c »?»|gS HX64098567 QP41.Se81888 A topical synopsis o RECAP mUMm 1 WSSSmSmmfm MJfPlflffllllffESB! A TOPICAL SYNOPSIS OF LECTURES ANIMAL PHYSIOLOGY HENRY SEWALL, Ph. D., M. D., PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF MICHIGAN. THIRD EDITION, REVISED AND ENLARGED, ANN ARBOR, MICH. : SHEEHAN & COMPANY. 1888. ii Km I I r / if The Courier Printing House, Ann Arbor, Mich. AUTHOR'S NOTE TO THE FIRST EDITION. This skeleton of a course of lectures on physiology has been prepared at intervals, with the sole object of helping students to fix the attention upon the main facts ot the subject. The topics have served simply as points of departure in the lecture room, and no effort has been made to render the " Synopsis " clear to any for whom the spaces between the paragraphs have have not already been filled in. The author has been burdened with no desire for originality, and for good reasons the admira- ble text-books of Professor Martin and of Dr. Foster, especially the latter, have frequently been followed in both order and substance in the preparation of these notes. Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/topicalsynopsiso1888sewa I. THE OBJECT OF PHYSIOLOGY AND THE FUNCTIONS OF LIV- ING MATTER. Physiology is the study of the chemistry and physics of the living body. Physiologically, Life is the sum of the functions of matter called Protoplasm. Protoplasm is made up of the elements C, H, O, N, traces of P and S ; some inorganic salts. Contains much water and probably residues of proteids, fats, and carbohydrates. Protoplasm has remarkable capacity for absorbing water. To make protoplasm needs building material and building energy. In the animal both are supplied by the food and oxygen taken in. In the green plant sunlight supplies energy. Living protoplasm is continually wasting through the pro- cess of oxidation. In the animal the waste matter contains less potential energy than the food ; the energy difference is the vital force of the animal. The general functions of all protoplasm are exhibited by the simplest living thing, as an amwba, or white blood corpuscle. These functions are : Contractility. Spontaneity . Irritability. Conductivity . Co-ordination. Assimilation. This leads to Growth by Intussusception. Growth stops when the weight of egesta equals that of ingesta. As the amount of waste matter depends upon the mass of protoplasm and the amount of matter assimi- lated upon its surface, growth must have its limit accord- ing to the law of unequal increase of mass and surface. —6— Reproduction. The highest animal exists first as an egg,, a single cell. Multiplication of cells by fission. The body is composed of cells, modified cells and intercel- lular matter. Differentiation of tissues. Physiological division of labor. Physiological division of tissnes into : — Undifferentiated. Supporting. Nutritive ; including assimilative ; secretory ; receptive ; eliminative ; respiratory ; metabolic. Storage. ' Irritable. Conductive. Co-ordinating and Automatic. Motor. Productive. Reproductive. II. THE NATURE OE THE LAWS SUPPOSED TO RULE THE ACTIV- ITIES OF THE EODY. The physiologist studies vitality as a manifestation of chemical and physical energy and believes the laws governing living and not living things to be equally inflexible. Energy exists in two states, Potential, and Actual or Kine- tic. Potential energy ; represented in the position of masses by position of atoms in molecules. Kinetic energy ; represented in the motion of masses and of molecules and atoms. The different kinds of energy. One kind of energy may be changed into another. Energy is indestructible. Energy cannot be created. The uses of a machine as illustrated by the steam engine, the pulley and the watch spring. The principle of the dissipation of energy. Consider the whole history of the energy represented in a stone thrown by the arm into the air. III. THE LYMPH AND BLOOD. The fluid parts consist of food matters dissolved and al- tered by digestion and the activity of metabolic tissues, and of the products of tissue change. LYMPH. The tissue elements are bathed in lymph. Physical and chemical characters of lymph. Lymph cor- puscles. Lymph derived from blood by diffusion. Nature of diffusion; influence of temperature; of the di- viding membrane ; of the concentration and composition of the diffusing fluids. The vital condition of the vascular wall as effecting the quantity and quality of substances which pass through it. The quality of the blood as affecting the formation of lymph. Effect of blood-pressure on the diffusion and