources of the discolorations that we find on teeth, especially in children, which are spoken of as green stain or brown stain. There are two sources. The coloring matter of the blood is the proteid sub- stance called hemoglobin. When in solution in the course of a short time, this color undergoes a change, becoming bluish or more purplish in color as the hemoglobin decomposes. In the course of further decom- position it assumes a greenish tint. This color change can be effected 186 DEPOSITS AND ACCRETIONS UPON THE TEETH much more quickly by adding hydrogen sulphide to the blood. Hydro- gen sulphide is produced by decomposition of albuminous matter, as in the decomposition of an egg, which then gives off that peculiar odor of hydrogen sulphide, which is due to the decomposition of the sulphur elements in the albumin, and it is the hydrogen sulphide arising from decomposition of the albuminous or proteid elements of the blood acting on the hemoglobin that changes its color to a dirty greenish tint. In cases of irritation of the gum margin, a little of the coloring mat- ter of the blood weeps out, putrefactive changes go on through the agency of mouth bacteria, and the albuminous portions of the saliva and the blood putrefies. Hydrogen sulphide is given off, the sulphur compounds unite with the coloring matter of the blood and produce that green or greenish-bro^vn stain observed on children's teeth and the teeth of those having irritated and bleeding gums in uncleanly mouths. The chemical make-up of the pigment of that stain is the decomposition product called sulphomethemoglobin. The children's teeth upon which it is observed are not properly kept clean. They have a history of lack of practical acquaintance with the toothbrush, and the ordinary technic of the dental toilet. Another of these green stains is in all probability due to pigmenta- tions of the normal covering of the enamel of the young tooth, which we speak of as Nasmyth's membrane, by certain color-producing or chromogenic bacteria bringing about that characteristic color. By treating the young tooth with very dilute acids we can isolate Xasmyth's membrane and examine it under the microscope, when we find it permeated with what looks like the result of bacterial activity. Both these types of green stain upon the tooth surface are readily removable by the application of iodin, and the subsequent use of polish- ing powders or pumice applied on an orange-wood stick. Iodin is not only an antiseptic, but also a bleaching agent. That sounds very pecu- liar, because it stains, but we can stain the surface structure of a tooth to a deep tint with iodin and simply let it alone, and when the patient returns the next day that tooth will be much lighter in color, due to the bleaching action of the iodin. We need never be afraid of perma- nently tinting a tooth with iodin, unless we apply it with a steel instru- ment, when iodid of iron is formed and a permanent stain will be pro- duced. Iodin itself may be used with perfect freedom upon tooth surfaces free from metallic fillings for the reason that it is ultimately a bleaching agent. CHAPTER Vn. DENTAL CARIES. By EDWARD C. KIRK, Sc.D., D.D.S., LL.D. Dental caries, or as it is commonly designated, tooth decay, is a disease which is practically universal in its distribution. It affects all civilized peoples, some uncivilized tribes and, under certain con- ditions, even some of the lower animals. Xo disorder that afflicts the human race is more common, as it has been shown by abundant statis- tics that from 85 to 95 per cent, of civilized human beings are more or less the victims of dental caries or have suffered from its ravages at some period of their lives. Dental caries is essentially a disease of childhood and adolescence, the developing individual appears to be peculiarly susceptible to its invasion, whereas when adult life is reached the tendency to tooth decay is noticeably lessened so that in the majority of cases when the individual has reached full maturity the progress of tooth decay appears to be markedly arrested. So manifest are these differences in the activity of dental caries as related to the age and development of the individual that the conditions of suscep- tibility and immunity to the disorder are accepted as characteristic of its activity. As further evidence of the same characteristic a small proportion of individuals are found to be quite free from any evidences of tooth decay, never having suffered from its invasion at any time or in any degree, these are regarded as being naturally immune. The period of childhood and adolescence being the period of greatest susceptibility to dental caries makes its relationship to the health of children of school age one of \'ital importance, not only from the hygienic point of view but upon educational and economic grounds as 'well. Comparatively recent studies of the question furnish abundant evidence of the fact that the prevalence of dental caries among chil- dren of school age is the fruitful primary cause of mental backward- ness, interrupted brain development, nervous disorders, errors of vision and of hearing, bodily malnutrition and a host of evils which not only retard or interfere with the educational process but impair the physical and mental efficiency of these developing citizens of the future generation to a serious degree. Hence the importance of not only a proper understanding of the nature of this important disorder but a clear appreciation of its gravity as a menace to human health and efficiency. For purposes of anatomical description a tooth is viewed as having 188 DENTAL CARIES a crown (corona) which is all that part of the tooth exposed beyond the gum, and a root (radix) or radicular portion which is all that part of the tooth embedded in the bony socket or alveolus beneath the gum. The portion at the gum line between the crown and the root is designated as the neck (cervix) of the tooth. Fig. .58. — Vertical section of a tooth 'in .silu (l.j diameters), c is placed in the puli> cavity, opposite the cervix, or neck of the tooth; the part above is the crown, that below is the root (fang); 1, enamel with radial and concentric markings; 2, dentin with tubules and incremental lines; 3, cementum or crusta petrosa, with bone corpuscles; 4, peri- cemental membrane: 5, bone of mandible, Dental caries is a destructive process affecting the hard dental tissues; these are three in number: (1) the enamel which is the hard outer protective cov^ering of the underlying dentin of the tooth crown and (2) the cementum or crusta petrosa covering the dentin of the root; and (3) the dentin which forms the principal body of the DENTAL CARIES 189 tooth. Within the body of the dentin in the central cavity of the tooth is located the tooth pulp, a soft, highly sensitive and vascular organ, commonly but incorrectly called the "nerve." From a group of specialized cells upon the surface of the dental pulp there radiate through the dentin innumerable fibers of living matter, richly endowed with sensation, which with their lateral processes ramify throughout the dentin structure. These are termed the dentinal fibers or fibrillse, and it is through their agency that we perceive the painful impressions arising from irritation of the dentin by cutting, by heat, cold, sweets, etc. Dental caries always has its inception upon the external or exposed surface of a tooth; it never arises from within the tooth. For a long period it was held by many students of the subject that tooth decay Fig. 59. — Longitudinal section of dentin showing distribution of dentinal fibers and stratum granulosum. (Miller.) was an inflammatory process similar in certain respects to necrosis of bone and those who accepted that view also held that caries originated within the tooth structure and gradually progressed outwardly toward the free enamel surface. This theory was maintained by some until quite recent times, but its fallaciousness was finally completely demon- strated by the researches of the late Prof. Dr. W. D. ^Miller, published about 1880, which finally gave to the world the true explanation of the process of tooth decay. Briefly stated. Miller, as the result of a long and exhaustive experi- mental study of the subject, found that the destruction of the hard structures of the tooth by dental caries was accomplished through the agency of a certain class of microorganisms which had the characterivStic function of fermenting certain of the sugars and con- 190 DENTAL CARIES verting these sugars into lactic acid, which acid in its turn attacked the soUd structure wherever it came into contact with it, dissolving out its mineral matter which caused the structure to disintegrate, forming a cavity which gradually enlarged until it eventually included the entire crown; indeed, if unchecked, the whole tooth may in this manner become disintegrated and lost. A tooth, however, is not wholly composed of mineral matter soluble in lactic acid. If we immerse a tooth for a sufficient length of time in an acid, for example, dilute nitric or hydrochloric acid, it will be found to have lost all of its enamel covering and the remaining dentin and cement structures while still possessing the general conformation of the original tooth will be found to have lost their hardness to such a degree that the structure may then be easily cut with a knife into chips or slices like a piece of cartilage which the structure now closely resembles. We say of a tooth so treated that it has been decal- cified, that is to say, the calcium or lime salts which gave to the tooth structure its characteristic hardness have been removed or dissolved out by the acid and what remains is an organic substance or animal tissue called the organic matrix or basis substance of the dentin and cementum. The relative proportions of calcium salts or mineral matter and organic matrix or tooth cartilage in the dentin and enamel structures are shown in the following analysis: DENTIN (Von Bibra). Tooth cartilage 27.61 Fat 0.40 Calcium phosphate and fluoride . . . 66.72 Calcium carbonate 3.36 Magnesium phosphate 1.18 Other salts 0.83 ENAMEL (Von Bibra). Cartilage 3.39 Fat 0.20 Calcium phosphate and fluoride . . . .89.82 Calcium carbonate 4.37 Magnesium phosphate 1 . 34 Other salts 0.20 Organic matter Inorganic matter Organic matter Inorganic matter DENTIN (Kuehn). CaO 53 .42 MgO 2. ,41 P2O6 39 .46 Fl. ,25 ENAMEL (Kuehn). CaO 53.75 MgO 0.84 P2O5 37.21 Fl 0.29 Organic matter and H2O 8.48 Organic matter and H2O 32.10 Miller showed that the first phase of the carious process was a dissolving out of the mineral substances or decalcification of the tooth structure by lactic acid produced by the ferment action of certain microorganisms on sugars. He further showed that when decalcifica- tion had taken place, infection of the exposed organic matrix of the DENTAL CARIES 191 tooth structure by a dift'ereut type or class of microorganisms occurred, these latter known as proteolytic bacteria, had the power to liquefy and bring about putrefaction of the organic matrix and to destroy it in the same manner that a dead animal body is destroyed and disin- tegrated by putrefactixe changes. These two phases of the carious process are essentially the same in principle, dependent upon the vital activities of microorganisms of two distinct groups, each having the power to decompose certain compounds which enter into the formation of tooth structure and to produce by their action certain characteristic physical phenomena and certain end or decomposition products equally characteristic. Thus in a cavity of decay the presence of acid may be easily demonstrated by bringing into contact with the decaying mass a strip of blue litmus paper which will at once turn red where the decaying mass touches it. The characteristic odor of putrefaction is readily recognizable, indeed, ofl'ensively so, in the breath of those suffering actively from tooth decay. This odor of putrefaction arises in large part from the decomposition of the organic matter of the dentin matrix through the agency of the proteolytic bacteria. The human mouth is not only the portal of entry for many disease- producing microorganisms, but because many of these microscopic vegetable organisms thrive, flourish and rapidly reproduce themselves under the conditions of moisture, temperature and food supply that they find in the mouth cavity many species continue to inhabit the mouth and those which are possessed of disease-producing dharac- teristics become the agency of infection by which a variety of bodily diseases are produced. An unclean mouth is therefore a constant menace to bodily health as well as the ordinary source of tooth decay. Fig. 60 shows a mixed infection of various bacteria from a tooth surface. • But though a great variety and an almost infinite number of micro- organisms are constant inhabitants of the mouth, and though the lactic-acid-producing bacteria which cause tooth decay are found in nearl}- all human mouths, it is well known that many teeth do not decay, and even where the decay process is active not all surfaces of the teeth are equally vulnerable to the process of decay. It has long been noticed that certain locations or areas upon the tooth surfaces are more lia})le to be the seat of decay than are certain other surface areas. In general, it may be said that those surfaces of the teeth that are subjected to the cleansing action of friction bv the tongue, the lining mucous membrane of the lips and cheek surfaces or teeth surfaces which are kej^t free of bacterial invasion by the friction of rough or fibrous food materials, are less liable to decay; whereas, those surfaces of the teeth not subject to the self-cleansing action of the foregoing causes are most likely to be the seat of decay, as shown in Fig. 61. Locations where food particles infected by mouth bacteria can find an undisturbed lodgement, such as the natural pits and depressions in 192 DENTAL CARIES the masticating surfaces of the molars and premolars, the sulci between the cusps, and especially the approximating surfaces of the teeth which by their mutual relations of contact afi'ord protected areas for the Fig. 60. — Mixed infection from tooth surface. (Williams.) ^!^5^C Fig. 01. — Caries localized above the "contact ijoint " on the approximating surfaces of contJKUOus molar teeth. (W'illiams.) lodgement of food jnirticles and its undisturlx'd decomposition by lactic-acid-producing bacteria are areas which in a suscej^tible indivi- dual are the selected locations of the carious process (Figs. 62 and 63). DENTAL CARIES 193 The determination of the location of tooth decay is in large degree a result of the form of the individual tooth and of the relations of the teeth to each other in the dental arches. Fig. 62.- — Beginning caries in sulci and enamel defects of morsal surface of a molar, also showing transparent zone of Tomes. (Miller.) \4^ \ / I'lu. 03. — Beginning caries on approxinial .surface. (.Milk'r.J The structure of the tooth itself, that is to say, whether it be hard and dense or whether it be relatively soft and imperfectly calcified, does not in the sHghtest degree influence the hability of teeth to decay 13 194 DENTAL CARIES or otherwise. Any tooth will decay in a mouth where the conditions causing decay are active and no tooth will decay whatever its structure may be in a mouth where the conditions causing decay are not active. Or, as stated by the late Prof. G. \. Black, "decay of the teeth is a factor of the environment of the teeth. It is not due to the structure of the teeth insofar as their structure is characterized by density, hardness, softness, etc. These factors may influence the rate of decay but they do not determine the liability to decay." When starchy food particles, sugars or any form of fermentable carbohydrate food material is lodged in contact with a protected area of tooth surface it becomes subject to the action of lactic-acid-produc- ing microorganisms and undergoes fermentation resulting in its decom- position with the production of lactic acid. A familiar example of this process is the souring of milk when left exposed for a time to the air at a warm room temperature. ]\Iilk contains a considerable quantity of a characteristic sugar called sugar of milk and chemically desig- nated lactose, having the formula C6H12O6. Bacteria from the air fall into the milk and set up a fermentation of the milk sugar decom- posing it or splitting it into lactic acid which when it accumulates sufficiently, gives the milk an acid reaction and a sour taste. The acid thus formed breaks up the combination of the casein with the base with which it was in chemical union and precipitates the casein as a curd so that the milk becomes thickened and when separated from its watery whey, this curd is the material from which cheese is made. The casein or cheesy portion of the milk will also undergo putre- facti^'e changes through the agency of proteolytic and other forms of bacteria which have the property of decomposing this type of organic matter so that the process of fermentation and subsequent putre- faction of milk is, in principle at least, quite analogous to the process of tooth decay. The conversion of sugar into lactic acid by the fermentative agency of bacteria is represented by a chemical formula as follows: Glucoae. liactic acid. CeHiaOe + the enzyme of B. acidi lactici = 2C3H6O3 that is to say, a molecule of the monosaccharid glucose is, under the actic)ii of the enz.yme of the B. acidi lactici, si)lit up into two molecules of lactic acid. Starches, cane sugar and the more complex carbohy- drates must first undergo changes in the mouth into the simpler forms like glucose l)efore they can l)e split into lactic acid and these pre- liminary changes are brought about by other enzymes, and particu- larly by ptyalin, the characteristic ferment of the saliva which pos- sesses marked amylolytic properties or the power to convert starches into sugars that may be subsequently broken into lactic acid by the agency of the j)roj)er bacterial enzyme. DENTAL CARIES 195 These chemical alterations as the result of the action of digestive ferments and bacterial enzymes upon the debris of food substances are constantly goino; on in mouths which are not kept clean and free from food remnants either by habitual use of the usual tooth-cleansing devices of brush and dentrifices, unless we may exclude those excep- tional cases which are naturally self-cleansing and therefore immune. It is this constant fermentative activity that initiates dental caries wherever on a localized area of tooth structure it is permitted to con- tinue undisturbed. It should be borne in mind that dental caries is a distinctly localized process in its inception. The disease may appear in one or many places in the same mouth, at the same time, but it is localized in the sense that it does not attack all surfaces of the teeth simultaneously, nor with equal impartiality. Many who in the beginning of their study of the pathology of dental caries have clearly grasped the fact that lactic acid is the agent which initiates the disorder by dissoh'ing out the lime salts of a localized area of tooth structure, and that the first stage of cavity formation is thus explained, not infrequently jump to the erroneous conclusion that lactic acid alone is the cause of tooth decay and cavity formation. As a matter of fact, a generally acid saliva, even if the acidity be due to lactic acid, will not give rise to tooth decay. An acid saliva is destructive of tooth structure by bringing about a general decalcifica- tion of the teeth which is manifested m.ore intensely in certain locations than in others, but this type of destruction of tooth structure is not dental caries but what is called chemical erosion of the teeth, a disorder not necessarily dependent upon bacterial activity, as it may be pro- duced by any free acid formed in the mouth, exuded into the mouth, or taken into the mouth. Dental caries is a characteristic disease with a well-marked and definite group of symptoms and within certain limits it has a known causation, which is the localized destruction of the hard tissues of the tooth by the solvent action of lactic acid generated at the point of decay by the agency of bacteria acting upon carbohydrate foodstuff. While localization of the decay process is to a large degree deter- mined by the forms of the teeth and their relations to each other, as already explained, there is another and somewhat complicated method by which fixation of lactic-acid-producing bacteria to a tooth surface is brought about, a method which because of its importance in relation to oral hygiene as well as to the causation of decay should be clearly understood and that is the localization of decay-producing bacteria upon the tooth surfaces by the precipitation of mucic acid from the mucin of the saliva by the lactic acid set free by the activity of the bacteria themselves. The precipitation of the mucic acid upon tooth surfaces is dis- cussed in detail in the chapter on Deposits Upon the Teeth, as it is a result of bacterial activity responsible to a considerable degree 196 DENTAL CARIES for the formation of those adhesive deposits upon the teeth to which the general designation of tartar is applied ; it is important to recapitu- late its main features here insofar as they are concerned in localizing the process of dental caries. In mouths Avhere caries is in active progress the saliva is ordinarily rich in mucin which when present in appreciable quantities, is recog- nizable by the glairy or ropy, adhesive character of the fluid. The sali^'a has the property of viscosity; it has a certain cohesiveness and may be drawn out into threads of greater or less length according to the quantity of mucin that it holds in solution. Such saliva is nearly neutral or faintly alkaline in reaction. If to a small quantity of such a saliva gathered in a test-tube a drop of lactic acid, or, indeed, any acid is added, there will be formed at the point of contact an opales- cent precipitate Avhich is the mucic acid set free from the alkaline base with which it was previously in chemical combination in the saliva as mucin. If the test-tube is allowed to stand undisturbed for some minutes, the precipitate will settle to the bottom of the glass. The precipitated mucic acid is adhesive and insoluble except in an alkaline or saline solution. If now we apply these data to our study of what takes place in the mouth, we shall find that they throw much light upon the mode of localization of the carious process. Assuming that in a susceptible mouth the saliva is rich in mucin held in solution by the alkaline salts of the saliva and that the mouth contains carbohydrate food material in the form of soluble sugars, the result of the amylolytic action of the salivary ferment ptyalin upon starchy food debris, then, in such a mouth infected by lactic-acid- producing bacteria, one or more of these organisms falling upon a tooth and temporarily lodged in some irregularity of the enamel surface, immediately sets up a fermentative action in the soluble sugar in its salivary environment setting free lactic acid in its imme- diate vicinity. The liberated acid at once decomposes the dissolved mucin of the saliva throwing down the adhesive mucic acid in con- tact with the body of the microorganism, cementing it, as it were, to its position upon the enamel surface. Multiplication of the bacteria proceeds rapidly and the process of acid production and mucic acid precipitation proceeds in harmony with the bacterial multiplication. The mass of bacteria thus organized and cemented to the tooth sur- face constitutes what is known as the bacterial plaque, the essential factor in the localization of tooth decay and the most important charac- teristic in the causation of the disease. (See Fig. 64.) The bacterial plaque presents a variety of physical appearances under the microscojx'. It may exist as a small glistening semitrans- parent mass occu])ying only a small spot of the enamel surface or it may present the aj)pearance of a film extending over a considerable area, in fact, over all surfaces of the tooth not subject to friction by food or the tongue and buccal mucous surfaces. The microorganisms DENTAL CARIES 19- found ill the plaque are never a pure culture of lactic-acid praducers but while these are presumal)l\' always present, the organisms are usually those constituting the mixed infection usually found in the unclean mouth (Fig. (K)). It has been shown that tooth decay is brought about in the first place by the decalcifying action of lactic acid produced by the ferment action of bacteria upon carbohydrate food debris. This is, however, a general statement of fact that requires somewhat closer analysis in order that the exact nature of the process may be more clearly under- stood. All carbohydrate material is not directly fermentable into lactic acid, thus cane sugar and starches, two important nutritive substances, must undergo certain chemical changes in the mouth by which they are converted into simple forms of sugar, the mono- FiG. 04. — Bacterial plaque, detarheil from enamel surface of the tooth in making the preparation. (Williams.) saccharids having the general formula C6H12O6, before the bacteria of tooth decay can con\'ert them into lactic acid, this preliminary change called hydration or hydrolysis, is brought about in the case of starches by the ferment ptyalin, an enzyme produced by the salivary glands and which is therefore a normal constituent of the saliva. Its func- tion is to prepare the starches and possibly some of the more complex sugars for later assimilation by the cells of the body in the process of nutrition. The physiological chemist Claude Bernard showed by experiment that cane sugar as such is not assimilated by the human organism when injected into the veins, but when taken into the mouth is later acted upon by a special amylolytic enzyme called invertase in the intestinal canal and is thereby converted into a monosaccharid assimilable sugar suitable for the nutrient purposes of the organism. 198 DENTAL CARIES The typical conversion of starch and of cane sugar respectively into lactic acid may be shown chemically as follows: Cane sugar. C12H22O11 + H2O becomes hydrolized through the action of invertase to Glucose. C12H24O12 = 2C6H12O6 which through the enzyme action of B. acidi lactici is split into 4C3HI03 s-i^d starch C12H20O10 + 2H2O becomes hydrolized through the action of diastase, or ptyalin, to Glucose. C12H24O12 = 2C6H12O6 which through the enzyme action of B. acidi lactici is likewise split into ' • Lactic acid. 4C3H6O3 From the foregoing it will be seen that the mother substance from which mouth bacteria produce lactic acid is a simple form of sugar belonging to the monosaccharid group of sugars called the hexoses from their chemical constitution, all having the formula C6H12O6, a compound which readily splits into two molecules of lactic acid having the formula 2C3H6O3. The sugars being soluble substances readily diffuse into or are capable of absorption by the bacterial plaque so that the bacteria thus fixed and localized upon a protected tooth sur- face are nourished by a food supply of soluble sugar directly convert- ible into lactic acid which being produced continually in these localized areas of bacterial fixation exerts its solvent and decalcifying action upon the enamel without interference. The manner in which enamel disintegrates under the solvent action of lactic acid is })oth interesting and important. The enamel covering of a tooth crown is made up of innumerable prismatic rods or prisms irregularly hexagonal in section and densely calcified. These enamel prisms stand endwise to the dentin and pursue a radiating and some- times wavy course to the peripher^,' or free enamel surface. The prisms are bound together by a material of much the same chemical nature as that constituting the prisms themselves, but it differs therefrom in the physical sense that it is more readily soluble in acids. If we take a thinly ground section of enamel and ))lace it on a slide and while examining it under the microscoj)e allow a drop or two of dilute acid to act upon the free edge of the specimen, we will see that the acid dissolves out the interprismatic cementing substance much more rapidly than it afl'ects the structure of the prisms themselves; hence DENTAL CARIES 199 the acid, because of this greater solubiHty of the interprismatic cement- ing substance, tends to jjenetrate between the prisms separating them from each other and causing them to fall apart as shown in Fig. 65. It is precisely this effect that we see in the opaque chalky white spots that make their appearance upon susceptible tooth areas and which the intelligent operator recognizes as the beginning of dental decay. The opacity and chalk\' appearance of these spots is due to the fact that the interprismatic cementing substance that formerly gave the appearance of homogeneity to the enamel structure has been dissolved out leaving air or fluid in its place having a different refrac- tive index than the enamel (Fig. 06). As the process proceeds the area enlarges and the enamel rods having lost the means of mutual sup- port, fall apart and are lost, leaving an open cavity in their former location. Fig. 65. — Section of enamel sulijected to the action of dilute acid showing solvent effect on the interprismatic cementing svibstance and penetration of the acid between the enamel rods. (Williams.) The irritative effect of the gradual penetration of acid through the enamel in the process of tooth decay is manifest at a very early stage. Even before an actual cavity has been formed or the acid penetration has reached the junction of the enamel with the dentin, the latter tissue will have manifested its reaction to the irritation by recording certain characteristic changes in its structure. In a section of a tooth attacked by slowly advancing caries there w'ill be noticed in the structure of the dentin lying subjacent to the line of invasion a cone- shaped area between the dentino-enamel border and the pulp cavity with the apex of the cone toward the pulp and the base toward the disinstegrating enamel. This cone-shaped area of dentin is more trans- parent than the surrounding dentin structure and from its peculiar transparency has been called the transparent zone of Tomes, from Sir John Tomes, who first described it. Various theories as to the cause of this alteration in the character of the dentin structure have been 200 DENTAL CARIES advanced, and such authorities as Tomes, ]\Iagitot, ]Miller and WalkhoflF regard it as l)eing an o\'ercalcification of the dentin structure as a result of the irritation of the hving matter of the dentin. Certain it is that it is the expression of a vital reaction upon the part of the dentin, for it does not occur in dead {i. e., pulpless) teeth and it always does occur from long-continued slight irritation to the dentin from whatever cause. Its main importance in connection with the study of dental caries is that it records indisputablv the fact that dental caries in its progress sets up irritation which is felt and recoi-ded by the vital elements of the tooth, even in the earliest stages of the disease and before the integrity of the enamel surface has as yet been seriously disturbed (see Fig. 02, a). CARIES OF DENTIN. ^Yhen the enamel has been penetrated and a cavity has thus been formed, invasion of the dentin rapidly follows. Caries of the dentin differs from caries of enamel in two important particulars arising out of the differences in structure and composition of the dentin as com- pared with that of the enamel. The dentin contains a relatively larger amount of organic matter than the enamel ; the earthy salts entering into the composition of the dentin are deposited in a cartilaginous substance having the general form of the tooth and known as the organic matrix or basis substance of the dentin. The organic matrix which in the formed tooth is fully calcified is everywhere permeated by fibrils of sensitive living matter encased in tubules which radiate from the surface of the pulp through the dentin structure. It is these fibrils of living matter that endow the dentin with sensation and which give rise to pain when the dentin is cut as in the preparation of a cavity of decay preparatory to the filling operation or when sweets, acids or other irritating substances are brought into contact with the walls of a carious cavity. The distribution of living matter in the dentin may be seen from Fig. 59, which is reproduced from a photograph of a section of the dentin cut in the plane of the long axis of the tubules in which the fibrillae run. As soon as loss of enamel exposes the ends of the dentinal fibrillse invasion of the tubules by the bacteria of decay promptly takes place and the tendency of the carious process is to follow the direction of the tubules toward the dental i)ulp. ^Yithin the dentinal tubule the bacteria of decay elaborate their characteristic lactic acid which dissolves the sides of the tubule enlarg- ing its diameter, the increased space being promptly packed with organisms reproduced from the parent pioneers of the invasion the dissolution of the tubular walls continuing until the area of decalcifica- tion involves adjacent tubules which have been undergoing a similar process of enlargement until coalescence of a number of tubes takes CARIES OF DENTIN 201 place (Figs. 07 and 0(8). Coincidently, as decalcification proceeds and exposure of the organic matrix occurs, that structure is attacked by a Fig. 66. — Section of tooth showing locahzed solution of interprisniatic cement sub- stance with enamel rods standing, constituting the "opaque spot" of beginning decay. (Miller.) Fig. 67. — Longitudinal section of carious dentin showing enlarged tubules packed with bacteria. (Miller.) group of bacteria known as proteolytic organisms which have the property of elaborating an enzyme that brings about liquefaction of the cartilaginous proteid material constituting the organic matrix. 202 DENTAL CARIES. Decomposition and putrefaction of the decalcified basis substance of the dentin thus takes phice with the formation of so-called liquefaction Fig. 68. — Cross-section of carious dentin showing enlarged tubules. (Miller.) Fi<;. ttO. — I.ifiuefaction foci in carious dentin. (Miller.) foci in the dentin wiiich liquefaction foci by their extension and coalescence idtimately produce what is commonly known as a CARIES OF DENTIN 203 cavity of tooth decay, the process couthiiiiiig until the pulp is reached or, if the process is not arrested, until the tooth is destroyed (Fig. 09). It has already been noted that invasion of the dentin by the bac- teria of caries is by way of the dentinal tubules which these organisms, generally speaking, follow toward the pulp and various considerations seem to indicate that this mode of invasion of the dentin is largely determined by the fact that the source of food upon which the organ- isms feed is found in the substance of the dentinal fibril or the juices of the fibril itself. It has been clearly demonstrated by the researches of jNIiller, already referred to and confirmed by. other able and trustworthy investigators, that dental caries can be, and is, due to decomposition of carbohydrate food particles in unclean mouths, from which we have drawn the conclusion that tooth decay is a filth disease, that if proper care as to oral hygiene is instituted and maintained that dental caries may be eradicated ; in short, we have come to regard it as an accepted fact that "clean teeth will not decay." This conclusion is probably too hastily drawn and without full consideration of all the factors involved. Experience shows that teeth decay more rapidly in early than in adult life, that the teeth of some individuals decay more rapidly than others, that the teeth of some never decay, that many who give scrupu- lous attention to their teeth are extremely susceptible to decay of the teeth, while others whose mouths never receive any attention appear to be immune. The problems of susceptibility and immunity to dental caries are as yet unsolved; there are, however, many indications that give color to the hypothesis that there are certain nutritional factors that have much to do with the susceptibility to dental caries or with immunity therefrom. Those who live upon an excessive carbohydrate diet are, as a rule, found to be more prone to carious invasion than those whose diet is largely of a proteid character. Probably under an excessive carbohydrate diet the percentage of sugar in the blood, normally about 0.001, is increased and if the salivary fluids and the juices of the dentinal fibrils derived from the blood reflect this increase in carbohydrate above the physiological normal would readily invite the invasion of 4ecay-protlucing bacteria. In 18S1 INIilles and Underwood expressed the opinion that the bacteria feed upon the juices of the dentinal fibrillse in dental caries as follow^s: "The organic fibrils upon which the organisms feed and in which they multiply are the scene of the manu- facture of their characteristic acids, which in turn decalcify the matrix and discolor the whole mass."^ If, then, susceptibility to tooth decay is in considerable degree dependent upon a constitutional predisposition, oral hygiene alone and unaided cannot wholly prevent it, although it can undoubtedly greatly ' Trans. Seventh International Congress of Medicine, London, 1881. 204 DENTAL CARIES diminish its ravages. It is highly probable from our present knowl- edge of the subject that complete control of this universal disorder can never be attained by local measures alone. The fundamentally important question of dietetics, of food habit, must be studied for what light it can throw on the solution of the problem, for even now the evidence is almost overwhelming that the inordinate and habitual use of sweets by civilized children is a custom pernicious alike to the integrity of their dentures and to their general health. Until the deeper underlying factors of the causation of dental caries are discovered we must rely upon the means at our command in the principles and art of oral hygiene to protect humanity as best we may from the scourge of dental caries and its consequent damage to health and life. CHAPTER VIII. THE TEETH AS A MASTICATING MACHINE. By CHARLES R. TURNER, M.D., D.D.S. An analysis of the reasons for preserving the teeth gives first impor- tance to their preservation that they may perform their functions as a part of the human organism, and play their part in that sum total of activities which go to make up the physical life of the human animal. As so much attention is now being given to the matter of tooth conser- vation it is proper to be informed as to the important part taken by the teeth in one of the most essential of the distinctive animal functions, indeed, one which is necessary to the preservation of life itself. Fur- thermore, it is one of the dictimis of physiology that any part of the body which ceases to perform its functions atrophies, or the character of its tissues degenerates, and in course of time is incapable of per- forming its function; and so the duties of the teeth have a twofold interest for us. In order then to present the case for the preservation of the teeth, as it were, something must be said about their functions in the human body, and in that connection as a machine, or as a part of a machine, concerned in the preparation of the food for subsequent stages in the digestive process. To appreciate fully the part taken by the teeth in the activities of the human organism, it might be interesting, and it will certainly give a good background for the study of the human dental mechanism, to take some account of the way the teeth have developed to perform their present functions. The basal functions of animal as distinguished from plant life, and as fundamental to existence itself, are: 1. Alimentation. 2. Respiration and circulation. 3. Locomotion. 4. Reproduction. Evolution of Tooth Forms. — In the simplest form of animal life, as for example in a unicellular body, the amcha, we have the process of alimentation, or the securing of nutrition, an extremely simple one. The animal is afloat in the water and extracts its nutriment there- from, the nutritive elements are absorbed through the cell wall and nutrition is effected through a simple process of osmosis. No one fact so impresses the student of zoology as the relation- ship between the form and structure of the various parts of an animal organism and the functions they are called upon to perform. It is 206 THE TEETH AS A MASTICATING MACHINE very interesting to note the adaptive modification of the structures to changes in these bodily functions, and to observe how they have been modified during the various stages in the development from the lowest organisms up to the highest forms. As the scale of animal life is ascended and a multiplication of func- tion occurs differentiations of tissue appearing here and there are found, which occur as a result of a certain function falling upon that tissue. Certain cells are given over to the function of reproduction; certain other cells or collections of cells are specialized for locomotion,, etc. In some of the lower forms of animals, before the vertebrates, there is a simple tube like a channel devoted to alimentation; the food goes in one end and the excreta are ejected at the other. There is no special collection of cells at the beginning of this tube to prepare the food. In the coBlenterata , for example, the alimentary canal is not separate from the general body cavity, but in the annidoida and annulosa it is a distinct tube. A little higher in the scale, as in some of the insects, the crabs and the crustaceans, there are at the beginning of this alimentary tract cells which are concerned to some extent with the preparation of the food for its passage through the canal. There is no real masticating apparatus, however, even in many of the lowest of the vertebrate animals, but the first thing that at all appears like it occurs in some of the lower fishes, in the hag-fishes and in the lamjjrey eels. The latter have a suctorial mouth which they attach to some object, either the side of a larger fish or a stone covered with moss, and obtain their nutrition from it by a process of suction. Inside of this mouth are layers of cells which are rather horn-like in character. They are for the purpose of imV)edding themselves in the substance to which the mouth is applied and of affording a firm hold so that the animal may draw its sustenance. This is perhaps the very simplest type of differentiation of tissue for this purpose. In the vertebrate animals the cells constituting the tissues at the entrance of the alimentary canal are specialized with a view to assisting in the process of either securing or preparing the animal's food. The apparatus is simple in the less highly developed orders and becomes a more complicated instrument as the scale is ascended. The food convenient to the animal or required by it, and the food-reducing mechanism are in constant correspondence. Out of this necessity has developed teeth. The teeth have developed in accord with and to meet the needs of the food which the animal utilizes. They are corneal or horn-like in some of the lower orders and as we go upward they become calcified. They are simple cones or they are modified under certain conditions to forms which serve better their functions. Fishes arc the lowest vertebrate type that have calcified teeth; they arc simply calcified cones arranged around the border of the jaws and serve, to hold tiie food. Some of the teeth are recurved and serve like the l)arb of a fish-hook to prevent the escape of the prey (Fig. 70j. EVOLUTION OF TOOTH FORMS 207 Of the amphibians some have no teeth, as the toad, while others, such as the frog, have teeth not iinhke those of fish, at least always in the uj)per jaw for the hiUfroq has no lower teeth. Of the reptiles- many have teeth. The lizards eat butterflies, worms, insect larvae, etc., while i'^aAr* live on am])hibians and their larva^ and fish, and the I'ijjerine snakes on small mammals. Crocodiles and turtles eat fish, small amphibians and insects. The snakes do not chew their prey but swallow it whole. The lower jaw is jointed in the center and articulates with the skull through the quadrate bone, thus allowing the mouth to open very wide, but the teeth serve only for seizing and holding the prey. In the venomous snakes in the upper jaw are found the "poison fangs" which have a channel leading to the poison sac. The chelonidcB or turtles have a horn-like covering for the border of the jaw. Fig. 70. — Specialized conical teeth in the higher order of fishes. The birds, of course, have no teeth, the beak being a horny sheathing of the ends of the jaw-bones. In some the edge is serrated. In no other class is found a greater variation in the food-preparing apparatus, or greater adaption to the food supply. The beak serves largely to obtain the food. In the grain-eating birds the gizzard performs mastication. Ducks have soft-edged beaks for sifting the food out of the mud. The skulls of the hawk, heron, English sparrow, crow, and toucan shown give an idea of this variation. The crow subs'ists largely on grain, and very often takes grain such as corn out of the husk. It has rather a strong beak suited for this purpose (Fig. 71). The skull of the blue heron is also shown. These are aquatic birds, and their food comes from the bottom of the water, or in fact, down in the mud where they go after little frogs and little fish, and various other inhabitants of the water. Also is shown passer domesticus or English sparrow, which subsists on very much the same type of food as the crow, only it is a little more omnivorous, and the beak is very much the same. We also have the skull of a South American bird, the toucan, which is a fruit-eating bird. The serrations on the beak, which 208 THE TEETH AS A MASTICATING MACHINE are useful in cutting through the skin of fruit and in sifting out the stones, will be noted as a rather interesting adaptation to the needs of this bird. Lastly, we see the skull of the hawk, one of the carnivorous birds. The beak of the hawk is very strong, and is used for the ^^« 9 C^**- 1 Fig. 71. — -Beaks of birds showing functional modifications. purpose of killing the prey : smaller birds, and mammals, in the case of large hawks, and insects and food of that sort in case of smaller hawks. There is very much the same type of masticating apparatus, if it may be so called, in the turtle. Fig. 72 shows the skull of a large greeji turtle, the hawk-bill turtle, whose bill is covered with a very hard, dense mem- FiG. 72.— Skull of a ix.rccu turtle. brane, which is very honi-hkc in cjuality, and is very much like the beak of birds, the jjurpose of it being j)urely to crush the food, and to cut off a definitely si/,ed amount of food in order that it may be swal- lowed. Of cours(; it it not possible for this animal to chew its food. EVOLUTION OF TOOTH FORMS 209 The first type of tooth that is of very great interest other than merely as a fang, or something of that sort, is the molar of the ungulates which are herbivorous and granivoroiis animals (Fig. 73). Herbivo- rous animals live on grain and on vegetable fiber, both of which require considerable trituration in order to be successfully acted upon by the digestive juices, solvents and ferments farther down in the digestive tract. For example, corn and other grains will pass down the alimentary tract of any of these animals entirely untouched unless the outer membrane is broken, therefore in order to be successfully digested they ha\'e to be well triturated. The series of molar teeth of the horse is a real grinding machine. The surface is raised into elevations alternating with depressions. The elevations are the enamel, the depressions between, the cementum. Fig. 73. — Skull of a sheep. The cementum is very much softer, and as the tooth wears down the enamel which is harder and more resistant than the cementum wears much less rapidly, so that the surface is continually kept rough for grinding purposes. This animal has a great latitude in the side-to-side movement of the jaw; or, to speak more technically, the lateral excursion of the mandible of herbivorous animals is very marked. The jaw does not move much backward and forward; in fact, it hardly moves in these directions at all, but it moves from side to side. The result is that these serrations run from front to back. This is exactly the reverse of the form of the molars found in the rodents, in which a backward-and- forward movement of the mandible is responsible for the grinding, necessitating a different arrangement of the occlusal surface of the teeth. 14 210 THE TEETH AS A MASTICATING MACHINE John Ryder, many years ago, pointed out the fact that from an exami- nation of the surfaces of the molar teeth of any animal, extinct or living, he could without reference to the skull indicate the way in which the mandible was accustomed to move. The front of the mouth of the horse is provided with incisor teeth which bite and pinch off the grass and other foods which the animal secures. The canine is quite rudimentary, and usually absent in the mare. Cows have incisors only in the lower jaw, and the biting is done between the upper lip and the lower teeth. 1 HH^I KI^I Fig. 74. — Carnivorous and herbivorous skulls. Now passing over one or two important orders as not being especiall}' interesting, next comes a very large family in the animal kingdom, the carnivorous animals, which differ from the class just described in the character of their teeth and also in the manner of the move- ment of the mandible. In studying these dentures three funda- mental elements and their relationship myst be constantly borne in mind; the food supply, the teeth, and the manner in which the mandible is capable of moving. For a comjjarison of dentures the skulls of a large western cat and of an ordinar.N' buck sheep arc pictured together (Fig. 74). A vast differ- ence in the grinding teeth, as shown in their respective mandibles, is EVOLUTION OF TOOTH FORMS 211 noted. In one the teeth are narrow, in the other the teeth are wide. Viewed from the side it is seen that the carnivorous molars have sharp edges and are rather more Hke knives than the grinders of the herbivorous . series. In one there are very pronounced canines. There is a very marked difference in the temporomandibular articu- lation of these two animals. In the case of the herbivorous animals there are broad, flat glenoid fossae to render possible the large range of lateral excursion of the mandible. On the other hand, the carnivor- ous animals have no lateral excursion. The condyles fit into the fossse so tightly as to make almost a hinge joint; and in some instances the distal part of the eminentia articularis so far overhangs its glenoid fossa that it cannot be seen. It is only with great difficulty that the condyles can be gotten out of these fossse; indeed in some instances they cannot be gotten out without breaking the skull. Fig. 75. — Skull of a tiger. In the skull of an Indian tiger, it may be noticed that the molar teeth are of the type described (Fig. 75). They are very sharp, and there are tubercles on each side just before the cingulum is reached, and in the closure of the mouth the teeth pass by each other very much like the blades of a pair of shears. Besides the articulation of the mandible which serves to keep it in line, the upper canines fit into the spaces back of the lower canines and, locking the occlusion like guide-pins, prevent lateral movement. The carnivora have greater crushing power in their jaws in com- parison to their size than any other animals. Thi^ is partly due to the tremendous temporal muscles which are attached to the broad temporal ridges. In the skull of a black hear is observed almost the same type of den- tition as that of the cats, only the canine teeth are a little less powerful, 212 THE TEETH AS A MASTICATING MACHINE and the carnassial teeth at the rear are not so strongly marked (Fig. 76). A typical carnivorous dentition is found in the canincp or dog family, and in a skull of the canis latrans illustrated are shown the several types Fig. 76. — Skull of a black bear. Fig. 77. — Kkull of u coyote. of teeth definitely marked; the incisors, three on each side, the canines, the ])romolars and the molars (Fig. 77). In the upper jaw there are four premolars and two molars, whereas in the lower jaw there are three molars and four j)remolars. The fourth uj)per i)remolar and the first EVOLUTION OF TOOTH FORMS 213 lower molar are known as the earnassial teeth and they are the chief cutting teeth of these animals. In the wolf and the American fox the dentition is precisely the same. In some of the smaller carnivorous animals, the badger, the otter, and the raccoon, the dentition is very much the same. The next family is the rodents, who have a highly developed type of incisor. Thus far attention has been given chiefly to the molar teeth. In the rodents the incisor teeth are of the greater importance. In the skull of the beaver the upper incisor tooth has a chisel-like beveled edge (Fig. 78). It has enamel only upon its labial surface, which is supported by the dentin. There is no enamel on the back of the tooth. As the dentin wears away the enamel is left standing and chips away and thus always preserves a sharp edge. It is really a self-sharpen- ing tool. It has a persistent pulp and grows out as it is worn off. ^^^^^^ 3 r 1 ^pf^. .• ^:^^^^^ fe ^ ^_T| E:\ T^->>,«rf(^^i1 ■ ^ ^^TgMl ^^^K. ' ': :^^^ii^By K ^^^^^^H ■ ■ ^^^2^1 Fig. 7S. — Skulls of rodents. The rodents have practically no lateral motion to the mandible, but great backward-and-forward movement. Their molars are ridged, but the ridges run transversely, so that in the backward-and-forward movement of the mandible they can do the sarne kind of grinding as the herbivorous animals do in the lateral movement (Fig. 79). Approaching nearer to man in the scale of animal life, as for example in the apes, dentures are found which are approximately like the hiunan one. Thus in the new world monkeys (Fig. 80) almost exactly the same type of denture is observed as that of man, except that there are three premolars instead of two. There are two incisors, a canine, three premolars and three molars on each side. The old world monkey is the first animal representing exactly the dental formula of man (Fig. 81). The three molars, the two pre- molars, the canines and the incisors are the same. There is, however^ a space between the upper lateral incisor and the canine which is to 214 THE TEETH AS A MASTICATING MACHINE admit the lower canine. These animals are largely frugivorous, and their teeth are suitable for this diet. Fig. 79. — Skulls of rodents showing transverse ridges in molar teeth. Fig. 80. — Skull of a new world monkey. The baboon has very long teeth and exactly the same dentition as has been seen before, that is, it has the same formula. The molar THE TEETH OF THE ANTHROPOID APES 215 teeth are very miicli the same in general form as the human molars. The chimpanzee has a deciduous denture which is even more Hke that Fig. 81. — Skull of an old world monkey. Fig 82. — Skull of a chimpanzee showing deciduous denture. 216 THE TEETH AS A MASTICATING MACHINE of man (Fig. 82). The gorilla has a very powerful mandible and the canines are very strongly developed. It is not such a very long step from the dentures of the anthropoid apes to one of the lower types of human denture (Fig. 83). The skull sho-UTi is not of the lowest aboriginal type, but the highly devel- oped jaws will be. noted while the skull case which contains the brain is not highly developed. Secondary Functions of the Teeth. — It might be interesting to dwell for a moment upon certain secondary functions developed in connec- ^H ■H- ^ ^ ^^d n ir^. 