CORNELL 
 
 UNIVERSITY 
 
 LIBRARY 
 
 FROM 
 
Cornell University Library 
 QP 42.C81 
 
 Laboratory directions for course one in 
 
 3 1924 003 184 565 
 
Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924003184565 
 
LABORATORY DIRECTIONS 
 
 FOR COURSE ONE IN 
 
 PHYSIOLOGY 
 
 Department of 
 PHYSIOLOGY AND PHARMACOLOGY 
 
 Cornell University, Ithaca, N. Y. 
 
 I P C PRESS ITHACA 
 
CONTENTS 
 
 PAGE 
 
 I. The Chemistry of the Body 7 
 
 Carbohydrates 7 
 
 Proteids 10 
 
 Fats I2 
 
 II. The Blood and Lymph 14 
 
 Coagulation, Plasma, Fibrin, Serum 15 
 
 The Red and White Corpuscles 17 
 
 Haemoglobin and its Derivatives 20 
 
 III. Muscle and Nerve 23 
 
 Stimuli and Stimulation 29 
 
 Electricity as a Stimulus..'. 32, 3g 
 
 Contraction of Muscle 35 
 
 Regulation of Electricity as a Stimulus 39 
 
 Electrical Stimulation of Muscle and Nerve 42 
 
 Stimulation of Human Nerves 48 
 
 Responses 51 
 
 Work of Muscular Contraction 54 
 
 IV. Plain Muscle and Gland 58 
 
 Reflex Action ^ 60 
 
 Visceral Movement and Secretion 62 
 
 V. Heart and Circulation 65 
 
 The Heart 66 
 
 Tne Human Heart yy 
 
 Blood Pressure 80 
 
 The Pulse : 84 
 
 VI. Respiration 87 
 
 VII. Animal Heat 90 
 
 VIII. Vision 91 
 
 The Eye as an Optical Instrument 92 
 
 The Clinical Examination of the Eye 106 
 
 The Phycho-Physiology of Vision 108 
 
 The Eye Reflexes 111 
 
NOTE. 
 
 The following presents an arrangement of experiments in Physi : 
 ology designed for use in the laboratory work of Course One in 
 Physiology. Wherever possible the work is so arranged that it 
 leads logically to the application of that side of physiology to Medi- 
 cine. Often, however, this application is not possible in the labora- 
 tory because of the necessarily limited nature of the work, but in 
 those cases the bearing of physiology on the later medical studies,— - 
 pathology and clinical medicine, — is emphasized in lecture and quiz. 
 The whole laboratory work is supplemented by lectures, demonstra- 
 tions, recitations and quizzes which unify the work of the course. 
 
 In preparing these directions, I am glad to acknowledge the 
 friendly assistance of my colleagues in the Department. 
 
 B. F. KINGSBURY. 
 
LABORATORY DIRECTIONS. 
 
 The laboratory work will be divided into six divisions : ( I ) 
 Chemistry (preliminary) and the Blood, (2) Muscle and Nerve, 
 (3) Plain Muscle and Gland, (4) Heart and Circulation, (5) Res- 
 piration, (6) Vision. 
 
 After the work of each division is finished, the laboratory note- 
 book is to be handed in for inspection and correction, and a quiz 
 taken, which may be arranged for by placing your name on a posted 
 list or handing it to the instructor in charge. Should the quiz show 
 insufficient knowledge or work carelessly done, the whole or por- 
 tions of the work of that division must be repeated. 
 
 The Laboratory Note Book. This should contain a brief, accu- 
 rate statement of results for each experiment, consisting of descrip- 
 tion, description and tracing or simply the tracing record neatly and 
 fully labelled. These tracings should be neatly mounted either 
 in the book or on card board. Interleaved laboratory guides may 
 be used as note books as well. 
 