filtration from the blood vessels. The use of lymphatics as drainage vessels. Various directions of the lymph currents of diffusion in the body. Influence of the blood circulation on the rate of diffusion by the supply of new and removal of waste matter. Physical and vital characters of lymph corpuscles. Coagulation of lymph. BLOOD. Consists physically of straw-colored fluid plasma and of solid red and white corpuscles. Relative number of red and white corpuscles. Conditions of its physiological variation. Size, shape, physical and vital characters of white cor- puscles. Number, size, shape, physical characters and function of human red corpuscles. —9— Distinction between the red corpuscles of mammals and of other vertebrates. Rouleaux of red corpuscles in drawn blood. Stroma and haemoglobin of red corpuscles. Cause of opacity of blood. " Laky " blood and means of producing it. Composition of haemoglobin ; haemoglobin crystals. Characters and production of haemin crystals. The colorless "blood-plates" of Bizzozero. COAGULATION OF BLOOD. Physical changes in blood on coagulating; jelly stage; solid clot; cupping; serum ; "resolution" of clot. Demonstration of fibrin threads in the clot produced on a microscope slide. Phenomena of clotting in a capillary tube. Effect of whipping fresh blood. (Plasma. Before clotting < (Corpuscles. Physical components of blood (Clot=fibrin + After clotting -| corpuscles. (Serum. Whipped blood=corpuscles+ serum. Red corpuscles have nothing to do with coagulation. The red corpuscles are somewhat heavier than the plasma. The huffy coat; its nature and conditions of occurrence. When blood clots sufficiently slowly the corpuscles settle some- what in the liquid, leaving a straw-colored layer of plasma at the top. When coagulation sets in the upper part of the clot, being free from corpuscles, is known as the buffy coat. The reason for its occurrence in blood in inflammatory dis- ease. Relation of the shape of the clot to that of the containing vessel. Color of clot at different distances from the free surface. Uses of clotting to a wounded animal. Fibrin does not exist as such in normal blood. The fluid of normal blood is plasma which is spontaneously —10— coagulable. Serum is formed only by the process of coagula- tion ; it is not spontaneously coagulable. CAUSES OF COAGULATION AND INFLUENCES MODI- FYING IT. Old theories that clotting was due to escape of ammonia; to taking up of oxygen. Significance of blood clotting under mercury. Views that clotting was due to loss of heat ; to cessation of circulation. Hypothesis that the internal coats of the blood vessels pre- vent coagulation. Evidence as to influence of internal coat. Formation of thrombi in ligatured vessels. The fluid condition maintained in the blood of carefully excised veins. View that blood does not tend to clot until chemically al- tered. The retardation of clotting by oiling the walls of a vessel into which an animal is bled. Influence on coagulation of temperature; of strong solu- tions of mineral salts; of stirring. White blood corpuscles always found in spontaneously coagulating fluids. The deposit of fibrin around a foreign object in flowing blood is preceded by accumulation of white corpuscles. In the thin clot upon a microscope slide the fibrin threads start from white corpuscles. In slowly clotting horses' blood the firmest clot is at the level of greatest accumulation of white corpuscles. Direct observation under the microscope of thrombus for- mation in a frog's tongue. The disintegration of white corpuscles and transition forms on drawing blood from the bod}'. All that has here been said of the white corpuscles prob- ably holds true for the colorless " blood-plates." Denis' plasmine. Clotting of the solution of plasmine. The blood clot, fibrin, is probably formed from a proteid body, fibrinogen, a constituent of the blood plasma, under the —11— action of a Mr in- ferment which is produced by the disintegra- tion of the colorless corpuscles (leucocytes or blood-plates, or both.) Fibrinogen is found in solution in transudation fluids; is precipitated by saturating with salines ; is dissolved by dilute salines. Hastening of clotting by addition of fibrin-ferment to di- luted plasma. Necessity of salines to coagulation. The action of the fibrin-ferment. The nature of animal ferments; conditions of action. The origin of fibrin-ferment and method of obtaining it. THE TRANSFUSION OF BLOOD. Transfusion as practiced on the isolated hearts of the frog and dog. The nature of the foreign blood is not indifferent. Danger in direct transfusion