'i^^^ ''^' ii^i^^^^^^H ^^E A Rw^Si^^^v^ih^^^^^lw^^^^^H PHM P^H i ^ 1 |P; ■ ' IB r^H 1 \n P' .: wm I '^ w ^ Hr ,^ w . M m gfc^ ■HlMhr^ fc~ i w ■ ^^HH^j^^^' H ^^R^^F^^^ ^^ 1 1 Fig. 83. — Architectural construction of skeletal portion of masticating apparatus: the fixed base, and moveable arm. Columns, arches, and buttresses of the fixed base; frontonasal column, A B; zygomatic column, C M D; pterygoid column (only partly visible), supra-orbital arch, B F D; infra-orbital arch, B I D; upper nasal half-arch, B G; palatal arch (not shown) ; lower nasal arch, A H; large molar arch, A C; molar buttresses (descending from M) ; pterygoid arches (not shown) . Columns and arches of the moveable arm; mental column, N K; coronoid column, P Q 0; and condyloid column, / L; external oblique column, Q N. (From a photograph of specimen No. 4237, Wistar Institute of Anatomy.) (Turner.) tion with the teeth. Since secondary functions are performed by the teeth of man, those we find in the animals may be briefly viewed. They are used as weapons of offence, as in the poison fangs of the snake, which is a very well-known example. The hypodermic needle really had its origin in the poison fang of the viperine snakes, a tooth with a tube extending through its center and leading to the poison sac. Upon the contraction of the digastric muscle and opening of the mouth the fang is erected, and when it is driven into the prey the sac at its base is compressed and the poison injected. , THE HUMAN DENTAL MECHANISM 217 The swnrd-fi.sh has a very dangerous projection which it uses to open the al)domen of fish from beneatli and thus kills them. The use of teeth as weapons in warfare is well known, as in the rhinoceros and even our domestic animal, the Jiorse. The teeth are also used for pur- poses of transportation and locomotion. The elepha?it uses his tusks, which are very highly developed upi)er incisors, to uproot trees, and dig up tuberous roots. He is trained in India to use them for the purpose of transporting lumber, etc. The walrus uses his upper canine teeth to pull himself up on the ice, and also for digging in the mud and uncovering small fish, shell fish, etc., which he consumes. One of the most interesting of the secondary uses of the teeth is found in one of the lemurs. The flying lemur (galeopithecus volans) has curious incisor teeth, the lingual side of which is very much like the teeth of a comb, and this the animal uses to comb its fur. Fig. 84. — Upper and lower teeth in occlusion. (From photograph of specimen in the Wistar Institute of Anatomy.) The Human Dental Mechanism. — The human dental mechanism prima- rily has to do with the preparation of the food for subsequent stages in its digestion, and it is a very interesting apparatus viewed as a machine, created for this purpose. To better understand it, for pur- poses of study, it may be resolved into its various elements. In the first place it consists of a fixed base and a movable arm (Fig. 84) . The fixed base is the upper jaw, and the movable arm is the lower jaw. It has been likened to a hammer and anvil turned upside down; but the metaphor of the fixed base and movable arm is a little more expressive. These two elements are equipped with teeth, the armament of the appa- ratus. Between these two elements extend the muscles which elevate 218 THE TEETH AS A MASTICATING MACHINE the mandible and constitute the motive power of the machine. Ordina- rily they are spoken of as the muscles of mastication; the masseter,i\\e temporal and the two pterygoids; and then at the front end of the man- dible are muscles attached to the genial tubercles to assist in lowering the mandible, the digastric and the geniohycrid, and the muscle which forms the floor of the mouth, the mylohyoid. This whole apparatus is found in the cavity of the mouth. The cheeks and the lips on the out- side serve as the outer walls of the cavity which contains the food while it is being masticated. The tongue on the inside is actively engaged in keeping the food between the crushing surfaces, and assists the cheeks and lips in that way. The last element of the apparatus is the salivary glands, the secretions of which have both a mechanical and physiological function. They lubricate the machine, soften and dissolve the food, and agglutinate it for deglutition, besides performing a digesti\'e function in connection with the food. The several portions of the apparatus will be taken up and discussed a little more in detail. The fixed base, which is the two maxillae united in the median line, is supported upon the skull by a number of very strong colmims or supports. It may be better seen if this base is considered as if it were upside down. There are several of these bony columns, one going inside the orbit and reaching the skull in the median line. {A B, Fig. 83.) There is another one from above the first or second molar going right up through the malar bones and the outer border of the eye {C M D). When the skull is viewed from below still another column is seen. This is the pterygoid, which supports the distal end of the dental arch. The Mandible. — The lower jaw is the movable element, the movable arm. It has the general shape of the letter "U" and the ends of the "U'^ are bent upward at the end and terminate in the condyloid pro- cesses. There are several layers of soft tissues intervening at the joint which are placed there to lessen the shock of mastication, and permit the movement of the joint. Between this point and the anterior end the muscles of mastication are attached. They move the man- dible as a lever, one end of which is fixed and constitutes the fulcrum. Ilie muscles are attached between this end and what is the weight end of tlie lever, the forward portion which does the work. Thus it is a lever of the third class. The fulcrum exists in the tempomandibular joint which is interesting from a mechanical standpoint because it has so much to do with the way in which the mandible can move. The form of the glenoid fossa is a large factor in this. The jaw cannot move backward but it can move forward and downward until it is somewhere near the summit of the eminentia articularis. It can also rotate about a horizontal axis, passing approximately through the condyles. In considering the manner of movement of the mandible it will be seen how the joint renflers these movements possible. Its movement is, of course, limited l)y ligaments. There is the capsvlar ligament which is thickened at the back into a very thick band, which THE MOVEMENT OF THE MANDIBLE 219 prevents the jaw from going too far forward. The external and inter- nal lateral Hgaments are really nothing more or less than still greater thickenings of the capsular ligament itself on the outside and inside of the joint respectively which prevent the motion of the jaw laterally. The other ligaments, the stylomandibular and s'phenomandihnlar, which are largely thickenings of the cervical fascia, do not have very much to do with the way with which the mandible can move. Of the muscular apparatus it is quite unnecessary to speak exten- sively. The masseter is the muscle most concerned in the elevation of the jaw, and the temporal and internal yterygoid aid in this movement. The function of the external pterygoid must be kept in mind in that it is attached to the interarticidar fibrocartilage as well as to the neck of the condyle, and serves to pull them both forward in the forward movement of the jaw. The direction in which the mandible can move may now be noted. First the simplest form of movement may be taken up, starting from that position of the mandible in which the teeth are in occlusion. This is the point toward which all the movements of mastication ultimately tend. With the teeth in occlusion, what happens when the mandible is depressed? The external yterygoid muscle on each side contracts and pulls its condyle downward and forward. The condyles slide down the walls of the glenoid fossae. The digastric and geniohyoid muscles attached to the genial tubercles contract and pull down the front end of the mandible. The effect of these contractions is to carry the front end of the mandible down and the distal ends forward. The mandible does not rotate about a fixed axis, but the condyles are being carried forward at the same time that rotation is taking place. In other words, there is a combination of sliding and of rotation. When the mouth opens the condyles slide forward and downward, and the front end of the mandible is depressed. The mouth could not be opened if the condyles remained in the back part of the fossae. There is then a combination of rotation about a horizontal axis passing through the condyles and a sliding motion. It so happens that the front teeth describe what is approximately the arc of a circle while they are sliding and rotating; but the center of that circle is not in the condyles, but considerably back of them. When the mandible is brought up again to the occlusal position the reverse of this takes place, but Tomes and Dolamore have found out by tracing a large number of jaws that the path of closing is always a little bit in front of that of opening. Direct opening and closing is a type of movement seen in the carnivora. The condyles do not slide forward. In the herbivorous animal there is a lateral movement. In that lateral movement one condyle remains in the fossa and the other one slides dowaiward, forward, and inward. This type of movement is also noted in the human jaw. One of the condyles remains in its fossa, the other one being pulled down- 220 THE TEETH AS A MASTICATING MACHINE ward and forward by the contraction of the external 'pterygoid muscle of the side. Of course that means that the two pterygoid muscles are capable of independent contraction. The mandible rotates approxi- mately about the center of the stationary condyle. The same occurs when the jaw moves to the other side, as it simply reverses the mov- ing and the stationary condyles. If both external -pterygoids contract, the jaw is carried forward or protruded. If they contract independent of the muscles attached to the front end of the mandible there is a protrusion of the mandible. That is a type of movement characteristic to the rodents or the gnawing animals. There is then in the human jaw the possibility of these three distinct types of movements. Now that the fixed base and the movable arm and the motive power of the apparatus, and the manner in which the mandible, or the movable element may be actuated have been described, the teeth will be dis- cussed from the standpoint of their form and arrangement as suitable to the working of the machine. A Study of the Human Denture. — In the first place the forms of human teeth are modified or fused cones, as are all animal teeth (Fig. 84). The incisors are cones with a flattened end and may be likened to the form of a chisel. This type of a tooth is especially well devel- oped in the rodents. The canine tooth is more nearly a cone of simple form than any other, although not perfectly circular in cross-section. It is similar in general form to the canine teeth in the carnivora, more like them perhaps in a general way than that of any other animal types, the canine in the herbivora being either lacking or very rudimentary in character. The bicuspids (the term being derived, of course, from their two- cusped or two-coned character) are, as has been indicated, merely two cones fused together. The molars, on the other hand, have a number of cones fused together, each cone represented by a cusp; in case of the lower first molar nor- mally five cusps, and the others only three or four. The teeth are arranged in two arched series, consisting normally of thirty-two teeth, sixteen in each series (Figs. 85 and 86). The actual outline of this arch varies with individuals, but within certain bounds this variation in form has no relationship whatever to its functional efficiency. The upper arch is larger and overhangs the lower. The upper teeth constitute the fixed base in relation with which the lower teeth move, therefore the upper arch would necessarily cover a larger area in order to permit the movement of the lower over its surface. On the inside of the teeth is the tongue, on the outside the lips and cheeks. The overhang of the molar and bicuspid series in the rear, and of the incisors in the front of the month not only serve the useful purpose of providing a larger area over which tlie lower jaw may move, but it serves to hold the lips and teeth out of the way and prevents THE HUMAN DENTURE 221 their being caught between the crushing surfaces. On the inside the fact that the lower teeth overhip and pass up the inner sides of the upper teeth serves a similar purpose of keeping the tongue out of the way. Fig. 85. — Occlusal surfaces of the upper teeth. One may realize how useful this provision is if one observes a set of artificial teeth in which this overhang is not properly provided, when the wearer will frequently complain that he bites his cheeks. Instances of the same difficulty are seen in mouths with full sets of natural teeth, the cusps of which have worn do\\ai, and in which the lower jaw has moved forward to what is designated an edge-to-edge bite. There is Fig. 86. — Occlusal surfaces of the lower teeth, no doubt of the authenticity of the reported case of a well-known man who lost his life tlirough cancer originating in the irritation of the cheek from biting it when the cusps of his teeth had worn off until he had an edge-to-edge bite. 222 THE TEETH AS A MASTICATING MACHINE The series of teeth normally present an unbroken surface from one end around to the other; that is, there are no spaces between them, as in some of the animals, particularly the carnivorous animals. Man is the only animal not having diastemata, or spaces between his teeth. This is provided for by the bell-like shape of the crowns of the teeth which do not touch at their necks but at the point of interproximal contact. This contact serves to protect the gum tissue below from injury from the food such as meat and vegetable fibers. If one has experienced what it is in one's' own denture to have a flat filling, or none at all, in consequence of which food packs in and produces the long train of uncomfortable results, one will understand how wise is this provision of nature. Occlusion. — The occlusion of the teeth, to attempt a very offhand definition, is the relationship of their morsal surfaces when the man- dible is in the position of the resting bite (Fig. 87). The phrase is used to indicate the relationship of the upper and lower teeth when in such contact that there is a definite fitting together of their surfaces. In the occlusal position the condyles of the mandible are in the most distal part of the glenoid fossse. When the teeth are in occlusion the muscles extending between the jaws are either in a state of tonic contraction, simply holding the jaw up, or they may be actively contracted, that is, pressing the lower teeth firmly upon the upper ones. This is a rather fundamental position of the jaw. It is a position of equilibrium. It is to this position and from this position that all the various move- ments incident to mastication take place. In the crushing of the food the jaw tends to return from its various excursions to the occlusal position. The occlusion of the teeth then means the definite relationship existing between the occlusal or morsal surfaces of the teeth. This must be carefully considered, for in order to understand the machine in motion it must first be studied in repose. Perhaps simplicity will be consulted by dividing the description of the occlusion into that of the incisor teeth, and that of the molar and bicuspid teeth. As to the incisors, which are flat and wedge-shaped, the upper over- hang the lower, the incisal edges of the lower resting normally in con- tact with the lingual or inside surfaces of the upper teeth. This nor- mal overhang or overbite is approximately one-third of the length of the lower teeth, although of course it is subject to slight variation. The canine tooth is really intermediate in the character of its occlusion between the incisor and the bicuspid series. It partakes of the char- acteristics of the incisors in that it overhangs the lower teeth, but it is like the bicuspids in having a sharp cusp exactly like the buccal cusps of the bicuspids. When the teeth have worn down either from having had a very small overbite and short cusps f)riginally, or from the use of coarse food, so that there is an edge-to-edge bite, the machine is by no means as eft'ec- tive as in the arrangment referred to as normal. In the latter case the A STUDY OF OCCLUSION 223 food is simply pinched off and not sheared off as when the upper incisors overhang. In the study of the occhision of the molar and bicuspid series of teeth the occlusal surfaces should be first considered (Figs. 85 and 86). It will be noted that they exhibit two rows of cones with depres- sions or fossae intervening between them. On this surface of the bicuspids there is a cone on the iimer and outer side. In studying the molars there w411 be found two cones on the inner and outer sides, except on the third molar where the distolingual cusp may be lacking. There are then a row of inner and a row of outer cones, with fossae or little pits intervening between them. There are transverse ridges dividing one fossa from another. The same thing is true of the occlusal surfaces of the lower series of teeth. They have a definite arrangement, a row of outer and a row of inner cusps w4th fossae between. However, there is a difference in the shape in these two rows of cusps. The inner ones are rounded in the upper series of teeth and are considerably larger than those in the outer row. Speaking technically, the lingual are larger than the buccal cusps, which are sharp and thin, while the reverse of this is true of the lower teeth. The buccal cusps, or outer cones, are the large round ones; the inner cusps are sharp and thin. The rounded cusps in both series are really the functionating cusps. They are the ones which are received into the fossae when the teeth are in the occlusal position. If an upper set of teeth is superposed upon a lower, it will be found that the lower buccal cusps occupy the fossae of the upper series and the rounded lingual cusps of the upper fit into the fossae in the lower set of teeth. It is not enough in the normal arrangement that any cusp should fit into any fossa. In normal occlusion there is a definite fossa for each cusp to occupy (Fig. 87). Orthodontists have accepted a simple method of determining when a denture is in normal occlusion. They look to see if the mesiobuccal cusp of the first upper molar occupies the buccal groove of the first lower molar and if so and the other cusps fit into their fossa^, and so on, then the occlusion is correct. If this cusp is in front of or back of the buccal groove then it would not be normal occlusion; there might be an interdigitation of the cusps but it would not be perfectly normal, unless each cusp occupied its own particular fossa. In an inner view of the denture (Fig. 88), the overlapping of the sharp and thin inner cusps of the lower teeth wdll be noted, each fitting into a groove or space on the lingual surfaces of the upper teeth. This inter- digitation has also another rather interesting advantage, and this is that each tooth of both series, with two exceptions, is opposed by two teeth in the opposite jaw. They do not meet end on end, but each tooth is in relation to two teeth. The exceptions are the upper third molar and the lower central incisor which have but one opponent each (Fig. 89). 224 THE TEETH AS A MASTICATING MACHINE Fig. 87. — Occlusion of the molar and bicuspid teeth, external view. (From photograph of a specimen in possession of Dr. F. A. Peeso.) Fig. 88. — Occlusion of the molar and bicuspid teeth, internal view. (From photograph of a specimen in possession of Dr. F. A. Peeso.) A STUDY OF OCCLUSION 225 Now that the relationship of the morsal or occhisal surfaces of the teeth ill the position of occhisioii has been described, it will often be referred to as the occlusion of the teeth. Fig. 89. — Occlusion of the molar and bicuspid teeth, occlusal view. Lines are drawn from the lingual cusps of the upper teeth and buccal cusps of the lower to the correspond- ing depressions into which they fit. (From photograph of a specimen in possession of Dr. F. A. Peeso.) There are certain other characteristics of the arrangement of the occlusal surfaces of the teeth which are related to what shall be spoken Fig. 90.- -The "Curve of Spee." Line passing through anterior face of condyle, a photograph of a specimen in the Wistar Institute of Anatomy.) (From of as the articulating or active relations of the denture that will be useful when the denture is in motion. One of these characteristics, 15 226 THE TEETH AS A MASTICATING MACHINE which is a very important part in the so-called articulation of the teeth, is as follows: If an imaginary line were drawn touching the buccal cusps of the lower series of teeth in a perfect denture, it would be found that they described approximately the arc of a circle, and if it is continued backward under a perfectly typical arrangement, it passes just anterior to the articulating face of the condyle (Fig. 90). Sometimes this line may go a little in front of it, more frequently it is back of the condyle; in a perfect arrangement it passes through the anterior face of the condyle. The same thing is necessarily true of the upper teeth. This is called the curve of Spec. It has been named after von Spec who first called attention to it. This curved arrangement of the occlusal surfaces of the molar and bicuspid teeth has an important bearing on the movement of the mandible. If two surfaces are to slide one upon the other without interrupting their contact at any point, that is, without being separated at any point, these must be either two perfectly flat surfaces like two panes of plate glass, where one can slide upon the other without admitting air underneath, or else two curved surfaces which are the arcs of the same circle. If they were any other shape, as for example, a parabola or hyperbola, or any irregular curve, they would separate at some point. Now if it were desirable that in the forward-and-backward movement of the mandible all of the lower teeth should slide upon all of the upper at the same time, then these teeth would have to be either in a perfectly plane surface, all absolutely level, or they would have to be arranged around the arc of a circle. In order to get a clearer understanding of this, it may be supposed that there are no cusps upon the occlusal surfaces and that a curved line represents the top surface of the lower teeth, and a similar curved line represents the occlusal surfaces of the upper teeth. Now if these surfaces are to slide upon each other, withaut breaking their contact, in the case of the human jaw the mandibular condyles, which of course slide upon the glenoid fossae, would havje to slide in exactly that same curve, otherwise the teeth would be separated at some point. Now this is the significance of this arrangement of the teeth, that the so-called curve of Spec is always either continuous with the path of the condyle, or it is concentric with it; at any rate they can both move around the same center. This, it must be remembered, is merely a very much simplified example taken to explain the principle involved. These are not plane surfaces, but' are cuspid sm-faces, and each one of these cusps fits into a fossa. However, it does not take a very great stretch of imagination to see that, though they have cuspid surfaces, the cusps may be arranged so that instead of sliding upon a smooth surface they slide upon the walls of the fossae into which they fit. That it is possible to have such an arrangement may be conceived and this is the arrangement in the perfectly typical and typal human denture. Of course the mandible has to be depressed CUSP ARRANGEMENT AS RELATED TO JAW MOVEMENT 227 the least })it in order to enable each cusp to slide downward on the front wall of the fossa into which it fits. The cusps slide forward on the walls of the fossre and back again; and the advantage of this is that every one of the cusps is functionating, is in contact at the same time, not just hitting here or there. But it is possible for a denture to functionate in this fashion only if the teeth are arranged in the manner described. It will presently be seen, however, that the lower teeth of a normal typical denture cannot slide very far forward without the teeth separa- ting, because the lower incisors strike the lingual surfaces of the upper incisors. After the cusps have moved perhaps half-way up the walls of the fossaj into which they fit, the lower front teeth strike the upper Fig. 91. — Upper and lower bicuspid and molar teeth (side view), showing relative height of buccal and lingual cusps of upper teeth. (From photograph of a specimen in the Wistar Institute of Anatomy.) incisors upon which they slide and the distal teeth are separated. But in the return movement, when the lower teeth strike the lingual surface of the upper and slide up until the distal teeth are in contact and then slide back into the occlusal position, each one of the cusps then slides back dowai the wall of its fossa into the position of the occlusion. There is another characteristic of the arrangement of the molar and bicuspid teeth which is related to the lateral excursion of the jaw. Taking a typically perfect set of teeth with the jaws slightly apart, it will be seen that, starting from the first upper bicuspid and going toward the rear, the buccal or outer cusps become relatively a little bit shorter than the lingual cusps and, in the case of the lower teeth, they become a little longer than the lingual cusps. Of 228 THE TEETH AS A MASTICATING MACHINE the second bicuspid in the upper jaw, the buccal and lingual cusps nor- mally occupy the same horizontal plane. Just in front of it the first bicuspid has a buccal cusp that is longer than the lingual. Return- ing to the first molar, the buccal cusps are a little shorter than the lingual, and going back farther and farther, they get relatively shorter than the lingual. In other words, the plane of the cusps, instead of being level, gradually curves rootword and outward toward the rear qf the denture (Fig. 91). This arrangement can be demonstrated in the mandible although the first bicuspid has a rudimentary cusp or none at all and is atypical in Fia. 92. — Lower bicuspid and molar teeth, front view, showing relative height of buccal and lingual cusps. Same mandible as Fig. 91. (From photograph of a speci- men in the Wistar Institute of Anatomy.) this particular; but farther back the buccal cusps are relatively higher than the lingual until at the third molar thev are considerably higher (Fig. 92). In looking at the upper teeth this characteristic may not be so well illustrated as in the lower jaw, but a gradual tilting out of the long axes of the teeth will be noted. This arrangement is due not only to the height of the cusps, but to a change in the inclination of the teeth. The second bicuspid occupies a perpendicular position; but the teeth back of it gradually tilt outward. Now what is the relationship of this arrangement to the lateral excursion of the lower jaw? When the mandible is moved to one side CUSP ARRANGEMENT AS RELATED TO JAW MOVEMENT 229 with the teeth in contact, if the teeth were arranged so that their cnsps occupied the same horizontal phme those on one side would be sepa- rated while those on the other side would be in contact. The reason for this is that when the mandible is carried to one side one condyle remains stationary in its fossa while the other is pulled forward and also downward as the surface of the glenoid fossa inclines downward and this side of the jaw must be carried a little lower than the side with the stationary condyle. If it were not for this difference in the level of the buccal and lingual cusps there would be a lack of contact on the side from which the movement was taking place. In order to compensate for this lower- ing of the mandible on the side from which the movement has taken place, the two longest or most prominent cusps come into contact; whereas on the other side, the side toward which the movement has taken place, there is a short and a long cusp in contact; and it is just the difference between these two w^hich compensates for the down- ward movement of the jaw on the side from which the movement has occiu-red (Fig. 93). Fig. 93. — Diagram illustrating contact of cusps in lateral excursion of the mandible. Section through jaws at position of second molar. O P, line touching lingual cusps of upper molars; L R, line touching buccal cusps of upper molars; S T, line touching buccal cusps of lower molars, showing the downward movement of the mandible on the right side necessary for contact of the cusps. What is the advantage of this arrangment? It has exactly the same functional advantage in the lateral excursion of the mandible as the curve of Spec affords in the forward and backward excursion of the jaw; that is to say, it enables both sides to be in contact at the same time. This principle is taken advantage of in making artificial dentures. If both sides of the plates were not in contact at the same time, so that the patient was biting foods on one side with the other side not touching at all, the plates would be thrown douTi from their base. So it is desirable to imitate the human denture in this particular because it prevents overstrain, and provides a denture that is more efficient mechanically. There is one other detail of the occlusal surfaces of these teeth relat- ing to their function which must be mentioned and this is, that clear- ance spaces are provided for the escape of food which has been masti- 230 THE TEETH AS A MASTICATING MACHINE cated. The upper row of buccal cusps overhangs the lower, and on the outer walls of all of these fossae, into which the lower buccal cusps fit, are grooves leading do^Miward and outward through which the food is squeezed. Anyone operating a cutting or grinding machine of any kind will realize the necessity of getting rid of the waste or the chip, as the mechanical terminology is. That is, after the substance has been crushed or ground, there must be an avenue of escape for the waste, and so these grooves, which are not visible on the side view, but which lead downward on the outside of the arch, and upward on the inside, are provided. When the food is crushed between these surfaces it is carried up above the tongue on the inside and downward into the pocket of the cheek on the outside where it may be pressed between the teeth when they are separated for the next crushing motion. Mastication of Food. — Having described the machine, its mode of opera- tion may now be considered; In the case of man the preparation of food in the mouth does not begin with prehension or gripping of the food, as it does in most of the lower animals. Man has, of course, developed very much beyond that point, and there is. no necessity for it. There is no provision for this in his denture therefore, and he has no sharp teeth to prehend the food. The first act of the human animal is to incise; but even incision or the cutting off of appropriately sized particles of food is largely rudimentary in man, since with the devel- opment of conventional methods of eating, bringing into use the knife and fork, the incisior teeth are not much exercised. The biting of cer- tain articles of food only is permitted by the usages of polite society. But w^hen incision is indulged in it is rather an interesting mechanical act. The lower jaw is depressed and carried forward, the food is pressed between the lips and upon the incisal edges of the upper teeth, when the lower jaw is carried upward. If the food is very hard, the ends of the upper and lower teeth are almost exactly opposite each other. This direct opposition is absolutely necessary from a mechanical stand- point, in order to bite through hard, resistant food. As soon, how- ever, as the teeth come into contact, or nearly into contact, the man- dible is carried backward as well as upward, and the lower incisors slide up the inner surface of the upper, just like the blades of a pair of shears. Then the food is carried back by the tongue to the distal part of the mouth. In order to understand clearly just what is demanded during tritura- tion of the food, it will be wise to refer again to the importance of a knowledge of the character of the food itself. Its chemical nature is not of so much interest as its physical character viewed purely from a mechanical standpoint. Man's food, broadly speaking, consists of meat fiber, vegetable fiber, grain or cereals and foods made from them, and legumes, although the last is not of the same importance as the others. The chief articles which must be prepared for digestion are vegetable and meat fibers, cereals or grain. It is necessary to reduce this food to a condition suitable for passage into the stomach. Its MASTICATION 231 physical consistence must be reduced that it can be acted upon by the digestive ferments and solvents. The crushing of grain, the starchy element of man's food must be very much more extensive than is neces- sary for the other elements. In the first place, its outer covering has to be removed, or at least broken, and the grains of starch themselves must be so ground up that they can be acted upon by the enzyme of the mouth, and l)y those farther down in the digestive tract. Masti- cation of cereals and foods made from them is therefore really much more important than the mastication of other foods. Baron Oefele has conducted some investigations to show the very poor ability to digest cereals exhibited by people who do not have a full complement of molar and bicuspid teeth. His results are very interesting, but it is only necessary for our purpose to state the fact that he has very conclusively shown the defective digestion of cereals by those whose molar and bicuspid teeth are defective. Vegetable fibers nuist be cut uj) into short lengths and crushed so that they can be readil}' acted upon by the solvents and digestive fer- ments. This is more important than the comminution of meat fibers. Many carnivorous animals eat animal flesh in great masses; carnivor- ous snakes always swallow their prey w^hole. Nevertheless it is important that meats should be masticated by man in order to break up the consistence of the fibef, and also it should be cut up into small masses to facilitate its passage through the digestive tract and that it may be readily acted upon by the enzymes and ferments. Dr. Black, who has investigated quite extensively the problem of the mastication of the various kinds of foods, is authority for the state- ment that the up-and-down movements of the jaw, very much like those of the carnivorous animals, are chiefly concerned in the masti- cation of meats, and that the lateral movements are chiefly concerned in the mastication of cereals and foods made from them. While it is not true that in the masticating of any type of food one is limited to any particular type of movement, it is a fact that the foods which require the greatest amount of crushing force are masti- cated in the return from the lateral excursion of the mandible. AVhen the cereal food is brought into the mouth and carried back to the molar and bicuspid teeth, mastication usually occurs on one side at a time; and if the mouth is in a state of balance and perfect health, it is very apt to occur first on one side and then on the other. The man- dible is carried to one side, the cusps are brought into contact, some of the food being cut off on the outside and some on the inside, but a mass remains which occupies the space between the cusps and in the fossae and on the return to the position of occlusion the cusps slide, into the fossae with a sort of mortar-and-pestle effect. In this movement the greatest crushing ability is exhibited. In ordinary mastication this lateral movement is combined with direct up-and-down movement. Mastication is not carried on in any precise mechanical order, but all of the movements are combined at times. 232 THE TEETH AS A MASTICATING MACHINE Dr. Black has also made in this connection what is rather an interest- ing table of the amount of force necessary to crush the various foodstuffs. Dr. Joseph Head, of Philadelphia, has also produced a similar table, though using a different method, and the two will be presented together. Dr. Black's experiments were most interesting. He had some brass castings made of the molar and bicuspid series of teeth, upper and lower, and had them arranged in a machine so that the lower could be brought up into contact with the upper by the movement of a hand lever: This simply had the up-and-down motion. He and a party of friends went at various times to restaurants in Chicago, and while they were dining themselves, they gave this automatic chewing machine various tidbits, and registered on it, as they could not on their own jaws, the amount of force necessary to crush the various foodstuffs. Dr. Head, realizing the value of the lateral excursion, and believing that much less force was required in the crushing of food with this type of movement, made experiments similar to those of Dr. Black, except that he took a human skull with a fine set of teeth and turned it upside down, bored a hole through the skull, and suspended weights from the mandible by means of string or wire. He proved that to accomplish the same amount of crushing, less force was required in this lateral sliding movement. Dr. Black's and Dr. Head's tables are here given. Dr. Head's Dr. Black's results. results. Raw cabbage 16 40-60 Raw onion 4 Head lettuce 8 25-30 Radish— whole 20-25 Radish— pieces 10-25 35-40 Corned beef 18-20 30-35 Boiled beef 3 Tongue 1-2 3-5 Lamb chops ■ . . . 16-20 Roast lamb 4 Roast lamb kidney 3 Tenderloin of beefsteak (ver>' tender) .... 8-9 35-40 Sirloin steak 10-20-43 Round of beefsteak (tough) 38-42 60-80 Roast beef 20-35 35-50 Boiled ham 10-14 40-60 Pork chops 10-13 Roast veal 16 35-40 Veal chops 12 Roast mutton 18-22 Very tough meats 90 Hard crusts 100 Hard candy 250 Dr. Black also experimented with a gnathodynamometer by means of which he could measure the strength exerted by the human dental mechanism, which for the average was from 150 to 175 pounds. He reported one case in ^^•hich 275 pounds were recf)rded on the instru- ment. He also tried it with persons wearing full artificial dentures, upper and lower, the result being that the average was from 35 to 40 MASTICATION 233 pounds. One may see a vast (liflerence in the amount of crushing ahihty of natural and artificial teetli. INIastication is of course a vohuitary act (si)eaking physiologically), that is, it begins voluntarily and is continued refiexly and automatic- ally. The food is rolled from one side to the other by the tongue. The teeth functionate first on one side and then on the other. The teeth have exquisite sensibility. It is through them that sensations are received that indicate the amount of chewing necessary to give any given mouthful, and also through them in conjunction with the tongue as to whether the food has l)een thoroughly triturated or not. After it has been thoroughly masticated it is rolled up into a bolus on the tongue, the tip of which is elevated, and by contraction of the muscle of the floor of the mouth, the mylohyoid, the food is forced back into the esophagus. The secretion of the saliva, while constantly going on in the mouth, is tremendously increased when any foreign substance, like food, is put into the mouth. The working of the muscles moving the jaw probably also increase the flow of saliva. The saliva serves to lubri- cate the various portions of the apparatus which are in the mouth. It contains a ferment, ptyalin, which has some digestive usefulness. The water in the saliva dissolves some of the food, and as it also con- tains mucin, the latter helps to agglomerate the mass and to lubricate it so that it is finally easily swallowed. The teeth are equipped with means of resisting the wear incident to the activity of this mechanism. The enamel is the outer envelope of the crowns of the teeth and is the hardest structure in the human body. It is of course necessary to have a very hard covering for the teeth to enable them to resist the wear incident to their long use. Under present conditions of civilization, where comparatively little mastication is neces- sary, not a great deal of wear of the teeth occurs. The teeth of prehis- toric man, and, indeed, of our own aboriginal races, wore very badly from the coarse character of the food. Any collection of skulls of North Amer- ican Indians which one may happen to see at once impresses one wdth the great amount of wear of these teeth. Of course this is due, not only to the rough character of the food, but also to the fact that Indian corn, a staple diet, being ground in stone mortars had fine particles of stone or silica mixed with it, which serve to grind the teeth down. Anatomists have recognized several degrees of wear. No one reaches the age of twenty-five without beginning to show some evidence of wear of the teeth. A little later the second degree is reached, where the enamel is worn through and the dentin exposed, and the cusps are really beginning to wear down a little; or it may even, under con- ditions of our civilization, get to the third degree, where the cusps are all worn away, and the teeth are reduced in height. Mastication has also a beneficial influence upon the teeth. The friction of the food exerts a cleansing influence as regards colonies of bacteria and deleterious food particles upon their surface. Disuse 234 THE TEETH AS A MASTICATING MACHINE of the teeth on the other hand, greatly increases the deposits of sali- vary calculus and sordes upon the teeth. Often upon looking into a mouth it is perfectly easy to judge upon which side a crippled tooth exists, because when the chewing is done on the other side, exclusively, deposits on the teeth of the crippled side identify it. The use of the denture in mastication also exercises the peridental membrane. As the teeth move up and down in their sockets, blood is pumped in and out of this tissue and thus it is kept in a healthy condition and degeneration of the pericementum is deferred if not prevented. Supplementary Functions of the Teeth. — In conclusion, certain second- ary functions of the teeth will be briefly considered. They participate rK&Q. Fig. 94. — 1, diagrammatic drawing showing place of articulation of the consonant sounds: 2, drawing showing contact of the tongue with molars and bicuspids in the formation of certain consonants. in the activity of the mechanism concerned in the production of speech. The lijjs and tongue with the teeth and the contiguous portions of the aheolar process are the most important factors in the production of consonant sounds. Thus the "F" and "V" sounds, for example, are pronounced by the sudden escape of air between the lower lip and the upper front teeth. It is unnecessary to go into this detail at length, but an alhision is made to it as an additional reason for care in the preserva- tion of the teeth (Fig. 94). They are al.so passive elements in the mechanism concerned with the facial movements of expression, which are movements of the facial muscles that either supplement language or convey ideas or emotions or states of mind. SUPPLEMENTARY FUNCTIONS OF THE TEETH 235 «VATOR ANGULI \i; SWPEHIOBIS Fig. 95. — The facial muscles of expression. r " P^ ^^^^^1 ^^^^H El [ Fig. 96. — Photograph showing effect of the loss of the teeth upon the mouth, and wrinkles established thereby. Fig. 97. — Photograph showing the effects of the loss of the teeth upon the profile. 236 THE TEETH AS A MASTICATING MACHINE The underlying structures in this mechanism are the skull and the teeth, overlying which are soft tissues including the facial muscles of expression. There is a large group of these centering around the mouth which makes it one of the most expressive features of the face. These muscles are superficial, converge toward the mouth and terminate in one big muscle, the orbicularis oris, of which latter the lips are chiefly composed. These are all supported beneath by the teeth and the alveolar process, over which as a sort of base they are moved by these various muscles. In some of these movements the lips are parted so that the teeth are disclosed. Both pleasurable and painful emotions may be so exjDressed (Fig. 95). Finally the teeth serve to support the lips and the cheeks and thus take part in the maintenance of the fixed expression of the face. Their loss is attended by a falling in of these tissues, an approxi- mation of the jaws, and by a marked change in the appearance in the face. To guard against this "last scene of all" is the final reason for their preservation (Figs. 96 and 97). CHAPTER IX. MALOCCLUSION OF THE TEETH By RODRIGUES OTTOLENGUI, M.D.S., D.D.S., LL.D. If the mouth hygienist, besides preserving the heahh of her charge, would aim likewise to guard against the attacks of disease, it is evident that she should have knowledge of such diseases as may prove a menace in her particular field of work, and she should likewise learn to recog- nize these diseases in their incipient stages that she may refer the patient for treatment before the ravages prove serious. Therefore, in presenting the subject of malocclusion, let us consider for a moment how dental caries is aggravated by irregular or mal- occluded teeth. DENTAL CARIES Areas of Susceptibility. — Students of the subject tell us that in the vast majority of cases caries begins in certain definite localities. Thus caries upon the masticating surfaces of bicuspids and molars first appears in the sulci or fissures between the enamel plates. Between the teeth or, as we say, on the approximal surfaces, caries has its initiation at, or just gingival to, the approximal contact points. While it may not be absolutely true that "a clean tooth never decays," it is true that an unclean tooth is more vulnerable than one that is clean. It follows, therefore, that the unclean or uncleans- able parts of a tooth are more likely to decay than the clean or readily cleansable parts of a tooth, and this is in consonance with the statements above made as to the locations where caries usually begins, because the sulci of molars and bicuspids, and the approximal con- tact points of all teeth, are the localities in which food debris is most apt to lodge and most difficult to dislodge. Another region in which caries often occurs is upon the labial and buccal surfaces of teeth immediately near the gum line. Here the seepage of mucus agglu- tinizes the food debris and the overhanging gum margins protect the accumulations from the natural cleansing agents. Still another place is in the grooves on the buccal siu-faces of the molars, which are analogous with the sulci upon the masticating surfaces. These, then, are to be counted the vulnerable places. Areas of Immunity. — The lingual surfaces of all the teeth, swept as they are by the tongue, constitute the most immune areas, though occasionally we find pits or crevices in the upper mcisors, which because they are pits or crevices become susceptible points. The labial surfaces of all incisors and cuspids, except at or along the gum 238 MALOCCLUSION OF THE TEETH margins, and the buccal surfaces of all molars, • except in the buccal grooves, are practically immune to caries. So we find that there are certain localities which are vulnerable and other definite parts of the tooth which are practically immune to caries. Also, that this immunity is closely related to the possibility of cleans- ing these areas. Between these vulnerable and immune locations are areas of com- parative immunity, this comparative immunity increasing toward the immune or most easily cleansed part, and decreasing as we approach the vulnerable or less easily cleansed part. Caries and Malocclusion. — Thus we arrive at the important relation between malocclusion and caries. We have seen that certain parts of the teeth are counted to be immune to caries, and that adjacent to these areas are other parts which are comparatively immune. But this is true only when all the teeth are in normal relationship one with the other, which in effect means when all the teeth are in normal occlusion. ^Malocclusion may not perhaps often increase the vulnerability of the occlusal surfaces of the teeth, though at times it may even have this effect; but malposition of the teeth will frequently increase the vulnerable approximal areas by increasing the con tactual areas beyond the normal; and it will likewise lessen the immunity of the immune and comparatively immune areas, by rendering cleansing more diffi- cult and at times even impossible. We will better comprehend this by the examination of a skull where we may see the teeth and bones freed from the soft tissues. Interproximal Spaces. Fig. 98 affords a good example of normally occluded teeth, one maxilla and one-half of the mandible with their teeth being shown. Attention should be called first to the spaces between the teeth knowTi as interproximal spaces. Note that these are, gener- ally speaking, triangular in shape, the base of the triangle being along the border of the alveolar bone, the sides of the triangle being the approximal surfaces of the adjacent teeth, and the apex at the point of contact of the two teeth. Select any approximal space distal of the cuspids and note that the apex of the cusp of the antagonizing tooth of the opposing jaw falls immediately opposite the center of this interproximal space, the obvious tendency being to force food between the teeth, and into this interproximal space. Hence the need of the contact point. Passing from the study of these bones and exam- ining a living specimen, we would observe that this interproximal space is filled with gum tissue, this particular part of the gum being denomi- nated the septum. This septum, filling as it does a triangular space, is conical in shape and is thicker than other parts of the gum. For this reason its outer surface is farther away from its bony support and con- sequently it is more easily injured than the gum elsewhere. This is an added need for close contact of the adjacent teeth, as a protection to this sensitive tissue from the impaction of food and the retention DENTAL CARIES 239 of it, if forced into the interproximal space. The student should note also that the gum septum, also called the gingiva, even in the healthiest subject, does not entirely fill the interproximal space, so that commonly there is a small but actual space between the approximal contact points and the septum or gingiva. It is because of this fact that approximal caries often has its inception just gingivally of the con- tact point, since it is just hi this space which is protected from the natural cleansing agencies that debris may collect and remain. If we study the matter more closely still, we must see that wise provision has been made for the exclusion of foodstuffs from the inter- FiG. 98. — Occlusion of the molar and bicuspid teeth, external view. (From photograph of a specimen in possession of Dr. F, A. Peeso.) proximal spaces. True the grinding cusps of the masticating teeth, falling as they do exactly opposite to the entrances to the interproxi- mal spaces, would seem to be advantageously situated for the forcing of food into these spaces, yet this accident is well guarded against. First we find that the cusps in typically formed teeth occlude against the mesial and distal marginal ridges of the two teeth with which each cusp normally antagonizes. These marginal ridges have planes slop- ing toward the central portions of the masticating surfaces, and hence away from the interproximal space. ^Moreover we find sulci serving as sluicew'ays to lead the food, during maceration, lingually and buccally away from the spaces between the 240 MALOCCLUSION OF THE TEETH teeth, and consequently it should require more force to crowd the food into the interproximal spaces than away from them into and out of the sluiceways. Additional protection of the gingivse is to be found in the form and position of the contacts, as well as in the form of the sep- tum itself. The contacts are closest occlusally and triangular in shape so that the width of the contacts increase slightly toward the gingiva, while the approximal surfaces of the teeth, curving rapidly apart, afford ample opportunity for the escape of food, especially as the sep- tum itself is conical and full enough buccolingually to extend some- what beyond the actual interproximal space and thus aid in receiving and carrying the food away from, rather than into, the space. All this may seem somewhat complex, whereas in reality when once fully comprehended, it will be seen to be quite simple and as admirable an arrangement as it is a simple one. Yet its efficiency depends entirely upon and is proportional with its typical normality. Any aberration from the typical in the formation of the teeth, and any departure from the normal in the position of the teeth, must proportionately destroy the balance between the several factors which, when present and work- ing in unison, will afford ample protection to even this vulnerable locality. Contact Points in Normal Arrangement. — Glancing again at Fig. 98, the student is asked to note that the teeth being in normal arrange- ment, the contacts are at the minimum, while yet being sufficient to afFord protection. Since caries starts at these points of contact, it must be manifest that any malposition of the teeth which will bring into contact a greater area than normally should be in contact, not only increases the actual area of the vulnerable region, but by altering the protective form of the contact points, must necessarily add also to the vulnerability. In Fig. 98 note also that as each tooth is in its nor- mal pose the greater portion of its exposed surface is brought into symmetrical alignment with its neighbors, so that any cleansing agency sweeping around the arch would come into touch with and conse- quently would cleanse the greatest width of such surface. Thus, where teeth are normally placed, a brush passing around the arch would cleanse nearly all the labial and buccal enamel, while a brush passed vertically over these surfaces would cleanse them entirely. An exam- ination of the lingual surfaces (Fig. 99) discloses the fact that the truly normal arrangment again brings beneath the influence of a cleansing agent the widest expanse of surface. It is equally evident that any malposition of even a single tooth must interfere with this cleansing effort. If a tooth be turned upon its axis, then a smaller part of its labial or l)uccal surface can be swept by the brush when the brush is used upon that part, and the same would be true when brushing the lingual surfaces. If a tooth extends beyond its neighbors, either buccally or lingually, not only will it become more difficult to cleanse that particular tooth, but its position must inter- fere more or less with the cleansing of its neighbors. NOMENCLATURE 241 It is seen then that any aberration from the normal in the inter- relation of the teeth renders them more difficult to keep clean, but it must be understood that aside from the artificial cleansing which is to be accomplished with brushes, powders, etc., the typical forms and arrangement of the teeth are such that the normal use of these organs leaves them moderately clean, so that the teeth in ideal normal occlu- sion are said to be "self-cleansing," this cleansing being accomplished by the lips, the tongue, and by the food passing over the surfaces of the teeth. Fig. 99. — Occlusion of the molar and bicuspid teeth, internal view. (From photograph of a specimen in possession of Dr. F. A. Peeso.) Terms Defined. — Occlusion: The relation between the upper and lower teeth when the jaws are closed. Arch: A term used to designate the upper or lower teeth collectively. Inclined Plane: The sloping sm-face of a cusp. Mesial, Distal: Position is considered in relation to the median line or center of the dental arches. Hence, "mesiaF' means toward or nearest to the median line, and "distal" means away from or farthest from the median line. Model: A reproduction of the dental arch or arches made in plaster of Paris. Labial: Toward the lips. Buccal: Toward the cheek. 