 Care of Apparatus. Each group of two students will be assigned 
 to a set of apparatus, which is to be kept in the lockers assigned. 
 The set includes (a) chemical glassware, (b) apparatus for experi- 
 mental physiology, (c) optical apparatus. Lists will be furnished 
 and the apparatus should be checked up when the assignment is 
 made. It will be in order when the student receives it. Should 
 this not be the case, notify 'the Instructor at once. After the appar- 
 atus has been used each time it should be put back in the locker in 
 good condition. Any repairs needed should be reported immediately. 
 Much of the apparatus is expensive and the student is held 
 responsible for the condition of the instruments while in his hands. 
 Other pieces of apparatus, not included here, may be obtained when 
 needed by applying to the Instructor in charge. At the end of the 
 term the apparatus is to be again checked up with the Instructor and 
 turned in to the Department. 
 
THE CHEMISTRY OF THE BODY. 
 Preliminary Work. 
 
 I. CHEMISTRY OF THE BODY. 
 
 (a) Carbohydrates. 
 
 (b) Proteids. 
 
 (c) Fats. 
 
 II. THE BLOOD. 
 
 (a) Coagulation: Fibrin, Plasma, Serum. 
 
 (b) Nature of Coagulation, 
 (cj The Blood Corpuscles. 
 
 1. Isotonicity. 
 
 2. Number of red and white cells. 
 
 (d) Hemoglobin and its Derivatives. 
 
 1. Hemoglobin Crystals. 
 
 2. Hematin, Hemin, Hematoporphyrin, Hemochromo- 
 
 gen. 
 
 3. The Spectra of the Blood Pigments. 
 
 There are certain chemical substances whose association with 
 the life processes is particularly close. While the study of these 
 belongs rightly to a special division of the subject, physiological 
 chemistry, and their thorough consideration will doubtless be taken 
 up later as Physiological Chemistry, it will be found necessary to 
 become somewhat familiar with them now at the beginning of the 
 study of Physiology in order better to understand some of the other 
 sides of the subject. The groups with which we have to deal are 
 the Carbohydrates, Fats, and Proteids, together with some of the 
 derivatives of these. While none of these chemical compounds occur 
 in inorganic nature, the Proteids are the most closely associated with 
 the phenomena of life. 
 
 CARBOHYDRATES. 
 
 These are chemical compounds occurring in plants and animals 
 and are composed of C, H, and O, the last two in water proportions. 
 There are three important groups: The Monosaccharids (formula: 
 C 6 H 12 6 ), The Disaccharids (formula: C 12 H„ O u ), and The 
 Polysaccharids (formula: (C„ H, O e ) n . The groups are closely 
 related and are convertible into one another in the animal body by 
 processes of condensation and hydrolysis. 
 
I. The Monosaccharids. Simple Sugars. The most im 
 portant ones are Glucose and Fructose- 
 
 Solubility. Test the solubility of glucose in (a) water, (b) 
 alcohol, (c) ether, by putting a small quantity in a test tube and 
 adding the. fluid and allowing it to stand for a time. 
 
 Tests. The simple sugars are chemically either aldehydes or 
 ketones, and possess a reducing power which is the basis of some 
 important tests. Thus silver nitrate may be reduced to metallic silver, 
 cupric hydrate reduced to cuprous hydrate or oxid. 
 
 Test I. Trammers' Test. To a solution of glucose in a test- 
 tube, add about 1-5 to 1-3 its volume of 20% NaOH or KOH, and 
 then, drop by drop, as much of a 10% solution of copper sulphate 
 as it will dissolve. Carefully heat the top of the liquid in the test- 
 tube when a yellow precipitate, changing to red, indicates the pres- 
 ence of a reducing substance, — in this case glucose. 
 
 Test II. Fermentation. Sugars are peculiar in undergoing 
 alcoholic fermentation with yeast. Place in a fermentation tube a 
 1% solution of glucose and add a few grains of yeast. Allow the 
 fermentation tube to stand for about 24 hours, when the collection 
 of carbonic acid gas (carbon dioxid) at the top of the tube indicates 
 that fermentation has taken place. 
 
 Other important tests need not be given here. However, there 
 will be demonstrated to you (a) that glucose rotates polarized light 
 (to the right), (b) Moore's test, (c) the phenyl hydrazine test, 
 (d) lactic acid fermentation, (e) the reduction of silver nitrate above 
 mentioned. 
 