of clotting in the transmission tube. Danger of injection of whipped blood because of its con- tained fibrin ferment. Experiments illustrating this point. CHEMISTRY OF BLOOD. Average specific gravity of human blood is 1055; relative weight of corpuscles and plasma. The average amount of fibrin formed in the coagulation of blood is only about 0.2 per cent of its weight. Reaction of blood ; its variation in clotting. The amount and kinds of gas given off in vacuum by a volume of blood ; by serum. Chemical composition of serum; water, 90 p. c; proteids, (serum albumin and paraglobulin), 8-9 p. c. ; fats, salines and extractives, 1-2 p. c. ; (the principle extractives are sugar, urea and lactic acid). The ash of serum contrasted with the ash of corpuscles. Chemical composition of the red corpuscles ; of the white. HISTORY OF BLOOD CORPUSCLES. Evidence for the transitory nature of the corpuscles ; varia- 2 —12— tion in number at different times ; probable derivation of uri- nary and bile pigments ; normal number quickly regained after hemorrhage. Origin of the red corpuscles in the embryo : metamorpho- sis of mesoblastic cells ; transformation of white corpuscles arising in the liver and spleen ; from the protoplasm of con- nective tissue corpuscles. Origin of red corpuscles in the adult : metamorphosed from transitional forms of white corpuscles found in the spleen and red medulla of bones. Fate of red corpuscles : probably destroyed in the spleen. White corpuscles : physiological variation in number. Arise in lymphatic glands and similar organs. They probably serve as occasional tissue builders, and give rise to red cor- puscles. THE QUANTITY AND DISTRIBUTION OF BLOOD IN THE BODY. About one-thirteenth of body weight is blood ;, of this is contained : One-fourth in heart, lungs, large arteries and veins. One-fourth in liver. One-fourth in skeletal muscles. One-fourth in the remaining organs. IV. THE CHEMISTRY OF ANIMAL TISSUES. All the activities of the body are due in the end to chemi- cal processes. The body is composed of living matter, protoplasm, and of not living matter which is made by protoplasm ; otherwise, the body is composed of Formative and of Formed matter. In general, formative matter exists in cells while formed matter is intercellular. The molecule of protoplasm probably contains residues of proteids, tats, and carbo hydrates, besides salines and extrac- tives. PROTEIDS. These form the principal solids of active tissues, of blood and of lymph. They must form a part of the food. The molecule is very complex ; composed of many atoms of O, H, N, C, with S and P. Proteids are amorphous. All are non diffusible except Peptones. Mostly coagulated by alcohol and ether. Soluble with change in strong acids and alkalis. Chemical reactions ; xanthoproteic ; Millon's ; caustic soda and copper sulphate, etc. CLASSES OF PROTEIDS. 1. Native albumins ; serum and egg albumin. Soluble in water. 2. Derived albumins or albuminates ; acid and alkali albumin; casein. Not soluble in water but in dilute acids and alkalies. Not precipitated by boiling. All proteids dissolved in acid or alkali become albuminates. 3. Globulins; globulin ; paraglobulin ; fibrinogen ; myosin. Not soluble in water but in dilute salines ; precipitated by strong salines. —14— 4. Fibrin. Insoluble in water and dilute salines. Soluble with difficulty in strong salines and dilute acids and alkalis. 5. Coagulated proteids, soluble only in strong acids and alkalis. 6. Peptones. Soluble in water. Not precipitated by acids, alkalis or boiling. Diffusible. Product of all proteid digestion. Many varieties. NITROGENOUS NON-CRYSTALLINE BODIES DERIVED FROM AND ALLIED TO PROTEIDS, BUT NOT CAPA- BLE OF REPLACING PROTEIDS IN THE FOOD. They contain the elements of C, H, N, O, and sometimes S. They give some of the chemical reactions for proteids. Mucin ; a secretion of mucous epithelium. Chondrin ; the organic basis of cartilage. Its solutions set on cooling. Gelatin ; organic basis of bone teeth and tendon. Solutions set on cooling. Elastin ; from elastic tissue. Its solutions do not gelatinize. Keratin ; from hair, nails, epidermis. Nuclein ; from nuclei of pus corpuscles. COMPLEX NITROGENOUS FATS CHIEFLY FORMING PARTS OF NERVE TISSUES. Lecithin (C 44 H 90 NPO 9 ). Protogon. Cerebrin. STORE MATERIALS LAID UP IN THE BODY AS FOOD FOR THE TISSUES; FATS, AND CARBOHYDRATES. FATS. Neutral fats are compounds of a fatty acid with glycerin. They are made up of the elements C, H, O. —15— Insoluble in water. Soluble in ether, chloroform and hot alcohol. Are decomposed by caustic