16 242 MALOCCLUSION OF THE TEETH Lingual: Toward the tongue. This term is used to describe the upper as well as the lower teeth. Protruding: The tipping of the axis of a tooth so that the crown projects labially to normal. Retruding: The tipping of the axis of a tooth so that the crown slants lingually to normal. A STUDY OF NORMAL OCCLUSION. Before the student can comprehend any description of malocclusion he must acquire a knowledge of normal occlusion. He should be able mentally to visualize a set of teeth in normal occlusion, as a standard picture with which to compare any set of teeth under examination, in order instantly to detect deviations from the normal. Definition. — Normal occlusion is the normal relation of the occlusal inclined planes of the teeth when the jaws are closed (Angle) . As occlusion means the relation betw^een the upper and lower teeth when the jaws are closed, it follows that normal occlusion means that all the teeth in both arches are so situated that they may best perform their functions, and that their interrelation shall be typical and there- fore normal. In a set of teeth in normal occlusion the teeth themselves are arranged in symmetrical parabolic curves, commonly called arches. This means that if a line be drawn across either arch, so as to touch the distal sur- faces of the last molars, and a second line be drawn at right angles thereto and through the median space, or between the central incisors, then any two similar teeth on opposite sides of the arch (as for example the first bicuspids) will be equidistant from this central line. Perhaps the next most noteworthy fact is that the upper arch is slightly larger than the lower, and that the outer cutting edges and cusps of the upper teeth droop over and consequently hide in part the similar portions of the lower teeth Mdien the jaws are closed (Fig. 98). This latter condition is called the "overbite." In a full denture there are thirty-two teeth. In the illustration which depicts one-half of an upper and lower jaw we should see sixteen teeth; but, as a matter of fact, the artist in endeavoring to expose the full surface of the upper central incisor has so turned the subject that in the lower arch we see an extra tooth, the lower central incisor of the opposite side. Mentally eliminating this extra tooth, by studying the illustration we observe that the smallest incisor is the central incisor in the lower arch, while the smallest molar is the last or third molar in the upper arch. It is in accordance with Nature's wonderful design, which aims to produce the highest efficiency in the use of the teeth collectively as a masticating apparatus, that this is true, for by this means every other tooth except these four occludes with two others. Again glancing at the illustration we see that the lower lateral incisor is in contact with the upper central and lateral; the upper central A STUDY OF NORMAL OCCLUSION 243 touches the lower central and lateral; the upper lateral antagonizes the lower lateral and cuspid, and so on around the arch, each tooth of either upper or lower jaw occluding with two teeth in the opposing jaw. The most important usefulness of this arrangement is seen when we consider those teeth which have cusps. For example, observe the first upper bicuspid, occluding wnth the cuspid and bicuspid of the lower arch. Any food caught in this locality is triturated between three powerful cusps, a much more effective plan than were each tooth to strike only one antagonist, as sometimes occurs where malocclusion is present. This at once brings us to one diagnostic point. It being a fact that in normal occlusion all the teeth except the lower central incisors and upper third molars occlude so that each tooth antagonizes two, we note that the only place in the entire denture where the interproximal spaces coincide is at the median line. Two facts then may be remem- bered. Whenever any interproximal spaces above and below coincide (except these at the median line), malocclusion exists. Conversely, whenever the spaces at the median line do not coincide, malocclusion is present. We should next consider those teeth which are supplied with cusps, viz., the cuspids, the bicuspids and the molars. In regard to the cus- pids and bicuspids, when in normal occlusion the crest or extreme angle of the cusp should be exactly in line with the interproximal space between the two teeth with which it occludes. Or to~ phrase it differently, a line drawn through the central axis of a cuspid or bicus- pid should pass between the two antagonizing teeth. In all the teeth which have cusps, including the molars, each cusp has four slanting surfaces called inclined planes; note that of these the mesial inclined planes of the cusps of the upper teeth occlude with the distal inclined planes of the cusps of the lower teeth; and of course the distal inclined planes of the upper cusps touch the mesial inclined planes of the lower teeth. As will be seen presently, however, a point of extreme significance, because used so often as a basis of diagnosis, is the occlusal relation of the upper and lower first molars. The student therefore should become thoroughly familiar with this cusp relation (Fig. 9S). The upper molar has two buccal cusps, known as the mesiobuccal cusp and the disto- buccal cusp. In normal occlusion the mesiobuccal cusp of the upper first molar occludes between the mesiobuccal and buccal cusps of the lower first molar, in such a manner that the crest or extreme point of the cusp coincides with a groove in the buccal surface of the lower tooth, known as the buccal groove. It is w^ell also to observe that the mesiobuccal cusp of the lower molar occludes in part with the similar cusp of the upper molar and in part with the upper second bicuspid; also that the extreme mesial surface of the lower molar is on a line with the central axis of the upper second bicuspid. Attention is called to this fact here, as it will be again elsewhere, because while in the normal 244 MALOCCLUSION OF THE TEETH relation the lower first molar is slightly mesial of the upper first molar, it should not be farther forward than the median axis of the upper second bicuspid. A study of the same set of teeth from the lingual aspect (Fig. 99), shows similar interlocking of the teeth and the general appearance is the same except that here it is the cusps and incisal ends of the upper teeth that are slightly hidden in consequence of the overbite, the converse of what is true of the buccal view (Fig. 98). Summary. — 1. Where teeth are in normal occlusion they are arranged in symmetrical parabolic curves and any two similar teeth on opposite sides of an arch will be equidistant from the central line, or axis. 2. The upper arch is larger than the lower and the cusps of the upper teeth droop over the lower. This is denominated the overbite. .3. With the exception of the two lower central incisors and the two upper third molars, each tooth in each arch antagonizes with two teeth of the opposite arch w^hen in occlusion. 4. The interproximal space at the median line above and below should coincide. ^Mien they do not, or when any other interproximal spaces do coincide, a malrelation of the arches is present. 5. A line draTsm vertically through the median axis of any cuspid or bicuspid should pass between the antagonizing teeth. 6. The mesial inclined plane of any cusp occludes against the distal inclined plane of the opposing cusp ; the converse therefore is likewise true. 7. In normal occlusion the mesibbuccal cusp of the upper first molar occludes between the mesiobuccal and buccal cusps of the lower first molar. MALOCCLUSION Definition. — Any deviation of the teeth or arches from normal rela- tion is termed malocclusion. Malocclusion of Individual Teeth. — A tooth may occupy any one of seven malpositions, and it is even possible for it to be malposed in four ways. These malpositions have been named as follows (Angle) : (1) Labial or buccal occlusion. (2) Lingual occlusion. (3) Mesial occlusion. (4) Distal occlusion. (5) Supra-occlusion. (6) Infra-occlusion. (7) Torso-occlusion. \. Labial or buccal occlusion means that a tooth cro-v^oi is so mal- posed that it is labial or buccal of its true normal position. 2. Lingual occlusion means that a tooth crown is so malposed that it is lingual of its true normal position. 3. Mesial occlusion means that a tooth crown is mesial of the posi- tion which it should normally occupy. 4. Distal occlusion means that a tooth crown is distal of the position which it should normally occupy. 5. Supra-occlusion means that a tooth has erupted to an abnormal height in its socket. CLASSIFICATION OF MALOCCLUSION 245 • 6. Infra-occlusion means that a tooth has not erupted to a normal height in its socket. 7. Torso-occlusion means that a tooth is turned in its socket so that it does not occupy its normal place in the arch alignment. In explanation of the statement that a single tooth may be in four positions of malocclusion at one and the same time, I would cite the following example: A molar tooth may be in torso-occlusion; in buccal or lingual occlusion; in mesial or distal occlusion; in supra- or infra-occlusion. Classification of Malocclusion.— It is manifest, therefore, that there are endless varieties of malocclusion when viewed in the light of single or multiple malpositions of the individual teeth. It remained for Angle, however, to discover the possibility of formulating a classi- fication for malocclusion, independent of these individual malpo- sitions but based upon the relations of the two arches considered as units. Other writers have endeavored to erect classifications which do depend upon the individual malpositions, but in none of these is the line of demarcation between the described classes so well drawn that it may serve as an absolute division between the multiplicity of conditions that arise. The result is that often cases are found which might fall into either of two such classes or even into both. For example, we have had classes for "outstanding cuspids" — cases where the cuspids have erupted labially of normal. Again, classes of "open bite," meaning an infra-occlusion or lack of antagonization of the incisors. What are we to do then with a case where we have "out- standing cuspids" complicated with "open bite?" In the Angle classification no such confusion can occur. His lines of demarcation are so distinct, that there can be no lapping of boundaries. Of his classification Angle writes:^ "These classes are based on the mesiodistal relations of the teeth, dental arches, and jaws, which depend primarily upon the positions mesiodistally assumed by the first per- manent molars on their erupting and locking. Hence, in diagnosing cases of malocclusion we must consider first, the mesiodistal relations of the jaws and dental arches, as indicated by the relation of the lower first molars with the upper first molars, the keys to occlusion; and second, the position of the individual teeth, carefully noting their relations with the line of occlusion." Angle then has divided all malocclusion into three great classes dependent upon the mesiodistal relations of the arches considered as units. It is evident, then, that to make a diagnosis, we must always begin with a picture of normal molar occlusion in the mind, and with the question, "Is the mesiodistal relation of the molars normal on both sides?" The answer to this mental question will invariably clas- sify' the case. 1 Angle, Seventh edition, p. 35. 246 MALOCCLUSION OF THE TEETH To have such a mental picture we must carefully study normal molar relations, as shown in Fig. 98, noting that the mesiobuccal cusp of the upper first molar occludes with the lower first molar in such a way that a line drawn through the apex of this cusp will fall directly into the buccal groove of the lower molar. Or to phrase it differently, the mesiobuccal cusp of the upper first molar occludes between the mesiobuccal and buccal cusps of the lower first molar, whereas the mesiobuccal cusp of the lower first molar occludes between the mesio- buccal cusp of the upper molar and the buccal cusp of the upper second bicuspid. Thus we see that the mesial siu'face of the lower first molar is normally slightly mesial to the corresponding surface of the upper first molar. Hence, in studying mesial occlusion of the lower first molar, it is important to recognize the limitations of the normal mesial position of this surface in relation with that of its antagonists. When the cusps are not mutilated by caries or bad fillings, how- ever, ^we may confine ourselves to an examination of the cusp relations. The Angle Classification. — In studying a case, if we find that the mesiodistal relations of the upper and lower first molars on both sides are normal, the malocclusion belongs in Class I. If the lower first molar on one or both sides is found to be distal to normal in relation with the upper first molar, it is said to be in distal occlusion, and the malocclusion falls into Class II. If the lower first molar on one or both sides is found to be mesial to normal in relation with the upper first molar, it is said to be in mesial occlusion, and the malocclusion falls into Class HI. The distinctions, therefore, between Classes I, II, and III are very definite and should be readily comprehended. Some confusion has been caused in the minds of beginners by the fact that there are divisions and subdivisions, but these likewise may be so plainly described that there should be no difficulty whatever. Once having learned to distinguish between Classes I, II, and III, we next learn that there are no divi- sions in Class I nor in Class III. But Class II is separated into two divisions: Division 1, wherein the upper incisors protrude, and Division 2, wherein the upper incisors retrude. These are the sole factors by which the divisions of Class II are determined, and there remains no more to learn except the subdivisions. A subdix'ision is any case of malocclusion where the mesiodistal relations of the upper and lower first molars is normal on one side and abnormal on the other. If the abnormality be a distal occlusion, the case must be a subdivision of Class II, because all cases of distal occlusion are in Class II. If the abnormality be a mesial occlusion the malocclusion must belong to Class III because all mesial occlusions arc in Class III. The following recapitulation of the classification is copied from Angle, omitting his references to etiological factors with which we are not at the moment interested: CLASSIFICATION OF MALOCCLUSION 247 Class I. Arches in normal mesiodistal relation. Class 11. Lower arch distal to normal in its relation to the upper arch. Division 1. Bilaterally distal, protruding upper incisors. Subdivimm. Unilaterally distal, protruding upper incisors. Division 2. Bilaterally distal, retruding upper incisors. Subdivision. Unilaterally distal, retruding upper incisors. Class III. Lower arch mesial to normal in its relation to the upper arch. SiMivisioti. Unilaterally mesial. To fix the differentiations of this classification more firmly in the mind let us examine the illustrations of a few typical cases. In Fig. 100, an examination of the first molars discloses that on each side the mesiodistal occlusal relations are normal. On each side the mesio- buccal cusp of the upper first molar occludes between the cusps of P'iG. 100. — Models of a case of malocclusion, Class I. the lower first molar, and a line drawn through the central axis of the mesiobuccal cusp of the upper molar, strikes the buccal grove of the lower first molar. This, then, discloses a bilateral normal mesiodistal occlusion of the arches, and the malocclusion consequently falls into Class I. For this illustration a case where the upper incisors protrude has been selected, that by comparison the student may better grasp the difference in the significance of protruding incisors in Class I and Class II, Division I. In Fig. 100, the normal mesiodistal relations of the first molars defin- itely fixes the case in Class I. Hence the protrusion of the upper incisors has 710 significance in connection with the classification of the case. In Fig. 101, an examination of the molars shows that the lower molar on each side is in distal occlusion. The mesiobuccal cusp of the upper first molar does not coincide with the buccal groove of the lower first molar, but on the contrary falls between the mesiobuccal cusp of the lower molar and the buccal cusp of the second bicuspid. The case 248 MALOCCLUSION OF THE TEETH therefore falls into Class II, and since the upper incisors protrude, it must be in the first dimsion of that class. Being bilaterally distal with the upper incisors protruding, it belongs to Class II, Division 1. Fig. 101. — Malocclusion: Class II, Division 1. In Fig. 102, we see a case quite like the last, and superficially like Fig. 100, but a study of the molars shows a distal occlusion on one side and normal mesiodistal relations on the other. And as the upper incisors protrude, it is placed in Class II, Division 1, Subdivision. It is in Class II, because there is a distal occlusion; it is in Division 1, because the upper incisors protrude. It is a Subdivision because the distal occlusion is confined to one side. It is therefore unilaterally distal with protruding upper incisors. Fig. 102. — Malocclusion: Class II, Division 1, Subdivision. In Fig. lOij, we find both lower first molars in distal occlusion. The case therefore belongs to Class II, which includes all distal occlusions. We note that the upper central incisors retrude, for which reason the case belongs to Division 2. It is therefore a case belonging to Class II, Division 2, because it is bilaterally distal with upper incisors retruding. CLASSIFICATION OF MALOCCLUSION 249 In Fig. 104, we see a case strikingly like the last, except that on close examination we find that the distal occlusion is confined to one side, for which reason it must be a subdivision case. It belongs, therefore, to Class II, Division 2, Subdivision, being unilaterally distal with retruding upper incisors. Fig. 103. — Malocclusion: Class II, Division 2. In Fig. 105, we find the lower first molars mesial to normal. Indeed, they are so far mesial that they have lost all occlusal contact with the upper first molars, so that the classification is very simple. The case must belong to Class III, which includes all mesial occlusions. An ex- treme case has been selected for this illustration, but the actual normal mesiodistal relations must always be in the mind as a mental picture Fig. 104. — Malocclusion: Class II, Division 2, Subdivision. with which the case in hand may be compared, and in the presence of the full complement of permanent teeth, if the lower molar is found to be mesial to normal, the case belongs to Class III. Observe, however, the qualification "in the presence of the full com- plement of the permanent teeth." The premature loss of a temporary molar, or the extraction of a bicuspid may permit a lower first molar 250 MALOCCLUSION OF THE TEETH to drift abnormally forward, presenting a confusing picture. It is always to be remembered, therefore, that this entire classification is dependent upon the presence, or space for the eruption of, all the per- manent teeth, and the drifting of teeth due to extractions or loss of temporary teeth is always a matter for separate consideration. Fig. 105. — Malocclusion: Class III. In Fig. 106, we find a mesial occlusion on one side, and a normal mesiodistal relation on the other, for which reason the case belongs to Class III, subdivision. So much then for the classification or diagnosis of cases in which the first permanent molars are present. It is more than likely, how- ever, that many cases will be seen before these molars are erupted or Fig. 106. — Malocclu.sion: Class III, Subdivision. after they have been badly mutilated or even lost through the ravages of decay. For this reason it is well to note that the occlusion of the second deciduous molars closely simulates that of the first per- manent m(^lars and consequently these teeth may be used as guides for classification. It has also been mentioned that the permanent ETIOLOGY OF MALOCCLUSION 251 cuspids are quite staple landmarks and are useful as guides to the occlu- sal conditions. At times the bicuspids may be all the individual has to offer from which to classify an abnormality. Hence the student can clearly see that an intimate knowledge of the normal relation of every tooth is absolutely necessary if an intelligent grasp of the abnormal is to be expected. Etiology of Malocclusion. — One might write at great length upon the etiology of malocclusion without at all exhausting the subject. In this particular work it does not seem essential to discuss all the theories of all the theorists. The aim will be rather to disclose those facts, the knowledge of which will enable the hygienist to fulfill her avowed purpose of calling attention to, and so far as possible abating, those acts or causes which might bring about or aggravate maloc- clusion. The factors involved as causative agents of malocclusion may be divided into the proved and the unproved. As examples of the un- proved theories in relation to the causes of malocclusion, enlargement of the tonsils, nasal obstruction, mouth-breathing, and adenoids may be mentioned. Whether these maladies do or do not contribute toward malocclusion, they are evidences of a reduced vitality, and as diseased conditions, should promptly be corrected. We are told that mouth-breathing causes malocclusions, and that adenoids cause mouth-breathing. Conversely, however, certain good rhinologists hold that mouth-breathing induces adenoids, due to the fact that the inlialed air, normally passing through the nares pro- duces a tonic effect .upon the upper pharynx, whereas when taken through the mouth and thus more directly into the lungs, the area usually occupied by the adenoid vegetations misses this tonicity sup- plied by the air, and the hypertrophies are induced. An ordinary rhinitis, or head cold, especially during early infancy, by occluding the nasal air passages, forces the child to breath through the mouth. If the rhinitis be long neglected, the mouth-breathing, which begins as a temporary necessity, may become a permanent habit. The theory at least sounds plausible enough. Consequently a hygienist who notices any negligence of this character, where her charges may be suffering with a head cold of long standing, should at once warn the parent or guardians of the possible ill-results. Far better would it be for the child to lose a few days' schooling while being kept in bed to cure a cold, than that the habit of mouth-breathing should become fixed. Among the proved causes of malocclusion we may enumerate: (a) The prematm'e loss of deciduous teeth. (6) Extraction of permanent teeth. (e) Pernicious habits, and (fZ))^Lack of use. There are other kno^\^l causes which may be found in text-books, but those mentioned are of special interest to the hygienist. 252 MALOCCLUSION OF THE TEETH (a) The Premature Loss of Deciduous Teeth. — The loss or extraction of a deciduous tooth, especially of the cuspids or any one of the buccal teeth, will almost inevitably produce a pernicious effect upon the per- manent teeth. The space made by the loss of the temporary tooth almost invariably closes, in part or entirely, so that the opening needed for the oncoming teeth in that locality is reduced in proportion. Why the Space Closes. — In the examination of a three-year-old arch, one wonders where the three large permanent molars will find space for eruption. This space, of course, must be provided by a growth of the maxilla and mandible distal to the deciduous teeth, distal therefore to the last deciduous molar. This growth is coincident with (if not actually caused by) the development and eruption of the per- manent molars. The result is a forward or horizontal movement of the whole temporary arch. Let us study it in detail. To make room for the arriving first permanent molar, the temporary second molar must move forward. To accomodate this movement the first tempo- rary molar must move forward, and so on around the arch, each tooth giving way as the tooth behind it advances. Let us suppose, however, that one of the temporary molars has been lost. A space is thus pro- duced so that the first permanent molar may erupt without influenc- ing the forward movement of any of the teeth anterior to the tooth extracted. Lideed, thi-ough lip pressure the space may even allow the anterior teeth to be forced backward. In this way, by closing of the space while the underlying bicuspid is yet deep in the bone, the bicuspid may be completely shut out of the arch, so that it either remains impacted, or else must erupt buccally or lingually of normal. (6) Extraction of Permanent Teeth.- — -The loss of any permanent tooth breaks up the continuity of the arch and destroys the occlusion. It directly effects no less than five teeth. The two adjacent teeth losing the support of the extracted member, are often forced to drift or tip toward one another. This tipping and drifting is more likely to be extensive when the extraction occurs prior to the eruption of the second molars, as the eruption of these distal teeth induces a dis- arrangement of the teeth distal to such spaces. This tipping of the teeth interferes with the normal cusp interdigitation of these two teeth with the three antagonists of the opposite jaw. Thus, as has been said, the loss of one permanent tooth may directly spoil the occlusion of five others. Hence, of course, all permanent teeth which can be kept in a state of health, should be preserved when in normal position, and when out of position should be brought to normal occlusion, if possible. (c) Pernicious Habits. — In regard to habits, perhaps the most common is sucking the thumb. This phrase, "sucking the thumb," is met throughout the entire literature, and is particularly supposed to induce protrusion of the upper anterior teeth. But the thumb is not always in the mouth in such a way as to produce this effect, nor is it always the thumb which the child introduces into the mouth. Recently a THE GROWTH OF THE JAWS 253 casual glance into the mouth of a baby girl patient of four, disclosed what seemed to be a protrusion of the upper incisors. The mother was asked, "Does this child suck her thumb?" Like a flash the child replied, "No, I suck two fingers; want to see me?" and she proceeded to give a demorstration. She placed just two fingers of her right hand in her mouth, the finger-tips curled downward under her tongue. In this manner it would seem that the weight of her arm had held the mandible downward and backward, so that a marked example of Class II, Division 1, had been produced, although none of the tem- porary teeth had yet been shed. The apparent protrusion of the upper teeth was no real protrusion at all. As the child was not a sufferer from adenoids, had no nasal obstruction of any sort, had never been a mouth-breather, and was the picture of health, it is rea- sonable to attribute the deformity of the jaws in her case to this peculiar method of sucking the fingers. The thumb is also sometimes introduced into the mouth in the same manner, and not always with the ball of the thumb against the upper teeth. Other baneful habits are sucking the lips or the tongue, or habit- ually resting the tongue between the incisors, not forgetting the abom- inable practice of nursemaids, and some mothers, of giving the baby a "pacifier" or "comforter." These habits are particularly mentioned here because it seems prob- able that in the near future the sphere of the dental hygienist will be so broadened that she will enter the homes of many children long before they arrive at the school age, in which case an important part of her duty would be to look for, and warn mothers against, these habits. (c/) Lack of Use. — This brings us to a consideration of a lack of use. It is a commonly accepted physiological law that the use of any organ, or part of the body, contributes toward its development. Nor- mal use results in normal development, where not hindered by other agencies. Abnormal or immoderate use may cause an overgrowth, as we see in the muscles of athletes; while disuse results in under- development or even atrophy. The Growth of the Jaws. — If we examine the normal child denture at the age of three or four, we observe twenty teeth symmetrically arranged about the arches and completely filling them. When we remember that these twenty deciduous teeth will be succeeded by twenty permanent teeth considerably larger in size, we recognize that if the latter are to erupt in normal occlusion, the bones of the arches must become enlarged, or in other words, there must be a growth increasing the circumference of the arches. Since the growth of the temporary teeth themselves is already complete, a growi:h of their bony supports must result in producing spaces between these teeth. We see this beautifully shown in Fig. 107, which illustrates the upper and lower arches of a boy of four and a half years of age. We have but to glance at such a set of deciduous teeth to see how admirably Nature, when unhmdered, will provide for all emergencies. We easily compre- 254 MALOCCLUSION OF THE TEETH hend that, by growth, space is being provided against the advent of a set of larger teeth. But what shall we think of such a set of teeth as is shown in Fig. 108 ? This child was five years of age, six months the senior of the other child, yet we find no spaces between the teeth and consequently no growth of the alveolar bone. We must wonder then, "Where will the permanent teeth erupt?" They certainly cannot appear in proper Fig. 107. — Normal growth of dental arches. Age ^\ years. alignment with such a lack of space. These two models then, illustrate well the contrast in appearance of a normally developing deciduous denture with one that is failing to take on proper growth. It is but natural to believe that this development of the bones about the deciduous teeth is largely dependent upon the extent and nature of the use or disuse of the teeth. The normal use of the teeth would necessitate the thorough masti- cation of food; food thus masticated would be properly insalivated. Fig. 108.^Uridcveloped dental arches. Age .5 years. and hence projjcrly j)rcparcd for its reception })y the stomach. With all the organs of digestion in a state of health, the result would be the thorough assimilation of the food, a correct metabolism, and hence a pr(^pcr share of the nourishment would finally reach the jaw-bones, so that the thoroughness of the work done by the (leiital organs would bring its own repayment in the normal share of ymbulum brought to the alveolar environments of the teeth. In this manner a normal MASTICATION IN RELATION TO DEVELOPMENT 255 physiological cycle would he established, and of course any disuse of the teeth would proportionately cause a disarrangement of this cycle. While it is well to bear these facts in mind, yet there is another aspect of use and disuse of the dental organs to which attention must here be called. Entirely aside from any interference with the proper nour- ishing of the body and of the jaw-bones, the use or disuse of the teeth directly affects the growth and development of the maxilla and man- dible, through the muscular and mechanical forces of mastication. Indeed it is claimed that not only the bones of the jaws, but the entire cranium may be thus affected. To emphasize this fact, a liberal quo- tation is made from an article by Dr. Lawrence W. Baker, published in Items of Interest, February, 1911. "Among the first voluntary coordinate muscular actions of a human being after coming into the world is that made with the muscles of mastication in taking food to sustain life. Long before the infant can hold up its head, or has gained control over those useful organs, the hands, the muscles of mastication are highly developed and are used with great vigor. "During the act of nursing, the action of this set of muscles is so vigorous that it demands an increased blood supply, to the extent that the heart's action is greatly increased; the excessive flow of blood to these parts is indicated by a reddening of the whole head, and the fon- tanelles themselves are caused to pulsate so that the untrained obser- vers comment on their movement. "Later, with the advent of the dental equipment, this group of muscles is given more leverage, and its action becomes consequently more powerful; in fact, the force exerted on the bones of the head from the pull of these muscles during life is tremendous and amounts to many hundreds of thousands of tons of force. I have long been convinced that this great force on the skull, and the great flow of arte- rial blood to the head caused by this muscular activity, is a powerful influence in the de\'elopment of the bones of the head and the impor- tant organs incased therein. "It occurred to me that if the hypothesis regarding the influence of the dental equipment on the formation of the bones of the head were correct, interference with the laws of occlusion in the lower animals would show consequent effect in the formation of the bones of the skull ; and if variation occurred it might throw some light on the most complex problem of the development of the human head. "To test the theorj^ the following experiment was performed: A litter of four rabbits was selected at the age of weaning. Two of the animals were operated on by grinding do^vm all the teeth on the right side of the lower jaw and the superior right central incisor. As the teeth elongated, repeated grinding rendered them useless, so that all the mastication was performed on the left side. The fourth rabbit was kept in the normal state for a standard of comparison. " After seven months, the skeleton of one of the rabbits was procured 256 MALOCCLUSION OF THE TEETH and the skull was found to vary as is sho\\ni in Fig. 109, which is a photo- graph of its upper aspect. It will be noted by the dra-^ai lines that there is a deviation of the bones to the left. (Right and left in this description refers to the right and left side of the animal). The suture between the parietal and frontal bones does not run strictly at right angles to the longitudinal axis of the skull; the right frontal bone projects farther forward than the left one. It will also be observed that the left zygomatic space is longer and more advanced than the right space. The most noticeable deviation is in the nasal bones, both bones being twisted to the left. Fig. 109. — The upper aspect of the skull of a rabbit operated on. Obser%'e the unequal development of each lateral half of the skull. Fig. 110.— Lower aspect of Fig. 109. "On the lower aspect of the skull. Fig. 110, it will be seen that the deviation extends throughout the entire skull. The most remarkable deviation is that the anterior root of the right zygomatic arch (the zygomatic process of the maxillary bone) is retreated while the body of the right maxillary bone itself with the teeth that it contained is greatly advanced. "The results of this ex-periment seem remarkable to me. "Who would have thought that by interfering with the laws of occlusion the skull would have decreased in weight, and that every suture and every bone in the head would have varied as we have seen? This experiment strongly indicates how important is the masticatory CAUSES OF IMPAIRED FUNCTION Zo< equipment of man to the development of the head, and it also brings fresh illustrations of the importance of the sadly neglected temporary dentition which serves during the important developmental period of childhood." The previous quotation gives in full the details of Dr. Baker's experiment, and his findings in one case. His examination of the second rabbit upon which he experimented disclosed exactly similar variations from the normal, whereas the control animal was practically symmetrical.^ Until future experimenters prove these deductions to be erroneous, we may agree with Dr. Baker that the disuse of the teeth may result in extreme interference with the development, not alone of the jaws, but of contiguous parts of the cranium. Reasons for Lack of Use. — Disuse of the dental organs may be either involuntary or \oluntary. It is involuntary when the habits of masti- cation are hastv, or where the food used is of such a character that Fig. 111. — Caries of teeth causing voluntary disuse of the teeth. heavy mastication is not necessary. What an injustice, then, is done to children who are fed upon gruels, sloppy food and other articles of diet which require little or no masticatory effort to reduce them to a consistency readily swallowed? The voluntary disuse of the teeth is the direct result of caries which renders the chewing of food so difficult, or so painful, that the child elects either to swallow its food unchewed, or else to select food that needs no masticatory effort. In Fig. Ill, we see the right and left sides of the occluded models of a child four years of age. On the left side of the mouth caries has destroyed the little molars and cuspids almost to the gum line. We cannot look upon this picture without thinking of the rabbits, whose 1 Dr. Baker has continued his experiments, and has had exactly similar results with animals other than rabbits. See his report thereon, Dental Items of Interest, July, 1916. 17 258 MALOCCLUSION OF THE TEETH teeth Dr. Baker filed or ground away to prevent mastication on one side. When we recall the results of the experiment with the rabbits, we begin to appreciate the seriousness of such conditions in a human young one, during the most stressful periods of development. The word stressful is used because, whereas an adult needs only to restore the tissues of his body which are lost by use, a child must likewise do this and at the same time obtain and assimilate sufficient food with which to increase his weight and stature. How can he do this handicapped with a masticating apparatus so destroyed ? In the experiment with the rabbit, Dr. Baker left the little animal one side of his masticating apparatus perfect, so that perhaps he might properly masticate suffi- cient food for the proper noiu^ishment of his body. It is this fact that made Dr. Baker's results so significant. There is every reason to believe that the rabbits operated upon ate just as much food as the control animal, so that the divergencies from normal found in the skulls were not attributable to lack of nourishment, but to lack of use of one side of the jaws. Fig. 112. — Same case as Fig. Ill, occlusal view. The child whose models are shown fared not so well as Dr. Baker's rabbits, because on both sides occlusion was extensively interfered with. The cavities in the teeth are so large that a considerable por- tion of their occlusal areas have been lost, and the approximal con- tacts likewise having been destroyed, the protection of the interprox- imal septa has disappeared, so that food readily packs upon these easily injured and sensitive tissues, with the result that mastication becomes painful, and the child voluntary declines to use his teeth. Fig. 112, shows the occlusal view of these two jaws, and the extent to which caries has destroyed the occlusal contactual area is disclosed. Comparing these models with those shown in Fig. 107, we note the lack of development. At this point it may be well to consider again the models shown in Fig. 108. These likewise show lack of development of the arches, yet the teeth themselves are not affected by caries, so the child could have used them perfectly; therefore it is not to be claimed that disuse is the sole cause of lack of development. It may be the chief cause THE RESULT OF IMPAIRED FUNCTION 259 in some instances and only one of several factors in others. In the case of the child whose models are shown in Fig. 108, the physical his- tory is not known. It will suffice for present purposes to consider two possible hypotheses. While this child cannot have suffered from vol- untary disuse of the dental organs, since the teeth are all sound, there may have been involuntary disuse due to the soft nature of his food. Fig. 113. — Malocclusion due to lack of use. Again, considering the perfectness of the teeth, this may not be a case of lack of development at all. There is no definite age at which a particular development of the jaws must occur. We cannot say cer- tainly that the first permanent molars will erupt at a stated age, the incisors at another, the cuspids at another. The writer has seen a complete denture of thirty-two teeth at the age of fourteen, and in Fig. 114. — Same case as Fig. 113, occlusal view. another case, the upper cuspids arriving as late as the nineteenth year, in which case all the previously erupted teeth had likewise appeared long after what is supposed to be the normal time of eruption. Look- ing at a child denture prior to the eruption of the first permanent molars, if we note growth spaces, as seen in Fig. 107, we may say that normal development is present, but in the absence of such growth 260 MALOCCLUSION OF THE TEETH spaces, as in Fig. 108, we cannot positively decide. It may be a case of lack of development (as a mere illustration of which the models are used), or it may be a case of slow or tardy development. As examples of a period slightly later than that shown in Figs. Ill and 112, P'igs. 113 and 114 are introduced. This child's mouth was first examined prior to the appearance of the permanent molars. Not a tooth in the two arches was free from caries. .The upper incisors were barely showing above the gum line, and all four were abscessed, for which reason they were extracted, as were three or four others. Com- .plete lack of occlusion existed. The child was undersized, anemic, and of a generally degenerate appearance. Her father was a physician, however, and after removal of the abscessed teeth he was advised to feed the child on food that would yield as much nourishment as possible. It was impossible to obtain models of her mouth; it would have been cruel to try. When next she was seen, two years later, the models here illustrated were made. Even with the eruption of the first molars, the masticating possibilities have not been greatly improved, as they decayed almost as fast as they appeared, so it was said. However that may be, we have here a marked case of prolonged lack of use and malnutrition and cannot be surprised at the resultant malocclusion. On one side we note that the lower molar is in distal occlusion. On the other side the occlusion of the molars is apparently normal, but there is little reason to doubt that the lower molar has drifted forward because of the premature loss of the two temporary teeth. In any event it is a marked example of malocclusion due to lack of use follow- ing the ravages of caries in the temporary set, so that from this case alone we may gain some cognizance of the possible evils of dental disease which might have been prevented to a great degree by proper attention to mouth hygiene. CHAPTER X. PYORRHEA ALVEOLARIS By R. G. HUTCHINSON, Jr., D.D.S. Strictly speaking, the term pyorrhea alveolaris can l)e apphed only to conditions in which there is an exhibition of pus. As this is the case in but a percentage of the pathological ])rocesses which destroy the tissues supporting the teeth, it is a most inadequate and inappropriate term to use as descriptive of such conditions in general. Common usage often brings about the acceptance of terms or words improperly applied, and as the profession has almost universally employed the name pyorrhea alveolaris in speaking of infections affect- ing the peridental membrane and alveolar process, together with the overlying soft tissues, we are therefore justified in accepting such application. As the general causes leading to infection, the ultimate results of such infection, and the treatment are substantially the same in all cases, they will be considered collectively. Etiology. — Every mouth contains many different forms of bacteria, pathogenic and otherwise. The mouth, with its temperature, moisture, and abundance of culture medium, is an ideal incubator. Cultures are therefore easily established. Normally, the tissues offer sufficient resistance to prevent destruction, unless an extremely unsanitary condition is permitted to exist. As the establishment of a destructive infection must result from the overcoming of resistance by attack, attention must be directed to the cause of lowered resistance as well as the direct cause of infection. Clinical observation has shown that in the great majority of cases the infection exists at some point of injury. In other words, trauma is frequently the starting-point of pyorrhea alveolaris. The tissues having been injured, inflammation results, the active organisms which are present establish a focus and the destruction begins. There are some cases, however, in which there is no appreciable traumatic condition. Such cases are due to general low resistance to the particular form of organism which establishes itself. The conclusion must therefore be that pyorrhea alveolaris is caused by an infection of tissue whose resistance has been reduced, either by traumatic influence, or on account of some systemic factor. It must always be borne in mind that the presence of bacteria is necessary, and pyorrhea alveolaris cannot exist without them. When 262 PYORRHEA ALV SOLARIS the tissues are uninjured and high resistance exists, no harm will be done by their presence, but when the attacking force is stronger than the defense, a pathological condition is the result. Therefore the matter may be summed up in this way: The causes of pyorrhea ah-eolaris are positive, active or direct; and negative, passive or indirect. The former are local and the latter constitu- tional. Even with a very high constitutional resistance, such resistance may be overcome by injury, and infection may occur. It is all a matter of the relative strength of attack and defense. Pyorrhea alveolaris is not, as has often been said, "A local expression of a systemic dis- order." If a systemic disorder which affects nutrition or elimination exists, of course a local lesion is more easily established, and its progress will be more rapid and destructive. Whatever strengthens the attack or weakens the defense, facilitates the establishment and progress of the local disease; and whatever weakens the attack or strengthens the defense, is unfavorable to the local pathological condition. Causes. — The most common cause of pyorrhea alveolaris is mal- occlusion. The improper apposition of the occlusal surfaces results in a venous hyperemia of the peridental membrane, so lowering resist- ance. x41so through malocclusion, the teeth are not performing normal function, and the tissues surrounding them suffer from malnutrition. When the teeth are crowded, the alveolar septum is thin and less resistant to attack, and it is always more difficult to maintain san- itation. Some of the other local exciting causes are faulty dental operations, such as ill-fitting crowns and bridges which not only lacerate the tissues but accumulate food debris which the patient cannot remove; fillings impinging on the gum margins; fillings improperly contoured, allow- ing impaction of food in the interproximal space; septic teeth; improper application of rubber dam and clamps; rapid or excessive separation of teeth; laceration of tissues in finishing fillings; injury by improper instrumentation, for the removal of tartar, etc. In short, anything which establishes trauma, invites pyorrhea alveolaris. As before stated, the systemic factors are passive or negative, and may be inherent or acquired. Some individuals possess to a high degree the ability to repair tissue which has been injured and to resist injury, or to resist many forms of infection, and others do not. This is an inherent factor. Where such systemic diseases as tuberculosis, diabetes, Bright's disease or syphilis occur, pyorrhea alveolaris may be present in an aggravated form on account of low resistance, but almost invariably the inception of the pyorrhea antedates the establishment of the sys- tcniif: disease. Progress of Disease. — Pyorrhea alveolaris begins with an inflamma- tion either at the point of injury or at the gingival margins, especially TREATMENT 263 in the interproximal space. The inflammation results in the formation of deposits of serumal calculus, which })ecomes what may be called a secondary exciting cause. In some cases pus is formed, and in others destruction of the tissues takes place without pus being present. This destruction will continue until the teeth are lost, unless correct treat- ment is given. Symptoms. — The symptoms vary according to the existing condi- tions and the stage of progress. In its inception, slight redness of the gingiva presents, sometimes w'ith more or less serumal deposits. In more advanced stages, the gums wull be highly congested, pus flowing profusely and teeth loosened. There are many cases, the existence of which can be determined only by careful thorough exploration under the gum margins. Where much tissue has been lost, or deposits on the necks or roots of the teeth are present, there is no diflSculty in determining the presence of a patholog- ical condition. Treatment. — The first step in the treatment of any case of pyorrhea alveolaris should be to determine w^here excessive stress exists in occluding the teeth, both at rest and in every possible position to be assumed by the jaw. All cusps must be properly ground and points of contact established in such a way that the stress will be equally distributed in all positions. All faulty dental operations should be corrected. Septic teeth must be sterilized or removed. The sooner this is done, the bettc'r the result of instrumentation will be. It must be remembered that not only must health be restored, but function must be established, and finally, sanitation maintained. Any tooth which cannot be kept in a sanitary condition by the patient, should be removed. A sanitary artificial substitute is always prefer- able to an unsanitary natural organ. All deposits of calculus must be removed and surfaces of roots deli- cately curetted for the removal of necrotic membrane, and finally, the teeth must be polished perfectly. In treating pyorrhea alveolaris, every factor which tends to injure the tissues or cause infection must be considered and properly removed, or failure is inevitable. The operator removes that which nature cannot overcome, but nature heals and builds up the tissues. Therefore nothing harmful must be left and nothing must be done to interfere with that reparative process which must take place in order to eft'ect a cure. Practically no systemic condition which does not prostrate a patient will prevent successful treatment, and most systemic factors can be ignored in the treatment, except that more delicacy and care must be exercised where general low resistance exists. Failure is often due to excessive injury attending unskilful instrumentation and is fre- quently followed by a secondary infection more serious than the original. 