 II. The Disaccharids. Double Sugars. These con- 
 sist of condensations of two molecules of simple sugar with the loss 
 of one molecule of water. M'-f M"=D+H,0. The important and 
 common ones are : Saccharose or cane sugar, Maltose or malt sugar, 
 I^actose or milk sugar. 
 
 The Reducing Power of Disaccharids. Test solutions of each 
 of the above by Trommers' test and record results. 
 
 Hydrolysis. The chemical structure of disaccharids, as made 
 up of two molecules of simple sugar, can be demonstrated by hydro - 
 lysing them. 
 
Experiment 4. Place a 1% solution of cane sugar in a test 
 tube and add a few drops of HCL and heat to boiling. Allow it 
 to become cool and apply Trommer's test. The abundant amount of 
 monosaccharid formed gives a strong reducing test, whereas cane 
 sugar gave none. Cane sugar does not give many of the sugar 
 tests ; thus, Moore's test is negative ; it is not directly fermentable. 
 Try, however, the fermentation test as above and note and explain 
 the result. Solutions of maltose and lactose could have been hydrc- 
 lysed in the same way. 
 
 III. The Polysaccharids. Multiple Sugars. Starches, gums, 
 celluloses. These are substances of high molecular weight which 
 has not yet been exactly determined. They are polymerization 
 forms from mono- and disaccharids into which they may be finally 
 split up by hydrolysis. 
 
 Starch is one of the commonest and most important. 
 
 Solubility. Test the solubility of Starch by putting a little in 
 a test-tube and shaking it up in cold water. Observe that there 
 is no apparent solution. Allow it to settle and add to a little of 
 the supernatant fluid a drop of iodine solution. Color? Shake up 
 t!he settled starch and add a drop of iodine solution as before. 
 Result? 
 
 Boil a pinch of starch in a test-tube of water and observe that 
 it swells up, becomes translucent and forms an opalescent solution. 
 Add to a portion of this solution a drop of iodine solution. Result 
 Boiling bursts the starch grain and converts insoluble starch into 
 soluble starch. 
 
 Dextrin. Test the solubility of dextrin by placing a few grains 
 in a test-tube of cold water. To a portion of the solution add a 
 drop of iodine solution and note the color. Compare with starch. 
 
 Hydrolysis of Starch. Half fill a test-tube with a 1% solution 
 of starch and add a drop or two of HCL and heat for half an hour 
 in a water bath. With iodine solution, test small portions of it at 
 intervals of 5 minutes. Note and explain the color changes. The 
 starch has been converted into sugar through dextrin. Apply Trom- 
 mer's test for the presence of a reducing sugar. The starch solution 
 itself gives no reduction. 
 
JO 
 
 Indiffusibility. Starch is further a non-diffusible substance 
 (See Proteids). 
 
 Cellulose makes up the framework of plant tissues. 
 
 Glycogen, sometimes called animal starch, is a storage form of 
 carbohydrate in the animal body. This substance and some of its 
 properties will be demonstrated to you. Glycogen, dextrin and cel- 
 lulose can all be hydrolyzed. 
 
 The carbohydrates that occur normally in our body are glucose, 
 (together with some fructose and galactose), lactose (only in nurs- 
 ing women), and glycogen. 
 
 PROTEIDS. 
 
 These are the most important chemical substances in the body, 
 occurring always in the living protoplasm wherever found, abso- 
 lutely necessary in the food. They are complex bodies, which are 
 little understood chemically. The proteid molecule is very large 
 and contains C, N, H, O, usually S., and sometimes as well Fe and T. 
 How these elements are grouped together in the proteid molecule is 
 as yet incompletely known. Some of the nitrogen and some of the 
 sulphur are loosely combined as may be shown by the following ex- 
 periments. 
 
 Experiment 8. To about 5 c.c. of diluted egg-albumen, add 
 a few drops of 20% KOH, warm slowly and hold a piece of moist- 
 ened red litmus paper over the mouth of the test-tube. The litmus 
 paper turns blue, showing that ammonia gas is being evolved. The 
 ammonia may also be detected by the smell. Hold a piece of filter 
 paper moistened with HCL over the end of the test-tube"; a clou i 
 of ammonium chlorid fumes is formed. 
 