alkalis, forming soaps with them, leaving the glycerin free. C 3 H 5 Palmitin 1 Y Y O, C 16 H 36 ) 3 ( C 3 H 5 Stearin \ Y O, (0 18 H 35 Olein ■! [ Y O 18 H 33 oJ The fats occur mixed together in the body. Their fusion points differ. Their molecule contains much more C and H in proportion to O than does that of carbohydrates. CARBOHYDRATES. -Composed of C, H, and O. Maltose (C 13 H 22 llt + H_.0) ; convertible into dextrose. Dextrose or grape sugar (0 6 H 13 6 ); capable of alcoholic fermentation : of lactic acid fermentation. Lactose or milk sugar (G 12 H 22 11 ) ; capable of lactic acid fermentation. Inosit (C 6 H 12 6 ) ; capable of lactic acid fermentation. Glycogen (C 6 H 10 O 5 ); convertible into dextrose. Dextrin (C 6 H 10 O 5 ); convertible into dextrose. SOME OF THE SUBSTANCES FORMED IN THE BODY; FOR THE MOST FART " WASTE " PRODUCTS OF TIS- SUE CHANGE. NON-NITROGENOUS METABOLITES. Lactic acid (C 3 H 6 3 ). Oxalic acid (H 3 C 2 4 ), in oxalate of lime. Succinic acid (H 3 C 4 H 4 4 ). —16— NITROGENOUS METABOLITES. Urea (NH 2 ) 2 CO ; and its oxalate and nitrate. Uric acid (0 5 H 4 N 4 ); and salts. Kreatin(C 4 H 9 N 3 2 ). Kreatinin (C 4 H 7 N 3 0). Sarkin (C 5 H 4 N 4 0). (C 6 H lt O) Leucin ■< r O. ( NH 2 ) Tyrosin (C.H^NC^). Hippuric acid (0 9 H 9 M0 3 ). Taurocholic acid (C 26 H 5 NS0 7 ). Glycocholic acid (C 26 H 43 jNO r ). V, EPITHELIUM, CONNECTIVE TISSUE, BONE, AND PHYSIOLOGY OF THE SKELETON, EPITHELIUM. The typical animal cell; cell membrane; protoplasm; granules ; nucleus and nucleoli; fibrillar net work. Scaly or squamous epithelium ; epidermis and buccal mu- cous membrane. Columnar epithelium; intestine. Pavement epithelium ; mesentety. Polyhedral epithelium ; glands. Ciliated epithelium ; trachea. Difference between " serous " and " mucous '' membranes. THE CONNECTIVE TISSUES. We may speak of the temporary skeleton, composed of epithelium and connective tissue, and of the 'permanent skele- ton made up of bone and cartilage. Function and distribution in the body. White fibrous tissue ; physical characters ; swelled by acids ; distribution. Yellow elastic tissue; physical characters; unaffected by acids ; distribution. Cement substance. Connective tissue corpuscles ; varieties of form and func- tion ; distribution. Riteform or adenoid tissue. The supporting function of connective tissue elements as illustrated in such organs as the brain. Gelatinous tissue; vitreous humor; umbilical cord. Areolar tissue ; composition and distribution. The development and condition of fat in the body. THE PERMANENT SKELETON.— CARTILAGE. Hyaline cartilage ; its physical characters ; the perichon- —18— drium; contains no blood vessels; histological appearance; cells and matrix; method of formation of matrix; transition forms between round cartilage cells and branched periosteal cells; distribution and function. Fibro-cartilage: physical and histological characters; ac- tion of acids; distribution and function. Elastic cartilage. Parenchymals cartilage ; physical and histological character ; unaffected by acids ; distribution and functions. THE BONY SKELETON. The skeleton is at once the fortress, the tools and weapons of the body. The skeleton should be made of parts which are strong, light, inflexible and symmetrical. Bones are composed of a mixture of organic and earthy matter. The former is flexible, the latter stiff and brittle; the origi- nal size and shape of the bone are retained when either is removed. Two-thirds of the weight of dry bone is mineral, chiefly 0a 3 2 (P O ). Mechanical advantage of this combination. THE LONG BONES. The periosteum, the nutritive membrane. The expanded articular end of long bones allows distribu- tion of strain. The advantage gained by the hollow cylindrical form of the bone. The cancellated extremities and the red and white marrow. Histological structure of a long bone ; the perfection of adaptation for firmness, lightness and elasticity. THE SKULL. Advantage of its curved shape. Fracture at the base of the skull from a blow upon the top. The two bony tables with diploe between. The outer bony plate is thicker, tough and fibrous. —19— The inner bony plate is thinner, dense and brittle. Use of diploe in deadening jars. Use of the sutures in limiting the extension of jars. THE BACKBONE. The separate vertebrae allowing the bending of the spine Porous structure of the vertebrae. The in vertebral pads allow bending without separation of vertebrae, and deaden jars. The curved shape of. the spine gives it a wide range of elasticity. JOINTS. Distinction between the axial and appendicular