264 PYORRHEA ALV SOLARIS Postoperative Treatment. — After the disease has been eliminated and health restored, it must be maintained. This is accomplished mainly through sanitary measures, both by the patient and the operator. The intervals between prophylactic treatments must be determined in each individual case. Prophylaxis means prevention of disease, therefore the cleaning of the teeth by the operator must be done before recurrent inflamma- tion is established. The fact that prophylactic treatment is necessary in order to main- tain health in the oral cavity in no way proves that the disease is not cured, but on the contrary, proves the local origin of pyorrhea alveo- laris. Even where systemic predisposing factors exist, pyorrhea alveolaris either primary or recurrent, can be prevented by local measures alone. The point at which resistance is overcome varies in different cases. Medication. — Medication, either local or constitutional, is practically useless as a curative factor. Foreign irritants and pathological tissue must be surgically removed, and causative factors eliminated. The only effective use of medicaments consists of the application of such materials as will tend to prevent recurrent infection and act as pallia- tives. Whatever is antagonistic to bacterial growth, without irritation or destruction of the tissues, is conducive to the establishment and maintenance of health. A healthy mouth can neither be established nor maintained, but by depriving the bacteria as perfectly as possible of culture medium, we lessen the number by a starvation process. The use of mild antiseptics inhibits bacterial growth in food deposits which the patient cannot remove, and reduces the virulence of the bacteria present. Vaccine Treatment. — The use of vaccines is not only unnecessary but detrimental, as such treatment merely makes possible the continued existence of mechanical irritants, bacteria, and pathological tissue with- out the exhibition of superficial symptoms. Such masking of symp- toms misleads the operator into believing that a cure has been effected when such is not the case. If the proper surgical treatment has been given, in every detail, and the patient faithfully carries out proper instructions, nature will rapidly repair the damaged tissues without any other assistance. This applies in a general way to powerful germi- cides and astringents applied locally. They give only temporary relief, and are liable to ultimately cause increased destruction of tissue. The only logical method of treatment of accessible infections is to remove direct causes, and not to establish an artificial resistance wliic-h permits their maintenance. Results of Pyorrhea Alveolaris. — Until recently little attention has been given by either the medical or dental profession to the appalling results often attending pyorrhea alveolaris. The dental profession has recognized the destructive effect locally, but not to the fullest extent. Such conditions as death of the dental pulp, necrosis of the PROGNOSIS 2G5 bone, empyema of the antrum, and, in fact, every pathological con- dition common to the nioutli often has as its starting-point, pyorrhea alveolaris. What is even more common and serious, is the great variety of sys- temic effects of this disease. Pus, septic discharges, toxins, and the organisms themselves enter the system, both by ingestion and direct absorption, are carried to every part of the anatomy, and establish pathological conditions which are often fatal. Such eminent medical authorities as Drs. Osier, Hunter, Mayo and others, regard mouth infections as the frequent source of such sys- temic diseases as all forms of digestive disturbance including appen- dicitis, nephritis, endocarditis, colitis, rheumatic fever, arthritis deformans, septicemia, anemia, general toxemia, tonsilitis and ])haryngitis, gastric ulcer, abscess of glands and other tissues, such as carbuncles, and all conditions having, as their origin, infection. Even the common communicable diseases are fostered by infected mouths. Statistics show a remarkable decrease of such diseases in institutions where oral sanitation is practised. Prognosis. — When correct treatment of pyorrhea alveolaris has been conducted, and proper prophylactic measures carried out subse- quently, there is practically no such thing as recurrence. When there is a continuance or recurrence, it is almost invariably due either to lack of knowledge or skill on the part of the operator, or failure on the part of the patient to carry out instructions; presuming, of course, that proper instructions have been given. CHAPTER XI. ODONTALGIA AND ALVEOLAR ABSCESS. By M. L. RHEIN, AI.D., D.D.S., D.R.C., U.S.N. ODONTALGIA. There is nothing that has a greater horror for the world at large than toothache. To the layman, every kind of pain in the dental region is summarized in that word. The variations in the nature and characteristics of such pains have a most important diagnostic value. While it is true that the tales of woe that the patient sometimes relates are very trying to the listener, nevertheless it behooves the dental hygienists to pay the most careful attention to the details of such conditions, if they expect to make a correct report on conditions that they find. The sensation of pain is transmitted by the nervous system. The nerves, as they ramify tlirough the human body, can readily be com- pared to a complicated telegraph line. The same pair of nerves that supply the dental regions go to the eyes, nose and ears. An irritation of a nerve terminal, frequently is not felt at the point of irritation, but at some other place, which may be the most remote point of the body. This is termed referred or reflexed pain. Following out our telegraphic simile, the shock goes direct to the brain, and is then transmitted to the terminal of some other line. Consequently, it is always well to bear in mind the possibility of almost all forms of pains having a dental origin. The most common form of toothache is that produced by the inroads of dental caries. As the enamel is at the very first destroyed, there is very little sensation, because the inner layer of dentin endeavors by nutritional changes to protect itself. As caries approaches nearer the pulp, there comes a place where this protection ceases, and where the slightest thermal change causes intense pain. Heat, cold or acid formations all produce the same character of pain, and the source of this jjain is very easily learned by observation. The entrance of the exphjrer in a cavity generally suffices to expose the cause, and the case becomes one for the dentist. There is, however, another form of odontalgia which should be of more interest to the dental hygienist. Without entering into the the- ories of erosion, it is sufficient to say that under certain circumstances the enamel is dissolved. This is most likely to take place at the gin- gival margin on either buccal or lingual surface, and frequently is followed by the most exquisite sensitiveness. The patient will gen- ODONTALGIA 267 erally call attention to the pain ])ro(Iuced when these surfaces are polished, in contrast to the feeling of intense satisfaction produced by proper manipulation of the orange-wood stick over an ordinary enamel surface. Careful observation will demonstrate the fact that the gingivae, which for years have not been massaged or cleansed, generally covers these most sensitive areas. Not uncommonly is it the case that the pain caused by such erosions has made the patient apply to the dentist. Often the distress will be so great that the patient is positive that the ofi'ending teeth mi^t be lost. There is nothing that regular proi)hylactic care will serve better than the cure or alleviation of such distress. Consequently, the hygienist is able to give such cases a very favorable prognosis if the patient will carefully follow out the proper daily hygienic care of the mouth. In such cases the terminal circulation has become impaired, and the result is an abnormality in the excretion of the mucous follicles. Debris of foodstuffs fermenting, leave an acid condition, and together with this, are found bacterial plaques. All these combined factors ])roduce the subsequent enamel dete- rioration. The proper use of the orange-wood sticks under the gingival margin of the gums will, in conjunction with frequent gum massage by the patient, tend to restore these tissues to a normal condition. Of course enamel that has been lost cannot be restored, but when the inroad of erosion has stopped, the solution of the enamel surface ceases, and after a while the dentin acquires a surface somewhat similar to enamel and the sensitiveness disappears. There are other forms of pain that come under the head of neural- gias or tic douloureux. These vary greatly in their symptomatology. There may be a sudden sharp, piercing pain, or on the contrary, a pulsating throb. This pain may occur at regular or irregular inter- vals. Pressure on nerve fibers is generally regarded as the cause of such trouble. In exostosis of the roots of teeth we find a common cause. As the roots thicken in size they begin to occup}' a space that had been tenanted by something else, and pressure on the peri-apical tissues is created; if the pressure is exerted against nerve fiber, one of the most severe forms of neuralgia is likely to ensue. An abnormal supply of nutrition to the cementum is the cause of exostosis. The Roentgen rays make the diagnosis very easy, where formerly it was one of the most difficult of conditions to diagnose. In like manner the calcific deposits in the pulp are produced by extra- ordinary nutritional disturbances. These deposits vary greatly in size, shape and appearance. They may simulate minute seeds, nodules or pulp stones of more or less rounded shape, or they may be jagged and star-shaped. They may appear to coalesce and form one large mass of inorganic material, completely occluding the pulp chamber. It does not take much imagination to conclude that a star-shaped and jagged pulp nodule pressing on nerve fibrils will produce very 268 ODONTALGIA AND ALVEOLAR ABSCESS great pain. Fortunately the roentgenogram here affords great diag- nostic assistance. There are two forms of toothache that have a very important bear- ing on the study of the symptomatology of alveolar abscess. The following is a typical histbry: The tooth is aching badly, especially when subjected to cold and heat. It becomes very sensitive to the touch. One morning, on awakening, the individual is very happy to find that all pain has ceased. Ice-water no longer produces this inde- scribable pain. The pulp in the tooth has lost its vitality. The sense of security on the part of the individual is not well placed. About a week later a sudden intense pain is experienced from heat that may reach the tooth. Cold now has a tendency to bring relief, but heat only produces a typical neuralgic effect. During this interval pyogenic bacteria have gained entrance to the pulp chamber, and infection of this organic tissue has begun. The tooth has now become exceedingly sensitive to the slightest touch. On opening the pulp chamber the pulp will be found more or less purulent, and the indescribable but well-known odor of dead pulp adds to the unpleasantness. An incip- ient alveolar abscess has already started in the peri-apical region. This is the acute stage of alveolar abscess. The pain that is caused from a dying pulp is almost the antithesis of the pain produced by an incipient alveolar abscess. It is frequently difficult to demonstrate to laymen that the severest form of tooth- ache can be present after the pulp is dead. It is, however, of supreme importance that this differentiation in the character of the pain, when the pulp is dying and that experienced where later infection of the pulp has taken place, should be thoroughly mastered by the dental hygienist. The primary object of introducing odontalgia in this chapter is for the very purpose of impressing on the dental hygienist, the ne- cessity of being able to differentiate between the various forms of odontalgia of which the patient will complain. It is important that the initial symptoms of a dying pulp, as indi- cated by the character of the pain, should be thoroughly mastered, as such a case should have immediate dental service. Dental atten- tion may })e postponed in such cases, without any further detriment than the suffering of the patient. When, however, the pulp has once died, and the tenderness and sensitiveness to heat indicates the onset of infection in the pulp chamber, no delay of operative treatment is excusable. A difference of twenty-four hours in opening the pulp chamber of such a tooth may have a vital bearing on the ultimate preservation of the tooth. At this time the pulp chamber should be entered with extreme care, so that no infection is forced through a foramen. If the peri-apical region has not become infected, every care should be taken that this evil be avoided. The besetting sin of dental operations is undue haste where great care is required to avoid inju- rious consequences. Time plays such an important role in dental ALVEOLAR ABSCESS 269 therapy that manj^ good dentists have been known to yield to the temptation of hasty procedure. The dental hygienist will frequently be found at the side of the dental chair acting in the capacity of a trained assistant to the dentist. Possessing a knowledge of the care requisite in the handling of such cases, her presence will unconsciously act as a brake on the desire of the dentist to go ahead at full speed without regard to consequences. Even when infection has once reached the peri-apical region, it is of the greatest importance that no treatment be employed that will tend to increase the area infected. In this respect too great caution cannot be urged in the use of any of the great number of proprietary preparations, which depend on setting free formaldehyde. The writer has a keen recollection of a case to which he was called in consultation by a much-worried physician. The patient's tempera- ture had risen to 105.5°. It was a case of acute alveolar abscess of an upper incisor. A large dressing of one of these proprietary nostrums had been placed in the root canal, which had a wide-open foramen. The great amount of formaldehyde passing through the foramen mechanically carried the infection up to the floor of the nose. Prompt surgical measures at this point, at least one-half inch above the end of the root, caused the temperature to drop to normal within twenty- four hours. ALVEOLAR ABSCESS. Between ISSO and 1890 the science of bacteriology began to have a marked influence both on the teaching and treatment of diseases of the body. Since that time the achievement of bacteriologists has produced an ever-changing transition in the point of ^'iew of mouth conditions. This change in the treatment of disease has been much more rapid in other parts of the body than in the mouth, and this is due to the fact that a large percentage of dentists are not medically trained men. It is worthy of note in this respect that one of the earliest works of value was the production of a dentist. Dr. W. I). Miller, at that time of the University of Berlin, who published in 1890 his classical work on microorganisms of the mouth. The stimulus of this work in itself would have kept the scientific progress of dentistry on a par with that of the rest of medicine if the majority of dentists had been medically educated. The eyer-widening gap between dentistry and medicine, since ^Miller's work was published, has been due to this unfortunate condition of affairs. It is impossible to separate one part of the body from another. ^Microorganisms that are found in the mouth may reach every part of the body. When disease becomes a serious matter it is found that the infecting microorganisms use the lymph channels and other media of circulation and by their own motile force they travel to any part of the body. Consequently, it is only a question of time when no one will be permitted to commence the practice of 270 ODOXTALGIA AXD ALVEOLAR ABSCESS dentistry unless thorouglily educated in the study of health and disease. It is on account of this absence of pathological knowledge, due to the lack of general medical education, that this subject is so inadequately understood by the majority of dental practitioners. The hygienist is to be educated to work in a field where the possibilities of infection caused by some of these microorganisms should be constantly borne in mind. It is important that the danger involved should be appre- ciated. Even if ^-ith the utmost care the hygienist does not help to produce infections, there must also be steadfastly in her mind the possi- bility of aggravating infected areas if the dentinal tissues are handled without a due appreciation of this danger. Abscesses are infectious degenerations of tissue. They are the result of an infection produced by some form of pyogenic bacteria. These bacteria yield in turn various kinds of toxins, which become the real agents of tissue destruction. AMien the organism is of a hemo- lytic or blood-dissolving type of sufficient virility, it produces irrita- tion, inflammation, and a resultant breaking down of the tissues into pus. Where, however, the bacteria have a very low power of virility, like the Streptococcus viridans, the tissues do not break down into pus, but nevertheless toxins are produced. When it is considered that at all times the mouth is filled with living bacteria, the ever-present danger of the individual to infection cannot but be apparent to any observer. If it was not for what is spoken of as the immunity of the individual, human life on this planet would have long since ceased to exist; but there are certain forms of cells that act as a protecting army against these attacking forces. This defensive power is lodged, to a large degree, in the white blood cor- puscles or leukocytes. The gum tissue itself, when unwounded, is a defensive agent. There are also certain elements in the blood itself, which help to maintain this condition known as immunity. While in this state the pathogenic bacteria have practically no effect against the defense which the individual possesses. There comes a period or periods in ever}' human life when this defense becomes weakened, and then infection is likely to take place in some part of the body. When this period arrives, the area to become infected is that part of the body which offers the least resistance. This state is known as locus minonis resistentice. In other words, the place with the least resistance is thg spot that the bacteria seek out when this defense becomes more or less weakened. If an indi\'idual has in his mouth one or more teeth which have been ineffectually treated, where imperfect pulp removal and imperfect root-canal filling has been done, this place will be at once invaded by the hostile bacteria as the point of least resistance, and is therefore likely to become the infected area. Unfortunately, an inferior type of constructive dentistry plays a very important role in leaving places of this kind in the dental region. The great demand in this country for dentistry at a moderate price ALVEOLAR ABSCESS 271 has been one of the greatest causes of this unfortunate condition of affairs. A tooth in which pulp work has been done imperfectly, may- retain a comparatively healthy condition as long as the individual retains this state of immunity. This condition is frequently destroyed by the intervention of some other infectious disease, as for example, a severe attack of influenza, which is very epidemic at certain times of the }'ear in this country. The weakened condition of the individual, from an attack of this nature, at once impairs his immunity and the parts about this imperfect dental constructive work become the place of least resistance which the pyogenic bacteria attack. In the same manner, imperfect mastication and faulty assimilation of food, lack of attention to common-sense rules of hygiene, and numerous other factors of this nature, in fact age itself, tend to depreciate more or less at times this condition of immunity and thus to bring the individual into a state where infection becomes possible. For the sake of convenience, these abscesses may be considered in their principal forms, acute and chronic. The initial attack is gen- erally spoken of as an acute al- veolar abscess. It begins with a local generation of heat, rise in body temperature, constantly in- creasing inflammation, and edema of the localized infected area. Then pus forms, and if the ab- scess produced is not opened f,«. ^S.-Acute alveolar abscess of a surgically, it seeks release from lower incisor in the third stage, with pus its environment bv the path of ca\-ity between the bone and the peri- Ipflst rpsistnnpp This is P-pnerallv o^t^"™- ^' P^^ ^^^'^^^ ^^ t^^ bone; b, least resistance. iniS is generain p^g between the periosteum and bone; through the plate of the alveo- c, lip; d, tooth; e, tongue. (Black.) lus; sometimes, however, it follows the sheaths of the tissues and is evacuated at some remote point, which always makes the diagnosis of the locus of infection of such cases more difficult. Abscesses of this nature have often been known to discharge into the clavicular region, and much more frequently through the cheeks of individuals. (Fig. 115.) When the active symptoms of an attack of this kind have subsided, as they will after a time even without treatment, the abscess assumes a latent form and now is spoken of as a chronic alveolar abscess. It is not an uncommon thing for dentists to assure their patients that an abscess has been ciu-ed because its active symptoms have disappeared, 979 ODONTALGIA AND ALVEOLAR ABSCESS when perhaps in a month or six months, or in a year or years, it may break out afresh, and thus show that it has not been cured. These outbursts of a chronic abscess are generally attended with none of the pain and discomfort which accompany the initial attack. They are often spoken of as harmless little gum boils, instead of being recognized as a very powerful factor in breaking down immu- nity. The extent of inflammation which takes place as a result of infec- tion of this kind, is dependent upon the nature of the infecting organ- isms. These vary largely in their degree of virility. The more powerful microorganisms are of a hemolytic type, and produce the ordinary acute alveolar abscess. A much more dangerous organism, however, is non-hemolytic, generally one of the streptococci, which possesses so small an amount of virulence that it is frequently incapable of produc- ing a degree of inflammation sufficient to cause an irritation that will be appreciable to the affected individual. As a result of this low degree of inflammation, nature builds up a defensive line of fibrous tissue around the infected area, which in a short time becomes a regular envelope entirel}^ covering the abscess tract. The product is known as a granuloma or blind abscess, perhaps the most serious in- fective result that could be produced (Fig. 116). In the dental region, a granuloma may become encased in the alveolar structure in the peri- apical space, where it may be unnoticed and dormant for years. However, it forces through this fibrous envelope into surrounding tis- sues, injurious toxins or products of its mul- tiplication. These toxins are carried by the lymph channels to the various organs, where their energy gradually tends to undermine these organs and to produce grave chronic diseases, among which may be mentioned arthritis deformans. It is now well recognized that many instances of grave cardiac disease of an infectious type can be traced back to untreated alveolar abscesses. Dental Pulp. — In considering this topic, a thorough understanding of dental histology is necessary. It is especially important to remember the division of this tissue into inorganic and organic. Inorganic material itself is not capable of becoming infected, but there is always strata of organic matter intermixed with the inorganic, which, becoming infected, help to break down the inorganic tissue. The pulp of the tooth in a normal condition is entirely of organic nature, and thus open to infection, as it affords an inexhaustible supply of nutriment for pyogenic bacteria. Perha])s the most imj)ortant single feature of the pulp is its vascularity. As long as it retains a normal blood circulation, infection of tins jelly-like mass is impossible. There are various wavs in which the normal circulation becomes Fig. 116. — Granulomata or blind abscesses. ALVEOLAR ABSCESS 273 impaired, and the pulp loses its vitality. Dental caries is perhaps the most common cause. The inflammation resulting from this disease invariably reacts on the pulp, manifesting itself in various wa>'s. It may lead to fatty degeneration, or abnormal fungous hypertrophy, etc. Under the conditions of caries near the pulp, it readily becomes the prey of invading bacteria with resulting infection (Fig. 117). i ■■», Fig. 117. — Fatty degeneration of the pulp. The irritation of the pulp, whether from caries or other causes, often produces an entirely different abnormal condition. Under certain conditions, there appears to be an effort of nature to protect the organ, and this results in an excessive supply of inorganic material which in turn results in a calcific degeneration of the pulp. This condition is usually found in adult life, becoming more marked as age advances. It is found in very varied circumstances. The pulp may be found im- pregnated with little seed-like bodies, crystalline in their formation. From just a few of these pulp nodules, the degeneration may progress 18 274 ODONTALGIA AND ALVEOLAR. ABSCESS until the entire pulp is found to be practically calcified with just a microscopic strata of organic structure permeating it (Fig. 118). This calcification often has a tendency to strangulate the already impaired circulation, and thus produce death of the pulp. The proper removal of such a pulp is no mean surgical triumph, and will l)e referred to later. Injudicious dental operations in the shape of large metallic fillings in close proximity to the pulp, are frequent sources of the irritation producing this degeneration and subsequent death of the pulp. Acci- dents are frequent causes of traumas resulting in a rupture of the bloodvessels entering the foramina and thereby causing the death of the pulp. Fig. 118. — Pulp calcification. The pulp having died, the tooth is left with this dead body in its interior, a prey to the first invading bacteria. Consequently, it is essen- tial that the corj)se be speedily removed. This means the removal of every particle of organic tissue under strictly aseptic precautions, and the hermetic sealing of the root canal. There is a type of these cases in which th(; pulp does not die, but as the calcification progresses to almost the })oint of ()l)literation, a severe inflammation of the end of the root and peridental tissues takes ])lace. This inflammatory process is caused by the microscopic elements of organic tissue left in the pulp. The pericementitis is often very severe, and is accompanied by serous exudation around the necks of the teeth. Only the cleans- ing of such canals through every foramina will cure this condition. An inflammatory exudate from this source is only too frequently diag- ALVEOLAR ABSCESS 275 nosed as })yorrliea alveoliiris, especially when the tooth sliows signs of loosening. All the recognized treatments for pyorrhea only increase the inflammatory conditions, hut when the organic matter has been conii)letely removed so that a broach will i)ass through every foramen, the tooth will at once tighten in its socket and all exudate will cease. The symptoms following infection depend largely on the nature of the infecting organism. When it is of the hemolytic variety, pus soon develops, and the extent of tissue invaded varies greatly. Cases of this type are frequently diagnosed and treated as pyorrhea alveolaris. To many medical men, as well as to many dentists, this is the only answer to the problem of pus in the mouth. Radiography has made the correct diagnosis of such conditions a comparatively easy matter. It is inexcusable, at the present time, to treat a supposedly pyorrheal mouth without first studying the roentgenograms of such a mouth. An alveolar abscess with a fistulous opening at the gingival border, while very deceptive from the standpoint of physical examination, becomes easy of diag- nosis in studying a properly focussed roent- genogram. The destruction of alveolar struc- ture around the end of the root makes this diagnosis very simple. While a pseudo form of pyorrhea may develop from the pus dis- charging around the neck of a tooth, all methods of treating the pyorrheal condition must fail, unless the pulp of the tooth is properly removed and the diseased structure in the peri-apical region is completely erad- icated (Fig. 119). In almost all cases of pulps dying from trauma, and frequently where the infecting microorganism attacks the foraminal entrance in the peri-apical region, the bacteria are of a non-hemolytic variety, and most generally when isolated are found to be the Streptococcvs viridans. It is a well-noted clinical fact that this attenuated form of streptococcus is not uncommon in this region. Wherever partial pulp removal is practised, and any method of med- ication of the remnant of the pulp tissue is employed, with the object of making the parts immune to infection (a procedure known gener- ally as a mummifying process), the pulp tissue is invariably subject to infection at its peri-apical entrance into the root canal. The virility of the viridans organism is so slight that no active inflammatory action takes place, and pus is not formed. As the Streptococcus viridans makes a habitat in the foramen at the end of the root, a protecting ring of fibrous tissue is formed around this point. It is a mooted question whether this envelope of the granuloma is intended as a protection to invasion of the tissues, or whether it is a protection to the strep- tococci against leukocytes or other antagonistic elements. Fig. 119. — Roentgen- ogram showing alveolar abscess erroneously diag- nosed as pyorrhea alveo- laris. 276 ODONTALGIA AND ALVEOLAR ABSCESS The fact remains, hoAvever, that from these infective foci, toxins may be constantly sent into the rest of the body. It is a very generally recognized fact that the toxins from different microorganisms appear to have a selective affinity for certain tissues. The toxins emanating from these granulomas appear to have such a selective affinity for the muscles and valves of the heart. The most unfortunate feature in connection with this type of alveolar abscess is the insidious manner in which it strikes at the individual's vital forces. Its lack of virulence appears to make it incapable of producing severe local irritation, and consequently a dangerous toxemia may be progressing without the slightest local manifestation. With the present-day knowledge of mouth sepsis, the physician is much more frequently referring cases of general infection to the dentist for his opinion as to whether a septic focus is present in any part of the dental region. Heretofore the dentist has simply demonstrated his incompetency in returning a verdict of an aseptic mouth based simply on ordinary mouth examination. Only a careful roentgenogram examination of each indi- vidual tooth socket will show the presence of these blind abscesses. The importance of the dental opinion, when a patient has been referred by the physician for a careful examination, has never in the past been properly appreciated. In the future, for a dentist to say that a mouth is free from infection, however beautiful and physiological it may appear, he must first carefully study the roentgenograms of every tooth in the mouth. Unless the dentist has such roentgenograms of the entire jaw and mandible at his disposal for study, he is incapable of giving an answer to this all-important question. The various types of arthritis, ulcers of the stomach, gall-stones and kindred toxic diseases, have had their origin definitely traced to abscesses about the teeth. PERICEMENTAL ABSCESS. There is still another form of abscess which closely simulates the alveolar abscess, and may exist for years without interfering with the vitality of the pulp of the tooth in the region of the abscess. It has no etiological connection with the dental pulp. It is called pericemental abscess, because the localized infection is found in the pericementum around the roots of the teeth. The most acceptable theory of the formation of these abscesses is that in the pericementum is left some remnant of the epithelium from which the original enamel germ was formed. These remnants of epithelium become infected in the same manner as does the organic tissue left at the peri-apical end of a root-canal foramen, which produces a blind abscess. Of course no one can say that this theory of the etiology of pericemental abscess will be borne out in the final studies of the cause of this malady. It is, however, of the utmost importance that in the diagnosis of other types of abscess this form of infection be pro])erly excluded. In the past pericemental abscess has rarely been correctly diag- PERICEMENTAL ABSCESS 277 nosed. Like the ordinary alveolar abscess, it is most frequently called pyorrhea alveolaris. Many men of ability, who have been able to exclude the symptoms of a pyorrhea, have erred in supposing it to be an ordinary alveolar abscess. Here, also, the roentgenogram has proved of the greatest value in making possible correct diagnosis (Fig. 120). Treatment. — In the treatment of pericemental abscesses, ionism has been found the most useful agent for their cure. Frequently, however, even though the pulp does not appear to be involved, it becomes necessary to remove this organ before a cure can be effected. It may not be out of the way at this time to deprecate the growing tendency to the use of the term, pyorrhea specialists. It should be clearly understood that pyorrhea alveolaris is only a symptom of something wrong in the equilibrium of the body. This something is not always the same thing, and consequently the cure and treatment of different cases of pyorrhea may call into therapeutic requisition any one of all the known dental operations from orthodontia to the introduction of an artificial denture. Nearly all of these self-styled special- ists begin and end their treatment with the pyorrheal pocket and its environ- ment. Such men succeed in doing an incalculable amount of harm. While recognizing the great benefits to be de- rived from the various specialties in den- tistry in their particular field, the treat- ment of pyorrhea alveolaris should never be termed a specialty, because its sue- fig. 120. — Roentgenogram of cessful therapy may demand the services pericemental abscess. of not only any one of our recognized dental specialists, but may also require various kindsof medicaltreatment. In this respect it is of great importance to be able to differentiate between physiological and abnormal gum tissue, not merely in a gross manner, but with all the niceties of gradations in color, texture and atrophy or hypertrophy of tissue. To be able to differentiate healthy from abnormal gum tissue, one must possess minute knowledge of the appearance of these tissues, which is only gained from the experience of repeated observations with this point in view. The eyes of pro- phylactic operators are so constantly turned on these tissues that they have exceptional opportunities for perfecting themselves in these differential observations. The gum tissue is nourished by terminal capillaries, which leave this tissue as venous blood. The extreme vulnerability of the gums is due to the fact that any impairment in nutrition leaves its first imprint on this tissue. It has become a well-known clinical fact that the effect of mal- nutrition upon the gums varies according to the nature of the cause. The simplest proof of this fact is found in the blue staining of the gums from toxic doses of mercury. Physicians for many years, in adminis- tering mercury, have been accustomed to look for this blue stain as 278 ODONTALGIA AND ALVEOLAR ABSCESS an indication that medication by mercury has been carried to its limit of safety. In Hke manner, every grave nutritional disorder in its action of gum starvation, leaves the tissue with a different appear- ance, depending upon the nature of the organic trouble. The severity of the disease, and consequent extent of injury to the system, to a certain extent, can be measured by the amount of variation from the normal appearance of gum in each specific case. Some of these ^ variations may be very slight and difficult to differentiate, while others may be widely dissimilar. For example, in Bright's disease the gum, while slightly inflamed, is paler than normal tissue at the gin- gival portion. Its real specific characteristic, however, consists in a narrow whip-cord-like hypertrophy on the lingual surfaces about one- sixty-fourth inch from the gingival margin, and conforming in contour to the scalloped shape of the gingivae. In diabetes, however, the char- acteristic appearance is quite the opposite. The inflammatory, condi- tion is much more marked, giving the gums an angry, dark reddish hue around the gingivse, which latter are very spongy in consistency, and have lost their attachment to the cementum. The gums bleed freely when even slightly irritated. When the mouth has been left open for a ver}^ short period, the palatal surface loses its moisture, and assumes a shiny surface similar to the outer skin of an onion. One of the most characteristic diagnostic signs in the dental region is shown in those cases where, on account of valvular disease or other heart disorder, there is an insufficient power in the force of the arterial circulation as it leaves the heart. In such cases the gum, extending from one-third to one-half inch from the gingivse, will be found to be more or less cyanosed. Above the dark blue area, the gum has the normal pink color. There is no blending of the normal pink color into the dark blue, but an abrupt transition that makes the diagnosis of circula- tory trouble of some kind a very simple matter. The writer has made a diagnosis of many cases of tuberculosis of the lung, simply from observing the abnormally increased excretion from the mucous follicles. This wonderful diagnostic field will be found especially interesting to the intelligent, studious and observing hygienist. It should not be thought that this can be easily mastered. It will take much observation and study to learn to subdivide properly and understand the different appearances in different cases. By taking a sympathetic attitude, and by the use of tact and judgment, it is easy to learn the physical history of these cases, and thus study the peculiar characteristics of the gums in different forms of mal- nutrition. To the individual who has the talent to master this differential observation, there is opened a wonderful field of useful- ness. It lies in the province of the dentist, if he has sufficient ability, to detect incipient signs of malnutrition. It is written in indelible type on the gums long before urinalysis discloses any tangible sign. It will be one of the great privileges of the dental hygienist to call the attention to these indexes of malnutrition. PERICEMENTAL ABSCESS 279 It seems scarcely necessary to say that the early diagnosis of many such conditions frequently means a possible cure at that period. Even where that is impossible, it often means a considerable prolonga- tion of life if proper treatment is pursued. Treatment of Alveolar Abscess. — Alveolar abscesses may be divided into two classes, acute and chronic. In the latter class would come the division of granulomas or blind abscesses. An acute condition of an abscess refers to the initial stage of infection, where for the first time pus is about to form in the peri-apical region. If such a case is seen early enough, the pulp chamber may be delicately opened, and a dressing of tricresol and formalin (formacresol, Buckley) placed in the pulp chamber and sealed in place with oxyphosphate of zinc cement. In a certain number of cases, seen at a very early stage, an abscess can be aborted in this manner. In most cases, however, when such an infection has begun, nothing will prevent its going to the point of resolution with the resultant flow of pus. If left to itself, the pus will follow the line of least resistance and will finally discharge explosively into the mouth. When it is evident that this result is imminent, heat is often applied to hasten the advent of suppuration. It is during this stage of edema and inflammation that the pain reaches its height, and consequently every effort should be made to bring about a flow of pus, and thus relieve the tension of the other tissues. At the very earliest moment possible the infected area is laid wide open, and if this does not result in a ready flow of pus, the alveolar plate is pierced and an outlet established for any pus which may be present. The fistulous canal is now kept open with gauze packing, and after a short time all symptoms of pain disappear. It is now feasible to remove the infected dead pulp, eradicate the pathological condition in the peri-apical region, and leave the tooth in a sound con- dition and free from the danger of reinfection. In this respect the treat- ment is practically similar to the cure of a blind abscess or granuloma. While dental hygienists will take no personal part in the operative procedure of pulp removal, they should have a thorough theoretic knowledge of what is required, not only for the removal of patho- logical conditions, but also for so leaving the tissues that reinfection is rendered practically impossible. It must be understood that there is a scientific reason for every procedure, and that nothing should be done which is empiric. Too many men of recognized ability have been satisfied with a technic which results in leaving the field free from infection when this operation has been completed. Nothing short of making infection in this locality impossible will give dental surgery that high position to which it is justly entitled in the field of pre- ventive medicine. It matters little what method is pursued if this result can be secured. To accomplish this object, it is necessary that: 1. Every particle of organic tissue, living oT dead, must be removed from the canals. 280 ODONTALGIA AND ALVEOLAR ABSCESS 2. Any diseased tissue in the peri-apical region must be entirely obliterated. 3. Infection of organic structure in the dentinal tubuli must be guarded against. 4. All foramina must be hermetically sealed both within the canal and on its peri-apical area. 5. Infection from the region of the pulpal chamber must be made impossible. The time has come when it must be recognized that all five of these requirements must be met. No compromise can be permitted in order to safeguard the future health of the individual. If for any reason any one of these results cannot be attained, the tooth must be extracted. Where diseased conditions have not advanced too far, there are not more than three or five per cent, of teeth that cannot be scientifically operated upon, so that all these requirements can be fulfilled. This result, however, is as a rule only possible at the cost of many hours of work, requiring great patience and skill of a high order. This always has been and always will be the great bar against the practicability of preserving in a state of health the vast majority of teeth with pulp involvement. Thousands of dentists appear to think that if the interior of the root canal is found free from infection, no harm can result from such a tooth. They appear incapable of appreciating the fact that the little blind abscess at the end of a root with the mildest kind of a strep- tococcus infection is the most dangerous factor that can be left in the human mouth. It can now be seen that the non-hemolytic strep- tococcus of low power of virility (so low that it is incapable of pro- ducing sufficient inflammation to produce the slightest perceptible irritation) is continuously sending a small quantity of toxins through the system. It is fortunate that a stage where these facts have been substantiated by exact laboratory study has been reached. No longer can the pompous practitioner assert, "my opinion is as good as yours." He must be made to realize that this subject has passed the stage of theory to one of established scientific proof. While, therefore, the future practice of dentistry is destined to bring the practitioner back to the point of extracting a great many more teeth, the greater value of the natural teeth over anything artificial must not be overlooked. Efi'orts at conservation of hiunan teeth should not be lessened wherever such a consummation is feasible. Although the operative technic of root filling does not come within the sphere of the dental hygienist, the writer feels warranted in giving in detail the technic of the improvement to which he has been giving continuous attention for over thirty years, so that this most important operation in dentistry may be clearly understood. It is his fondest hope that in the future someone will unearth a method PERICEMENTAL ABSCESS 281 that will be less laborious and require less time, but up to the present this procedure appears to meet the demand more thoroughly than any other. Only since the introduction of the .r-rays has it been possible to place root-canal therapy on a scientific basis. It is the most important aid at the command of the dentist today in performing a scientific opera- tion. It is continuously required from the outset to the conclusion of the work. It is important before beginning, to have a roentgenogram that will give a general outUne of the anatomy of the roots and indi- cate if any pathological condition exists, and the visible extent to which tissue destruction has taken place. The first essential in the mind of the operator, should be that when the operation is completed, the filling material must seal the peri- apical end of the root, and consequently he must be able to pass a broach through every foramen. To accomplish this it is essential that the point of entrance to each root canal should, as nearly as possible, be on a straight line with the foramen at the end of the root. By the aid of the .x-rays this is reduced to a geometric problem, and many teeth can have apparently badly curved roots straightened by making the point of entrance at the correct spot. In attaining this object, no consideration must be given to conservation of tooth sub- stance. Having solved the geometric problem, it is best to remove at the start as much of the crown as it will be necessary to remove at any stage. After some experience this can be readily gauged. Much time can be sayed, the work can be made less difficult, and better results can be ob- tained if the operation of removing every portion of tooth to be removed is completed before any canal is entered. There are cases in which it may be necessary to remove the entire crown, and where a root is to be crowned, it is naturally far preferable to do this at the outset. The operator must become thoroughly familiar with the ordinary anatomy of the different teeth so as to expedite matters as much as possible. Where living pulp is to be removed, it is supposed to be previously anesthetized. Before the pulp chamber itself is entered, the rubber dam should be adjusted and the field of operation carefully washed with alcohol or a ten per cent, solution of formalin. Every possible precaution should be taken to insure strict asepsis at every stage of the operation. If a live pulp is to be removed, a perfect Donaldson bristle is selected, after the barbs have been carefully scrutinized under a magnifying glass to insure against the fracture of a defective broach. The fine Donaldson barbed broach is then passed gently alongside of the pulp tissue as near the end of the canal as possible. Only practice can bring the skill that the delicate manipulation of this broach requires. It might be said that firmness and exquisite delicacy of manipulation is a combination of application that is neces- sary in the use of the broach. It is requisite, in the manipulation of the broach or in any other 2S2 ODONTALGIA AND ALVEOLAR ABSCESS form of canal instrumentation, that the operator's attention should never be deflected in the sliglitest, because of the danger of breaking an instrument in a root canal. The same care in instrumentation is necessary if the pulp be dead, lender such circumstances, too much attention cannot be devoted to avoiding the forcing of any infected material, however minute, through the foramen. It is frequently an error of judgment to prolong instru- mentation too far. After the removal of all masses of tangible tissue, whether living or dead, or in any particular degree of decomposition, chemical measures must be employed. For this purpose recourse may be had to sodium and potassium, (kalium-natrium). This unique mixture of metals was made by Dr. Emil Schreier, of Vienna, over twenty-two years ago, and to those who have learned its merit, it is unquestionably the most valuable means at our disposal in root-canal therapy. It has an intense affinity for water, and as a result unites with any form of organic matter with such great avidity as to produce immediate oxidation of everything connected with the union. Thus, a given quantity of sodium and potas- sium imites with a given quantity of organic tissue, and the result is complete destruction of that much organic matter. Only a portion as large as a pin-head should be introduced at one time, on account of the violent reaction which takes place. In the case of a putrescent canal, as soon as a point has been reached where there is the slightest danger of forcing infection tlirough a foramen, instrumentation ceases, and sodium and potassium is utilized. On the end of a barbed broach a very small quantity of the medication is introduced into the canal. The result is flame, smoke and gas, and when this has subsided we introduce another particle^ our broach constantly passing nearer the end of the root, until finally ever}- particle of putrescent matter has disappeared, and the broach has passed through the foramen. Properly carried out, one need not fear, with this technic, that septic matter may be forced through the foramen, and when irritation results, which rarely occurs, it will subside within from twenty-four to forty-eight hours. In the removal of living pulp tissue, the sodium and potassium unites and destroys all of the immerous shreds of organic matter that are found at the orifices of the dental tu])uli. This destruction proceeds some distance into the tubuli. Only when all chemical action has ceased, and the broach has passed through the foramen, can it be said that the canal is void of organic tissue. In the removal of living pulp, this result is never i)ossiblc until the second or third sitting. There is then no longer any anesthetic condition, l)ut generally some sensa- tion remains until the last particle of ]:)ulp has been removed, when what is left of the medication becomes inert in the canal. The greatest value of this material is found in chemically reaming such canals as appear impossible to penetrate on account of })eing occluded with calcified matter. In all such cases some organic matter PP.RWEMENTAL ABSCESS 283 is always present even if it is not perceptiljle to the naked eye. As long as the slightest moisture is left, the kalium-natrium will destroy this stratum of tissue. When at times the kalium-natrium becomes inert on account of the absence of moisture, it is necessary to moisten the canal with a few drops of distilled water. After some progress has been made in blazing a path in the canal, a fine, sharp-pointed instru- ment, made of superior hard-tempered steel, is introduced into the fine opening. These instruments are called dental picks, and with the organic strata removed, it is not difficult to break up the calicified mass into very fine fragments, which cling to the picks and are readily removed when fresh sodium and potassium is introduced. The repe- tition of this technic will finally succeed, not only in carrying the broach through the foramen, but also in widening the canal sufficiently to make it readily accessible to the canal plugger. Often it is impossible to pass the broach through all the foramina until the patient has had a mnnber of sittings. The operation can cease at any point. The use of sodium and potas- sium has rendered the canal aseptic and no medicament of an}' kind should be placed in the canal. The general practice of sealing in the canal some • antiseptic remedy cannot be too strongly discouraged. If there is any abnormal pathological condition at the apex, it will usually be obscured by the drug. Then, again, it interferes with that absolute cleanliness of root struc- ture which the operator is exerting every energy to attain. When ready , !• • ,1 ," , n 1 ] • ' FiG- 121. — Roentgenogram to dismiss the patient, a fine gold wire ^^^^^,.^^ ^.^i^ ^,.^^^ ^^^^.^^^^^ ^^e should be passed up the canal as far as foramina. possible through the foramen, when this can be done. The external end of the wire is then bent so as to make it easily removable. A small dressing of sterile Japanese paper or cotton is now packed around the wire to prevent the ingress of filling materials, and the cavity is sealed with base plate gutta-percha. The tooth is then radiographed and the picture discloses whether the wires have passed through the foramina, and if not, how far they are from the root end (Fig. 121). Not infrequently it will be found necessary to cut away more tooth structure in order to permit the broach to enter at the correct point, which the gold wire now for the first time discloses. These wires become most valuable for diagnostic purposes in teeth having pulp nodules and canals impacted with calcified matter. A stage has now been reached where it can be consistently said that the canals are clean. The roentgenogram shows the wires through every canal foramen. The canals are now washed out with a solution of 1 part of sublimate to 500 parts of hydrogen peroxide (Marchand or 284 ODONTALGIA AND ALVEOLAR ABSCESS similar). This solution, after the canals are dried, will leave traces of sublimate along the orifices of the tubuli. If there is any diseased area in the peri-apical region, it has not up to this time been disturbed, but is now ready for extirpation. The canals are now flooded with physiological salt solution. The negative pole of a galvanic rheostat, properly constructed for this purpose, is now attached to some part of the cheek by means of a wet sponge (Fig. 122). The positive pole consists of a wire of chemically pure zinc, which is held in the different canals in turn. Care must be taken not to allow the zinc point to pass through the foramen or to occlude the opening, so that it may not interfere with the egress of gases (emanating from the peri-apical area when the granuloma or other form of pathogenic tissue is being destroyed) through the tooth. These rheostats are worked by a shunt system, so that the amperage can be gradually increased without causing any discomfort. One or two milliamperes of current is generally easily borne, and the anode should remain in each canal from five to twenty minutes. In this manner ions of electricity, together with nascent chloride of zinc, are forced through the foramina. The tubuli themselves are thus placed in an absolutely germicidal state. Any ordinary granuloma can be entirely obliterated in this way, to be followed by the growth of new alveolar structure if no place is left for any invading bacteria. When, however, the cementum of the root itself has become necrosed, apicoectomy must be resorted to after the root filling has been completed. The root canals are now ready for filling. The first essential for the root filling is that it should be easily forced through the foramen; it should be most compatible to the dental structures, indestructable and void of any irritating properties. As long as the filling material fails to encapsulate the outside of the end of the root it is inviting reinfection. Paraffin always presents the possibility of becoming absorbed, and is therefore contra-indicated. Cements composed of oxy chloride of zinc, or containing any irritating substance like formaldehyde, are con- tra-indicated. No cement substance can be depended upon to fill compactly every crevice and deflection of the normal canal, to say nothing of the miniature foramina that are found. The frequent discovery of foramina on the side of the root makes it essential that the canal should be filled with a solid homogeneous mass, unchangeable in its nature, and which will hermetically seal the mouth of every dentinal tubule. Gutta-percha meets the requirements of an ideal root filling better than any other material. Points made from base plate gutta-percha are selected of a diameter which will enable them to go to the end of the canal. They are placed in a 10 per cent, solution of formalin, so that their surfaces will be aseptic. The canals are thoroughly dried with warm air. A fine broach, upon which are twisted a few fibers of PERICEMENTAL ABSCESS 285 cotton, is dipped in a very liquid solution of chlora-percha; this is carried to the very ends of the canals. With an aseptic pair of tweezers Fig. 122. — Specially designed rheostat. 286 ODONTALGIA AND ALVEOLAR ABSCESS the gutta-percha point is taken from its bath, is carefully dried in an aseptic napkin and gently carried into the canal. A plugger, which will pass to the end of the canal, is dipped into alcohol, ignited at a lamp, and the warm plugger firmly but delicately forces the gutta- percha point to the end of the canal. One or two more fine gutta- percha points are introduced in this manner. A small piece of Japanese paper is then twisted around the plugger; this is soaked in chloro- FiG. 123. — Roentgenogram showing end of roots encapsulated with gutta-percha root fillings. form, then passed into the canal, and the gutta-percha repeatedly packed with this chloroform tampon. This causes the gutta-percha to become soft and, under pressure, makes it pass tlu-ough the foramina and into every depression. Fresh gutta-percha points are treated in the same manner until the filling is complete. With cold air every particle of chloroform is volatilized, and it is then covered with an oxy chloride of zinc cement in order to prevent infection tlirough the crown. Fig. 124. — Roentgenogram taken two years after aljscess had been eradicated by ionism. It shows regenerated alveolar structure and protruding gutta-percha root filling enmeshed in the bone cells. 