 Experiment p. To about 5 c.c. of 20% solution of KOH, add 
 two drops of 'lead acetate solution ; a precipitate forms which redis- 
 solves on shaking. When clear, add some solution of egg albumen 
 and boil. A brown or black color indicates lead sulphid. 
 
 Indiffusibility. One of the results apparently of the large size 
 of the proteid molecule is its inability to pass through the pores of 
 an animal or vegetable membrane, — i.e., its indiffusibility. 
 
 Experiment 10. Place some egg albumen, glucose, and salt, in 
 solution in a dialyser and suspend it in a beaker of distilled water. 
 
II 
 
 Allow it to stand for a day and test the water in the beaker for 
 sugar (Trommer's test) and for salt (with silver nitrate solution), 
 and for proteid by the color test below. The first two will be found 
 to be positive, the last negative. 
 
 The Tests for Proteids. Thesemay be conveniently grouped 
 ' as Color tests, Precipitation tests, and Coagulation tests. 
 
 I. The Color Tests. 
 
 (a). The Biuret Test. ( Piotrowsky's Reaction). To a solu- 
 tion of egg albumen, add a few drops of dilute copper sulphate 
 solution and then KOH to excess. A violet color appears which 
 indicates the presence of proteid. Proteoses and peptones (formed 
 in digestion) give instead a rose pink coloration. 
 
 (b). The Xanthoproteic Test. To a solution of egg albumen 
 in a test-tube, add strong nitric acid; a white- precipitate is formed. 
 Boil it and the precipitate turns yellow. Cool it under the water 
 tap and carefully add ammonia to excess; the yellow turns to an 
 orange. Dilute solutions may give these color reactions in solution. 
 
 (c). Millon's Reaction. To a solution of egg albumen in a 
 test-tube, add some Millon's reagent (this consists of a solution 
 of mercurous and mercuric nitrates in nitric acid). A white pre- 
 cipitate forms upon the addition of the reagent which turns a brick 
 red on boiling. 
 
 II. The Precipitation of Proteids by neutral salts is of im- 
 portance in separating them from other substances in solution, and 
 from each other. It depends upon varying their solubilities in 
 solutions of neutral salts. 
 
 Solubility. Proteids are insoluble in alcohol and ether. Some 
 are soluble in distilled water (e.g., albumen), some in dilute saline 
 solutions (e.g., globulins) while some are soluble in concentrated 
 saline solutions (some vegetable proteids.) The salts usually em- 
 ployed in precipitating proteids from solution are: Magnesium 
 Sulphate, Ammonium Sulphate, Ammonium Chlorid, and Sodium 
 Chlorid. 
 
 (a) Magnesium Sulphate. Saturate some white of egg solu- 
 tion with magnesium sulphate by adding crystals until no more will 
 dissolve. A precipitate of globulin falls. The albumen remains in 
 solution as may be demonstrated by filtering and testing the filtrate 
 
12 
 
 for proteid (Biuret test). Ammonium chlorid and sodium chlorid 
 act like magnesium sulphate. 
 
 (by Ammonium Sulphate. Saturate a solution of egg white 
 with ammonium sulphate and note that a precipitate is formed, 
 including this time all the proteid, as could be demonstrated by filter- 
 ing and testing the filtrate. If to the solution of proteid an equal 
 volume of a saturated solution of ammonium sulphate were added, 
 the globulin is precipitated while the albumen remains in solution. 
 These salts, therefore, afford a means of separating and distin- 
 guishing between proteids, e.g., albumen and globulin. 
 
 III. Coagulation. This is the precipitation of the proteid as 
 a changed insoluble compound. Important coagulants are (a) heat, 
 (b) strong acids, (c) certain other acids (phosphomolybdic, phos- 
 photungstic), (d) other organic compounds (picric and tannic acids), 
 
 (e) soluble salts of the heavy metals (Hg., Cu., Pb., Zn., etc.), 
 
 (f) alcohol on prolonged action, (g) certain enzymes or ferments 
 (clotting of milk, coagulation of blood). 
 
 Test the action of representatives of these groups on a solution 
 of egg albumen. 
 
 The tests that will usually be made use of in this department 
 are the color tests, the action of heat, nitric acid, picric and citric 
 acids. 
 