skeleton. Ball and socket joints. Hinge joints. Pivot joints. Gliding joints. The synovial sac and its influence. The capsular ligament. Bones are held together by atmospheric pressure. THE BONY LEVERS. The mechanics of animal movement. Lever of the first order ; nodding motion of the head I F \ p— " vv Lever of the second order; raising the bodv on the toes by the calf muscles. . . t £ f W Lever of the third order; raising of fore- arm by the biceps muscle .... \ £ \v f F VI. THE CONTRACTILE TISSUES, AMOEBOID CELLS. CILIATED CELLS. MUSCLE. Contractility is a function of Protoplasm irrespective of any special form in which this matter may be found. Contractile tissues in the higher animals may be divided according to the degree of their specialization of function into, — 1, amoeboid cells ; 2, ciliated cells ; 3, non-striated muscle; 4, striated muscle. All visible movements of higher animals are due to the contraction of a special set of organs, the muscles, which are in no case able to set up movements spontaneously. The amoeboid cells contract throughout their body sub- stance and have usually the power of locomotion. CILIATED CELLS. Ciliated ceils are fixed and are usually columnar in shape. The free margin of the cell is thick and firm, and has pro- jecting from it ten to thirty long protoplasmic lashes, the cilia. The movement of the cilia is a to and fro whipping motion. The movement is two or three times quicker in one direc- tion than in the other. The rate of movement is accelerated with elevation of tem- perature. Foreign bodies resting on the cilia are urged in the direc- tion of the more rapid motion. The function of cilia in the trachea and bronchi : they cause expulsion of foreign particles and aid the mixture of gases. The movement is automatic and co ordinated. The move- ment of a series of cilia is not isochronous, but proceeds in a wave form along the row. The circulation of fluid carried on by the cilia on the gills of the fresh water mussel. The impulse to the movement is probably conveyed directly from the protoplasm of one cell to that of the next. —22— The energy produced by each cell is calculated as sufficient to raise its own weight each minute 4^ metres. THE MUSCLES. The muscles are not automatically contractile. They are usually red in color from contained haemoglobin, but the color is not essential. The pale muscles of an animal contract more quickly than the red. There are two great groups which are distinguished histo- logically and physiologically: (1) Plain or unstriated. muscle; sometimes called visceral or organic or involuntary muscle (2) Cross-striated muscle; sometimes called skeletal or vol- untary muscle. All striated muscles contract quickly after a short latent period. All non-striated muscles contract slowly after a long latent period. The visceral or involuntary muscles of some animals are striated. HISTOLOGY OF NON-STRIATED MUSCLE. The flattened lanceolate cell; the rod-shaped nucleus. The method, of aggregation of the muscle cells, and their distribution in the bod}^. THE STRIATED MUSCLE. The manner of aggregation of muscle and other tissues as shown in the cross section of a linb. Each muscle is made up of separate bundles of fibres. The fibres may be oblique or parallel to the long axis of the muscle. The length of the individual muscle fibre in man does not exceed one inch and a half. The binding together of fibres in fasciculi. The union of muscle with tendon. —23— HISTOLOGY OF STRIATED MUSCLE. The muscle fibre; the sarcolemma; the nuclei; the cross markings. The cross marking is due to alternate bright, dark and dim bands. The juncture of muscle fibres by their beveled endings. Two modes of ending in tendon. The greater part of the living muscle fibre is semi-fluid in consistency. PHYSIOLOGY OF STRIATED MUSCLE. The function of the muscle fibre is to contract or to draw its two ends nearer together. The complex results which are obtained by this simple means. Muscle exists in the body in two natural conditions, in an active and passive state; the shape and elastic properties of the muscle are different in the two conditions. The shortening of the muscle is active and due to distinct chemical processes ; the elongation is passive. The shortening is caused by the transverse swelling of the fibres. The muscle does its work by shortening, not by becoming thicker in contraction. The muscle does not perceptibly alter in volume in con- traction. The molecular cause of contraction is probably the absorp- tion of the more fluid parts of the muscle fibres within defi- nite layers of more