'ilie tooth is now again radiographed in order to determine if the end of the root is encapsulated with chlora-percha (Fig. 123). If the root filling has not passed through the end of the root, it be- comes absolutely necessary to remove all of the root filling and again attemj)t a ccjrrect filling. ""J'he final roentgenogram is essential in determining whether the tooth has been left safe from the possibility of reinfection. When this procedure has been correctly carried out, PERICEMENTAL ABSCESS 287 there can be no possibility of reinfection, and in time new alveolar structure will be found in the peri-apical region, as is shown in Fig. 124. There remains one class of cases in which it is impossible to eradi- cate the pathological condition by means of ionism. Whenever any part of the cementum of the root is necrosed, surgical interference becomes imperative. Usually nothing short of root amputation will absolutely cure these cases. Unfortunately it is not always possible in the reading of the roentgenogram to know whether or not the root surface is necrosed. The great advantage in being able to cure such a large number of peri-apical infections by ionism makes it better practice to try ionism in all doubtful cases. When this has failed, root amputation takes its place as the correct procedure. It must, however, be understood that like all other measures, it must be applied in such a manner that no pathogenic spot remains. Imperfect surgical operations are, like imperfect root-canal technic, absolutely valueless to the patient. CHAPTER XII. DENTAL PROPHYLAXIS. By ALFRED C. FONES, D.D.S. THE CELL. Ix order to appreciate health it is necessary to be famihar with the facts concerning the individual cell, and the effect of various influ- ences upon the unit must be studied before an understanding can be had of the action and influence upon the cells in the aggregate. If a drop of water is taken from the side or bottom of an aquarium and put in a glass under the microscope, a minute jelly-like mass may be seen. Its outer circumference slowly changes its shape, while near the center there is a very minute globule termed the nucleus. This is the lowest and simplest form of animal life and is known as the ameba. This simple cell has seven distinct properties. It may extend its wall in projections like false feet or protuberances or may flatten itself out in a long line, therefore it has the property of elongation. When irritated by being brought into contact with dilute acid it will contract into a round form; hence, it has the property of contraction. These two properties give it its power of motion. It appreciates the presence of irritants, of food and of thermal changes, therefore it has the power of sensation. It can digest food and discard waste tissue, therefore it must have the properties of secretion and elimination. The cell and nucleus have the power of dividing themselves in two, thereby forming two cells. It has the power of reproduction, and the new cells have the property of gro^^i:h. When all of these functions or properties of this simple cell are work- ing normally, the ameba is in a state of health or balance. Rob it of one or more of its properties and it is diseased. Stimulate the cell by applying certain agencies and its motions become more rapid, it consumes its food more rapidly, it will subdivide and reproduce itself more rapidly. A greater stimulant will cause a still greater activ- ity', but if this is continued the cell soon becomes exhausted and par- alyzed from exertion and the ultimate result will be death. The reverse takes place under sedation produced by applying cold. The motions become slower, also digestion and reproduction. If the temperature is dropped too low, the cell dies. Pollute the water or rob it of its oxygen and the cell dies. Cell life is maintained chiefly by a chemical process of oxidation. It must have water and it must have a food sup- ply to replace the lost substance which is gradually being utilized THE CELL 289 in performing its various properties and functions. It is therefore apparent that cell life is dependent upon oxygen, water and food, a proper temperature and removal of waste matter. Nature, in the building of all matter, builds from the unit. Although the atom is the smallest unit, the molecule of the mineral kingdom and the cell of the animal and vegetable kingdoms are the general bases for study. All earthly creations visible to us are formed on this one plan. The trees, the flowers, the grass, the mountains, the beach, the sea, all animal life, including man, each is made by the combining of these units, all working with an intelligence and subject to chemical laws far beyond our comprehension. Why it is that the contents of the cell, which is called protoplasm and which appears to be nothing but a jelly-like mass, has the property of manifesting life and intelligence, is difficult to understand. This substance can be analyzed and even the proportion of its elements estimated, yet what unseen force imbues it with energy and intelli- gence and what becomes of this life-giving power when the cell dies and disintegrates, is not known. Cell action can be studied, and the cell can be supplied with the essentials for growth and development. It is a realized science that in animal life, certain factors properly applied at the proper age can greatly develop its function and intelligence, the same as in vegetable life, but it cannot be explained. It is known that all manifestation of life and of intelligence is expressed through this matter contained within the cell. In the gradual evolution of these simple cells like the ameba, com- bining to form larger and more complex organisms, it is fovmd that the cells choose a specialty of two or three of these properties, and those whose specialty is the same are grouped together. As animal life develops into higher planes the cells become more proficient in their specialties, until in man is found the greatest variety- of highly special- ized cells in animal life. While the ameba possesses a balance of seven properties, some of the specialized cells of man concentrate on but one function. It may now be seen how these cells of man that have under- gone a slow evolution of millions of years to reach theii* present degree of intelligence are reflected in this low and simple order of life — the ameba. It has been stated that the ameba has seven properties. Its power of contraction is exemplified in the muscle cells of the human body, whose specialty is contraction. These cells are capable of wonderful development and training. The finger touch on the piano keys, the surgeon with his instruments, the dancer, the juggler, the athlete, the artist, and the artisan, all demonstrate how these minute individuals receive impressions from the brain and nerve centers and interpret them with such wonderful intelligence. The nerve cells specialize on the transmission of sensation and vibratory influences to and from the brain. Digestion and elimination, being very much more complicated in higher animal life, require innumerable cells which perform separate functions — the passing on of food, the secretion of 19 290 DENTAL PROPHYLAXIS fluid for its solution and its preparation for absorption. In the blood stream are cells floating along, each intent on its special duty. The liver, with its cells actively engaged in preparing the waste pro- ducts for elimination by the kidneys, the sweat glands, the lungs, the brain (that wonderful terminal station, headquarters for all orders), all are composed of these specialized units working together like so many people in an immense city, each adding his mite in labor and service for the common prosperity and health. The intelligence displayed by the individual cells of the body is the marvel of scientific investigators in physiology and pathology. jNIuch is yet \\Tapped in mystery and many years will pass before some of the deep problems of nutrition and the hard-fought battles waged against disease will be fully understood. When the body is abused this abuse is imposed upon millions of intelligent beings who do their utmost to offset ignorance and wilful acts by patiently combating the impositions and trying to correct and repair the damage wrought. In early youth the cells are in abun- dance and the supporting structures are but partially formed. In adult life the work of the cell is completed, and the intercellular struc- ture is in predominance. The great period for structure building and for the guidance of proper cell development, physically and intellec- tually, by applying scientific factors to properly influence this result, is from infancy to twelve years of age. As a spider spins his web so do these minute cells create tissue to aid them in their work. The individual reflects the composite texture and make-up of the aggregate cells of the body, and the period for molding, refining and advancing this cell development to its high- est plane is in early youth. Factors for Cell Life. — ^The scientific factors for infiuence are numer- ous, but there are a few that stand out conspicuously. First of all comes pure air, for cell life is dependent upon constant oxidation. Next comes a proper food supply. The character of food will eventu- ally determine the character of the cell, and as the body is physically composed of millions of cells, the food supply in a great measure determines the character of the individual. This is exemplified in the glutton, the drunkard or the savage. What is eaten, how much is eaten, and the manner in which it is eaten, are some of the chief factors for health balance. The question of food values, the quantity consumed and the importance of thorough mastication and insalivation should be a study for all hygienists. Next comes cleanliness, for if disease is to be prevented clean food, clean water, clean mouths, clean bodies and clean environments are necessary. Mental attitude is another powerful factor and should have fourth j)lace. Self-control, oi)timism, that mental poise that can discard fear and worry, that holds an even balance under varying circumstances and that can radiate good cheer and kindness through their health-giving influences to every cell of the body, are elixirs THE CELL 291 iineqiiak'd in the buildiujij of the charaeter as well as. in regulating a perfect balance and functioning of the entire system. Although heredity, too, plays a strong part, yet the first four factors named can greatly modify the inherited disposition of the cells if wisely applied. When we speak of coarse natures, we speak of an imfortunate inheritance of a type of cell life that might have been greatly softened and modified in childhood. Exercise is also exceedingly important, for rest means rust even in animal tissue. If man lived what is termed a "natural" existence, which means, in other words, an outdoor and primitive life, with simple coarse foods and work or exercise in the open air, which develop the animal side, there would be but little need of the physician or the dentist. The coarse food would mechanically clean and polish the teeth by friction, and the out-of-door exercise or work would cause an enforced breathing which would mean a greater intake of oxygen to burn up the slag and waste products in the system. But this so-called natural existence is not possible to 70 per cent, of the people of the present day. Their very existence depends upon their work or artificial life in the cities, and the yearly increase in numbers in the cities rather proves the preference for the city over the country. Therefore this health problem of city life must be solved. The factors which are productive of health in the animal life must be substituted artificially. The passing generation cries that children are being brought up too much by the teaching of science and the book instead of in the good old-fashioned way of letting nature look after them. Take, for ex- ample, the wild rose of the field that depends upon sunshine and shade, warmth and moisture and proper soil for its growth. Natiu-e does not and cannot always supply these in sufficient degree and in proper bal- ance, and although the flower is beautiful it cannot be compared with the beautiful rose that the horticulturist can grow when these essen- tials are scientifically and artificially supplied. In the hot-house the correct temperature can be maintained, moisture in sufficient quan- tity supplied, sunshine and shade regulated at will and fertilizers essential to stimulate growth added to the soil. The work of Burbank in scientifically handling vegetable life is well known and our modern methods of agriculture and fruit raising. The w'onderful feats of the horse, hurdling, running and trotting are due in great measure to the scientific training by man. Many instances can be given in which nature far excels her natural state of environments if the essential factors she needs are supplied artificially and scientifically^ in sufficient abundance and degree. And so it is in the growth and development of the city child, and even in that of the adult. If the proper factors for health can be scien- tifically administered, it is possible to grow children as far superior to those of the present-day average in the public schools as the American Beauty is superior to the wild rose. Man has had his progressive period; woman is having hers. The coming one belongs to the children. 292 DENTAL PROPHYLAXIS THE ALIMENTARY TRACT. Before confining thought and attention chiefly to the teeth and their surrounding tissues and considering how disease may be prevented, a few simple thoughts regarding the body must be presented, that it may be better understood how important a part the mouth plays for health or for disease. There is no better way of doing this, perhaps, than first to consider a country with its many people, and show the factors upon which it is dependent for health, for a close analogy may be drawTi between the life of a simple cell, the individual and the nation as a whole. Egypt is the best for illustrating this thought, for here is found a strip of life running through a region of apparent death. Suppose a piece of green cloth, six inches wide and a hundred feet in length, was laid on the sands of the seashore, running straight upon the beach from the water's edge. If in the center of this cloth was laid a long white string to illustrate the river Nile, it would be a fair repre- sentation of Egypt. The Nile runs through a desert and the water with its life-giving power has created a living body close to its borders. In this living body are millions of people who are dependent upon this alimentary tract or river for their existence. Along the banks may be seen the water buckets, operated by the natives to supply their fields and gardens. In the season of the overflow the soil is soaked with moisture, the crops are plentiful and there is ample for those who will work. Canals or arteries lead from the river bank across the fields to supply life and growi:h to the soil that would be desert waste with- out it. If it were possible to poison the source of the Nile so that its waters carried their life-giving properties no longer, but contained some chemicals that were destructive to plant life, or sufficient sewage to poison the inhabitants, Egypt would soon cease to exist. Just in proportion to the amount of poison carried down the river would the country and people suffer from starvation and disease. The bodies of all animal life are constructed around their alimentary tract. The lowest forms of cell life when changing to a higher organism, find it essential to develop first a mouth and digestive tract, for the intake of food, is of first importance with all material life. The body with its millions of cells is dependent upon the flow of nourishment through the alimentary tract and as the individual lives and feeds so will his body thrive or deteriorate. The mouth is the vestibule or gateway to the whole system. All the nourishment and food supply to the body must pass through this one portal. The placing of the food in the mouth is a voluntary action and it can be controlled as long as it remains there, but the moment it is swallowed it is beyond voluntary control and is sent on that mysterious journey called digestion, absorp- tion and assimilation. Assuming, first, that the food eaten is clean and pure and above criticism, and enters a clean mouth, is properly masticated and swal- lowed, digestion takes place normally, provided the mental attitude THE ALIMENTARY TRACT 293 be one of tranquility during this period. If the mind is excited or irritated, it will send depressing messages throughout the body and the process of digestion is retarded and disturbed. Under such clean conditions the normal processes of digestion can take place with a minimum amount of effort and energy being expended by the tissues in their work, and the product after digestion is fit for the blood stream to offer to the cells of the body the nourishment they need to perform properly their respective functions. But the reverse situation exists regarding the mouth. The food may be clean and pure but the mouth unclean. Decomposing Food Debris. — In discussing the harmful effects of decomposing food in the mouth, the subject cannot be better presented than by giving some of the thoughts of Dr. E. C. Kirk from a paper read by him in Providence, R. I., October 16, 1900, and published in the Dental Cosmos in May, 1901, entitled "Some Considerations Relative to the Infant jNIouth." Regarding the artificial feeding of infants he refers to the training of the nurse to sterilize the milk and feeding apparatus in order that the milk shall be delivered to the child's stomach free from bacteria " which when present in the food supply so alter its composition as to reduce its nutritive value and, what is still more important, set up decomposition processes within the alimentary tract of the infant which are direct causes of irritation and disease to the infant organism." Great care having been taken in preparing the food and in feeding, no attention was paid to the film of milk left in the mouth after feeding. It is apparent that if fresh milk is poured into a bottle that has con- tained sour milk, infection of the fresh milk will immediately take place. In the feeding process the sterile milk passing over the infected surface caused by the residue of the last feeding at once infects the milk. Dr. Kirk says, "There can be but one result; fermentation of the infected fluid begins in the stomach; putrefaction of the proteid ele- ments may take place; quantities of gas are formed, distending the walls of the stomach and intestines, causing pain and irritation, further increased by the irritating effects of organic acids ^\%ich are end-products of this fermentative process. Digestion is interfered with or arrested, the fermenting mass of food becomes a mechanical as well as a toxic irritant ; diarrhea sets in, the whole nutritional process is interfered with and development is damaged in proportion to the length and severity of the attack. " The rational remedy for this state of affairs is clear when once the conditions to be therapeutically met are understood. In the first place, removal of the primal cause by thorough oral cleanliness and sterilization in so far as that end may be obtainable. This may be practically accomplished by wiping the mucous membrane with a saturated solution of boric acid to which borax has been added in the proportion of ten grains to the ounce, or with a very dilute solution 294 DENTAL PROPHYLAXIS of phenol sodiqiie, one-half dram to the ounce, applied on a cotton swab or with a soft linen handkerchief \ATapped around the finger of the nurse." Now apply the same principle to the growing child and to the adult. The teeth of a child between the ages of six and twelve years will present surfaces equal to twelve to sixteen square inches. In an adult the surfaces wUl average about twenty-five square inches. This means that if it were possible to peel the enamel off of each of the five sur- faces of each tooth and place them side by side they would cover a piece of glass three and one-half inches square in the case of the child, and in that of the adult a piece about five inches square. This will give a rough idea of the amount of surface presented in the mouth to permit of the retention of a certain quantity of food that must decom- pose unless it is removed. The more perfect the teeth regarding form, occlusion and enamel surface, the more self-cleansing they are, and proportionately, the amount of food so retained is comparatively small. The mouths that present such ideal conditions are rare, espe- cially among those who are born and live in the cities. Where the teeth are irregular in shape and position, are decayed and broken down, the amount of food that remains is considerable and the volume of decom- posing material constantly being swept mto the intestinal tract will eventually breed illness. In a growing child such mouth conditions are vicious. "Suppose," said a prominent educator in dentistry, "that a prescription was given to a mother by a physician, to mix, with each meal that the child ate, a half-spoonful of garbage. Would she carry out such a prescription, and if she did and the child became ill, would not the physician be liable for damages?" And yet in reality that is what is taking place in the average* mouth of the children in our public schools and in the mouths of the great working classes. This constant drain of poison into the intestinal tract in child life causes an intestinal indigestion where bacterial products are absorbed into the system and produce fevers, headaches, eye-strain, anemia, malaise, constipation, and dizziness, Nature finally takes away the child's appetite and forces it to bed until a good house-cleaning of the body can be accomplished. These poisons from the mouth are insidious and slow in action. Many can and do withstand them for years, but as the constant drop- ping of water will wear away the stone, so will the products of decom- posing food in the mouth soon destroy good digestion and undermine the system. Vaughn and Novy, in their book entitled Cellular Toxins, say, "The effect of a chemical compound upon the animal body depends upon the conditions under which and the time during which it is admin- istered. Thirty grains of quinine may be taken ))y a healthy man (hir- ing twcnt.y-hnir hours without any apprecial>le ill-effect, yet few would be willing to admit that the administration of this amount daily for months would be wise or altogether free from injury. In the same THE ALIMENTARY TRACT 295 manner the administration of a given quantity of a bacterial alkaloid to a dog or a guinea pig in a simple dose may do no harm, while the daily production of the same substance in the intestine of a man and its absorption, continued through weeks, and possibly years may be of marked detriment to the health." It must be borne in mind that the manifestation of sickness does not come from the presence of bacteria, but from the poisons generated by the bacteria. " Abbott in his book on The Principles of Bacteriology, quotes Roux and Yersin who claim that the potencies of the poisons that have been isolated from cultures of Bacillus diphtheria have been determined by experiments upon animals, and it has been found that 0.4 milli- gram is capable of killing eight guinea-pigs. Please remember that four-tenths of a milligram represents but y^^j part of a grain. Aside from the products of decomposing food in unsanitary mouths we must seriously consider how much of the bacterial poisons may be generated in such mouths daily by the millions of microorganisms present, and whether these poisons are not of sufficient quantity eventually to weaken the organism and render the body susceptible to infection from the pathological group of microorganisms. In the battle being waged against tuberculosis, this feature will be given much impor- tance and the day is not far distant when some scientist will be able to compute with a reasonable degree of accuracy how much bacterial poison can be generated in twenty-four hours in a mouth containing decayed teeth and food debris. Bacterial Propagation. — In considering the products of decomposing food with their detrimental action on the system, their action upon the human mouth, than which there is no better breeding ground for germ life, must also be considered. The mouth is an ideal incubator, for here we find all of the essentials for the propagation and develop- ment of these microorganisms. The right temperature, sufficient moistm-e, air, darkness and a menu to choose from that would tempt any member of this large family. Germ life is comparatively harmless when robbed of a food supply, but give it a pabulum upon which to feed, develop and multiply, and it becomes active and virulent. It must be borne in mind that all mucus-lined tracts of the body have their flora of microorganisms and that the individual must live among them, that the few friendly ones are company, but that too many are a crowd, and that in this crowd are our enemies who feed upon the host if they but get a chance. An unclean mouth means an increased number of bacteria, and with increased numbers come increased dangers from infection. The cavities of decayed teeth harbor millions of these mischief-makers, as do also the food debris and calcareous deposits around the necks of the teeth. They may enter the mouth in a very subdued state, but under these favorable environments they soon multiply rapidly. The usual order is to consider their activity and growth in unsani- 296 DENTAL PROPHYLAXIS tary mouths, but this will be reversed and the medium upon which they best are cultivated in the laboratories be first noted. The saprophytic class are those which exist upon dead animal or vegetable matter. The parasitic class prefers to gather its nourishment from the living host. [Many of both classes can live in either medium, as occasion demands. As the unorganized ferment of gastric or intestinal digestion has the power of changing the food by rearranging its elements, usually by a process of hydration, so do these microorganisms have the power of breaking down tissue or decomposing food and liberating its ele- ments in their search for carbon and nitrogen. The media chiefly used in laboratories for cultures of microorganisms are bouillon, gelatin, agar-agar, potato, sugar and blood serum. If these are kept at the right temperature at least to grow mixed cultures, the sapro- phytic class is quite easily developed, for the extracts of beef, sugars or starches form an attractive pabulum. Many of the parasitic variety can also be growTi in these substances, such as the typhoid bacillus, anthrax and others, w^hile the tubercle bacillus and the bacillus of diphtheria are cultivated in the blood serum. These culture media with the exception of agar-agar, are all found in the average mouth, even to the blood serum. When the teeth are decayed the amount of food retained in the mouth is considerable, but especial attention should be called to con- gested and bleeding gums. Here is an ideal medium for the propa- gation of infectious germ life, and it is not only the cavities in the teeth and the food debris, but also the pernicious condition of the gum tissue in unsanitary mouths, especially in those of children, that is of serious concern. The germs of tuberculosis or of diphtheria can here find a pabulum for their propagation and development, and undoubtedly the prevailing condition of the gingival borders of the gums is one of the most important steps toward infection. The bleed- ing and congested gums and the decomposing food is present, all that Ls now necessary is the bacterium. All observant practitioners will readily agree to the statement that mouths that contain no congested areas on the gingival borders of the gums are exceptions. The dark red surfaces will bleed upon the slightest pressure, and in between the molars and bicuspids where the food can lodge undisturbed in ill-kept mouths, even a slight suc- tion will start a copious l)leeding. It will be the privilege of the hygien- ist to note in the treatment of each new patient how easily the gums will bleed upon the slightest touch of instrument or porte polisher. The oozing of serum and blood from these congested points is of equal importance in the consideration of infectious diseases of children as the dec(jinposing of animal and vegetable matter found in the decayed teeth or around their surfaces. To those who have thoroughly inves- tigated the subject, the mouth is now conceded to be a most impor- tant field for bacterial growth and systemic infection. TUBERCULOSIS 297 Tuberculosis, — One of the greatest battles being waged in preventive medicine is the fight against tuberculosis, and this fight can never be won as long as the mouth conditions of the mass of the people remain as they are at present. Examine the mouths of the children in our large cities who leave school, say, at fourteen and fifteen years of age, and you will note that at least oO jier cent, of them have lost or are losing their molar teeth through decay. At the very start of their lives, then, the nutritional system is handicapped by the lack of power of the teeth to crush prop- erly the food which enters the alimentary tract. The bolting of food becomes a habit, the stomach is daily called upon to dissolve large particles, which means that the blood is retained in the stomach much longer than otherwise necessary, the glands become overworked in secreting sufficient gastric juice, an extra supply of blood is maintained in the digestive tract longer than necessary, and this means a lessened amount of energy to expend in physical and mental work. As to young women employed in factories, the sedentary life only adds to the weakening of the vital forces, especially if the ventilation is poor and the environments depressing. Add to this the lack of sani- tation found in such mouths and we can understand why it is that housewives rank second on the list in tubercular sanitariums, shop hands exceeding them in numbers by a small margin. When these women marry and bear children their forces are still further lowered until their resistive forces are so weakened that infection is a very small matter. The offspring of such a parent must necessarily be a weakling, especially in youth, and its tissues most susceptible to tuber- cular infection. People so seriously lacking vigor, life and good spirits become the great "sick" class, and this class spells but one word • — poverty. Much stress is laid upon insufficient quantity and poor quality of the food supply as a great causative factor in this disease. This con- dition is brought about more through ignorance than because of lack of funds with which to purchase proper food, for the body can be well nourished daily for a very moderate sum if judgment and knowledge are used in the buying. Scientific investigators are now agreed that tubercular infection takes place through the intestinal tract much more frequenth' than previously surmised. In fact many pathologists insist that this is the chief path of infection. If this is true, the bacilli must either be taken in with the food supply in sufficient quantities to prove danger- ous, or they must find lodgement in the mouth in decayed teeth or congested gum surfaces where they become numerous and aggressive. In our state sanitariums where the tubercular patients are segregated, the mouth conditions are deplorable. It is true that with plenty of fresh air, good food and rest, the body can and does neutralize much of the poison. The resistive force is increased and the disease is pro- nounced arrested. The word cure is cautiously used. 298 DENTAL PROPHYLAXIS Could the mouths of these patients be made sanitary at the beginning of the treatment and rigid rules enforced regarding their daily care, a marked benefit would surely be observed. Systemic Infection. — If syphilis and wounds of the surfaces of the body are excluded, there are but three ways, ordinarily, for bacteria to gain entrance into the blood stream: (1) through tooth passes, such as root canals and diseased peridental membranes; (2) through the tonsils, and (3) through the intestines. Infection through the tonsils or through the intestinal tract is dependent in a great measure on mouth conditions. If unsanitary or septic conditions exist in the buccal cavity, many bacteria in a state of virulency are constantly drained over the tonsils and into the stomach. Any physical depres- sion that lowers the normal resistance of the body, might permit of the invasion of these pathogenic organisms. When the mouth is clean and wholesome, the liability to this form of infection is greatly lessened. The greatest sources of systemic infection are through the root canals of decayed and pulpless teeth, and infected peridental membranes. A streptococcus may be non-pathogenic and non-hemolytic in the fluids of the mouth, yet, if ingress be found through the root canal to the apical space, the character of the organism may undergo a change and become pathogenic in its new environment. Bathed in serum and compelled to secure nourishment from the new source, it may develop the power of dissolving blood. If conditions are favorable and it is swept into the blood stream through the lymphatics, or if it pene- trates the walls of the capillaries, its lodgement in some other tissue or organ of the body will set up a local and a systemic dis- turbance that will cause a serious illness, with possible death, to the individual. Pyorrhea alveolaris is an infection of the peridental membrane. Should the tooth become loosened from the disease, and pus exude from the socket, the play of the tooth up and down in its socket during mastication acts like a pump, and forces the bacteria through the walls of the capillaries into the blood stream. Another short period of scientific investigation will substantiate the fact that tooth passes constitute one of the greatest sources of systemic infection. In order to secure all possible results from practising mouth hygiene, our efforts should be concentrated upon the children in our public schools. Here we will find the source where most of the evils of adult life have their origin, and not until this work is started and seriously carried on in our public schools can wc hope to wi])e out infectious diseases, or preserve the teeth, or get control of dental decay with its attendant ills. Seemingly defective eyesight in childhood is commonly caused by the poisonous ])roducts of mouth iufcction al)Sor})cd from the alimen- tary tract. What seems to be astigmatism disapi)ears when decayed teeth are filled, mouth hygiene practised, and the digestive tract cleaned up. THE PRINCIPLES OF DENTAL PROPHYLAXIS 299 Anemia can in a great measure be traced to the same source, and there is no doubt but that better mouth conditions will greatly aid the medical inspectors to solve this problem, THE PRINCIPLES OF DENTAL PROPHYLAXIS. The initial cause of nearly all the pathological or disease con- ditions of the tissues of the mouth is the combination of microorgan- isms and food debris. Bacteria alone or food debris alone would be quite harmless in the mouth. Nearly all germ life, in order to become virulent, or its presence dangerous or even objectionable, must have a pabulum upon which to thrive. It is therefore dependent upon some attractive food supply in order to reproduce and multiply. It is known that foods will "spoil" if allowed to remain in a warm tem- perature for any length of time, and that in order to prevent this action the germs are killed by boiling or heating the food, tightly sealing it from the air in cans or jars that have just previously been boiled or have had boiling water poured into them, and allowing them to stand long enough for their surface to become sterilized. Food may also be placed where it will be kept cold, as in an ice-box, where the presence of the ice will so reduce the temperature that the organisms are rendered sluggish and inert. For years, many efforts have been made to find some drug or chemical that could be used in the mouth to kill all bacteria, and thus make the mouth sterile, or at least to render them inert. The futility of even hoping for a sterile condition of the mouth has long since been demon- strated. It is impossible to sterilize the human mouth, and even if it were possible, such a condition could be maintained but a very short time. Therefore, if it is impossible to keep the mouth free from bacterial life, and as the combination of food debris and bacteria is the chief cause of dental diseases, is there not some way in which the food debris can be thoroughly removed? It is upon this thought that the principles of prophylaxis are based. Dental prophylaxis is that scientific effort, either operative or thera- peutic, tchich tends to prevent diseases of the teeth and their surrounding tissues. Correcting and restoring to normal function all abnormal or pathological conditions of the teeth, and maintaining that normal condition, is a prophylactic procedure. This includes practically all the operations in dentistry. The mere filling of a tooth cannot be termed prophylactic unless the operation is performed with a knowl- edge and skill that tends to prevent future decay at that point and that will restore the surface of the tooth to normal contour and normal function. Crowns and bridges, root-fillings, approximal fillings with proper contact points, and smooth, flush margins, the correction of malocclusion, the removal of all calcareous deposits, polishing, the insti-uction in the proper home care of the mouth, may all be made prophylactic if properly done. 300 DENTAL PROPHYLAXIS Field of Service. — The exposed surfaces of the teeth, the necks of the teeth directly under the free margin of the gums, and the gum tissue itseh', are the parts of most concern to the dental hygienist. Bearing in mind that from now on the battle is to be one of extreme cleanliness on the one hand, and on the other an effort to starve and render inert the bacteria, the mouth of the average adult may now be examined. It is first noted that the enamel is without luster and covered with a pasty and colorless film. The necks of the teeth are stained; calcare- ous deposits are seen on the inside surfaces of the lower incisors and also on the buccal surfaces of the upper molars ; if there are gold fillings, they are tarnished and spotted with dark stains; other fillings in the teeth are rough and the margins are extended beyond the tooth surface so that the}^ hold particles of food debris. The gums are quite a deep red in color, especially upon the gingival borders, and if they are pressed upon even lightly by an instrument they will bleed. Between the teeth may be seen food debris, and at these points the gums will bleed copiously if wounded. Even if there are no decayed surfaces of the teeth, although the chances are there are many, the whole mouth presents an unsanitary condition that means a breeding-ground for mil- lions of microorganisms and a menace to the health of the individual. It must be borne in mind that these people should not be censured for this condition of their mouths, for the chances are they have never been trained or taught how to care for them properly. No one has taught them how to use the tooth-brush or the floss. No one has been careful to see that the fillings were smooth and polished so that they would not retain food. Nor have they been taught the necessity of brushing their gums or been advised as to how the mouth should be properly taken care of. So it is the duty of the hygienist to be kind in her criticism to these patients, and it w411 be found that the great majority of them will be only too glad to reform and faithfully follow instructions W'hen they are once enlightened. The dental hygienists are to be the educators, to spread the gospel of cleanliness, and to aid both children and adults to keep well. Many times mouths will be found that are not as they should be; some may be quite shocking in fact, but it must be remembered that the chief mission is to treat and help others to know how to keep well, and after these unsanitary mouths have been seen to grow and develop into healthy ones under prophylactic skill and instruction, it will be realized that the service of the hygienist to humanity is a very important one. Analyze one of these unsanitary mouths and study the conditions that are present. If the mouth contains alloy fillings the surfaces should be examined and also the margins of the fillings to see if they are rough. If so, the dentist must carefully grind and polish them in order that the results which may be expected from prophylaxis may be secured. If these alloy fillings are in the approximal surfaces of the teeth and the space between them is sufficiently large to permit the food to be squeezed down between the teeth and to injure or inflame THE PRINCIPLES OF DENTAL PROPHYLAXIS 301 the gum tissue, then the dentist should aid the hygienist by removing these fillings and replacing them with smoothly finished ones having proper contact points that will prevent the food from getting between the teeth. If there are gold crowns or banded crowns that do not fit tightly to the tooth or root and that will permit the end of the explorer to pass up between the root and the band or crown, it may be taken for granted that such a space is filled with decomposing food and is an ideal haven for bacteria. The odor arising from such crowTis after their removal makes one realize the necessity for tight-fitting bands and flush joint operations. Hygienists will come to loathe the average gold crown and will use their influence against their insertion. ]\Iany of them are sources of systemic infection and nearly all will destroy the peridental membrane around the tooth, and result in the event- ual loss of the tooth. Such dentistry is a serious menace to public health and has undoubtedly been the cause of many severe illnesses that have resulted even in death. If an ill-fitting gold crown is placed over a tooth containing a live pulp, it is but a question of time when the bacteria and the poisons generated b}' the decomposing process of the food debris lodging in the space under the crowns where the cement has disintegrated and washed away, will penetrate the dentin and infect and destroy the pulp. Alveolar abscesses from teeth carry- ing gold crowns are common. It would be far better for the patient who could not afford to have the work done properly, to have such teeth extracted. Ill-fitting bridges so constructed that it is impossible to properly remove the food with the brush and washes, will badly hamper work for mouth hygiene. It is not necessary to know the details of the work of construction of crowns or bridges or of fillings, but it is necessary to know what constitutes good dentistry and sanitary construction. A small pimple on the gum, termed by the layman gum-boil, is in reality a fistula opening from an alveolar abscess. The attention of the dentist should be called to these fistulse so that he may open the root canals and cure the abscess. The gum tissue should now be examined. The term congested gums is applied to enlarged capillaries, engorged with blood and having a sluggish circulation. External irritation from lack of use and func- tion in the mastication of proper foods is usually the cause for this congestion. The deep red color is due chiefly to the sluggish flow of blood laden with carbon dioxid. Perfect metabolism is not taking place in the cells of this tissue and the waste products are not being carried away with sufficient rapidity. Any local irritant on the sur- face or border of the gums will produce this congestion, and the mouths are rare that do not contain a number of congested surfaces. In children this condition is produced chiefly by the sharp edges of decayed or broken-down teeth, temporary and permanent, and sufficient blood and serum ooze from these blood-engorged surfaces to form an excellent culture medium for pathogenic bacteria. The 302 DENTAL PROPHYLAXIS protruding edges of poorly made alloy fillings and abscessed roots of temporary teeth are common causes for these red and bleeding surfaces. Every organism has its vulnerable or vital area which if sufficiently injured will eventually cause its death. The tooth is no exception to this rule. Its vulnerable point is the border of the peridental mem- brane directly beneath the gingival margin of the gum around the neck of the tooth, and this must be carefully safeguarded. This membrane forms the most vital part of the foundational structure of the tooth. Upon its health and resistance depend the function and life of the whole tooth. If it becomes injured, irritated or infected at its border and the lesion or infection is neglected, the membrane dies at this point, and in dying it causes the death and absorption of a similar area of the alveolar process which was in apposition to the affected membrane. This means a space or so-called pocket under the margin of the gum where food debris can find lodgement and where bacteria, well out of the currents of the saliva which flow freely around the teeth, can hold a tenable position. The rapidity of the progress of death and absorption is dependent upon the resistant force contained within the cells of the membrane and upon the virulency of the attacking microorganisms. In child- hood this membrane is thick and highly vascular and can resist almost any invasion of bacteria even when wounded, if not too seriously. In adult life it gradually becomes thinner, its blood supply is lessened, and as age advances the cells lose the high resistant force that they possessed in youth; and if the person is in what we call a run-down condition physically, from improper feeding of the body, unclean envi- ronments, harmful habits, excesses, or from any cause that will disturb the proper metabolism of the tissue by disturbing the nutritive or the nervous systems, the resistant force is still further lowered and the peri- dental membrane and the surrounding supporting tissues of the tooth become easy prey to the invading bacterial host. Although it will be possible to raise the resistance of this membrane again by prophy- lactic treatment and training of the patient in the proper methods of artificial stimulation, it can readily be seen that it is far more desirable to prevent the original disturbance at the neck of the tooth and save the patient the surgical treatment necessary in the hands of the den- tist in order to get control of this much-dreaded and serious condition of absorption and infection of the supporting tissues of the root of the tooth. It must always be borne in mind that the most important part of the tooth is the root and any irritation of the gingival border of the gum, especially in adult life, is a menace to that tooth which is in closest proximity to the point of irritation. PRACTICAL WORK. In considering the ])ractical work of dental prophylaxis the opera- tion in the mouth of the adult will be first described, for as a rule the PRACTICAL WORK 303 chiklrcM do not need iniich instrumentation and their cases are there- fore more simple. In examining the mouth of a new patient regarding the gum tissue and the surfaces of the teeth, the hygienist should make sure that the patient has removed all of the food debris from the teeth that it is possible to remove with the tooth-brush, floss silk and mouth wash. It is never the duty of the hygienist to operate in a mouth that contains food debris. For her own self-respect and for the dignity of her calling, she should make it an absolute rule never to start an oi)era- tion of prophylaxis when the patient has failed to clean his teeth of food debris before coming to her department. It is never her duty to remove food debris excepting the small quantities that roughened surfaces have made it impossible for the patient to remove. These cases will require some diplomacy on her part, for she must realize that the patient has not intentionally insulted her by presenting such an unclean mouth. It is merely that he has never been taught better. For years dentists have consented Avithout remonstrance to operate in the mouths from which the food has not been removed from between the teeth, and it will be one of the missions of the hygienist toward the uplift of the dental profession to teach the public that they must not present themselves for any dental service whatsoever unless their teeth have been thoroughly brushed and flossed. She should be kind and considerate in the handling of such cases, and tell the patient that there is danger of infecting the gum tissues if the instru- ments are used around the necks of the teeth where there is decompos- ing food, and that, in order to obviate any such danger it will be neces- sary for him to step to the bowl and thoroughly brush and rinse his teeth before the operation. A stock of tooth-brushes should be a part of the equipment of every dental office and should be charged up against the expense of dental supplies. The fifteen or sixteen cents the brushes cost, if bought in quantities, amounts to but little when we consider their absolute necessity for instruction, and their use when needed under these conditions. Patients soon learn the rules of an office and in a comparatively short time it will be a rare thing to be obliged to send a patient to the bowl to brush his teeth before the prophylactic treatment can be started. Much of the soreness of the gums after these treatments in the mouths of new patients is due to crowding some of this infected material under the gum margin with the instrument, and it follows that the cleaner the necks of the teeth are before instrumentation, the quicker will be the recovery of the congested gums after treatment. With a pledget of cotton soaked with peroxide of hydrogen, the necks of the teeth and also the approximal surfaces should be bathed. The boiling of the peroxide will mechanically aid in loosening minute par- ticles of food debris. After rinsing the mouth with warm water the teeth should be thoroughly sprayed on all their surfaces with com- 304 DENTAL PROPHYLAXIS pressed air and an atomizer. The air pressure should be at least twenty-five pounds, so that it may have enough force to blow the spray with sufficient speed between the teeth to aid in this mechanical cleansing. It makes no difference what liquid is used in the atomizer if it is harmless and has a pleasant taste. Surfaces of the Teeth. — ^It must be remembered that in this work hygienists are not to cross the border-line into surgery. The laws in all States prohibit surgical or medicinal treatment by any but graduate practitioners. Therefore the entire efforts of the hygienist are to be confined to the exposed surfaces of the teeth and the area directly under the free margin of the gum. The base of the crown of each tooth has four lines or boundaries. This is the entire field for the use of the instruments unless a root sur- face is exposed. It can be readily appreciated what a slow and pains- taking piece of work it is to go over carefully each of these surfaces and remove all of the deposits of tartar. In the first treatments of neglected mouths the deposits are likely to be large and are usually found on all the surfaces at the necks of the teeth. It is impossible to remove all of these deposits at one sitting without subjecting the patient to an unnecessary strain. The large deposits may be broken down and scaled off and many of the smaller nodules can be removed, but it is quite impossible to be really thorough in the first treatment. Again, it is unwise to subject the patient to a too strenuous session, for if they are timid, they are apt to become discouraged by the long and tedious sitting. It is far better to arrange two sittings of an hour and a quarter to an hour and a half each than one of two hours and a half. If the appointment is made for two hours, the balance of the time may be spent in polishing and in instruction of the home care of the mouth. The subject of calcareous deposits has been so thoroughly covered by Dr. Kirk, that it is unnecessary to go into the subject very deeply, but attention should be called to the irritating action they display in their porousness in absorbing liquefied debris, therefore forming an excellent retainer for bacteria. It is absolutely essential for the health of the gums and the roots of the teeth that all such deposits be removed at frequent periods. The time may come when people may be induced to eat the proper foods in proper quantities, then this deposit will be greatly lessened, but until this goal of good sense is gradually reached, artificial care of the mouth by prophylactic treatments will have to be resorted to. ^luch of the evil from the forming of serumal deposits in the subgin- gival space can be obviated by eliminating the congested condition of the capillary circulation found in the gum tissue of the mouth of the average adult. But the mouths are indeed rare in which no new deposits can be foinid imder the gingival border after a period of two months. System for Instrumentation. — In order to perform a prophylactic operation intelligently one must must work by system, and the instru- PRACTICAL WORK 305 mentation as well as the polishing must have a definite starting-point in the mouth and should always proceed in the same given direction over the surfaces of the teeth in the case of every patient. This is necessary for thoroughness and also in case of interruption, for if one will but note mentally the last tooth being worked upon before leaving the chair, the chain will remain unbroken upon resuming. It matters little what system is finally adopted, but the one here suggested will be advocated to start with. Lower Jaw. — Beginning at the lingual surface of the last molar of the right side, lower jaw, at the gingival line, distolingual angle, instrumentation puoceeds mesially until the lingual border of the left lower central is reached. The same direction is now followed but the 8 FINISH 1 START Fig. 125 line of operation becomes distal on the left side, still keeping on the lingual surface until the distolingual angle of the left lower last molar is reached. Again starting on the distobuccal angle of the left lower last molar, the instrumentation proceeds bucally and mesially until the left lateral is reached, where from this point the operation continues on the same surface to the distobuccal angle of the right lower last molar. The following cuts are taken from Plate VI of the American Sys- tem of Dentistry, and will, by the dotted lines and arrows, better illus- trate the directions followed as just described. Fig. 125 represents the teeth of the lower jaw with crowns excised at the gingival border. These cuts will illustrate the lines to be followed and field of operation to be covered by the dental hygienist with the instruments. 