 Classification. Although a consideration of the classification 
 of the proteids belongs to a more detailed study of them in physi- 
 ological chemistry, an idea of their occurrence and relations would 
 be of assistance now. It is recommended that the simple classifica- 
 tion given in Beddard, etc., "Practical Physk>logy," p. 175, be con- 
 sulted. Especially important for the work in physiology are the 
 simple proteids, nucleo-proteids, and nucleins. 
 
 FATS. 
 
 The fats and oils occur in vegetable and animal tissues. They 
 are compounds of fatty acids and glycerin (a tri-acid alcohol) and 
 other higher alcohols. 
 
 The Fatty Acids. These belong to a series* whose sim- 
 
 *01eic acid, however, belongs to another parallel series, the acrylic acid 
 series. 
 
13 
 
 plest members are formic and acetic acid. Stearic, Palmitic and 
 Oleic acids are the usual fatty acids occuring in animal fat, the 
 first two are solid at ordinary temperatures, the oleic acid liquid. 
 
 Saponification. Just as the lower members of the fatty acid 
 series, e. g., acetic, unite to form salts with metals, so the higher 
 members unite with metals to form Soaps. 
 
 Experiment if. Place two or three flakes of stearic acid in a 
 test-tube and add water and shake. Note that it does not dissolve. 
 Add a little 20% KOH and shake again, warming if necessary ; solu- 
 tion occurs, a soap being formed. Sodium and potassium soaps are 
 soluble in water, certain other soaps, e.g., calcium soaps, are not. 
 
 Neutral Pats. The glycerin compounds of the fatty acids have 
 certain properties which are more or less familiar to you. (a) They 
 form a grease-spot on paper which remains as a permanent stain. — 
 does not evaporate on standing; (b) they are insoluble in water; 
 soluble, however in (hot) alcohol, ether and chloroform, benzin, 
 benzene and other similar solvents, (c) Burnt fat has a character- 
 istic odor due to the formation of a substance, acrolein. 
 
 The fats that occur in the adipose tissue of the animal body are 
 mixtures of stearin (tristearin) palmitin (tripalmitin) and olein 
 (triolein), the proportions being different in different animals and 
 upon this depends the consistency of the fat. In ourselves, the 
 olein forms about )% of the fat. 
 
 Emulsification. Since fats are insoluble in water, they soon 
 separate from it when shaken up with it. If, however, soap is 
 present, the globules of oil remain suspended, forming an emulsion. 
 
 Experiment 18. Place in one test-tube some water and in a 
 second test-tube some soap solution. To each add some cotton-seed 
 or olive oil and shake. Note the result. 
 
 Experiment 19. The oil doubtless is somewhat rancid, that is, 
 contains some free fatty acid. Add to a little in a test-tube, some 
 weak KOH and shake. An emulsion is formed. Explanation. 
 
 Divide the emulsion into two portions. To one portion add a 
 little mucilage, shake well and allow it to stand. Observe that the 
 portion containing the mucilage "stands up" much longer. 
 
u 
 
 Lecithin and Cholesterin, two compounds occurring especially 
 in the nervous system and red blood corpuscles, will be considered 
 elsewhere. 
 
 Experiment 20. Test .for proteids (a) muscle (b) nervous 
 tissue, (c) gland (pancreas, kidney, salivary gland) proceeding as 
 follows: The blood is first well washed out by injecting a 0.9% 
 solution of common salt through the arteries until it comes clear 
 from the veins. Take pieces of . the organ and grind it up with 
 0.9% salt solution and filter. Test the filtrate for proteids as .you 
 deem best. Take small fragments of the tissue, place them in dis- 
 tilled water and apply Millon's reagent. 
 
 Experiment 2.1. The Xanthoproteic test may.be applied, to your 
 own skin by touching a spot with nitric acid, washing it. away with 
 distilled water and applying then a drop of ammonia. 
 
 Experiment 22. Place pieces of subcutaneous or omental fat 
 in a test-tube with some 5% KOH. Warm it gently. 
 
 Cautiously add HCL and allow it to cool. A layer of fat and 
 fatty acid forms upon the top in the test tube. 
 