solid particles. Whatever excites a muscle to contract is called a stimulus. The contraction begins at the point stimulated, and moves along the fibre in the form of a wave, which travels in the frog's muscle with a velocity of about three metres per second. The wave moves slower the lower the temperature. THE PHYSICAL PROPERTIES OF MUSCLE. Compare the curve of elasticity of muscle with that of steel. Compare the curves of elasticity of resting and active muscle. —24— The elasticity of resting muscle is perfect within narrow limits. When a muscle contracts its elasticity decreases and its extensibility increases. The resting muscles in the body are always slightly stretched between their attachments. Proof of this and signi- ficance for the welfare of the body. The protective use to the body of the increased extensibil- ity of contracted muscle. The elasticity of the muscle enables it to store up its energy of contraction. The lifting power of the muscle diminishes with contrac- tion. Show how in the movements of the bony levers the con- tractile energy of the muscle is economized according to the preceding principle. In practice, before a voluntary contrac- tion, we stretch the muscles to their greatest length. The muscle possesses the distinct properties of contractility, conductivity and irritability. The peculiar nature of physiological couductivity. Irritability is the capability possessed by some tissues of being stirred up to functional activity by a stimulus. Its peculiarity is the disproportion between the amount of energy represented in the stimulus and in the effect produced. Irritability is decreased by low temperature, by fatigue, by various drugs. The old view that contraction of muscle was due to swell- ing of its substance by the in-fiow of ' fc animal spirits." Proofs of the independent irritability of muscle : contrac- tion of embryonic muscles before the establishment of nervous connections; the "idio-muscular" contraction; the nerve free ends of the sartorius ; the manner of action of curare. The various kinds of stimuli capable of exciting muscle; nervous; mechanical; thermal; chemical; electrical. The character of a muscular contraction caused by the application of a galvanic current. The contraction caused by a single induction shock. —25— The general law for the stimulation of irritable tissues: It is only the change of intensity of a stimulus that excites an irritable organ. The most favorable rate of change of intensity of the stim- ulus differs for different kii;ds of tissues ; the intensity should vary most rapidly for nerve, less so for striped muscie, and still more slowly for unstriped muscle. The muscle answers a single stimulation by a single twitch or contraction. The contraction is prolonged by cold, by fatigue, by various drugs. The prolonged contraction of a muscle poisoned with vera- trin. The " graphic method " of recording observations. The curve of a single muscular contraction; the latent period of stimulation; the phases of the contraction curve ; the " contractur." The latent period of stimulation is the interval elapsing between the application of a stimulus and the* beginning of contraction. Its average duration in the frog's muscle is .01 second. During the latent period the muscle molecules are undergoing chemical, electrical, thermal and mechanical changes. The period is lengthened by cold, by fatigue, by in- creased load. The " contractur " is due to the "elastic after action " of the muscle substance, not to vital changes. Influence of fatigue and of load upon the contractur. The contractur of ths flexor muscles of the hand after clenching the fist.. Maximal and sub-maximal single contractions; with a cer- tain strength of stimulus the muscle gives a barely visible contraction; with increase of stimulus the height of contrac- tion increases to a certain extent, and then no stronger stimu- lus causes a greater single contraction. The fatigue curve of muscle excited to single contractions repeated at a definite rate is a straight line. The line falls more rapidly with a shorter interval between the stimuli. The effect of rest is to increase the height of the succeeding con- traction, but the contractions soon regain their position on the fatigue curve. —26— Practical illustrations of the fatigue law. The waste products of contraction diminish the irritability and contractility of the muscle. A blood free muscle exhausted by stimulation may be made to contract again after washing out with dilute salt solution. The work done by a contracting muscle is measured by the load x