20 306 DENTAl PROPHYLAXIS As shown by the dotted Hues m Fig. 125, this first use of the instru- ments on the lower teeth covers only the lingual and buccal surfaces. By working along on the same surfaces of the teeth on the same jaw, considerable time may be saved by not having to change instru- ments every moment or two, as one instrument frequently will adapt itself to eight teeth before it will be found necessary to change. ^0 0^ Fig. 126 R After the deposits have been removed from the lingual and buccal surfaces, attention is given to the distal surfaces. Once more begin- ning on the distal surface of the right lower third molar, the distal surface of the right lower molars, bicuspids and cuspid are carefully scraped. Next the distal surfaces of the left lower cuspid, bicuspids and molars, as illustrated in Fig. 126. One instrument will usually PRACTICAL WORK 307 adapt itself to these surfaces. Next the mesial surfaces of the right lower molars, bicuspids and cuspid, then the mesial surfaces of the left lower cuspid, bicuspids and molars. These surfaces, too, may usually be covered with one instrument. Lastly, the approximal surfaces of the lower incisors, which may be covered with two instruments (Fig. 127). Upper Jaw. — On the upper jaw at the point corresponding with that where work was first started on the lower jaw, the distolingual angle of the right upper third molar, the lingual surfaces of the superior set are cleaned of all calcareous deposits, working mesially until the left central is reached, then distally to the left third molar. Again start- ing at the distobuccal angle of the right upper third molar the buccal FINISH 1 START Fig. 128 surfaces are gone over, working mesially to the left central then distally to the right third molar (Fig. 128). Now beginning at the right third molar, the distal surfaces of the right molars, bicuspids and cuspid are scraped. Next the distal surfaces of the left cuspid, bicus- pids and molars (Fig. 129). In the same order the mesial surfaces are gone over, leaving the approximal surfaces of lateral and centrals until the last (Fig. 130). If this briefly outlined system is followed there will be but little chance that the deposits may escape the play of the instruments. There is nothing that instills a greater confidence in the operator, in the mind of the patient, than the gentle touch of his hand and the instruments. The very first requisite is to try to develop a firm yet 308 DENTAL PROPHYLAXIS gentle touch. In handling the lips, the cheek, the tongue, the motions should be slow enough and deliberate enough to insure gentleness. Such precautions in self-training soon improve the technic in hand- Fig. 129 ling the instruments, and it is much the better fault to be over- gentle and a little less thorough to begin with than to be heavy-handed, rough and overstrenuous with the instruments. There is no better application of the golden rule than in dentistry, and the operator R 5 6 ^- 4 Fig. 1.30 who masters a fine sense of touch and constantly keeps in mind a sympathetic consideration for his patient, has conquered much that is productive of success. PRACTICAL WORK 309 One of the most perplexing and yet one of tlie most essential things to master at the start is the proper handling and use of the mouth mirror. The mouth mirror is especially essential in operating on the lingual surfaces of the upper teeth and can also be used to advantage in holding the tongue away from the lingual surfaces of the lower teeth. As the motion reflected in the mirror is reversed from that of direct observation, it is puzzling at first to place the instrument properly, but a little practice will soon obWate the difficulty. The Dunn cheek distender is used to expose the buccal surfaces of the teeth, both in instrumentation and polishing, and its use adds much to ease of vision and access to these surfaces. The Four Motions. — In instrumentation, as well as in polishing, there are four distinct motions. These mav be termed digital, wrist, rotarv Fig. 131 or forearm and rigid arm. In acquiring these movements the fulcrum point of the hand in relation to the hold of the instrument is the deter- mining factor. If the digital motion is to be used, the instrument or polisher is grasped as illustrated in Fig. 131. The end of the right thumb is the fulcrum-point or rest. This position permits of a perfect control of the instrument and allows a play of the instrument in either a push or a pull stroke. This motion is used particularly on the teeth of the upper jaw. It might be well to state here that no instrument should be used in the mouth unless the hand is first braced by a suitable rest for one or more of the fingers of the hand holding the instrument. No free-hand motion should be used. Such motions would be almost sure to invite a slip of the instrument and result in laceration of the gum tissue. The wrist motion is acquired by holding the mstrument as illustrated in Fig. 132, using the end of the second 310 DENTAL PROPHYLAXIS or third fingers as a fulcrum. This motion may be used in various parts of the mouth, especially on the lingual surfaces of the molars and bicuspids, but it is not as effective for general use as the forearm or rotary movements. The forearm or rotary motion is used on both the upper and lower jaws and usually the end of the thu'd finger serves as fulcrum, although that of the second finger can sometimes be used. This motion is produced by holding the muscles -quite rigid, allowing the rotation of the radius around the ulna bone of the fore- arm to play back and forth in a limited area. After a little practice this motion permits of a rapidity of work with the instrument under perfect control, and to master this stroke is to master much of the technic of instrumentation and polishing. Fig. 132 rig. 1 33 illustrates the position of the hand when using the rotary motion. The rigid-arm motion is used for polishing nearly all of the labial and buccal surfaces of the teeth, both upper and lower, and for the lingual surfaces of the molars and bicuspids. The rest is usually found by using the side of the second joint of the right thumb on the chin or the second joint of the third or fourth finger as illustrated in Fig. 134. The muscles of the whole arm are made fairly tense and the arm is made to travel forward and backward in a short, limited area. All of these motions should be practised over and over again on manikins or on natural teeth set in modeling compound before being tried in the mouth. They are not easy to master and the nuisdes must be trained by repeated practise. PRACTICAL WORK 311 In the removal of tartar around the necks of the teeth, there are two strokes that may be utilized, a push stroke and a pull stroke. Which to use is determined in a great measure upon the quantity or bulk of the deposit and also upon the tenacity with whicli it may cUng Fig. 133 to the tooth surface. In scaling off pieces of hard deposits, large or small, the draw' or pull stroke will be found most effective. The instru- ment is carefully carried a little below the gingival border of the gum and hooked securely over the shoulder of the deposit. Then with the Fig. 134 hand properly braced, the instrument is firmly drawn toward the masti- cating surface or cutting edge of the tooth — a second digital motion. When the deposits are small and fairly soft, a short, pushing stroke will be more effective. 312 DENTAL PROPHYLAXIS INSTRUMENTATION 313 Instruments. — Before the handling of the instruments is described in detail a set of scalers will be considered that should be sufficient for the beginner for all {Jrophylactic work upon the necks and crowns of the teeth. These include nine instruments and may be described as follows: P'ig. 135. The two small curved instruments with the spoon-like ends are known as Nos. 17 and 18 of the set of Darby-Perry excava- tors. They are curved in opposite directions to each other and are paired as rights and lefts. Dr. C. W. Strang, of Bridgeport, Ct., suggested their use. Nos. 6 and 7 belong to the D. D. Smith set and are made by J. W. Ivory, of Philadelphia. Fig. 136, Nos. 13 and 14 were designed by Dr. E. S. Gaylord, of New Haven, Ct., and are a Fig. 137 part of the Smith set. They are also made by J. W. Ivory. No. 3 sickle-shaped instrument is made by the S. S. White Company, and is used for the removal of heavy deposits by the pull or digital stroke. Fig. 137 illustrates Nos. 3 and 4 from the Harlan set of scalers made by the S. vS. White Company. INSTRUMENTATION. Lower Jaw. — Assuming that the deposits are not unusual in quantity and are reasonably easy to remove, the adaptation of these instru- ments will be described, proceeding as in Fig. 125. Starting at the distolingual angle of the last lower right molar, No. 18 of the Darby-Perry excavators is selected and held at an angle, 314 DENTAL PROPHYLAXIS as sho\Aai in Fig. 138. The stroke used is a short downward push, and a ^^Tist motion is used with the blade held at nearly a right angle with the tooth. On the downward stroke, the back of the blade with its smooth, blunt surface will strike the gingival border of the gum and prevent the cutting edge of the instrument from traveling far enough to injure the peridental ligament. This short stroke is rapidly repeated, the operator making a wave-like motion of the instrument, gradually moving it forward, mesially, on the lingual surface of the molar until the mesiolingual angle is tiu-ned, and using the mouth mirror with the left hand to keep the tongue out of the way. The instrument is now transferred to the next molar and the operation is repeated. This Fig. 138 is continued with the same instrument until the left lower central is reached, from No. 1 to No. 2 in Fig. 125. The mate to this instrument, No. 17, is now substituted and the operator, starting on the lingual surface of the left central. Fig. i:3(), and using a rotary stroke, continues until the distolingual angle of the left lower last molar is reached, Fig. 140 or from No. 3 to No. 4 in Fig. 125. These small instruments greatly magnify the sense of touch, so that each small deposit is readily felt, whereas a larger instrument might pass it })y. Again starting at the distolniccal angle of the left last molar with instrument No. 18, Fig. 141, this short, pushing stroke with a wrist motion is used until the left lateral is reached. From No. 5 to No. G in Fig. 125. Altliough the same instrument can be used eft'ec- INSTRUMENTATION 315 lively on the lal)ial surfaces of the incisors, it will be found advanta- geous to change for its mate, No. 17, and, leaning slightly in front of the Fig. 139 Fig. 140 patient, brace the hand by the thu-d finger on the masticating surface of the first bicuspid (Fig. 142), using a wrist motion which permits 316 DENTAL PROPHYLAXIS Fig. 141 Fig. 142 INSTRUMENTATION 317 of a careful handling of the festoons of the lower incisors. After the labial surface of the left lateral is finished, the hand is moved forward to engage the next tooth. At the right cuspid the rotary stroke is now adopted and continued to the last molar. Fig. 143 or from No. 7 to No. 8 in Fig. 125. The finger rests for the work just described are found on the masticating surfaces of the bicuspids or on the cutting edge of the cuspids or incisors. The base of each tooth has four lines. Two of these lines have now been covered, and there remains the approximal surfaces or the distal and mesial lines. No. 13 is an instrument with the end bent at an Fig. 143 angle of forty-five degrees, having a long blade with a file-cut surface, the numerous small blades of which are very effective in removing the small deposits. This instrument should be used chiefly with a pull stroke, starting at No. 1, in Fig. 126, which is the distal sur- face of the right lower last molar, as shown in Fig. 144. The distal surface of the last molar being free, the blade is carefully passed down under the gum line until the sense of touch determines the bot- tom of the subgingival space. The blade is then brought tight against the tooth surface and pulled upward. An eighth to a quarter of an inch play of the blade is sufficient to dislodge the deposits. This stroke 318 DENTAL PROPHYLAXIS is rapidly repeated across the back of the tooth. In adapting this instrument to the distal surface of the second molar the blade is inserted Fig. 144 Fifj. 145 sidewise from the buccal surface (Fig. 145), and with a short push-and- pull stroke the instrument is worked between the teeth in order to INSTRUMENTATION 319 cover the entire distal line. If the teeth are so shaped and are so close together that they will not permit the blade to pass between them, then the instrument should be inserted also from the lingual surface Fig. 146 and in this way that part of the distal line that was inaccessible from the buccal surface is covered. With the same instrument the distal sur- faces of the teeth may be scaled to the incisors, or from No. 1 to No. 2, in Fig. 126. Again, with the same instrument, the operator should start Fig. 147 on the distal surface of the left cuspid, and entering from the buccal side, proceed on to the last molar, or from No, 3 to No. 4, in Fig. 126. The procedure for the mesial surfaces is the same as described for the distal, 320 DENTAL PROPHYLAXIS except that the instrument used is Xo. 14, and one position is ilhistrated as in Fig. 146. Both push and pull strokes are employed. The lower incisors are scaled on their approximal surfaces by the bayonet-shaped Smith scalers, Nos. 6 and 7, from No. 5 to No. 6 of Fig. 127, which shows this area. Fig. 147 illustrates the adaptation of these instruments. Upper Jaw. — On the upper jaw, at the right distolingual angle of the last molar, instrument No. 17 is placed at nearly a right angle with the tooth and, with the hand braced on the top of the left lower lateral and cuspid teeth, using the third finger as fulcrum (Fig. 148), a wrist and digital motion is employed, the instrument being made to travel forward with a short up-and-down, push-and-pull stroke combined, perhaps better described as a waving stroke. The fulcrum-point is maintained, the instrument being drawn in or shortened as the inci- sors are approached. When the left central is reached (Fig. 128), Fig. 148 instrument No. 18 is substituted, the second finger used as a fulcrum on the cutting edge of the right upper cuspid (Fig. 149), and the lingual surfaces of the upper teeth of the left side are gone over with a wrist and digital motion. This fulcrum-point is maintained and the instru- ment advanced in length with the tiuunb and first finger (Fig. 150). Again starting at the distobuccal angle of the left upper third molar, the third finger is placed slightly back of the cutting edge of the right upper lateral and central while the second finger rests on the cutting edge of the left upper central (Fig. 151). This i)osition can be held until the left lateral is reached, the motion })eing wrist and digital. Shifting the fulcrum-point to the end of the third finger on the edge of the right upper cuspid, the labial surfaces of the left central and lateral may be scaled with the same instrument. With the hand resting against the chin just below the lower lip, and the third joint of the little finger serving as a fulcrum, with instrument No. 18, the right central and INSTRUMENTATION 321 from there back to and inctuding the third molar is scaled, using the digital motion, as in Fig. 152. The lingual as well as the labial and buccal surfaces, having been covered, No. 13 is used for the distal surfaces (Fig. 129) of all the upper teeth excepting the incisors. For the molars, bicuspids and cuspids of the upper jaw the description of the use of this instrument for those on the lower jaw may be applied, the hand rest being found chiefly on the cutting edge of the lower incisors, the end of the third finger Fig. 149 serving for fulcrum. No. 14, P"ig. 153, is used in a similar manner with the hand rests the same as for No. 13. Nos. 5. and G are best adapted for the approximal surfaces of the incisors, their use at this point being too self-evident to need explanation. Even with this detailed description, much will be found lacking to the beginner, but after a little prastice on the manikin the hand will soon adjust itself to the proper rests to secure the greatest efficiency and control of the instrument. 21 322 DENTAL PROPHYLAXIS In removing the heavy deposits the sickle-shaped instrument, No. 3, will be found most useful. In skilful hands it is possible to scale Fig. 150 Fig. 151 INSTRUMENTATION 323 roughly nearly all the surfaces of all the teeth with this one instrument, the exception heinji; approximal surfaces. It is used with a draw or Fig. 152 Fig. 153 pull stroke and has the advantage of not being dangerous around the anterior teeth, for the point of the instrument as well as the side of 324 DENTAL PROPHYLAXIS the blade is inserted under the deposit and pulled directly upward on the lower teeth and downward on the upper teeth. But in the back of the mouth where its adaptation necessitates the drawing of the instru- ment forward under the border of the gingiva, the point is likely to slip and travel too deep into the subgingival space unless care is used. A firm hold on the instrument and a secure brace of the hand is abso- lutely essential. This sickle-shaped instrument is used almost entirely with a digital motion and the two principal positions are illustrated in Figs. 154 and 155. It is very difficult to scale the teeth thoroughly with this instrument, but the larger deposits having been removed at the first sitting, Nos. 17 and 18 can be used to advantage at the second and all subsequent treatments. The Harlan instruments, Nos. 3 and 4, are also used with a draw stroke and are helpful in removing the small, hard, tenacious deposits under the free margin of the gums. They are adaptable in nearly all sections of the mouth and their use is usually self-suggestive. When these small deposits resist Nos. 17 and 18, especially on the bicuspids, cuspids and incisors, these Harlan instruments will be found very effective. If uncertainty exists in the mind regarding the thorough removal of all deposits, an instrument known as an explorer carefully passed around the neck of the tooth under the gingivae will readily detect any small deposits or uneven surfaces. The smaller the instrument, the more greatly is the sense of touch magnified. It is for this reason that the use of Nos. 17 and 18 is advised wherever practical. There are two special features to be considered under instrumenta- tion. First, the sensitiveness that is frequently found around the necks of the teeth, and second, the bleeding of the gingival borders of the gums. In adults where the lime deposits have been heavy, their removal will frequently cause much sensitiveness for a week or two, sometimes even longer, to heat and cold and to sweets and acids. The deposits have caused an absorption of the border of the alveolar process and the soft tissues around the necks of the teeth, and when they are removed a portion of the cementum is exposed which later disappears and exposes the interglobular spaces on the border between the dentin and the cementum, forming an area that is highly sensitive to the touch of the instrument or polisher. It is frequently wise to inform the patient that he may expect the surfaces to be responsive to heat and cold for a short time, in order to allay any fears on his part. The deposits acting as a covering for these surfaces have protected them from extern'al irritation, and the patients are apt to wonder why it is that their mouths are so much more sensitive than they were before the deposits were removed. Acids are especially irritating to these surfaces and the use of bicarbonate of soda, half a teaspoonful to a third of a glass of warm water, used as a mouth wash two or three times daily, will aid greatly in tiding over this short period of discom- fort. If the soda can be used clear by dipping the finger in water, INSTR U ME NT A TION 325 Fig. 154 Fig. 155 326 DENTAL PROPHYLAXIS touching it to the soda and then rubbing it on these surfaces, it will all the more quickly neutralize any acid that may be irritating to this sensitive tissue. The thorough rubbing and polishing with the stick and pumice and the extreme cleanliness from the faithful use of the tooth-brush will soon bring these troublesome areas under control. A 10 per cent, solution of nitrate of silver is sometimes advised, but if it is used, it should be followed by a thorough polishing with the stick and pumice. The second feature, which will be considered briefly, is the bleed- ing of the gums during instrumentation. When the gums readily bleed there is congestion of the capillaries, and the more blood allowed to escape from the gingivae, the sooner the congestion will be relieved. Instead of trying not to make the gums bleed, just the reverse course should be followed, although of course this does not mean that they should be lacerated or the tissue wounded. The bleeding process is produced by using the back or smooth surface of the blade of the instru- ment with pressure, and this is done while removing the lime deposits, and if there is a copious flow of blood from some of the approximal surfaces, it should be encouraged by rapid, gentle pressure strokes directly on the gingivae. Healthy gums will not bleed during instru- mentation, and when bleeding occurs enlarged and congested capilla- ries are sure to be found. No fear of causing injury to the gum tissue in causing a flow of blood need be felt as long as care is taken that the blade of the instrument does not cut the tissue. Frequently after such a treatment the gums will take on a color two shades lighter before the patient leaves the chair, and after a few days of stimulation with the tooth-brush it will be hard to recognize it as the deep red, congested tis.sue that it was at first. POLISHING. • It is impossible to obtain the same results in prophylaxis with the use of the dental engine in polishing as may be secured with the hand polishers. This belief is based upon personal experience in faithfully trying out both methods, and is an accepted fact by all prophylactic workers who have become proficient with the hand polishers. The object of this polishing process is threefold. First, the removal of stains, placques and films or all soft accretions on the exposed sur- faces of the teeth. Second, a polishing of the enamel surfaces and a stimuhiting ett'ect that seems to be imparted to the living tissue of the tooth itself by the vigorous massage. Third, the beneficial results obtained on the gingival borders of the gums by the slight bumping of the stick, causing light i)ressure and release which imparts a massage effect and aids greatly in producing a perfect flow of blood through the capillaries in the peripheral circulation. If a new case presents itself in which the teeth are very badly stained, it is perfectly reason- able, if desired, to use the dental engine for the first treatment to aid POLISHING 327 in cleaning off these stains from the enamel surfaces, but all subsequent treatments should be made with the hand polishers. An engine revolving at six or eight hundred revolutions a minute, with the rubber cup or buff charged with pumice, cuts too viciously and if used at each prophylactic treatment, will in time affect the enamel and tooth struc- ture at the necks of the teeth. With the dental engine all sense of touch is lost, and besides it is not as adaptable on the approximal surfaces or on the surfaces of the molars as the stick held in the hand. The gingival borders of the gums, in many mouths, have been badly wounded or damaged by the revolving cups or buffs in the dental engine, and if one hopes and expects to secure the best results in obtain- ing ideal health conditions of these tissues, one must become proficient i w 1 Fig. 156 with the hand polishers. Those who would advocate the dental engine are those who have failed to make themselves proficient with the hand polishers. There can be no choice if the latter is faithfully tried. There are a number of different woods that may be used for polishing, as cedar, maple, hard pine, etc., but the closest-grained wood and the one best adapted for this purpose is orange wood. There are two sizes of sticks that may be had from the dental depots, known as large and small. The large size is cut about three quarters of an inch in length and one end is cut wedge-shaped. This stick is used on all the broad surfaces of the teeth excepting the masticating surfaces. The small stick is cut about the same length and one end is cut like the point of a lead- pencil. The smaller stick is used on the approximal surfaces and around the necks of the teeth where it is impossible to adapt the larger stick. 328 DENTAL PROPHYLAXIS In order to work with facility, two holders for the two sizes of sticks should be employed. Fig. 156 illustrates the Jack porte polishers with sticks in position. As a slight abrasive and polish to be used with the sticks, the finest grade of pumice moistened with water will prove to be the most satisfac- tory. Although other polishing mediums are used with good results, it is doubtful if there is anything superior to fine pumice for this special work. A scant spoonful placed in a small porcelain dish, and wet sufficiently with water to be almost liquid, will make a mixture that can readily be picked up on the point of the wet stick and used in the mouth. System for Polishing. — Just as a definite system is employed in going over the teeth with the instruments, so should a system for reaching all surfaces of the teeth with the polishers be followed. Fig. 157 The following system is very effective and its adoption is suggested, at least for beginners: Starting on the labial surface of the right upper central with the large stick, the polishing progresses backward to the right lateral, then to the right cuspid and so on until the right last molar is reached. I'rom this point start on the buccal surface of the right lower last molar and progress forward around the buccal and labial surfaces of all the lower teeth to the left lower last molar. Transferring the stick to the buccal surface of the left upper last molar, the polishing is continued forward to the median line to and including the left upper central. All the labial and buccal surfaces have now been polished with the use of only the larger stick. Fig. 1 57 illustrates direction for polishing. Then starting on the lingual surface of the right lower last molar with the large stick, the polishing of the lingual surfaces proceeds forward to the incisors, then backward, or distally, to the lingual surface of POLISHING 329 the left lower last molar. Again beginning on the lingual surface of the left upper last molar, all of the lingual surfaces are covered, ending on the right upper last molar. So far only the large stick has been used. Now with the pointed stick the same course should be followed over the teeth as has just been described, polishing in between the teeth as far as possible and rubbing the necks of the teeth under the free border of the gingiva?, keeping the edges of the sticks sharp. When they become frayed or brush-like, they should be trimmed off with a pair of scissors, or if, after this, the edges are still too blunt, sharpened with a knife. The polishing is confined almost entirely to two motions, the rigid- arm and the forearm or rotary. The one exception is the digital that should be used by beginners on the labial surfaces of the upper incisors. Fig. 158 In order to polish effectively pressure must be used. It is this one point of being able to apply pressure on all the surfaces while polish- ing that makes the operation difficult. This is noted especially in polishing the lingual surfaces of the molars and bicuspids. The proper hand rests are essential and also muscular practise of the motions used for this work. Beginning on the labial surface of the right upper central with the large stick, and using a digital motion, the stick is made to travel up and down the full length of the face of the tooth, rubbing the surface with both up and down strokes. The stick is allowed to bump the gum lightly but not hard enough to cause discomfort. Considerable pressure is used and the motion is rapid. Fig. 158 illustrates the posi- tion of the hand with the thumb rest on the cuspid for the digital motion. When the right cuspid is reached the rigid-arm motion is 330 DENTAL PROPHYLAXIS employed, with the back of the second finger, between the second and third joints, resting on the chin and the two bicuspids are rubbed and Fig. 159 Fig. 160 polished up and down or longitudinally, the right thumb pressing on the polisher at the end of the stick (Fig. 159). Now inserting the Dunn cheek distender, the buccal surfaces of the molars are rubbed POLISHING 331 crosswise, using the rotary motion and the same fulcrum position that was used with the cuspid and bicuspid, but the porte polisher is shifted in the hand and grasped as one woidd hold a pen-holder (Fig. 160). The end of the stick may be made to travel up and down part way on the approximal surfaces, but the principal motion for polishing is crosswise. The polishing of the right lower molars is the same as described for the upper molars. For the right lower cuspids and bicuspids, the same as for the upper. The first finger of the left hand now is placed across the inside of the lip to depress it and with the polisher grasped in the fist with right thumb resting on the left forefinger (Fig. 161), the lower incisors are polished. For the left cuspid and bicuspids the same position as for the right is used. In polishing the left lower and upper molars the back of the third finger Fig. 161 becomes the fulcrum on the side of the chin and the polisher is grasped pen-holder fashion, as in Fig. 162, using the rigid-arm motion. The descriptions of the right cuspid and bicuspids, lateral and central, will apply to the left. It will be noted that, with the exception of the upper incisors and right molars, the motion used on all the outer sur- faces of the teeth has been rigid-arm. That on the inner surfaces of both lower and upper is forearm or rotary. The difficulty met with is that of producing pressure and at the same time retainmg control and length of stroke. With the mouth mirror in the left hand to hold the tongue away, the back of the third and fourth fingers are pressed against the chin, and the polisher held as the pen-holder in a rigid grasp (Fig. 163), the stick is made to travel up and down on the inner surface of 332 DENTAL PROPHYLAXIS Fig. 162 Fig 103 POLISHING 333 the right lower molars, the edge of the stick pointing up and down with the long axis of the tooth. This polishing motion, it will be noted, is just the reverse from that used on the buccal surfaces. By shorten- FiG. 164 Fig. 165 334 DENTAL PROPHYLAXIS ing the hold on the poHsher the same position is used for polishing the bicuspids and cuspids. Other adaptations of the stick will be found that are advantageous Fig, 166 Fkj. 1 07 POLISHING 335 for these surfaces, such as using the side of the stick with an up-and- down stroke instead of its sharpened end. By leaning forward in front of the patient the second finger is placed on the top of the left cusi)id or bicuspid and with a rocking or rotary Fig. 168 Fig. 169 motion of the arm and stick the lower incisors are polished (Fig. 164). The left lower molars are polished with the same pen-holder grasp, using the second finger as a fulcrum on the right lower. cuspid or lateral 336 DENTAL PROPHYLAXIS (Fig. 165). The mouth mirror can be used to good advantage while polishing the lingual surfaces by having the patient sit low enough in the chair. Starting on the lingual siu-face of the left upper last molar, the porte polisher is held like the pen-holder and, with the end of the third finger resting on the labial surface of the right lower cuspid (Fig. 166), the molars are rubbed chiefly up and down with the edge of the stick. Holding the same fulcrum-point, the grasp on the polisher is gradually shortened and the incisors are polished as shown in Fig. 167. The lingual surfaces of the left cuspid, bicuspids and molars are polished with the same hold of the polisher, the rest being found on the chin, using the back of the second joint of the third finger (Fig. 168). The motion used is mostly forearm or rotary. Fig. 170 All of the positions and fulcrum-points described for the large stick apply also to the small stick. The pointed stick is used between the teeth, rubbing the surfaces as far as the stick can reach and also around the necks of the teeth on all of the surfaces. Its use should start at the same point, the right upper central, and travel over the teeth with the same system as that described for the large stick. The points of both polishers should be kept trimmed with the scissors and when they become too blunt, sharpened with a knife. Where the gums between the teeth are congested, the side of the stick is pressed against them with a fast, quick stroke to encourage the bleeding. Care should be taken in the use of both sticks not to abrade the gingivte, but the light pressure with the side of the stick against the gum margin will prove very beneficial (Fig. 169). AVhen sensitive surfaces are found at the necks of the teeth, the pointed stick freely POLISHING 337 charged with pumice is appUed with vigor and considerable pressure. A thorough poUshing of their surfaces will greatly aid in reducing the sensitiveness. Floss Polishing. — After polishing with the sticks there still remain the contact points and an area on the approximal surfaces that have not been reached. By doubling a length of ligating silk, twisting it and dipping it in water and then in pumice, these surfaces may be polished quite effectually. When the teeth are very close together a single strand will be found sufficient, as this silk is larger in size than that sold for every-day flossing. Cutters' wide floss may also be used to advantage where the space will permit. When using the floss for polishing it should be passed between the contact points with care, Fig. 171 so that it will not snap on the gum, drawn back and forth on the distal surface of the tooth and then pressed backward rubbing the mesial surface of the adjoining tooth. Most of the decay takes place in these surfaces and they must be given careful attention. If the ends of the floss are wound around the first fingers as illustrated in Figs. 170 and 171, it can be easily manipulated. Brush Wheel. — The masticating surfaces are so uneven that a stick cannot be used on them very well, so it will be necessary to use a brush wheel in the engine to reach down in the fissures to polish these surfaces. With the wheel dipped in water and the edge of it touched to wet pumice, the engine should be run at a moderate speed and the edge 22 338 ■ DENTAL PROPHYLAXIS of the wheel apphed down in the fissures of the molars and bicuspids. The Dunn cheek-distender should always be used. It is almost unnec- FiG. 172 essary to state that the sticks, the pumice, the floss and the brush wheel should not be used a second time. Figs. 172 and 173 show the adaptation of this wheel. Fig. 173 Children. — In the prophylactic treatment of children it is seldom necessary to use the instruments. As it is the roots of the teeth that are most susceptible to disease in adults, so are the approximal surfaces most susceptible in children. These surfaces should be care- BRUSHING 339 fully polished with the floss and piuniee, and the fissures in the masti- eating surfaees with the Inrush wheel in the engine. The polishing of all the surfaces of the teeth with the sticks should be done as described for the adult. In order to assist in the removal of the green stains on the surfaces of the teeth at the first treatment a small napkin may be used to dry the teeth, and a pledget of cotton soaked with Churchill's compound tincture of iodin applied to the stains and allowed to penetrate them. It is sometimes necessary to make a second application of the iodin after the first thorough polishing, but after the teeth have been thoroughly polished and the patient is coming at regular intervals for these surface treatments, no further use of the iodin will be necessary. Attention is called to a preventive treatment of the fissures in the first permanent molars of children that comes within the province of the dental hygienist. When these fissures are found to be exceptionally deep, likely to retain food debris and thus susceptible to decay, a quick-setting, hy- draulic cement should be mixed, and with cotton rolls on each side of the tooth, the fissures should be dried with warm air, and washed with a pledget of cotton soaked with alcohol, again dried and then with an explorer the soft cement worked down into the fissures. As the cement begins to toughen and set, the end of the second finger is dipped in a glass of water and with the ball of the finger the cement is pressed firmly down into the fissure and held there for a moment or two until it has become fairly hard. The surplus can easily be trimmed away and the cement in the fissures will last for some time, acting as a protection to theu' sm-faces. It takes but a short time to renew it when it wears away, and will frequently save these teeth from decay at the susceptible period of from six to twelve years of age. BRUSHING. Because a remarkable condition of health and beauty of the gums and a high resistance and increased vitality of the peridental membrane may be developed by the proper form of brushing, it may be well to consider first the blood supply to the peridental membrane and how its vitality may be greatly increased by establishing fast and perfect circulation in the gum tissue itself. Plate VII illustrates, diagramatically, the blood supply to the peri- dental membrane of a tooth. The small arteries entering the apical space break up into branches, one or more of them enter the pulp canal through the apex of the root, and the others pass down between the fibers of the peridental membrane. During their course through the membrane on their way to the alveolar border and the gum tissue they both give off and receive branches through the alveolus and connect with the plexus of small bloodvessels and capillaries of the gum tissue. It wull thus be readily seen that the blood circulation in the gums is very intimately associated with the peridental membrane. It fre- 340 DENTAL PROPHYLAXIS queiitly happens that when an alveolar abscess develops at the apex of the root of a tooth, these bloodvessels in the apical space are destroyed, yet the peridental membrane does not sufi'er from lack of blood, for the branches coming to it from the walls of the alveolus soon enlarge and produce a sufficient supply. It must therefore be noted that in order to stimulate the blood supply of the peridental membrane it is merely necessary to stimulate circulation in the gum tissue. Fibers of the peridental membrane radiate out into the gum tissue and strong bands of fibers which form the dental ligament blend into the peri- osteum of the alveolar process. Because some of these fibers are so close to the surface in the gum tissue it is not difficult to under- stand why an unusual response to health may be obtained by surface stimulation. In the process of masticating coarse foods a natural massage takes place in the following manner: The teeth, being occluded with con- siderable force, are pressed down in their sockets. The peridental membrane is thus compressed and the blood is squeezed out of the small bloodvessels. As the jaws open and release the pressure on the teeth, the pressure on the small bloodvessels in the membrane is also released and the blood comes rushing in again. This pressure and release is similar in its action to a massage of the tissues on the surface of the body. The coarse foods sliding over the surfaces of the teeth press upward on the upper gums and downward on the lower gums. This pressure and release on the bloodvessels in the gum tissue acts in the same manner as that on the peridental mem- brane. Such a process always stimulates a free flow of blood and pre- vents congestion or stasis in the capillary circulation. Keratin. — In the basement layer of the skin, cells are constantly being formed and forced slowly upward toward the surface of the body. During their transit the cells slowly change their shape, becoming long and flat in appearance and finally form the pavement or squamous type of epithelum on the surface of the skin. During this period, from the time of formation to their arrival on the surface of the body, a gradual metamorphosis or change takes place in the protoplasm of the cell. Slowly the contents of the cell begins to toughen and this process continues just in proportion to the needs of protection against undue friction or exposure. The horny hands of the day laborer, or the corns that form on the feet, are exami^les of the extreme expression of the activity and change in these cells. The contents of the cells when so changed or toughened is known as keratin. The mucous membrane of the mouth is but a continuation or an infoUling of the skin. Its epithelium is of the squamous type similar to that of the skin. If the gum tissue is artificially stimulated three or four times a day with the bristles of the tooth-l)rush, a noticeable change takes place in the texture of the mucous membrane. It soon loses that smooth, glassy or slazy appearance and under a magnify- ing glass shows a thickened or toughened surface which seems to act BRUSHING 341 as a protective armor for tlie underlying tissues and makes the ingress of infection tiu-ough tiie gum tissue, or at the gingiva', extremely diffi- cult. Inference should not be made that there is produced a hornified mucous membrane, except in a modified sense, but a beneficial change takes place that is much to be desired. A similar texture of membrane may be found in the mouths of carnivorous animals. The Gums. — In considering the health of these dentinal tissues the gums found in the average mouth should first be noted. Aside from the unsanitary aspect of the crowns of the teeth, the gums will be found to be of a deep red color, the gingiva usually showing even a deeper red. The blood is almost stagnant on some of the margins, and the tissues will bleed upon the slightest touch. Waste products are not being properly eliminated, oxidation is imperfect and blood serum, which contains the lime salts for serumal deposits, oozes in the subgingival sj)aces and forms an ideal mediiun for bacteria. These are the average gums of adults, who eat food which requires but little mastication and produces but little friction on the gums, and who take scant care of their mouths. But how quickly all of these con- ditions will change under artificial stimulation. The instant the gums are brushed properly, the blood starts to flow more rapidly and a new life and color make their appearance. After a thorough prophylactic treatment and a lesson in gum brushing it is not unusual to see the tissues lighten in color, possibly two or three shades in twenty-four hours. At the end of a week or ten days they assume a still lighter shade and after periods ranging from three to six months they become a light coral pink, and hold this color as long as they are daily brushed and stimulated. There is apparently a peculiar pink shade that practically every individual may acquire if the brushing is faithfully followed. In fact this color may be taken for so sure an index, that it is easy to tell at a glance whether the patient has been brushing the teeth and gums four times daily or not. Virtue, in this case, has its own reward, for the color is always obtained when the brush has been used according to rule. The gums should be of uniform color in all parts of the mouth, the gin- givjp showing no difference in shade from that of the body of the gum. Tissue Stimulation. — If the following rules are honestly observed the same results are assured in every mouth: 1. The form of brushing as described in tliis chapter. 2. Brushing long enough — not less than two minutes. 3. Brushing four times a day. Many cases have been baffling because they would not respond to treatment, but when the patient gives a demonstration at the wash bowl,' it will show that he makes some omissions or uses an incor- rect form of brushing which, when corrected, will bring results in a short time. Sometimes patients will claim to have followed the rules when, upon close investigation, it will be found that they have not done so. 342 DENTAL PROPHYLAXIS ^Yhen the gum tissue -will not assume this hght pink shade in six months' time, and when the patient is expert with the tooth-brush and claims to follow the rules faithfully, it may be suspected that in some way the rules are not lived up to or that otherwise a very rare excep- tion has been found. Evidently this color that the gums assume under the daily brushing is due to the fast flow of blood through the capillaries, the perfect oxidation of the cells and thorough removal of their waste products, as well as a thickening or toughening of the epithelial layer of cells on the siu-face. The festoons become pink and tough, the surface of the mucous membrane loses its thin, glassy appearance, and when dried looks tough and firm. Also when the edges of the gum are dried they do not weep. Little or no serum oozes now from this tissue and it will be noted that the serumal deposits, found so plentifully under the congested borders of the gums, almost entirely disappear at subsequent treatments. It must not be assumed that the miraculous happens under these unusual health conditions or that merely learning how to brush the gums will eliminate all present and future disease of the mouth. This is not so, but one cannot help being enthusiastic when one sees so many returns to health of the dentinal tissues under stimulation. The peridental membrane seems to acquire new life, and apparently feels the stimulation in every fiber and cell. Loose and sore teeth become tight and free from soreness, providing that too much of their support- ing tissue has not been lost. Chronic cases of pericementitis disap- pear and even the pulp itself may be relieved of congestion if it is slight and has not progressed too far. There is no doubt but that the osteo- blasts, under prophylaxis and this stimulation, do at times replace small areas of lost alveolar process. Where roots have been exposed on the labial or approximal surfaces, especially those of the incisors and cuspids, it is not uncommon to see gum tissue creep back over the exposed root to a considerable degree and on approximal surfaces there has been a filling in of the bony tissue to support the gum which is undoubtedly a new deposit of process. When it is considered that the osteoblasts are present in the peridental membrane throughout life and slowly add to the alveolar wall of the socket, it is not unreason- able to expect them to lend their aid when stimulated and the irritat- ing cause removed. Fig. 174 illustrates what gum brushing will do. All the teeth in this mouth were affected by pyorrhea. They were loose and the left central found to })e beyond saving. The gums are a light coral pink, the teeth firm and for nearly thirteen years there has been no percep- tible change in absorption or recession. Fig. 175 shows the result of a case of acute gingivitis. This occurred eight years ago, and the exposed surface of the root at the time was nearly a third longer. By proj)hylaxis and ginn stimulation a portion of the root was covered by new gum tissue. There has been no change in the intervening eight years. BRUSHING 343 Fig. 176 shows the right cuspid in the mouth of the same patient. This gum was also affected by acute gingivitis and the root was exposed Fig. 174 Fig. 175 Fig. 176 344 DENTAL PROPHYLAXIS nearly an eighth of an inch before the inflammation dissappeared. There was undoubtedly a replacement of lost tissue here and it has proved to be very stable. Fig. 177 shows another case of the destructive process of acute gingivitis. Eleven years ago the indications were that this tooth could Fig. 177 not be saved. The apex was nearly exposed and a larger area of the root uncovered. The gum tissue is now hard and pink and the tooth firm and useful. Fig. 178 is a similar case but a year old. The conditions are bad, as the space between the lateral and central will not permit of thorough cleansing without much efl'ort. There has been a replacement of con- siderable tissue, the teeth have tightened and can no doubt be retained for some time to come. Fig. 178 It seems probable that it is not only possible to sterilize tissue by this active hyj)eremia, artificially induced, but also that small serumal deposits may be dissolved and disposed of by the blood or possibly by the action of the cells in these tissues. This statement does BRUSHING 345 not mean that when the dental surgeon treats a case of pyorrhea alveolaris, that merely teaching the patient how to brush his gums will cause the dissolution of the dei)osits and kill the infection. It means that it is exceedingly important that gum brushing should be taught and the patient trained by repeated lessons until he acquires this art, for it really is an art. With the additional aid of the gum brushing the pus will soon cease, the pockets will contract and close, soreness will be relieved and any small granular deposits that may be left will gradually disappear as the tissue hugs up tightly to the root. The tisslies, thus artificially stimulated, seem to possess five properties, analgesic, bactericidal, absorbent, solvent and nutritive. The analgesic effect is no doubt produced by the relief of tension and toxic influence. Whether the bactericidal effect is one of phagocytosis or of, opsonins is immaterial. There is no question but that when cleanliness is established and the tissues regularly stimulated by brushing, the infection is destroyed. The absorption in the tissues is accomplished, not only by the lymphatics but by the capillaries themselves. It is a well-known fact that a ligature of catgut in the body is dissolved and disappears. Landois has shown that the blood serum of every animal has the power of dissolving the blood corpuscles from a different species. Where or how this solvent originates that causes the disap- pearance of the small granules of serumal deposits can only be con- jectured. Induced active hyperemia will demonstrate that they do disappear. The nutritive property is self-evident, and is due chiefly to a perfect oxidizing process. There is still much to learn concerning these artificial stimulants. If the existence of human beings were more like that of animals, this condition would be induced each time that the meal of coarse food was chewed. Since the artificial rather than the animal life is preferred, and coarse food is not attractive, why should not this condition of health be produced artificially? Tooth-brushes. — Opinions vary greatly concerning the size and shape of the tooth-brush. One educator of the middle West states in a letter that he did not recommend a hair-brush, a nail-brush or a shoe-brush for brushing the teeth, but a tooth-brush. His position might have received serious consideration if it were only the crowns of the teeth that were involved, but as the brushing of the gums is of equal impor- tance with brushing the teeth, a brush that will adapt istelf to both surfaces is the one to use. Again, if cross brushing is indulged in or a slow twisting massage or wiping motion is employed, the form and size of the brush may be varied. Personally, the AATiter has not been able to secure as satis- factory results with either of these forms of brushing. The cross brush- ing seems to irritate the festoons, at times will create absorption, and lacks the cleansing action upon the outside surfaces. The wiping motion with the sides and ends of the bristles is more cleansing and the gums take more kindly to this form of brushing, but when it is con- sidered that nature intended that the pressure should be chiefly upward 346 DENTAL PROPHYLAXIS on the upper gums and do^Muvard on the lower gums, such as is induced by food shding over the sm'faces of the teeth in mastication, it can be seen that this process can be better simulated by a rotary stroke than by any other way. The gums appear to thrive under the rotary stroke, a stimulus is imparted to the circulation and a thorough cleansing effect is produced along the curved lines of the festoons and upon a third of the approximal surfaces. A slow^ deliberate stroke is not as stimulating as a fast, light stroke. The best way to bring blood to the sm-face of a tissue in a short space of time is to use a light, rapid massage. The results will justif}" the means, so a rotary stroke for the buccal and labial surfaces is advised. In order to secure the proper adaptation of a brush to the surfaces of the gums and the teeth, the shape of the bristle ends of the brush is important. Many of the popular brushes on the market are nearly concave in shape, having a long toe and heel with the shorter bristles near the center. Such a brush, placed squarely across the front teeth, seems to fit when at rest, but if slowly moved about the mouth, it will be found to ride in many places on the toe Fig. 179 and heel alone or, if pressure is used, these long bristles ride sidewise or any other way. Although the cranium is convex in shape, it has never been deemed expedient to use a concave hair-brush. In fact, a concave brush would not be as effective as a straight one, although it might seem to fit better when at rest. Apparently a straight-cut tooth- brush with a slight tuft on the end is best adaj^ted to most of the sur- faces in most mouths. The bristles should be of sufficient length to be flexible yet springy and stiff enough not to lose their life or spring after the first two or three days' use. This necessitates using a brush with bristles a trifle hard, for such a brush becomes softened after a few days' use. Fig. 179 illustrates the two shapes of brushes just referred to. When instructing a new patient in the art of brushing, a soft brush should be recommended to start with, otherwise the patient should be warned not to be too strenuous with the stifl" brush until the gums have had a chance to become tough. and the mucous membrane thickened, otherwise slight abrasions of the mucous membrane will be produced, and a sore and tender surface will result if the gums are BRUSHING 347 brushed at first with too much pressure and vigor and with a stiff brush. Instructions for Brushing. — The process of the brushing of the gums and the teeth may be divided into three parts: First, the outside or buccal and labial surfaces. Second, the inside or palatal and lingual surfaces. Third, the occlusal or masticating surfaces of the teeth. The Buccal and Labial Surfaces. — "With the brush held in the hand, as in Fig. 180, and with the teeth nearly closed, the brush is placed inside the cheek on the left side, so that the ends of the bristles are lightly • in contact with the gums over the upper molars. Now, with a fast, circular motion the brush is swept backward and downward, reaching Fig. 180 as far down on the lower gums as the brush can travel in this posi- tion, then forward and upward as high on the gums of the upper teeth as possible (Fig. 181). The brush should travel in a perfect circle, not in an oblong tract, and in as large a circle as the vestibule of the cheek will permit. Very little pressure should be used, for the stimulating as well as the cleansing process is accomplished by the rapidity of the stroke and the direction traveled by the ends of the bristles. Continuing this fast, circular motion the brush should be made to travel very slowly for- ward until the heel of the brush engages the right cuspids. Pausing on the incisors to stimulate thoroughly the gums on both jaws, start back again slowly to the region of the molars (Fig. 182). 348 DENTAL PROPHYLAXIS It will be understood that the brush is constantly in motion, travel- ing in a large circle with the ends of the bristles lightly touching the gums and teeth with as rapid a motion as possible. Fig. 181 Fig. 183 illustrates the position of holding the brush for the right side. On this side some persons find it easier to maintain a circular I'l.;. 182 motion by reversing the stroke, or brushing from the lower gums back- ward and upward. It makes no difference in which direction the brush BRUSHING 349 travels as long as the circular stroke is adhered to. Assuming that one is using the right hand for brushing, it will not be possible to brush Fig. 183 farther forward than the right cuspid teeth (Fig. 184). Directions for brushing the left side are applicable to the right. Fig, 184 Lingual Surfaces. — 1. Uj^per. The brush should be held as shown in Fig. 185. The roof of the mouth as well as the lingual surfaces of 350 DENTAL PROPHYLAXIS the upper teeth are brushed with an in-and-out stroke, as in Fig. 186. The ends of the bristles should be placed against the gums of the right Fig. 185 molar teeth, and the brush drawn straight forward until the heel of the brush (the last bristles nearest the hand are called the heel) wipes the lingual surfaces of the right incisors and cuspids and protrudes from the mouth for a short distance. The upper lip should be drawn Fig 18G downward to prevent the moisture from being thrown outward by the snap of the bristles passing over the edges of the incisors. The brush is BRUSHING 351 now pushed straight back again on the gums and this in-and-out stroke is rapidly made and confined on this surface for a few seconds. This fast in-and-out stroke of the brush is kept up and carried across the roof of the mouth until all of the hard palate is covered and the gums on the left side of the mouth are reached. Here the in-and-out stroke is applied rapidly for a few seconds, as far back as the distal surfaces of the third molars. The same stroke should be used on the return, the palate should be crossed to the right side again, and again back to the left side. Special care should be used to reach the gums around the last molars, there is a tendency not to brush back far enough. 