 THE BLOOD AND THE LYMPH. 
 
 The blood and the lymph form the nourishing fluids of the body, 
 carrying to the tissues the food stuffs absorbed by the intestines, 
 and taking from the tissues the waste products to the excretory sur- 
 faces. A second function of the blood is to convey to the various 
 parts of the body the oxygen absorbed from the lungs. There cir- 
 culate in the blood, protective bodies and other complex products 
 in minute quantities ; drugs, poisons, and other adventitious sub- 
 stances, so that chemically it is of great complexity. 
 
 Structurally, blood consists of the corpuscles, red or erythro- 
 cytes, white or leucocytes, and the blood plates, floating in the fluid 
 portion, the plasma. Before proceeding to a study of the blood, the 
 phenomenon of clotting which serves to protect the body against loss 
 of blood by Hemorrhage must be considered. 
 
 The Coagulation of the blood ' is due to the formation of a 
 sponge-work of fibrin entangling the corpuscles and by its contrac- 
 tion squeezing out the fluid portion as the Blood Serum. 
 
 There are several important questions to be considered here, — 
 
15 
 
 the origin of fibrin, the conditions under which it is formed and 
 why coagulation does not take place in the circulating blood. 
 
 Experiment 23. Allow some cat's blood to flow into a test-tube, 
 cool it and allow it to stand in the cold for 24 hours. Note the clot 
 and its appearance ; -the exuded serum. 
 
 Take a fragment of clot from the horse blood and wash it out 
 under the tap until the . corpuscles are washed away and only the 
 fibrin is left. Note the texture and elasticity of the fibrin frame- 
 work. 
 
 Place a small piece of the fibrin in a test-tube and apply the 
 Xanthoproteic test and Millon's reagent. 
 
 The Serum. Obtain from the stock table half a small test- 
 tubeful of serum from horse blood and add to it an equal volume of 
 saturated solution of ammonium sulphate. The serum-globulins are 
 precipitated out. Filter out the precipitate and apply to the filtrate 
 the heat test (for albumin) after acidulating with acetic acid. 
 
 Filter again and dilute the filtrate with an equal volume of dis- 
 tilled water. To one-third of this add a few drops of silver nitrate 
 solution. The result indicates chlorides in the serum. The other 
 portions may be tested for phosphates and sulphates by means of the 
 Ammonium molybdate test and Barium chlorid solution respectively 
 (Consult your inorganic chemistry). 
 
 Glucose is also an important constituent of plasma, but tests 
 for it are too difficult to be tried in this course, and it further dis- 
 appears from the serum on standing (why?). 
 
 However, Trommer's test for a reducing substance in fresh 
 serum may be applied to the serum obtained from the cat's blood. 
 
 The Coagulation of Blood. This is retarded or hastened by 
 different conditions which may be contrasted as follows : 
 
 Retarded. Hastened. 
 
 (1) Addition of neutral salts. Dilution with distilled ■water. 
 
 (2) Addition of soluble oxalate Addition of soluble calcium salts. 
 
 or oxalic acid. 
 
 (3) Cold. Heat - 
 
 (4) Prevention of contact with Agitation and contact with 
 
 foreign bodies by collect- rough substances. 
 
 ing under oil. Foreign bodies in the blood-ves- 
 
 (5) Retaining within the living sel; diseased condition of flhe 
 
 uninjured blood vessel. blood vessel. 
 
 (6) Albumoses, etc. Nucleo-proteids. 
 
 (7) Heating to 56°. "Fibrin ferment." 
 
i6 
 
 Experiment 24. This is best performed with fresh blood, but 
 because of the difficulty of providing so many with fresh blood, 
 "salted" horse blood will be employed. Different features of the 
 experiment will be demonserated to 'you with fresh blood. 
 
 Allow some blood to flow from a cut artery into a saturated 
 solution of magnesium sulphate until the vohime reaches four time.* 
 the original amount of magnesium sulphate. The magnesium sul- 
 phate prevents clotting. 
 
 Allow the mixture to stand in a cool place until the corpuscles 
 have settled. Pipette off the supernatant "salted plasma." 
 