height of lift. The work done increases with the load to a certain extent and then diminishes as the load becomes greater. The lift power of a muscle increases with its thickness, or the number of fibres side by side. The extent of the shorten- ing increases with the length of the fibres. The maximum lift power for frog's muscle is 2800-3000 grammes per square cm. of cross section ; for the human muscle it is estimated to be 6000-8000 grms. PHYSIOLOGICAL TETANUS. When one contraction succeeds another in a muscle before the first is finished, the result is a longer and more extensive contraction or tetanus. The tetanus is smooth when each contraction begins during the ascending phase of the preceding one. The tetanus is vibratory when the muscle has time to relax from one contraction before another engages it. Distinction between physiological and pathological tetanus. Proof of the formation of tetanus by the summation of single contractions. A tetanus may be sub-maximal or maximal in extent. A muscle may be shortened hj tetanus to one-third its original length. In tetanus the duration, the amplitude, and the power of the contraction may be made greater than by the use of a single stimulus. The natural contractions of the living body are sub-maxi- mal and tetanic in character. The motor nerves cell is the source of the physiological stimulus. Fatigue and exhaustion are probably not so much phenomena of nerve and muscle as of the nerve cell. Proofs of the foregoing statement: comparison of the power of voluntary and artificially excited contractions. The —27— duration of the shortest voluntary contraction compared with that excited by a single artificial stimulation. The muscle note and its pitch. Voluntary contractions are probably due not to the simul- taneous, but to the successive stimulation of the different fibres of a muscle. Free circulation of blood in the muscle is necessary to vol- untary contraction. THE ELECTRICAL PHENOMENA OF ACTIVE MUSCLE. The ; " natural muscle current."" " current of rest." or " de- markation current." The " negative variation" of the ; " demarkation current.' 5 When a muscle is stimulated, the part excited becomes electro-negative to the resting parts. The electric change is due to the chemical changes of the active molecules. The chemical change set up in the muscle by stimulation is conducted along the fibres, and the electro-negative condi- tion accompanies it. The rate of this progression in the frog's muscle is about three metres per second. It has already finished its course during the latent period of stimulation. If an electric conductor be made to connect the excited electro-negative part of the muscle with its resting electro- positive part, a current of electricity will flow through the conductor. This current is called the " action current " of the muscle. The physiological action current is not to be confused with the electrical current which is used as a stimulus. Experiment of the ,; rheoscopic frog.*' The secondary muscle is thrown into tetanus when the primary muscle is tetanised, thus proving the interrupted nature of the electric changes in the latter. When the vital continuity of the nerve supplying the first muscle is broken by tying a string around it. the tetanus fails in both muscles. An action current is set up in a muscle by any stimulus, electrical or otherwise. 4 —28— The secondary contraction of a frog's nerve-muscle prepar- ation caused by the beat of the mammalian heart. COMPARISON OF THE PHYSICAL AND CHEMICAL CHAR- ACTERS OF LIVING AND DEAD MUSCLES. Living resting muscle is soft, glistening, elastic, semi-trans- parent and alkaline or amphichroic in reaction. Living working muscle is less elastic, but more extensible and becomes acid in reaction. Dead muscle is dull, opaque, inelastic and is acid in reac- tion. A dying muscle loses gradually its irritability, and then goes rather suddenly into rigor mortis. Rigor is attended by a considerable production of sarcolatic and carbonic acids, by a rise in temperature, and by a shortening of the muscle. The shortening is not powerful ; limbs remain in about the same position as at death. The fluctuation in length of a muscle in rigor. Rigor passes off as decomposition sets in. THE CHEMICAL CHANGES OF WORKING MUSCLE. The excised muscle gives off no oxygen under the air pump, but when made to contract it develops sarcolactic and carbonic acids in an oxygen free atmosphere. The living muscle in the body consumes more oxygen, and produces more carbonic acid in the active than in the resting condition. The weight of muscle