2. Lower Linr/nal Surfaces. — The lingual surfaces of the lower teeth are the most difficult to brush and it takes quite a little practise before Fig. 187 the gums can be deftly reached, especially on the right side. Nineteen out of twenty mouths will disclose a congested gingival border on the lingual surfaces of the right molars, and in order that the wrist may bend freely so that the toe of the brush may reach this surface, it is suggested that the brush be held in the hand as in Fig. 1S7. These gum surfaces are brushed almost entirely with the toe or tuft of the brush, the motion being a fast in-and-out stroke, similar to that used on the hard palate, as in Fig. 188. Starting on the right side with the bristles of the tuft resting on the gum next to the last molar, the brush is drawn forward. In this case the bristles at the heel do not sweep the lower incisors as the handle of the brush is tipped slightly upward, so that the brushing is done almost entirely with the tuft. The brush is now forced backward in the same line, leaning slightly 352 DENTAL PROPHYLAXIS toward the tongue, and the in-and-out stroke" is appHed rapidly to this surface. jNIaintaining always this fast stroke, and slowly coming forward, the handle of the brush is now raised to a sharp angle and the gums below the incisors are brushed with an up-and-down stroke, ^^^^^^^H^T m W^ I^^^B a '^^1 1 [^9 HT^f;'^ /'' i ^ !ttL^B..-*^4^^^^l Fig. 188 going back and forth across them several times. Continuing the in- and-out stroke the tuft is adapted to the gums of the left side and they are brushed in a manner similar to that described for the right side, again slowly returning to the right and repeating once more to the left side. A slight gagging sensation will sometimes be felt in trying to Fig. 189 reach as far back as the brush should actually go, but with persistent practise this can be greatly overcome in a short time. Masticating Surfaces. — Lastly the masticating surfaces should be brushed in order to remove any food debris in the fissures or sulci of BRUSHING 353 the molars and bicuspids. The tuft of the l)rush sliould also be carried to the flistal surfaces of the last molars on both the upper and lower jaws and with a wiping or twisting motion these surfaces should be cleansed. The foregoing description of brushing gives but a stereotyped form. The mouth should be gone over three or four times until the gums begin to tingle and a slight sense of numV)ness is felt. The festoons on the palatal and lingual surfaces cannot be properly brushed with the circular stroke. It may be noted that they assume a much straighter line than on the buccal surface and that the bristles traveling in and out with this straight line reach all surfaces and are more stimulating and non-irritating in their action. In the roof of the mouth are the posterior and anterior palatine arteries which help to supply the gum tissue, hence the importance of brushing the hard palate (Fig. 189). It should be noted that the brush is used with a full-arm motion and that a fast but light stroke is essential to secure the desired results. Number of Daily Brushings. — Not so very many years ago more than one bathtub in a private house was considered a luxury. Today it is realized that frequent bathing is a necessity. Some dentists advise their patients to brush their teeth before retiring; some, night and morning; and the patient who followed tliis last rule, thought himself virtuous indeed. The matter of brushing the teeth is piu"ely educational and resolves itself into a habit. Time can always be found for any habit— it is merely a question of what habits are acquired. After each meal a certain amount of food is retained on the surfaces of the teeth. . In less than an hour's time this food begins to decom- pose. If the teeth are brushed at night and in the morning before breakfast, remnants of the breakfast remain on the teeth until bed- time, joined through the day by those of lunch and dinner. There may be some arguments in favor of not disturbing the decomposing food in the mouth all day, but such arguments are usually based on the statement that people do live wdth unbrushed teeth, so why handi- cap them with an extra daily duty when they have so little time to spare. Those who advance these arguments usually have a breath far from pleasing. It cannot be shown scientifically that a mouth containing decomposing food is as healthy and wholesome as one that is free from it. The teeth should be thoroughly cleaned after each meal with brush and dentifrice, and given a vigorous brushing with clear water the first thing in the morning. This means four brushings a day. Of course it is not always possible to follow^ this rule to the letter, but where one has access to a bowl and one's tooth-brush, the teeth should be cleaned. All children should be taught this habit, as there can be no greater insurance for health and freedom from infectious diseases than a mouth free from decomposing food. 23 354 DENTAL PROPHYLAXIS Dentifrices. — The most important ingredient in a dentifrice is soap. Next, a slight abrasive, such as a fine grade of precipitated chalk. The rest of the formula is of but little value and is used chiefly to dis- guise the soap and impart a pleasant taste. The removal of grease is a chemical action and soap is essential for thoroughly cleaning the teeth. If fat is rubbed on the hands or on a slab of glass it will be difficult to remove it with clear water and a brush. Although with considerable effort it may be done, soap will remove it much more quickly. A fine grade of powdered Castile soap is the best, but it is seldom found in the preparations on the market, as it does not give sufficient lather to suit either manufacturer or purchaser. The most harmful element in a dentifrice is the use of cheap coarse grades of chalk. In fact some preparations contain pumice and in one foreign ■production, powdered oyster shells were found. The teeth should be cleaned, not scoured, and the daily use of a gritty dentifrice will even- tually cause abrasion of the thin enamel surfaces at the necks of the teeth. The grit may be readily detected by placing some of the paste or powder between the teeth and biting on it. Finer tests may be made by putting it between two glass surfaces, rubbing them to- gether and examining them with a magnifying glass. A slight abrasive is helpful in aiding in the removal of the slippery film of mucin and viscid accretions on the surfaces of the teeth. Its daily use is harmless providing the grit is fairly soluble and not coarse. ^Nhen one computes the number of occlusions that take place daily between the masticating surfaces of the teeth diuing the three meals and notes what little wear of the enamel cusps is exhibited at thirty- five or forty years of age, it may be concluded that the use of a fine grade of precipitated chalk as a base for a dentifrice is not a serious menace to the enamel tissues. There is but little choice between pow- der and paste, as regards efficiency. Powder has to be worked into a paste-like condition in the mouth with the brush, while paste quickly spreads itself over the teeth for immediate action. The majority of people find the paste much pleasanter to use. The difference in the formulae of the two preparations consists in leaving out the saccharin in the powder and mixing the powders and oils with glycerin to form paste. A simple, cheap and effective powder may be made by placing the following ingredients, all of which may be bought at any drug-store, in a quart Mason jar: Finest grade English precipitated chalk 5 pound Powdered Castile soap If ounces Light carbonate of magnesia i ounce Oil of clove 46 drops Oil of wintergreeu 35 " Oil of sassafras . 35 " Oil of peppermint 18 " Saccharin — finely powdered 4 grains BRUSHING 355 The glass top should be securely fastened on and the contents shaken vigorously. This mixing process takes some time, but as it takes at least twenty-four hours for the oils to permeate the powders, the jar may be picked up at varying intervals and its contents thoroughly shaken. A larger bottle with the same quantity of powder will permit of a more thorough mixing in a shorter time. The brush should be very wet when the powder is placed upon it and care should be taken not to inhale when introducing the brush into the mouth. A properly prepared tooth paste is a much pleasanter toilet article to use and, as there are some on the market quite effective and harm- less, one of these may be recommended to patients for use. Each tooth has five surfaces. Three of these can be cleaned with the brush, but the two approximal surfaces, the most susceptible of all, cannot be reached with it. In other words three-fifths of the sur- faces of the teeth can be cleaned with the tooth-brush but not th(3 remaining two-fifths which most need it. It should then be apparent that if all the food is to be cleaned off all the surfaces of all the teeth, additional means of so doing must be employed other than the tooth-brush. Up to the present time nothing is known that will accom- plish this more efficiently and harmlessly than the floss silk and lime- water. Fig. 190 Floss Silk. — If the floss silk is skilfully and frequently used, the approximal surfaces may be kept quite free from dental caries. To induce patients to use the floss silk with regularity is a task, but by being persistent in requesting and logical in the reason for its use, they may be made gradually to acquire the floss habit. To insure the proper 356 DENTAL PROPHYLAXIS use of the floss the fiUings in the approximal surfaces should be smooth and poHshed, with just sufficient pressure at the contact points to allow the floss to snap through without too much effort in forcing it. Care Fig. 191 should also be taken not to allow the floss to snap through on the gum tissue hard enough to wound it. There is but little danger of this Fig. 192 after a little j)ractise, esi)('cially after the gums have become hard and tough from brushing. A reasonably sniall-si/ed waxed floss is the best to use. For adults the piece should be fourteen or fifteen inches in BRUSHING 357 length. The end of the floss is taken between the thumb and first finger of the left hand and two wrai)s made around the end of the first finger, and this act repeated with the other end of the floss on the Fig. 193 Fig. 194 358 DENTAL PROPHYLAXIS right forefinger. The floss is now held securely and will permit the ends of the two thumbs or the two second fingers or a combination of a thumb of one hand and a second finger of the other, to guide the silk into its position in the mouth and force it between the teeth. Fig. 190 shows adaptation of floss for right upper teeth. Fig. 191 shows adaptation for left upper teeth. Fig. 192 shows adaptation for all the lower teeth. After the floss has passed through the contact points it should be rubbed back and forth against both approximal surfaces to polish them mechanically. In withdrawing the floss, if the end held opposite the lingual surface is brought over on the buccal surface and the silk is pulled through the contact points in the form of a loop, it will be more effective in polishing or cleaning these surfaces than if merely snapped out (Figs. 193 and 194). The floss will not, however, thoroughly remove all the food between the teeth, therefore we must have recourse to a mouth wash. Lime-water. — Practically all the mouth washes on the market are formulated to accomplish two results. First, a neutralizing action, either acid or alkaline, and second, a germicidal action. It will readily be understood that the latter result cannot be obtained in the mouth, while the former is immaterial. In order to secure immunity to decay, the bacteria must be robbed of any pabulum, upon which to feed and any placques or glue-like accumulations on the surfaces of the teeth must be dissolved. Acid mouth washes have been advocated because it has been found that the lactic acid forming bacteria are retarded in their growth and activit}^ in an acid medium. Alkaline washes have been prescribed because of the belief that they will neutralize any lactic acid formed that will induce caries. Both of these theories are based on partial facts only, for it has been absolutely proved that the chemical action of an acid or an alkali used as a mouth wash for neutralizing purposes will not inhibit dental caries to any great degree. All of these washes are supposed to contain germicides that will immediately destroy the micro5rganisms of the mouth. This is of course untrue, especially when the short time they are retained in the mouth for this purpose is considered. The peroxide of hydrogen is religiously used by many, in the belief that the oxygen liberated is a germicide of sufficient power to destroy all the bacteria. The mechanical action of the peroxide in its boiling process, while it does liberate the oxygen, is more effective in dislodging particles of food debris around the necks of the teeth than in its germicidal action on the organisms in the mouth. In the study of dental caries it must be concluded from the present knowledge of the subject that in the main Professor Miller's theory still holds good, namely, that the exciting cause is due to the production of lactic acid by the action of microorganisms on carbohydrates, and that decay takes place most readily on those sur- faces least exposed to friction during mastication, such as the fissures or pits, approximal surfaces, and the necks of the teeth. Dr. J. Leon BRUSHING 359 Williams was the first to point out the fact that a thin gelatinous placque was first formed on the surface of the enamel and under and in this thin film the bacteria obtained a secure position that made their dislodgement difficult. Their action in the production of acid was intensified when thus protected. Other scientific investigators have corroborated Williams' observations. The mucin, which is a product of the salivary and mucous glands, plays an important part in the formation of these placques. Laying aside any theories regarding susceptibility and immunity, it must be admitted that the battle just now should be the thorough removal of all food debris and the removal of these placques and glue-like accretions. At the present time there is considerable agitation in dental circles regarding the use of fruit acids to prevent dental caries. Mucin is precipitated from the secretions in the mouth by the presence of an acid. This precipitate forms on the surfaces of the teeth and becomes the factor in incasing the bacteria with food debris and in forming the so-called placques. Mucin thus precipitated is soluble in or may be dissolved by an alkali. It has been found that the pres- ence of fruit acids in the mouth excites a flow of saliva which possesses quite a strong alkaline reaction. It is claimed by these investigators that the increased alkalinity of the saliva has a solvent action on the precipitated mucin and a neutralizing action on lactic acid and thus becomes a natural preventive of dental caries. Other investigators have as yet been unable to find that the alkalinity so produced is of sufficient strength to have this solvent action. Again, it is claimed that the acids of fruits have a curdling effect on the mucin, forming it into flakes which are easily removed from the tooth surfaces. There is a serious question concerning the habitual use of these acids for this purpose. Practically all of the acids of fruits, especially those of oranges and lemons, if used too freely will in time act as sol- vents for the cementing substances between the enamel rods. If the deductions of these investigators were entirely correct the inhabitants of the tropics would be found to be quite free from dental caries, which of course is not the case. Williams has observed that the peasants working in the orange and lemon groves of Sicily were quite immune to caries, and Pickerill also cites the natives of New Zealand as an example. The Italians and the Sicilians are very fond of hard bread and coarse food, and if a scientific investigation were made regarding their immunity to caries other powerful factors would be found besides the fruit acids. Those who live in the orange groves of Florida are far from being immune, in fact the reverse is the rule. The American Indian, who did not eat much fruit, enjoyed a considerable immunity from caries. In fact, if every one lived an out-of-door life, eating coarse food and less sugar, there would be but little need of the dentist. A reasonable amount of fruit is healthful and desirable, but denti- frices and mouth washes containing fruit acids, must be used with considerable judgment. 360 DENTAL PROPHYLAXIS If it can be scientifically shown that dentifrices and mouth washes containing fruit acids in certain proportions are harmless to the teeth and the tissues of the mouth and are superior to any of the present-day preparations as prophylactic agents for dental caries, it would prove to be a valuable contribution to dental prophylaxis. As it will take a number of years to demonstrate this as a fact it will be necessary for the present to adhere to those agents that have proven themselves to be harmless and efficient in the past. The most cleansing and the least harmful of all fruits is the apple. This with its dense texture acts as a mechanical cleanser, and the malic acid is comparatively harmless. Where it is impossible to have access to a tooth-brush the eating of an apple will be found an excel- lent substitute. There is a solvent for the placques and accretions on the surfaces of the teeth that is quite positive in its action. This solvent is lime-water, and is made from the coarse calcium oxid or unslaked lime. Its preparation is simple and cheap, and when its efficiency for the use and purpose intended is considered, it will rank as an important agent for the prevention of dental caries. Some coarse lime, such as is used in making rough plaster, may be secured from a paint store or from a mason. The refined product found in the drug-stores apparently does not have the same effect. The refining process robs it of some of its beneficial properties. It is cream white in color. The lumps should be broken up into coarse powder and a half-cupful put into a quart bottle. The bottle should be nearly filled with cold water, room enough being left to per- mit of thorough shaking, shaken vigorously and set aside for three or four hours to allow the lime to settle. Then as much of the clear water as possible should be poured off, for this contains the washings of the lime. It will be found impossible to pour off all the water without losing some of the lime, but by pouring slowly nearly two- thirds may be drawn off. The bottle can then be filled with cold water and shaken thoroughly, when, after it has settled again, it will be ready for use. A bottle of convenient size should be procured; one holding ten or twelve ounces, and filled with the clear water from the large bottle. This smaller bottle will be more convenient to use at the bowl. The large bottle can be again filled with cold water, shaken thoroughly and set aside to be used as needed (Fig. 195). This operation may be repeated over and over again, for the original half- cupful of lime will make five or six quarts of lime-water. If the first use of the w^sh proves that it is a little strong, it can be diluted in the small bottle. With new patients and those having tender gums it may have to be diluted, but as soon as ])()ssil)le it should be used undiluted. When taken into the mouth it should be forced IrM-k and forth vigor- ously between the teeth with the tongue and checks and the rinsing contirmed until it })reaks into a foam. Not that there is any particu- larly beneficent action to the foaming, but if it is worked through the BRUSHING 361 teeth long enough to make the foam it will have been in contact with the surfaces of the teeth long enough to have a solvent action on the placques and accretions. Afterward the mouth should be thoroughly rinsed with warm water to take away the taste of the lime-water. It is the unpleasant taste of the lime that makes it difficult to induce the patients to use it at the start, but after a short time the cleansing effect is so pleasing that they soon forget about the taste. It may be flavored with saccharin or any flavoring material, but this will hardly be found necessary. The lime-water should be used after the brushing and flossing, after each meal. Fig. 195 Summary of Prophylaxis. — One prophylactic treatment does not con- stitute prophylaxis. It is only by a systematic, continuous course of treatment and home care of the mouth that these ideal conditions can be secured. It is estimated that all great educational movements that possess real merit take thirty years for their final acceptance and adoption. Mouth hygiene has been agitated for fifteen years. The next fifteen years will see its rapid spread throughout the country and its practise quite general. Preventive dentistry can be had quite cheaply and is within the reach, financially, of nearly everybody. Good operative dentistry is expensive and always will be, as is surgery or the services of any educated and skilled specialist. Prophylaxis is the only hope of solving the dental problems for the masses and as time goes on it will be found as necessary a form of insur- ance for health as life insurance is for the protection of those left after one dies. When the public really becomes educated to the fact that for the 362 DENTAL PROPHYLAXIS expenditure of a very moderate sum of money and a little energy on their part, they may retain their teeth throughout life quite free from pain and disease, there will be a great demand for this form of service. Every mouth would be greatly benefited if these treatments could be admuiistered e\ery two months. Many mouths require monthly treatments, especially those of children and adults who are susceptible to caries. In an analysis of susceptibility it will be found, in many cases, that the individual is indulging in too much candy and free sugars. Children are given crackers or cookies just before going to bed, and not infrequently in bed, to keep them quiet. Women and children especially are fond of sweets, and it is the promiscuous eating of them between meals that creates such havoc with the teeth. England, France and America are consuming too much sugar. An educational campaign to check this large consumption would be of great help in our problem. Statistics show that the countries where the greatest amount of sugar is eaten are the countries where the worst conditions of teeth are found. The sugar consumption per capita has increased amazingly during the past forty years and so has dental caries. If dentistry, as a science, had not advanced so rapidly during this same period, ruined mouths would be even more prevalent. In the search for some easy solution of the problem of dental decay many ideas are advanced for its ultimate control, and it is expected that a simple method of doing away with this great disease-producing disorder will be found. There may come a time when a lozenge will produce immunity but that time is not in sight as yet. As long as people live artificially, as most people do, eating the various concoc- tions called "food" that they feel free to eat at the present time, the one hope of escape from the ill-effects of dental decay and its attending serious efl'ects on the body is through the present knowledge of extreme cleanliness, or mouth hygiene. Until something can be presented more definitely shnple that will show equally beneficial results, it will be necessary to adhere to the form of prophylaxis herein advocated. SOME OFFICE FACTS AND STATISTICS. In the writer's practice many cases of interest have been observed; individual cases, however, always lack force, for there may be a ques- tion of doubt about them, but a demonstration made by thirty or forty people simultaneously permits of comparisons and brings conviction to even doubting minds. This enthusiasm in oral prophylaxis is due to the ideal health con- ditions obtained in the mouths of patients, to their consequent physi- cal betterment and to their hearty endorsement. In the early part of the year 1914 the following letter was sent to two hundred of the writer's patients: SOME OFFICE FACTS AND STATISTICS 363 Bridgeport, Conn., January, 1914. My dear , In preparing some lectures on the subject of prophylaxis, I have found it desirable to offer some facts and statistics concerning my own practice, and would consider it a personal favor if you would kindly fill out the enclosed card and return it to me. It is not my intention to use any names or any individual cards. I merely wish to get at the truth to verify statements I have felt war- ranted in making concerning the comparative immunity from sickness when the mouth is kept in a clean and wholesome manner. We know that many of the infectious diseases of childhood emanate from unsanitary mouths, these with their decayed teeth and decom- posing food debris being ideal incubators for germ life. We know, too, that in adults whose mouths are unclean and diseased, the intestinal tract as well as the whole nutritive system is seriously disturbed and organic infections are frequently produced. A clean, sanitary mouth is not, of course, a panacea for all of our ailments, but we know that it is a powerful factor for good health. It is a fact, frequently mentioned at my office, that it is extremely rare for a patient to cancel an appointment on account of illness, and I feel it would be helpful to the dental profession in advancing this work of prevention if additional facts of this nature could be secured. I realize that it is something of an imposition and rather an unpre- cedented thing to do, but feel that the cause involved is sufficiently great to warrant my asking this favor. If for any reason you would rather not fill out the card please feel free to ignore it. Yours very sincerely, Alfred C. Fones. With this letter w^as enclosed a card on which were printed. the following questions: Name Have you been ill duiing 1913? , If so, was the illness of long duration? If you do not object will you state illness? •. . . Do you feel that mouth hygiene has benefited you physically? Any remarks Signed The object in sending these letters and cards was to secure some data relative to the physical influence of mouth hygiene upon the every- day life of both children and adults and also to get an expression of opinion as to whether or not mouth hygiene, as a factor for good health, was appreciated by the patients. Perhaps the last question was not very fortunately worded. It w^as not expected that the patients would experience any pronounced glow of health coming over them after following the system of mouth cleanliness for a period of time; still in 364 DENTAL PROPHYLAXIS spite of this perplexing question the answers were both interesting and quite satisfactory, as the tables will show. At the time it became neces- sary to use this data, one hundred and sixty cards had been returned, or 80 per cent, of those sent out. A study of the following tables of the answers returned will at least prove interesting, even if no scientific data are found. To the question, "Have you been ill during 1913?" the cards showed the following answers: 14 stated illness. 11 had colds (now and then). 135 had no illness. These figures show that 85 per cent, of these patients had been free from all sickness. Of the fourteen who had been ill the following table gives details: Duration of Illness. SFumber. illness. Child. Adult Grippe .... 2 3 days each 1 1 Tonsillitis . 2 4 days — 2 weeks 2 Nervous trouble . 1 "Not long" 1 Whooping-cough . 1 "Quite long" 1 Acute indigestion . 1 2 days 1 Appendicitis . 2 4 weeks — "not long" 2 Pleurisy 2 1 week — ^"not long" 1 1 Sore throat 2 5 days — "not long" 2 Bronchitis . 1 "A few days" 1 Although a diseased or unsanitary mouth would be capable of producing most of the ailments noted in this list, it must be remem- bered that these patients present healthy mouths and are reasonably faithful in their care. Under such conditions it would seem justifiable to eliminate the following from the table: Two cases of appendicitis, the operation for one of which had been previously planned for two months and the other one being a recur- rent attack soon controlled and not requiring an operation, one of acute indigestion, one nervous trouble, and two of pleurisy. This list, under the above conditions, would not be susceptible to serious debate as being caused through mouth infection. The remain- ing ailments partially prove that mouth hygiene does not secure abso- lute immunity to infectious diseases, yet it must be conceded that the length of illness, with the exception of the two weeks of tonsillitis, is sur[)risingly short. If the eleven who stated "colds now and then" are eliminated and charged up to overfeeding, there are, as a last analysis, eight people out of one hundred and sixty who were ill during 1913 with forms of illness from which to the writer's minil, mouth hygiene sliould liaxc made them immune. To try to claim everything in sight would be discourteous to the medical profession, but in a broad sense it may be stated that, omitting the list of colds, over 90 per cent, were free from sickness and ninety-five were free from infec- tions di.seases. A SYSTEM FOR PIIOPIIYLAXIS IN DENTAL PRACTICE 365 Considerable interest may be found in the answers to the last question which was: "Do you feel that mouth hygiene has benefited you physically?" 53 answered "Yes." 10 answered "Cannot say." 3 space blank, no comment. 37 stated an appreciation of prophylaxis. 51 specific statements of physical betternu>nt. This question was inspired by the comment of numerous dentists who had stated that patients would have but little appreciation of prophylaxis. If the question had been instead, "Do you feel that mouth hygiene is a physical benefit?" it would have shown whether or not the patients had an understanding of its importance and would in itself have answered the comments. Considering the blunt way the question appeared on the card, the answers were highly satisfactory, and although they give no scientific data, they surely indicate a reasonable degree of enthusiasm for the science of prophylaxis. Twenty-seven stated their appreciation without comments of physical betterment. Fifty-one stated, in a general way, that they felt mouth hygiene had benefited their general health and six named the disappearance of their ailments. Of the latter two had recovered from chronic indigestion, one noted the dis- appearance of headaches, and three stated the disappearance of throat irritation. It must be remembered that these cards form a record of but one hundred and sixty people of all ages for but one year. Whether an additional one hundred and sixty cards would add to the interest of these tables is hard to determine without trying it out. Scientific facts cannot be based on any general investigation of this kind, but it must be admitted that the evidence submitted is at least favorable to mouth hygiene. A SYSTEM FOR PROPHYLAXIS IN DENTAL PRACTICE. First a new patient is given two appointments, a week or ten days apart, with the dental hygienist, for a thorough instrumentation and polishing of the teeth. At the end of the first sitting he is supplied with a tooth-brush, dentifrice, floss silk and lime-water for a mouth wash, taken to a wash bowl and taught how to properly brush teeth and gums, and given full instructions in the home care of the mouth. At the end of the second sitting one-half hour is reserved for him with the dentist for a thorough chart examination. Appointments are then arranged and the teeth restored to a sound condition. At the end of the last appointment the dentist gives the patient a thorough prophylactic treatment. The patient is then put on a list and sent for each month for a 366 DENTAL PROPHYLAXIS treatment by the dental hygienist. At the end of six months he again goes into the hands of the dentist for a thorough prophylactic treatment and examination of the teeth and gums and if the condition of his mouth warrants, the interval between the treatments is now lengthened to six weeks. At the end of the next six months he again goes through the dentist's hands and if good mouth health is attained his name is placed on a two months' list and he is given treatments by the dental hygienist at these intervals, going into the dentist's hands for every third treatment, or once in six months. Patients whose mouths are very susceptible to dental caries, such as children and young people, should be retained on the monthly or six weeks' list. When the patient's mouth has been put in order and his name placed on one of the lists to be sent for at regular intervals, his name is also entered in the appointment book against the date when his next appointment for a prophylactic treatment falls due. A week previous to this date the patient is notified of the appointment by means of a return card system. This consists of an appointment card bearing the name of the patient and date and hour of his appointment, a return card bearing the same date, and a stamped return envelope. If the date designated proves convenient, the patient signs the return card and returns it in the enclosed envelope and the appointment is checked in the appointment book. If not convenient, a new appointment is made. The various lists of patients — monthly, six weeks and two months — are kept by means of a card-index file. CHAPTER XIII. CHEMISTRY OF FOOD AND NUTRITION. By RUSSELL H. CHITTENDEN, Ph.D., LL.D. Sc.D. Part I. In a popular sense, under the term food is included all those sub- stances which man, following the dictates of a capricious appetite, is in the habit of eating. In this sense, food comprises a large number of substances or products belonging to the animal and the vegetable kingdoms. If, however, we attempt a chemical analysis of the various foods which man is accustomed to eat, it is found that they contain one or more of six distinct classes or principles. These are known as proteins, albuminoids, fats, carbohydrates, inorganic salts or mineral matter, and water. In a physiological sense, a food is a substance which helps maintain the integrity of the body tissues, thus insuring a normal condition of the body protoplasm. This implies not merely the integrity of the tissues of the body as a whole, but likewise the integrity of each indi- vidual unit of the tissues, i. e., the tissue cells. Food must supply material for the growth of new tissue as in the young, and for the repair or maintenance of wasting tissues in the adult. Further, a food, in the strict physiological sense, must not only contribute to the maintenance of the tissues, but it must likewise fur- nish energy to meet the daily needs of the body; energy which will manifest itself in the form of heat or work, as the case may be. It should also help maintain and strengthen the defenses of the body against disease, or disease germs. In other words, physiologically speaking, a food must help keep up the normal nutritional rhythm of the body. Again, a food, if it conforms to the physiological defini- tion, must not be in any sense inimical, or harmful, to any of the tis- sues or any of the processes of the body. Of the various food principles, the proteins taken as a class are, for many reasons, the most important. They are composed of carbon, hydrogen, nitrogen, oxygen, sulphur, and some contain phosphorus. As a rule they contain approximately 52 per cent, of carbon, 7 per cent, of hydrogen, 16 per cent, of nitrogen, 22 per cent, of oxygen, 0.5 to 2 per cent, of sulphur, the phosphorus when present being con- tained ordinarily in small amount. Protein foodstuffs are widely distributed throughout the animal and vegetable kingdoms, and while they differ somewhat among themselves, both in chemical composi- tion and in physiological behavior, they are alike in containing approx- imately 16 per cent, of nitrogen. They are therefore referred to as 368 CHEMISTRY OF FOOD AND NUTRITION nitrogenous foods. Proteins, furthermore, are likewise spoken of as essential foods, because they are absolutely essential for life. In the definition given of a food, it was stated that a food is a substance which helps maintain the integrity or normal condition of the tissues of the body, which means as well the condition of the cell protoplasm. The functional activity of a tissue, whatever it may be, depends upon the functional activity of the individual elements of that tissue, i. e., the tissue cells, and the chemical basis of a cell is the cell protoplasm. Again, the important part of the cell protoplasm is the ptotein material which it contains. Every living cell of the body, whatever its nature, whatever its origin, whether it be an exceedingly active tissue like the muscle tissue or brain tissue, or whether it be a very inactive tissue like bone and teeth, is made up of cell protoplasm, and the cell protoplasm in every case is composed largely of protein material. These tissue cells, or their contained protoplasm, are not able to renew the waste of cell substances except through the intake of protein food. Growing tissues likewise are dependent upon the intake of fresh pro- tein material to accomplish growth. The nitrogenous or protein foods are therefore essential foods, necessary for maintenance and for growth. In no other way than by the intake of protein food can the protein material of cell protoplasm be renewed. As has been stated, phosphorus is not common to all proteins; but there is a certain group of very important proteins practically present in all tissue cells, and consequently playing a very important part in nutrition, substances which contain phosphorus in quite appreciable amounts. These phosphorized proteins are generally termed nucleo- proteins, since they are composed of a peculiar phosphorized substance known as nuclein or nucleic acid combined with protein. Albuminoids are substances closely related to the proteins, contain- ing nitrogen in essentially the same amount as a true protein in addition to carbon, hydrogen, oxygen and sulphur, but they differ from the proteins proper in that they have a different nutritional value. Gelatin is a typical albuminoid, a substance which, while resembling protein in many respects, is not able to support life to the same degree that a true protein can. As distinguished from the proteins, fats and carbohydrates are fre- quently termed non-nitrogenous foods, owing to the fact that they contain no nitrogen, but are composed solely of carbon, hydrogen, and oxygen. Carbohydrates contain approximately 40 per cent, of carbon, while the hydrogen and oxygen present are in such proportions as to form a certain number of molecules of water; hence the name carbohylainly that excessive eating of i)rotein food, meats and kindred products, is not necessary for the doing of muscular work. There must obviously be sufficient protein in the daily diet to meet the needs of the cells of the Ixxly to keep the machine in good working order, but the energ}^ called for in even excessive muscular work, is derived ordinarily and most advantageously from carbohydrates and fats. A mixed diet, one which contains protein, fat and carbohydrate, CHEMISTRY OF FOOD AND NUTRITION 385 together with salts and ^^'ater, is the most beneficial to the })ody and one which accords witli physiological experience. As stated many times, a certain amount of protein food is needed for the construction and maintenance of cell protoplasm; fats and carbohydrates are required to supply the energy needs of the body. Fats and carbohy- drates may be substituted one for the other in some measure, but carbohydrates, for many reasons, constitute the larger proportion of the non-nitrogenous food with most peoples. This is due not alone to the fact that carbohydrates are relatively easy of digestion and oxida- tion, but also because of the abundance and consequent cheapness of carbohydrates as a class. A study of the dietary habits of peoples throughout the world has shown that in most countries carbohydrates are usually present in the daily diet in amounts five to ten times greater than the quantity of fat. From an energy standpoint, as already explained, one part of fat is the equal of 2.3 parts of carbo- hydrate, such as sugar or starch. Consequently, in the replacing of starch by fat, or vice versa, they must be substituted one for the other in isodynamic amounts; that is, 1 gram of fat will take the place of 2.3 grams of sugar, so far as the yield of energy^ is concerned. The average daily diet with its heat value, advocated by the cele- brated physiologist Voit, of Germany, is as follows: Grams. Calories. Protein 118 483 " Fats 56 520 Carbohydrates 500 2050 3055 Ranke, on the other hand, recommended a diet composed as follows: Grams. Calories. Protein 100 410 Fats 100 930 Carbohydrates 240 984 2324 Moleschott, another authority often quoted, gave the following data as representing an average daily diet: Grams. Calories. Protein 130 533 Fats 40 372 Carbohydrates 550 2275 3180 From these statements it is apparent that the authorities quoted considered that man needs approximately 100 to 130 grams of protein food a day, with sufficient fat and carbohydrate to make a fuel value ranging from 2300 to 3100 calories. It is obvious, however, that the calorific value of the daily food, so far as the physiological needs are 25 386 CHEMISTRY OF FOOD AND NUTRITION concerned, must vary with the degree of physical activity. Where a large amount of muscular work is performed there is need for a corre- sponding increase in the non-nitrogenous foods, and since, as before stated, carbohydrates are both cheap and easily digestible, the increase usually comes from this class of foods. A study of the table showing the chemical composition of some common food materials given on page 369 shows at once the advantages of a mixed diet for meeting the needs of the body for protein and total energy. Assuming the Voit standard to represent the daily needs of the adult, namely, 118 grams of protein with a total fuel value of 3053 calories, it is apparent that animal food, such as meat, would by itself be quite impossible for a steady diet. As fresh beef contains 22 per cent, of protein, it would be necessary for a person to eat 500 grams, or a little more than a pound, of beef to obtain the needed 118 grams of protein, but the fuel value of one pound of beef is only 540 calories. Consequently, in order to obtain the necessary 3000 calories, at least six pounds of beef would be required, or six times the amount of protein food really needed. This, plainly, would be physiologically undesirable and exceedingly uneconomical. If, on the other hand, bread with a fuel value of 1395 calories per pound, macaroni with 1665 calories per pound, or rice with 1630 calories per pound, are used to replace the larger portion of the meat, a mixture can be obtained much more advantageous as a daily diet. In other words, almost any single food, if eaten in sufficient quantity to supply the nitrogen or protein requirements of the body, will give either too little or too great fuel value. A typical animal food, such as meat or eggs, when eaten in such amount as will furnish the neces- sary nitrogen or protein, fails to furnish more than a fifth of the fuel value required. As a rule a diet made up solely of vegetable foods, consumed in such quantity as to furnish the necessary protein, means the consumption of much more carbohydrate or total fuel value than the body really needs. There are, to be sure, certain vegetable foods, apparent from the table of food compositions, which may advanta- geously be used for supplying both the nitrogen and energy require- ments. Practically, however, most people are accustomed to obtain their supply of proteins, fats and carbohydrates from both animal and vegetable foods. It is a fact well appreciated by physiologists that the mechanism of digestion and nutrition as a whole should not be subjected to undue strain. Consequently, the danger of consuming too large amounts of any one class of foods is just as serious as the danger of not consuming enough to meet the real needs of the body. The protein of the day's diet may well come frbm meat, milk, rice, bread, potatoes, and other vegeta})l('s, thereby introducing along with the nitrogen, (luantities of carbohydrate and fat by which the protein requirement and the body requirement can both be met with- out consumption of an undue quantity of any one of the several classes of foodstufi's. CHEMISTRY OF FOOD AND NUTRITION 387 The two following ta))les, giving the average food consumption of peoples in Swetleii and Finland, are well worthy of study as showing first the different foodstuffs made use of during a single week, the distribution of the protein in the form of vegetable and animal pro- ducts, as well as the amounts of fat and carbohydrate with total fuel values for a week, from which is calculated the average daily consump- tion per individual. SWEDISH— PER WEEK. Food. Total amount, grams. Protein, grams. Fat, grams. Carbo- hydrate, grams. Calories. Rye flour Wheat flour Scotch barley . Oatmeal Peas Potatoes Skimmed milk (liter) Margarine Fresh meat . Salt pork Salt fish .... Salt Pepper .... Tubers .... Vegetables . Bread .... Total . . Per day . 450. 275. 315. 210. 630. 3. 4. 185. 340. 255. 250. 139. 1. 200. 500. 4760. 51.8 33.0 36. 27. 144. 41. 159. 1 57.8 28.1 30.0 2.4 0.8 366.5 9.0 4.1 4.7 12.6 12.0 3.2 31.9 157.3 34.0 140.3 30.0 0.4 0.1 61.0 315.0 198.0 223.6 1.38.6 330.8 435.2 227.7 1.1 16.0 4.0 2222.9 980.8' 140.1 501.5 71.6 4112.9 587.6 1,588 985 1,109 797 2,062 1,985 1,883 1,472 553 1,420 402 79 21 11,192 25,548 3,650 FINLAND— PER WEEK. Food. Total amount, grams. Protein, grams. Fat, grams. Carbo- hydrate, grams. Calories. Scotch barley 420 48.3 6.3 298.2 1.479 Barley flour 700 80.5 10.5 497.0 2,464 Oatmeal 220 28.6 13.2 145.2 835 Peas . . 280 64.0 5.4 147.0 914 Cheese . 385 138.6 25.0 23.1 895 Butter . 60 0.4 51.0 0.4 478 Roast beef 300 51.0 30.0 490 Pork 210 21.0 105.0 1,065 Suet . . 84 0.3 83.2 775 Salt fish . 1050 115.5 73.5 1,157 Potatoes 1365 27.3 2.1 285.6 1,302 Cabbage 90 1.2 0.3 7.2 39 Syrup 40 0.4 29.6 124 Bread 3990 459.9 74.9 2809.8 14,105 Total 1037.0 480.4 4242.7 26,122 Per day 148.1 68.6 606.1 3.732 It is interesting to note in the two series of observations that the peoples in both countries derived the larger part of their protein from the vegetable kingdom, only a small amount coming from meat, 388 CHEMISTRY OF FOOD AND NUTRITION though in Finland a relatively large proportion of protein came from cheese and from salt fish. The chief source of protein, however, in both countries in these observations was bread. Again, it is to be observed that the daily protein consumption per individual was high, 140 to 148 grams. The daily fuel value was likewise high, 3650 calor- ies and 3732 calories. By observations such as these, made in many countries and under different conditions of life, work, etc., so-called dietary standards have been adopted. These standards are more or less generally assumed to represent the requirements of the body for food. In Sweden, laborers doing hard work were found by some observers to consume daily on an average 189 grams of protein, 714 grams of carbohydrate, and llO grams of fat, with a total fuel value for the day's ration of 4726 calories. In France, it is stated by a prominent physiologist that the ordinary laborer working eight hours a day must have 135 grams of protein, 700 grams of carbohyrate, and 90 grams of fat daily, with a fuel value of 4260 calories. In England, weavers were found to consume daily 151 grams of protein, with carbohydrate and fat sufficient to make the total fuel value of the day's ration equal 3475 calories. Observations of this character, which might be multiplied indefinitely, may suffice to give an idea of the average food consumption of European peoples doing a moderate amount of work. In our own country very extensive observations have been made, especially by the office of the experiment station in the Department of Agriculture, under the leadership of the late Professor Atwater. For a period of ten years, from 1894 to 1904, dietary studies of the actual food consumption of people of different classes in different parts of the United States were made on about 15,000 persons — men, women, and children — as a result of which certain standards have been adopted, indicating the so-called food requirements of persons under different conditions of life and work. These standards vary from 100 to 175 grams of protein per day, with a total fuel value ranging from 2700 to 5500 calories. Some of the foregoing statements are brought together, in tabulated form, in the following table: Subjects. Swedi.sh laborers, at hard work . Russian workmen, moderate work German soldiers, active service . Italian laborers, moderate work French laborers, eight hours' work English weavers Austrian farm laborers American subjects. Man with very hard muscular work Man with hard muscular work 150 Man with moderately active muscular work Man with light to moderate muscular work Man at "sedentary" or woman wilh moder- ately active work 100 2700 Protein consumed daily, grams. Total fuel value of daily food, calories. 189 4726 132 3675 145 3574 115 3655 135 4260 151 3475 159 5096 175 5500 150 4150 125 3400 . 112 3050 CHEMISTRY OF FOOD AND NUTRITION 389 These figures by no means represent the maximum food consump- tion. Thus, with hnnbermen in the Maine woods, it was found by the United States Dejjartment of Agricultiu'e that the intake of pro- tein food averaged 185 grams per day, per in(U\'i(hial, with a total fuel value of 6400 calories. The tendency has been to assume that figures such as the above, which are merely an expression of the dietetic habits of people, show the actual food requirements of persons under difi'erent coiKlitions of life and work. This, however, is an assumption which, while it has met with more or less general acceptance, may be questioned as being strictly logical. Such data are indeed interesting and important as giving information regarding dietary customs and habits, but there seems to be no logical reason for assuming that such data represent the actual food requirements of the body. As stated by another: "Food should be ingested in just the proper amount to repair the waste of the body ; to furnish it with the energy it needs for work and warmth; to maintain it in vigor; and, in the case of immature animals, to provide the proper excess for normal growth, in order to be of the most advantage to the body." Other physiologists, like Voit, have clearly emphasized the general principle that the smallest amount of protein, with non-nitrogenous food added, that will suffice to keep the body in a state of continual vigor, is the ideal diet. Any habitual excess of food over and above what is really needed to meet the actual wants of the body is not only uneconomical, but may be distinctly disadvantageous. Mankind has always been guided in dietary matters by appetite; that is, by a conscious desire for food and the desire for special kinds of food. But man is a creature of habits; he is quick to acquire new ones, and he is prone to cling to old ones when they minister to his sense of taste. Yet everyone knows that it is quite easy to acquire new habits in matters of diet as in other things, and it is difficult for the physiologist to see how habits and cravings can constitute reliable indices of true physiological requirements. There would seem to be no reason why physiological experiment cannot be applied to a study of this general question of the true food requirements of the individual. This is especially true of the pro- tein requirement, since it is plain, from what has been stated, that variations in activity, work performed, and matters of that kind, do not call for material increase in the intake of protein food as it does in the consumption of non-nitrogenous foods. The very way in which protein foods behave in the body makes one question the necessity or desirability of their excessive consumption. The fact that nitrogen equilibrium can be established with a relatively low nitrogen intake and that the eating of larger amounts of protein food is followed by a corresponding increase in nitrogen excretion renders one skeptical of the real value of this larger intake of nitrogenous food. If protein food — in the larger amounts — is so important for the body, why should there be such rapid decomposition and excretion of the larger part of the contained nitrogen? 390 CHEMISTRY OF FOOD AND NUTRITION Careful observations have been made upon fasting people, in some cases where fasting has continued as long as thirty days, the income being solely water. In three somewhat notable cases the daily excretion of nitrogen through the urine was determined and recorded. Such data are shown in the accompanying table, in the cases of Breit- haupt, Cetti, and Succi. In Succi's case the daily average loss of nitrogen, from the 11th to 15th day, was 5.11 grams; from the 16th to 2()th, 5.3 grams; from the 21st to 25th, 4.7 grams; and from the 26th to 30th, 5.3 grams. A daily loss of 5.3 grams of nitrogen means the burning up of 33 grams of protein, or a little more than an ounce. It is to be noted from the table that in all three of these cases the amount of nitrogen eliminated on the 6th day was essentially the same — practically 10 grams. This would mean the breaking down of 62.5 grams of protein. Can we assume from this that men of the body weight here recorded need 62.5 grams of protein food per day to make good the loss? Obviously, this conclusion would not be justified. Much would depend upon the condition of the body tissue, NITROGEN EXCRETION THROUGH THE URINE. Breithaupt Getti Succi Day of (59.9 kilos), (50.5 kilos), (62.4 kilos), fasting. grams. grams. grams. 13.0 13.5 16.2 1 10.0 13.6 13.8 2 9.9 12.6 11.0 3 13.3 13.1 13.9 4 12.8 12.4 12.8 5 11.0 10.7 12.8 6 9.9 10.1 10.1 7 10.9 9.4 8 8.9 8.4 9 10.8 7.8 10 9.5 6.7 as to the amount of contained fat and carbohydrate. In the complete absence of food, the body must necessarily feed upon itself, and in fasting the degree to which protein is broken down will depend upon the amount of available fat in the tissues. If the body fat has been largely used up, then it is plain that all the energy needs of the body must come from the l)reaking down of protein. In other words, the feeding of fat and carbohydrate would naturally diminish the break- ing down of protein, so that quite likely these three subjects were eliminating more nitrogen, i. e., breaking down more protein in the 6th and lOth days of fasting, than th(>y would if they were consuming a certain proportion of fat and carbohydrate. A large number of experiments upon various classes of peoi)le in my own la})oratory, covering long periods of time, have led me to believe that for a man weighing 70 kilograms, or 154 pounds, there is required daily 60 grains of i)rotein food to meet the needs of the body. These are jjerfectly trustworthy figures, with a reasonable margin of safety, carrying perfect assurance of being fully sufficient CHEMISTRY OF FOOD AND NUTRITION 391 to supply all the physiological demands of the body; an amount equal to j)ra('tic'ally one-half the Voit standard for a man of this body weight. In this connection we must emphasize the fact that no general state- ment can be made applicable to mankind in general, l)ut there must be due consideration of the size and weight of the individual structure. In other words, a man of 170 pounds body weight has more protein tissue to nourish than a man of 130 pounds body weight, assuming that the difference in weight is not due to difference in adipose tissue. Putting the matter concisely, 1 believe that adults require daily 0.85 gram of protein per kilogram of body weight. SIXTY GRAMS OF PROTEIN ARE CONTAINED IN Fuel value, calories. One-half pound fresh lean beef, loin 308 Nine hens' eggs 720 Four-fifths pound sweetbread 660 Three-fourths pound fresh liver 432 Seven-eighths pound lean smoked bacon 1820 Three-fourths pound halibut steak 423 One-half pound salt codfish, boneless 245 Two and one-fifth pounds oysters, solid 506 One-half pound American pale cheese 1027 Four pounds whole milk (two quarts) 1300 Five-sixths pound uncooked oatmeal 1550 One and one-fourth pounds shredded wheat 2125 One pound uncooked macaroni 1665 One and one-third pounds white wheat bread 1520 One and one-fourth pounds crackers 2381 One and two-thirds pounds flaked rice 2807 Three-fifths pound dried beans 963 One and seven-eighths povmds baked beans 1125 One-half pound dried peas 827 One and eleven-twelfths pounds potato chips 5128 Two-thirds pound almonds 2020 Two-fifths pound pine nuts, pignolias 1138 One and two-fifths pounds peanuts 3584 Ten pounds bananas, edible portion 4600 Ten pounds grapes 4500 Eleven pounds lettuce 990 Fifteen pounds prunes 5550 Thirty-three pounds apples 9570 To make quite clear just what such a standard of 60 grams of protein food means, attention may be called to the above table, in which are given the amounts of different kinds of foodstuffs which will yield 60 grams of protein, and also the fuel value of such quan- tities of the foods in question. From this table it is seen that the daily protein requirement of 60 grams can be obtained from one-half pound of uncooked lean meat, from three-fourths pound of halibut, from one pound of uncooked macaroni, from five-sixths pound of uncooked oatmeal, or from two quarts of milk, etc. Plainly, however, these quantities of foods must be reinforced by addition of non-nitrogenous foods, in order to bring the fuel value to the required amount. Lastly, it is to be emphasized that no definite figure can be given regarding the 392 CHEMISTRY OF FOOD AND NUTRITION amount of carbohydrate and fat required in the daily diet, or the total fuel value, since this is dependent upon the degree of activity of the body. In a general way, it is perfectly clear that the sedentary indi- vidual doing little muscular work needs far less of non-nitrogenous foods, than the individual who is doing vigorous work. My own opin- ion is that the average man leading an ordinary life, involving only an average amount of muscular activity, needs in his daily food a total fuel value of not more than 2800 calories. The importance of protein food in the nutrition of the body has been repeatedly emphasized. Stress has been laid upon the quantity of protein necessary to meet the needs of the body, but in addition it is important to recognize the existence of diflferent nutritive values for the individual proteins. In the animal and vegetable kingdoms are many different forms of protein all superficially alike, but with a cer- tain degree of individuality. The casein of milk is different from the albumen of the egg; the gliadin of wheat floiu* differs from the gelatin of connective tissue; the protein of nuts has a chemical nature differ- ent from that of the cereals; and so we might make comparison of hundreds of different proteins scattered throughout the animal and vegetable kingdoms, all of which are used in some degree at least as foods. ^Yhile they are superficially alike, they are distinctly unlike in their chemical structure. This difference in structure implies a difference in physiological behavior. The blood of one species of ani- mal, with its contained albumens, cannot be injected into the blood- vessels of another species without causing harm or even death. Albu- minous substances which are foreign to the blood of a given species may act as a poison when introduced directly into the circulation. We, as human beings, however, are feeding upon a mixed diet of pro- teins from all sources and utilizing these different forms of protein to our own advantage. The domestic animals as sheep and cattle, graz- ing side by side in the same pasture, eat exactly the same food under the same conditions and yet each species has in its own fluids and tissue proteins peculiar to itself. This implies a process of transformation or synthesis, by which individual proteins may be transformed into other quite different forms of protein. Native proteid Protoproteose Heteroproteose 1 I Deuteroproteose Deuteroproteose I I Peptone Peptone I I Amino-acids Amino-acids CHEMISTRY OF FOOD AND NUTRITION 393 Protein foods, when eaten, are subjected to the action of gastric and pancreatic digestion, reinforced by such ferments or enzymes as are present in the intestine, and as a result the native proteins are broken down by successive stages through proteoses and peptones into the comparatively simple bodies known as amino-acids, by a process per- haps analogous to the scheme here presented. As representing these amino-acids we have relatively simple crystalline nitrogenous sub- stances, such as glycocoll, leucine, proline, tyrosine, arginine, lysine, tryptophane, etc. It is apparently with thesq amino-acids that the body has to deal in the construction of its own tissue proteins. These amino-acids are recombined by processes of selection through synthesis to form organ- ized proteins of the kind characterizing the different tissues of the body. Just how this synthetical construction is effected we do not know, but it is assumed that the several amino-acids are combined one with another, thus gradually building up the complex protein molecule. Probably such amino-acids as are not needed to make the required proteins are burned up to supply energy. The fundamental idea, therefore, is that from the supply of amino-acids furnished to the body by the digested food proteins, the ones needed are selected to construct the particular tissue proteins of the animal, so far as these are required for growth or tissue repair. The other point necessary to be emphasized from the standpoint of nutrition, especially with reference to food values, is that the individual proteins are chemically unlike, and con- sequently have different nutritive values. In the laboratory it is possible to break down protein artificially through hydrolysis with boiling acids, in which case the molecule is broken apart into its component amino-acids. These can be separated and the amounts determined. In the following table the composition of eight distinct proteins is given, showing the percentages of amino- acids contained in them. A study of this table shows at once what a striking difference there is in the chemical nature of these individual proteins. Casein of milk, for example, as contrasted with the gelatin of bone, contains no glycocoll, while the latter contains 16.5 per cent, of this substance. Casein contains 10.5 per cent, of leucine, while gelatin contains 2.1 per cent. Casein has in it 11 per cent, of glutaminic acid, while gelatin has less than 1 per cent, of this amino-acid. Casein contains tryptophane, while gelatin has none of this substance. Again, contrast casein with its 1 1 per cent, of glutaminic acid with the vege- table products hordein of barley and gliadin of wheat, both of which contain over 35 per cent, of this particular amino-acid. These eight examples are merely illustrations of the differences which exist in the chemical natiu-e of the individual proteins, and since physiological behavior depends in large measure upon chemical constitution, it is quite apparent that the individual proteins must possess different nutritive values. 394 CHEMISTRY OF FOOD AND NUTRITION Aniino-acids. g .0 a S c 3 a II Hi GlycocoU 16.5 0.6 0.55 0.89 0.94 Alanine . 0.8 0.9 2.33 0.43 1.8 2.0 4.65 4.45 Valine 1.0 1.0 1.51 0.13 1.04 0.21 0.24 0.18 Leucine . 2.1 10.5 8.7 5.67 9.65 5.61 5.95 11.34 Proline 5.2 3.1 3.65 13.73 2.77 7.06 4.23 3.18 Phenylalanine 0.4 3.2 3.55 5.03 3.25 2.35 1.97 3.83 Aspartic acid 0.56 1.2 3.85 + 5.24 0.58 0.91 3.35 Glutaminic acid 0.88 11.0 12.94 36.35 14.54 37.33 23.42 6.73 Serine 0.4 0.23 0.38 0.13 0.74 Tyrosine 4.5 3.03 1.67 2.18 1.2 4.25 3.34 Arginine 7.62 4.84 16.02 2.16 4.89 3.16 4.72 5.94 Histidine 0.40 2.59 1.47 1.28 1.97 0.61 1.76 2.83 Lysine 2.75 5.8 1.64 3.92 1.92 2.75 Ammonia 1.8 4.87 2.06 5.11 4.01 1.41 Tryptophane 1.5 + + + + + + Cj'stine . 0.06 + 0.45 0.02 38.61 50.42 61.09 71.32 54.27 65.81 59.66 50.32 Feeding experiments made upon animals have shown that certain proteins contain all the amino-acids necessary for maintenance and growth; such proteins are frequently spoken of as ''adequate" proteins. Others suffice for maintenance; that is to say, they furnish material for the energy needs of the body and for the repair of tissue waste, so that an animal fed upon such proteins does not lose body weight, but they are quite inadequate for the purposes of growth in young animals. Lastly, there are still other proteins which, when fed as the sole protein food, are insufficient both for maintenance and for growth; such proteins are frequently designated as "inadequate" proteins. Gelatin is a good illustration of a protein of the latter type. It is readily digested and ultimately undergoes oxidation in the body, its energy being utilized; but owing to its lack of certain amino-acids, such as tryptophane and tyrosine, it is quite incompetent to maintain life; it is not able to maintain nitrogen equilibrium; it is not able to supply the nitrogenous material needed for the repair of the tissues of the body. If, however, an animal is fed upon a diet in which gelatin is the only protein substance, it can be kept alive by adding trypto- phane, cystine and tyrosine, showing that these amino-acids which are lacking in the gelatin molecule are necessary for the construction of the i>roteins needed b}' the animal system. In other words, where growth and maintenance are to be accomplished, the protein food must contain the needed amino-acids, or building stones, from which the tissue proteins are constructed. The gliadin oi wheat and rye is a prot(!iu characterized by contain- ing a relatively large proportion of glutaminic acid and ammonia- yielding groups, with an almost complete absence of lysine and glyco- CHEMISTRY OF FOOD AND NUTRITION 395 coll, and very small amounts of the amino-acids, histidine and arginine. It has therefore a very unique constitution, very different from the tissue proteins of animals, as well as from most of the other proteins which are commonly present in the food of man and animals. With such a peculiar and one-sided protein, feeding experiments were carried out by Osborne and INIendel on white rats for long periods of time cover- ing more than 500 days. Using pure gliadin as the sole f(jrm of protein food, these animals were maintained in apparent health and strength throughout the long period of the experiment. There was no impair- ment of the capacity to produce healthy young and to nourish them, one female giving birth to a litter of four at the end of 178 days on the gliadin foo(l mixture. These young rats were nourished satisfactorily by their mother during the first month of their existence, so far as could be judged by comparison of their increase in weight with that of nor- mally reared rats. The results of this experiment leave no doubt that here where there was such a marked renewal, or new formation, of body tissue, very large in proportion to the original weight of the mother animal, there must have occurred a synthesis not only of the building stones or amino-acids deficient in the protein intake, but likewise of tissue and milk components of great variety and complexity which were completely missing in the special food intake that had formed the sole food of the mother during several months. There is another side to this experiment, however, that must not be overlooked, as it is full of significance. At the end of thirty days three of the young rats were removed from the mother and placed upon diets of milk and other foods more nearly approaching the normal, while the fourth animal was allowed to remain in the cage with the mother, whose sole source of nutriment was the gliadin food mixture. The three removed animals manifested a normal growth on their new dietaries, but the fourth animal, kept with the mother, began to evince a failure to grow at about the period (30 days) when young rats are wont to depend upon extraneous food for nourishment. In other words, the young animal, forced to depend upon the gliadin food mixture in place of the milk of its mother, showed a failure to grow on the diet upon which the mother had not only been maintained, but had actually produced young and secreted milk sufficient in quantity and quality to induce normal growth in her oft'spring. Young rats fed on a single protein of a difi'erent type, aptly termed an adequate protein, such as the casein of milk, glutenin of wheat, etc., will show steady growth up to say 300 days, at which age they normally grow very little more. A young gliadin rat, on the contrary, fed solely on gliadin as the protein part of its food, can be maintained for long per- iods, 500-600 days, but there is no growth to speak of. The youthful appearance of animals thus maintained without growth corresponds in every respect, so far as external characters go, with the size rather than the age of the animal. The power of growth in these cases, how- ever, is not lost, but is simply held in abeyance. Thus, in one experi- 396 CHEMISTRY OF FOOD AND NUTRITION ment, reported by Osborne and Mendel, with gliadin as the sole pro- tein of the diet, after 270 days of stunting, changing the diet to milk powder in place of gliadin, growth began at once and continued up to 314 days. The animal body can be maintained so long as the protein supplied is not deficient in certain indi\idual amino-acid groupings or building stones, but there is some other factor involved when the problem of gro\\i:h is considered. Given a diet composed of some pure protein, suitable in character, reinforced with fat and carbohydrate, the animals will grow up to a certain point and then for week after week they remain practically stationary. Maintenance may be perfect, health and strength seemingly quite normal, but there is no growth. The diet, so far as its content of nitrogen and fuel or energy value are concerned, may be more than adequate. Increasing the volume of the food, even when fully eaten and digested, brings no result. The animal remains stunted. If now, without any other change in the diet, a minute portion of dry milk powder, for example, is added to the food, growth at once recommences, and this happens even though the ani- mal has been stunted for a relatively long time. The milk powder is too small in amount to give any added fuel value, and it may be freed from all traces of protein without causing any loss in efSciency. There is plainly some accessory factor here which is directly concerned in the growth function. This suggests that in the nutrition of the body, certainly in growth, there are factors involved which are wholly unrelated to energy supply or to the amount and character of the protein intake. In a general way, it may be said that the needs of the body for food are met by so many grams of protein or nitrogen per day and so many calories or kilogram degree units of heat. The chemical processes concerned in nutrition have for their main object the breaking down of these com- plex materials of the food into simpler fragments, with liberation of the contained energy; a series of progressive chemical decompositions in which large molecules are broken down into smaller ones, and these in turn into still smaller ones, until finally the ultimate end-products are reached which are cast out of the body. Now, however, we see the necessity of giving some heed to the character of the protein intro- duced into the food supply, and the necessity of recognizing the physiological distinction between growth and maintenance as two dis- tinct phases of nutrition. Finally, we have forced upon us the experi- mental evidence that there are certain accessory factors concerned in imtrition, which in the process of growth at least are of fundamental importance. As Professor Hopkins, of England, has recently written, it is possible that what is absent from artificial diets and supplied in such addenda as milk and tissue extracts is of the nature of an organic complex (or of complexes) which the animal body cannot synthetize. IJut the amount which seems sufficient to secure growth is so small, that a CHEMISTRY OF FOOD AND NUTRITION 397 catalytic or stinnilatin■ t ^i- -^^" ^ Fig. 208. — Eczema. This is an example of infantile eczema. The skin is red and a little thickened. There is weeping and crusting, and considerable itching. There is also pus formation under the crusts. Note the white nose and lips. Acute eczema consists of circumscribed patches or diffuse areas of edema and redness with the formation of vesicles. It is not unlike dermatitis venenata. There is usually considerable burning or sting- ing. In severe examples the edema may be a marked feature and "weeping" (exudation of serum) is noticeable. In some instances the eruption may even become pustular, simulating impetigo. Chronic eczema (V\g. 208) usually occurs in patches. The skin is thickened, scaly, dull red and more or less itchy. There may or may not be vesicles. Chronic eczema may result from an acute attack or it may develop more or less insidiously. The scales are dry and harsh TIJE INFECTIOUS EXANTHEMATA 417 and are shed in flakes. The scaliness is not the shiny, micacious type seen in psoriasis. Occasionally, the skin becomes so thick and hard that painful fissures develop. This is seen especially on the hands. A characteristic feature of eczema is that the patches do not have, as a rule, sharply defined margins, but gradually fade away into normal skin. It should be understood that there is no sharp line of demarcation between a dermatitis and an eczema. As has been mentioned, an erythema is a redness of the skin — a flushing. It is simply an increased amount of blood in the skin and may be due to many causes. Let us assume that a mild, irritating substance is applied to the skin and it produces a transient erythema. Now, if this irritation is continued, the erythema ceases to be temporary, there is a congestion and serum and white blood cells pass from the vessels into the connective tissues. In other words, there is an inflammation — a dermatitis. These con- ditions are well demonstrated in dermatitis venenata. Now, if the inflammation continues, all the elements of the skin increase numer- ically, so that the skin becomes thickened; the outpouring of serum, if the horny layer is intact, causes the formation of vesicles or, if the horny layer is absent, a "weeping." This is catarrh of the skin or eczema. Ebzema, then, is simply a reactio7i of the skin to an irritant. This irritant may be applied from without or it may be some poisonous substance circulating in the blood and which has been produced by faulty metabolism. Primary eczema is from the latter cause, while secondary eczema is a sequel to various forms of dermatitis, such as dermatitis venenata, scabies, pediculosis, etc. The Infectious Exanthemata. — The infectious exanthemata are acute, febrile, infectious, self-limited conditions, associated with eruptions of the skin. We will consider only the more common of these affections. Scarlet Fever. — ^The onset of scarlet fever is sudden. After an incu- bation period of from 3 to 7 days, the disease is ushered in with indis- position, fever, headache, vomiting and sore throat. The tempera- rises rapidly to from 101° F. to 104° F.; it remains high until the eruption is fully developed, when it gradually declines. The tongue is coated and shows numerous red spots — the "strawberry tongue." The rash appears on the second day and is first seen on the neck. It then rapidly spreads to the face, chest, arms, legs, etc. It reaches its maximum of development about the fourth day and then gradually fades. This is followed by desquamation of the skin. The eruption consists of a bright red flush with closely crowded puncta (pin-point elevations). The disease is said to be infectious for three weeks, so the patient must be isolated for this period. The afl^ection varies markedly in severity, but it is always dangerous. Severe complications and sequelae are common, such as aft'ections of the eye, ear and brain. Measles. — After an incubation period of about 10 days, the individual develops a "cold" — an inflammation of the nose, eyes and throat. 27 418 DERMATOLOGY The temperature rises to 101° F. to 103° F. After about four days small red spots with a minute bluish-white center can be detected on the mucous membrane of the cheeks. About this time the eruplion begins on the neck and face and gradually spreads downward over the entire body. The eruption consists of red macules which range in size from a pin-head to a bean or finger-nail and are irregular in outline. After the disappearance of the eruption there is a slight desquamation. An uncomplicatefl case runs a course of from 7 to 14 days. ^Measles is not in itself very dangerous. The most common compli- cation of the disease is pneumonia — an affection with a high mortality. German measles is hardly anything more than a very mild case of ordinary measles. Chicken-pox. — Chicken-pox is not a serious disease. After an incuba- tion period of from 14 to 17 days, an eruption of umbilicated vesicles occurs on the neck and face and then over the entire body. The vesicles develop in crops about 12 to 24 hours apart, so that there are always lesions in various stages of evolution. After a few hours the contents of the vesicles become cloudy and in a few days they dry up and disappear. Occasionally a scar is produced. There is usually some itching. There is not much fever. The disease lasts about a week or ten days. Syphilis. — This disease may be considered as the most important of all the diseases in dermatology. It is an afl'ection which attacks individuals of all ages; a disease that can be passed from a mother to her unborn infant; a disease that is highly contagious and one that will produce the most horrible results if neglected or improperly treated. The increase in our knowledge of syphilis has been so great in the last few years that it will be worth while to outline the history of the disease. History. — Syphilis became known to the civilized world in 1494. It first appeared in Spain upon the return of Columbus and his crews. There is no record of the disease having existed, prior to this time, in any civilized country, but there is plenty of evidence regarding the existence of the afi'ection in Central America, previous to the voyages of Columbus. After its first appearance in Europe, the disease spread rapidly throughout the entire world, attacking people of all classes. The disease then was much worse than it is now. This was because there was at first no adequate method of treatment and, also, because the aftection was working on virgin soil — that is, it was destroying the most susceptible subjects and leaving the more or less immune individuals to ])roduce i)rogeny who were less susce])tible. The ravages of the disease in the loth and Kith centuries almost -, on the buccal mucosa — lii)s, cheeks, tongue, palate and throat. It is covered with a dirty, grayish-white mend)rane which. SYPHILIS 423 when removed, leaves a superficial excoriation. There may he but a single patch or there may be several of them (Fig. 211). Another lesion of interest to dentists is the so-called split i)ai)ule. This is a l)ai)ule at the corner (connnissure) of the mouth, and which is j)artly in the skin and partly in the mucous membrane. On account of its location it is usually fissured. All the lesions of early syphilis are rich in Spirocheta pallida and are therefore conta(/ious. If, however, the skin covering the lesion is unbroken, there is no danger of contagion. On the other hand, all moist lesions of early syphilis, such as the mucous patch, the chancre, the split papule, etc., are extremely contagious. The blood of a syph- ilitic patient, unless obtained directly from a lesion, is very slightly if at all dangerous. The secretion and excretions, such as the saliva, need not be considered dangerous unless contaminated with the dis- charge from a lesion. Fig. 211. — Syphilis. Mucous patches in the secondary period of an untreated case. The patches in this individual were of long duration and had become somewhat warty. Tertiary Period. — There is no sharp line of demarcation between secondary and tertiary syphilis. In a general way the secondary period may be considered to end at the termination of the second year. The tertiary period, beginning at the end of the second period, lasts through- out life, providing, of course, that the disease has not been cured. Manifestations of the tertiary period may develop early in the period, or the disease may remain quiescent for months or even for many years, only to have lesions appear late in life. Tertiary syphilis is noted for its destructive skin lesions (Figs. 212 and 213) and for its tendency to produce serious involvement of the internal organs, (viscera) and the nervous system. Tumors may develop in the brain and produce pressure symptoms; the symptoms, of course, depend upon the particular part of the brain that is involved. The entire brain may become affected, producing a 424 DERMATOLOGY condition known as paresis. Certain portions of the spinal cord may be diseased, resulting in a condition known as locomotor ataxia. The arterial system is usually more or less affected, giving rise to arteriosclerosis. In fact there is hardly any part of the organism that may not be attacked by tertiary syphilis. Fig. 212. — Syphilis. An example of an eruption composed of ulcerating nodules in neglected syphilis of the tertiary period. Note the gyrate configuration, also the scars and pigmentation. In the skin, tertiary s^^3hilis is manifested by slow-developing, large, deep-seated ulcers. These ulcers are not infrequently preceded by deep-seated, soft tumors. Another type of the tertiary skin lesion is a group of deep-seated, half-dime to dime-sized, raw-ham-colored nodules, which undergo ulceration w^ith crust formation. Fig. 213.— Syphilis. An example of an ulcerating deep-seated tumor (gumma) in neglected tertiarj' syphilis. The points to remember about tertiary skin manifestations are that the lesions tend to ulcerate and to produce scars. The color is a dark red or raw ham. There is usually a marked pigmentation. The lesions are, as a rule, unilateral — on one side of the body only — and hardly ever symmetrical. The disease at this stage very frequently attacks the bones (Fig. 214), SYPHILIS 425 Instead of being ulcerative or gummatous (tumors) or nodular, the lesions may be of the squamous type (scaly), especially on the palmar surfaces of the hands and plantar surfaces of the feet. Such lesions resemble eczema, but they can be differentiated from this disease because in syphilis the patches are always sharply marginated and unilateral. In fact all syphilitic lesions are sharply marginated and they almost always tend to produce peculiar configurations — scalloped edges, gyrate and annular lesions, etc. Another point is Fig. 214. — This shows syphilitic involvement of the bones as seen in hereditary and tertiary syphilis. The lesion consists of a thickening of the periosteum and multiple abscesses in the bones — a periostitis and an osteomyelitis. that late syphilitic lesions tend to progress slowly, while the older parts heal — this is known as a serpiginous lesion and is quite t\'pical of s\T3hilis, although such lesions do occur in other rare skin affections. As a rule the tertiary lesions of syphilis are not contagious, or at least very slightly so and children born during this period may never show manifestations of the disease. Hereditary and Congenital Syphilis. — If pregnancy occurs during the early secondary period of syphilis the disease is likely to cause the 426 DERMATOLOGY death of the fetus. If, however, a li\'e infant is born, it will usually demonstrate evidence of congenital syphilis within a few weeks. The manifestations of congenital syphilis are a discharge from the nose (snuffles) a poorly nourished condition, sores in the mouth and an erup- tion of bullae, vesicles or papules on the body. Such infants usually die within a few months in spite of treatment. If a child is born in the late secondary period, it also may develop congenital manifes- tations or it may escape congenital syphilis, only to demonstrate hered- itary syphilis sometime during life. Hereditary syphilis is manifested in various w^ays. We will mention only the most common types, any one of which, or any combination of which may occur in a given individual : Faulty mental development which may range from a slight "defective" to complete idiocy; signs of nerve involvement, such as deafness, blindness, etc.; faulty physical development — stunted growth, "box-shaped" head, "saddle" nose (bridge of nose concave instead of convex), Hutchinson's teeth, etc. Hutchinson's teeth represent one of the most common hereditary taints. This feature consists of a central notching of the superior central incisors (Fig. 215). Fig. 215. — Syphilis. An example of Hutchinson's teeth seen in untreated hereditary syphilis. Usually only the upper permanent central incisors are centrally notched. Here both the upper and lower central incisors have a central notching. Besides the above hereditary manifestations there may be destruc- tive lesions of the skin and especially of the bones — as seen in tertiary syphilis. The symptoms of hereditary syphilis may occur early in life or they may not become manifest until the individual is nearly twenty years of age. The buccal lesions of late syphilis are of special interest to the dentist and his co-workers. These manifestations may consist of tumors (gummataj, ulcers (ulcerating gummata) or leukoplakia. Gummata. — While gummata may occur anywhere in the mouth or throat, the most common site is the dorsal surface of the tongue where they usually form a soft, circumscribed, oblong, considerably elevated, painless tumor, which, if neglected, tends to break down and produce an ulcer. Ulcerating gummata are also commonly found on or near the soft palate wliere the tendency is for the disease to perforate the roof of the mouth (Fig. 21(j). These same lesions may occur on the mucous surfaces of the cheeks, especially in the neighborhood of SYPHILIS 427 the mouth. Here, there is more hkely to be a rather diffuse and une^'en infiltration, the mucosa is thrown into folds and there is more or less ulceration. Buccal gummata must be differentiated from tuberculosis and cancer. Both tul)erculosis and cancer of the mouth are more or less painful. They both develop ^'ery slowly as compared with syphilis. Fig. 216.^Ulcerating gumma of soft iKilatc with perforation. Cancer is always indurated (hard) and there is likely to be a cervical adenitis. Tuberculosis of the mouth is almost always secondary to that of the throat or lungs. Finally, there is the Wassermann test for syphilis and the therapeutic test. ^ "■"' '^^■'' ^■^ ^Ib, '^ K"'' -. -'-. Fig. 217. — Syphilitic leukoplakia. (Dr. Parounagian's patient.) Leukoplakia. — This consists of a slight thickening of the mucosa which assumes a pearly white or pure white color. It may occur in from pin-head- to split-pea-sized areas or it may be scattered as a solid patch over the mucosa of the cheek or of the tongue (Fig. 217). Leuko- 428 DERMATOLOGY plakia is not always syphilitic, as it may be due to excessive smoking or to irritation from fillings, bridges, etc. In any event leukoplakia must be considered as a preepithelioma — a forerunner of cancer. Syphilis also causes, at times, an atrophy of the superficial tissue of the tongue with the result that the lingual surface appears smooth and glistening. On the other hand the disease may produce a glossitis consisting of h^-pertrophy instead of atrophy, so that the surface of the tongue is thickened, thrown into folds and, perhaps, fissured- — the so-called scrotal tongue. chaptp:r XV. FACTORS IX PERSONAL HYGIENE. By C. ward CRAMPTON, M.D. Racial Hygiene. — The subject of hygiene is one of the most impor- tant that can engage the attention of anyone. • Not personal hygiene alone, but racial hygiene, the consideration of the health, illness, birth and death of whole races of beings. Paleontology teaches us that various forms of animals once lived on this earth and possessed it; huge mastodons and dinosaurs, and other big, strong, wonderful animals; but they have died, and their species is extinct. Those races have vanished. Something unhygienic hap- pened. The deduction from this is that there is a possible peril to the human race. There are signs of bad hygiene and signs of impending danger, and perhaps of partial death of the race. Race Death. — When the environment of a race changed to such an extent that it was unable to adapt itself to the new conditions, it died. Other races survived because they w^ere able to make some slight adaptive structural change by process of evolution, fitting them- selves to the changes in environment and making further progress. They were perhaps the progenitors of some of the forms of life today. The Present Emergency. — Today the human race is changing its environment very rapidly. Within a few thousand centuries, which is a very short time, speaking biologicalh^, many changes have been made, one of the most important being the gradual change from rural to city life. Two hundred years ago perhaps not more than 5 per cent, of the population lived in the city. Today 45 per cent, of the people of the United States live in cities. The problem of the human race of the future is the problem of the city. Now that means bricks instead of trees, asphalt instead of brooks and fences, and the iron tramway instead of country roads and the good solid earth; in short the things that are hard, things that bruise and tear and destroy the biological soundness and vitality of humanity. Therefore city life means the relative abandonment of the hope of biological continuance. Put the whole human race in cities and it would die. It is rare to find in New York City a grandchild of a New York City man and woman. Races die in cities; the biological strain is wiped out. The conditions that make for the racial death in cities are of the greatest concern; they are problems of hygiene and of health. They are not matters of business nor of politics nor of art; they are matters of life and death, not of the individual only but of the whole race. ^ 430 FACTORS IN PERSONAL HYGIENE The biological death of city peoples has led, of course, to the coming in of people from outside, the country people and the people from abroad, to take their places. The country boy and the country girl in the city naturally come to the top to replace those at the top that are biologically unfit. That explains why there has been no cry of racial degeneration in the United States as there has been in England and in Germany. Four or five years ago England became alarmed because it could not get soldiers of the requisite height and strength. The government was anxious for the integrity of England and for the health of Englishmen. There had not been sufficient influx of hardy lower peoples to keep the race up, because much of the biological cream of England had been skimmed and sent over to the United States. And in Germany the same thing, to a somewhat lesser degree, had happened. This is the reason why the United States is not yet alarmed over a similar condition of affairs — the racial degeneration of old American stock. Children in Schools. — So much for the importance of general hygiene. The dental hygienist will deal with children in schools, and the child in school will be found a very different thing from a mere child. He becomes a unit, one of a hundred or a thousand. He is under the teacher, the teacher is under the principal, the principal is under the superintendent, who must, in turn, look to the Board of Education, or the school committee. The child in school is not a child, but a child in relation to all of these different things; and the hygienist, going into the school, must know where she and her work may stand in rela- tion to the other teachers, the principal, the superintendent, and the Board of Education. She is not an independent person, not even a dental hygienist, but a dental hygienist in relation to all of these per- sons and the influences for which they stand. Therefore it is necessary for her to know the administrative pulse and the methods and ways of conducting school affairs. These are different in each school locality; it is for the hygienist to find them out, for she will do her best work in ways that are known to the pupils, the teachers, and the principals. Forces operating along certain lines are found in schools, which cannot be pushed aside and cut across without unnecessary difficulty and fric- tion, but if the hygienist will move along with them in ways that are known, efficiency will be trebled. In other words, the best work will be accomplished by adjusting the work — and oneself — to existing methods. If the work is carried on in harmony with the school organ- ization, it will have a telling effect; otherwise the hygienist in the school will l)c as a cinder in the eye, something foreign to it, which will cause trouble. Teaching. — The business of the school, theoretically, is to teach; practically, it is to develop children along many lines besides the regular courses of stud\'. There is a subtle difference between teaching and developing children. They may sound like the same thing but it is the recognition of just that subtle difference which has led to the SUBJECTIVE AND OBJECTIVE HYGIENE 431 teaching of hygiene in an entirely different way from that which foi-- merly obtained. The old method, introduced by a group of devoted, enthusiastic and very efficient women interested in temperance as to alcohol and tobacco, was text-book instruction. Text-books, every other page filled with warnings of the dangers of alcohol and tobacco, were put into the hands of every school child. On the statute books of most of the States is a requirement to the efl'ect that certain things shall be "taught out of a text-book, and the text-book shall be in the hands of each child." It may readily be seen that a much greater emphasis is placed upon the text-book, than upon the child. Text- book instruction has resulted in the forcing of information upon chil- dren, most of which they are unable to grasp, and which is therefore a failure. As an illustration of the newer methods of instruction, the things which are being done in New York City will be presented briefly. SUBJECTIVE AND OBJECTIVE HYGIENE. Objective hygiene is the doing of things with the person or persons as an object, such as surrounding them with good conditions in the schoolroom, good light, heat, ventilation, etc. In this group also fall physical training, athletics, folk dancing, playing, recesses, and other recreations. The hygiene of insirudion comes under this head. The medical inspection of the pupil is at first objective, and then, if it is to be successful at all, it leads the pupil to doing things for himself and becomes subjective. The teaching of health laws and conditions, on the other hand, is subjective. It is the endeavor to get the child to do something for himself, to inculcate habits, to form tendencies for right action, and leave him with a lasting impression that will affect conduct. The purpose of the hygiene of instruction is the counteracting and elinjinating of health-depressing influences of school life. It is not only engaged in the endeavor to keep away bad things, but it is engaged also in the endeavor to bring good things into the school. The earliest efforts were made toward the cure of disease when it already existed; next came the prevention of disease; and now the efforts are made toward acquiring a condition of euphoria (which means a great degree of vigor), or the ability to cast aside all disease influences. Each of these courses has been traveled in our school work, and traces of the earlier stages are left, as the cure of disease and its pre- vention; but the most modern effort is toward a development of the superabundance of vigor, health and happiness of the children, far beyond the mere prevention of disease. The hygiene of instruction is not only designed to counteract and prevent health-depressing influences of school life, but to make for stronger, more \igorous lives among the children. This method con- 432 FACTORS IN PERSONAL HYGIENE trols first, the seating of the child. The school desk is an evil of long standing in the schools. Even the dental hygienist should inform her- self about it, for it will avail little to keep a child's mouth in order if he is allowed to sit at a desk which necessarily cramps him until he is crouched over, with his chest caved in and his head down and body twisted. The height of the desk should be such as to permit the child to sit straight, to lean forward without bending except at the hips, and to keep the body straight; to be able to place the hands upon the desk so that the fingers may be held properly for writing, and yet that the body may be seated against the back of the chair. The system should require the teacher to make a note of all defects of hearing and eyesight. They are now recorded by the examining physician, and the teacher places the children found deficient in one of the front rows. The teacher herself may be called upon to conduct examinations in sight and hearing, and in default of an efficient medical inspection system the hygienist should, if possible, induce the teacher to make the tests of eyesight and hearing herself. The following case is of interest. In the truant school there was a boy who had been adjudged a bad boy and a truant. Something about his eyes attracted attention, and he was asked to read from a book which was handed to him. It was soon found that he could not do it. Books with larger and still larger tj^e were given him and finally a placard with letters an inch and a quarter square, and it was only by bringing this huge t^q^e within six inches of his eyes that he was able to read it. That boy was not so much a truant, or a bad boy as a blind boy, and no one knew it. If such a case can be pictured to the imagination, and the damage done, not alone to a human life but a human soul, by such stupid and almost criminal neglect could be estimated, the advis- ability of having some kind of hearing and vision test will be readily appreciated. The temperature of the schoolroom should be kept between 60° and 68° F. If it is allowed to rise above 70°, it is bad for the pupils and teachers and for the efficiency of instruction, and the temper and spirits of both pupils and teachers. This may be demonstrated by a person trying to study, first in a room which has a temperature of 78°, and then in another room with temperature of 65°. The differ- ence will be obvious. Immobility. — There is another important point and that is immo- bility — that is, requiring the child to sit still. The importance of tooth massage by tooth use, the importance to the tooth of its daily work has recently been demonstrated to the writer by Dr. Fones. The rhythmic, alternate compression and relaxation occasioned by chewing or eating alternately squeezes the bloodvessels, and then allows them to expand. All tissues of the human body depend for their health upon massage of this kind. The reason that any ill health of the digestive tract exists, for instance, is because peopje have become sedentary animals SUBJECTIVE AM) OBJECTIVE HYGIENE 43.0 instead of walking, running, jumping, throwing, swimming animals, and from being inactive the tissues become stagnant. The result of tooth stagnation, caused by simply swallowing foorls instead of properly chewing them, is known and the same relative harm occurs to the whole body when the tissues are inactive and have become stag- nant. If a child is put in school for five hours each day and required to sit still during all that time, every tissue of his body is seriously damaged. This is not theory, it is a fact. A house damaged by fire plainly shows the damage, but that done to the body can only be detected by such signs of damage as the hangdog expression, poor posture, or pallor. To correct this the following directions are given to the teachers for use in the lower grades. " Care should be taken not to require the children to sit still for a long time. In addition to the two-minute exercises which occur three times a day, quiet or vigorous games may be used when desirable, and every hour a three-minute recess may be given in which free movement about the room and quiet conversation are allowed." This is but a poor substitute for human child activity, but it is some- thing that can be done, while if the children were turned loose to act like children there could be no teaching done. "In the first and second years the children may, when necessary, place head upon the arms on the desk, close the eyes, and relax com- pletely for a moment or two." This is one of the most human things ever seen in a classroom. Upon a signal from the teacher the children simply lay their heads down on the desk and act as if they were asleep, and it is quiet. An idea of what that means to the nervous, irritable child of the city streets can hardly be imagined. It is like a breath of fresh air. Now follows the school-teacher's part of it. "The children should be called to strict attention immediately following the rest periods. Before any lesson requiring severe concen- trated effort, a short preliminary relaxation of this kind is most help- ful and the contrast between the rest and work should be decidedly marked; a principle of very great importance." Further directions are as follows: "Children should be urged to take part in the order and cleanliness of the desks, their own and those of the classroom at large. In the upper grades this interest should be extended to the school and community." " The light should fall upon the desk from the left side. Eyes should never be closer than ten inches to the work." Observation in the school- room w^ll probably show quite a number of noses within four or five inches of the pen-point. "The eyes should be occasionally raised from the work. Books should be held off of the desks and in the hands, not laid down upon the desks." If the book is laid down the eye is placed at a disadvan- tage, shortening the vision, and the head goes down and then the hand 28 434 FACTORS IN PERSONAL HYGIENE comes up, the body is twisted and the whole child slumps down in a very characteristic and common fashion. Physical Training. — Just here something should be said about physical training. This includes games in classroom, playground and gym- nasium, and gymnastics of a formal type (i. e., exercise at the command of the teacher) ; athletics, folk dancing, and the like. All of these serve different purposes and have correspondingly different results, which are important. Educational Exercises. — The results desired from physical training are various; first, neuromuscular education, which is a mental thing. The muscles have nothing to do with it except to abide by the decision of the nervous system, which is trained by exercise. Who has not seen a city man in the country, particularly going down to a float on the river and confronted with the necessity of stepping into a boat. He will approach the edge of the float with great care, get down and grasp something, put one foot in and then perhaps he will fall over- board. He is a motor dullard, and the motor dullard is an increasing character of our population. On the other hand, another, no doubt, would walk confidently across the float, step in the boat, grasp the oars and row away. That is motor ability and the motor dullard can only hope to acquire it by exercise and training of the nervous system which controls the motor system. All of the seven hundred thousand youngsters in New York City and all school children elsewhere should have that kind of ability. It consists in coordination of the various body parts, ability to move with precision, ability to move at the right time, to be alert, accurate, definite, complete and graceful in movement. ]\Iost of these coordinations are unconscious, the result of practise, not thought about, but just done. Motor education is thus one of the greatest things in physical training. Hygienic Exercises. — The other great thing resulting from physical training is health of body tissue by means of exercise of the muscles. When the muscles are exercised everything else in the body is exercised, the heart, the lungs, the arteries, the veins and the nerves, in fact the whole body is made to work in exactly the way it was intended that it should work. If each muscle were taken separately and exercised and brought to a condition of health, and also each organ, as the stomach, liver and spleen, and so on throughout all the organs of the body, it would prove quite a task. That is the modern method of education, by the way, but not modern physical education. Natural exercises of the muscles are used and nature stimulates the rest of the body in the process of repairing the busy muscles. The method of evolution has been such that those whose muscles have been exercised in walking, jumping, climbing and throwing have survived, and those anemic beings that do not exercise do not survive. So our ancestors, in their more active physical life exercised and kept in health. Exercise is the only way. Therefore physical training is put in the schools to make the tissues of the children healthy and strong. SUBJECTIVE AND OBJECTIVE HYGIENE 435 That is the hygienic side of physical training, a very different thing from the educational exercises previously described. Posture. — Next, exercises are used to straighten the boys and girls. The debutante's dance of civilization has resulted in the toleration of such things as the debutante slouch, a very curious thing indeed; but if the children themselves are observed it will be seen that many of them have a slouch of the same kind. The chest is down and all of the contents of the thorax are pressed down upon the abdomen, which bulges; the head is hung down and the whole attitude is a picture of dejection. That is the result of acute or chronic fatigue, occasioned by bad health, lack of exercise, bad teeth and such hygienic errors. In short, poor posture is a depression due to lack of tone. Good pos- ture on the other hand, is an attitude of vigor, characterized by a raised position of the various parts. If one stands tall, with head and chest held high, the whole body and the mind also are placed at the greatest advantage. The children are being taught to stand up straight, because it is a sign of vigor, and in itself leads to a better state of health, both physical and mental, a fact easily proven to oneself. If one is mentally depressed; one is also, as a rule, physically depressed, and if he will stand up straight and lift his chest and forcibly get away from the physical depression, a mental uplift will be experienced. Actually more physical and mental vigor will be developed by using this very simple and cheap device. Instruction in Hygiene. — The purpose of instruction in hygiene is to inculcate habits of cleanliness, care of the body, good posture, etc., which will maintain and promote good health and this superhealth, vigor. The emphasis of instruction should be placed upon the practical affairs of daily life. The modern method of education is one that takes the subjects and experiences of life and uses them as texts, considers them in relation to something new% and returns to the child a habit, a thought, a tendency to react in the proper way toward daily life. Formerly- a different method was used. It was the practice to present for inspection a bone that the child had never seen and probably never would see again, and consider that bone and other bones and finally the entire skeleton. Then the muscles and the nervous system were considered in turn. The structures of the body mastered, physiology was studied in the same systematic, logical manner. Then the children were told, in effect, "inasmuch as you are thus made and inasmuch as you see how all of these things which comprise your body work for your good or ill, >ou will readily see that you must do thus and so in order to keep well." The structure of the teeth was taught, and how the teeth worked, and finally the care of the teeth. Now, in teaching hygiene, it is pro- posed to start with the tooth-brush and the use of the tooth-brush daily, four times a day and two minutes each time ami endeavor to get a practical result immediately — the habit of using that tooth-brush. 436 FACTORS IN PERSONAL HYGIENE It matters little whether the six-year-old child knows anything at all about the structure of the teeth or not, but it does matter much whether or not he learns to take care of them. Later he may be interested in the logical way in understanding what he has been doing, but children in the first grade in the elementary school are not logical persons despite the fact that many college professors are attempting to raise their children upon the basis of the theory that they are. Hygiene is to be taught upon the basis of telling the children to do things, without emphasis upon the reasons for doing them, then seeing that they do them, which is most important of all, and last comes the logical motivation. The strongest and most effective motivation is compulsion. This may be reactionary, but it is effective. There are two methods. The first is a hygienic inspection of each child every day by the teacher, the object of which is to get the child into the habit of coming to school clean and orderly in person and in clothing. Second, to render concrete and practical the instruction in hygiene, to determine the ability of the pupil to put into practice the instruc- tion received. They are told to do something. The next morning it is noted whether or not they have done it. Every morning the teacher will receive the pupils at the desk and look over two or three points among the following which are considered of importance: cleanliness of face, neck, eyes, nose, teeth, finger-nails and hair; collars, waists, caps, shirts, coats, shoes, outer clothing, handkerchiefs; books, lunch boxes, and desks. This daily inspection should include as many details as practicable. When unhygienic conditions are discovered an endeavor to cure them should be made by conference with the individual pupil in such a manner as not to occasion embar- rassment. The children exliibiting certain symptoms indicative of disease are immediately sent to the physician. When this daily inspection of the children can be held, it will no longer be a common thing as it once was, for a pupil to come to school with red, inflamed eyes, with parasites in the head, with dirty clothes, grimy hands, black finger-nails — meanwhile getting a mark pf "perfect" in hygiene for handing to the teacher a very carefully prispared picture of the skeleton of a human being. There is a motivation for this sort of interest in personal hygiene and that is the desire of the child for a])})r()])ation, or a reward of some kind. It may be developed iudi\'i