substance soluble in water decreases, while that soluble in alcohol increases in the active as com- pared with the resting condition. The amount of acid produced by tetanising an excised muscle is substracted from the amount finally produced by the death of the muscle. The living muscle molecule probably consists of an essen- tial nitrogenous part capable of building on to itself certain carbon compounds by whose oxidation the energy of contrac- tion is produced. Every contraction is attended by an evolution of heat. Comparison of the muscle with the steam-engine. —29— THE CHEMISTRY OF LIVING MUSCLE. The contents of the living muscle fibre are chiefly semi- fluid in consistency. This matter is the muscle plasma. The artificial preparation of muscle plasma. The clotting of muscle plasma and its separation into clot and serum. The muscle clot is myosin ; its formation in dead muscle causes rigor mortis. The clot of myosin is granular ; its formation is accompa- nied by the development of acid. THE CHEMISTRY OF DEAD MUSCLE. The dead muscle contains seventy-five per cent, water. Its dry substance contains : — Proteids: myosin; serum-albumin. Extractives : kreatin ; sarcolactic acid ; xanthin ; hypoxan- thin; uric acid; inosit (in the heart) ; inosinic acid; sugar. No urea. Fats in quantity. In living muscle there is glycogen which is changed to sugar on death. The nitrogenous extractives are products of the chemical changes of the muscle substance. Myosin does not exist in living muscle. THE PHYSIOLOGY OF UNSTRIATED MUSCLE. Unstriated muscle is not found unmixed with other tissues of the body. Organs containing unstriated muscle have to some extent power of automatic contraction, which may be due to con- tained nervous elements. The contraction progresses slowly in a wave form from the spot stimulated, and is preceded by a long latent period. In striated muscle the contraction wave passes only length- wise throughout the fibre ; in unstriated muscle the wave may pass both in the direction of the length and the breadth of the cell. The impulse to contraction may probably be communicated directly by one muscle cell to another without the intervention of nerves. —30— Unstriated muscle is more readily stimulated by the make and break of a galvanic current than by induction currents. A succession of shocks produces a series of increasing contractions. Consider the action of unstriated muscle as seen in the peristaltic action of the intestine and ureter and in the con- traction of the urinary bladder. The rheoscopic frog ; secondary tetanus. Secondary contraction of frog's muscle from the beat of the mammalian heart. Formation of acid with the death of the muscle. VII. NERVOUS TISSUES. The nervous tissues consist of the nerves and of the per- ipheral and central irritable non contractile organs in which they end. THE MINUTE STRUCTURE OF NERVES. Nerve fibres are bound together in bundles, the funiculi. Each funiculus is inclosed in several sheets of membrane, the neurilemma. Each nerve is composed of many funiculi inclosed in a common sheath. The lymph channels of nerves. Nerve fibres fall into two groups: (1) Medullated or white nerve fibres. (2) Non-medullated, gray or sympathetic nerve fibres. Histology of the medullated fibre ; the primitive sheath ; the medullary sheath or white substance ; the axis cylinder ; the neuro- keratin frame-work; the nodes of Ranvier ; the cement substance. Significance of the nodes in the nutrition of the nerve. The medullary sheath is chiefly fat, and is not visibly differ- entiated in perfectly fresh nerve. The axis cylinder is protoplasmic and is the conductor of the nervous impulse. Nerves lose their medullary sheath before reaching their peripheral and central terminations. The ending of nerves in voluntary muscle ; ending in involuntary muscle. Histology of gray nerve fibre; absence of medullary sheath ; nuclei found in the substance of the fibre. The physiology of gray nerve fibre. In general, the gray nerve fibres arise from the sympathetic system and are distributed to organs whose function does not involve consciousness. Nerves of the sympathetic system leave the spinal cord as —32— medullated fibres of much smaller calibre than those of the sensory-motor system. The medullary sheath of the sympa- thetic nerve is lost in its passage through one or the other four chains of sympathetic ganglia. (Gaskell.) CLASSIFICATION OF NERVES ACCORDING TO THEIR FUNCTIONS. ( MARTIN. ) Sensory. Reflex. Afferent. { Excito-motor. j Vaso motor. ^ Inhibitory. Peripheral Nerves. f Motor. Vaso-motor. Efferent.