 Divide it into four parts in 'four test-tubes. To each of the 4 add 
 about 8 times its volume of water. Place in tube A a few drops of a 
 54% solution of ammonium oxalate; in tube B a small piece of blood 
 clot. Place tube C in a water bath at 38 . Add to tube D a few drops 
 of oxalate and heat to 6o° C. It will be found that in test- 
 tubes B and C clotting takes place sooner probably in C than in B. 
 To test tubes A and D now add a few drops of calcium chlorid solu- 
 tion. Tube A now clots while D remains unclotted. The above 
 experiments illustrate three of the conditions favoring and retarding 
 the coagulation of the blood, indicating that the presence of calcium 
 is necessary for clotting, that clotting is hastened by heating, that 
 there is something in clotted blood which furthers coagulation, and 
 that the power to clot is destroyed by a temperature of about 60 
 desr. C. 
 
17 
 
 The usually accepted interpretation of the process is well shown 
 by the following scheme from Beddard, etc. "Practical Physic 
 ology." 
 
 Living blood. 
 
 Plasma. 
 
 I 
 
 Albumin. Globulin. 
 
 Corpuscles. 
 
 White. ,• Red. 
 
 Ca. salts + Pro-thr ora bin. 
 Fibrinogen + Fibrin ferment. ' 
 
 r ' 
 
 2nd globulin. 
 
 Fibrin. 
 
 Serum. 
 
 Clot." 
 
 I 
 Dead blood. 
 
 The nucleo-proteid seems to be especially set free by the disinte- 
 gration of the leucocytes whence conditions 4 for retarding and 4 
 and 5 for hastening coagulation are to be explained. More obscure 
 are conditions 5 and 6 for retarding and 6 for hastening. 
 
 Defibrinated Blood. Blood may be freed from fibrin, "defibrin- 
 ated," by beating it with a bundle of sticks or wires as it flows from 
 the body. Such blood is useful for many tests and will be employed 
 in experiments below. 
 
 THE RED CORPUSCLES. 
 
 Isotonicity. The red blood corpuscles react readily to changes 
 in the density of the surrounding medium, retaining their form and 
 shape together with their content of hemoglobin when they are iso- 
 tonic with the surrounding plasma. Conditions of Hypisotonicity 
 cause them to swell and lose their hemoglobin ; excessive density or 
 hyperisotonicity in the surrounding medium causes shrinking. 
 
 Experiment 25. Dilute equal volumes of defibrinatcd blood 
 with (a") water, (b) physiological salt solution, (c) 2% salt solution. 
 Note that test-tube A becomes clear, a condition known as laking. 
 
i8 
 
 Other substances can cause the hemoglobin to leave the corpuslces 
 and break them up; such are, — (a ) freezing, (b) acids, (c) ether. 
 Teste the power of ether and acetic acid to dissolve out the hemo- 
 globin by shaking up separate amounts of defibrinated blood with 
 ether and with 2% acetic acid. Chemical substances that have the 
 power of destroying red blood corpuscles are known as Hemolysins. 
 Shake up some blood in a test-tube with about J4 its volume of a 
 solution of the drug Saponin in 0.9% salt solution. Result. 
 
 A solution of about 0.9% of Sodium chlorid is isotonic with 
 human blood, hence that is the strength of the Physiological Salt 
 Solution employed in work with mammalian tissues. For "frog tis- 
 sues, 0.6% solution is more normal. In general, a 0.75% (n|8) 
 solution may be employed as a physiological salt solution. 
 
 Counting: the Red Blood Corpuscles. By means of the 
 Thoma-Zeiss Haemocytometer furnished you, determine the num- 
 ber of red blood corpuscles per cubic millimeter in your blood, pro- 
 ceeding very carefully according to the following directions. 
 
 A. Caution. In counting the blood corpuscles, it is necessary 
 to proceed with the utmost caution as a slight error due to care- 
 less technique becomes much magnified in the final result. The count- 
 ing pipettes will be given to you clean and you will be expected to 
 return them in the same condition. Dirty pipettes will be cleaned 
 or new ones furnished at your expense. 
 
 The Method consists in diluting the blood a known amount, 
 counting the number of corpuscles in a small known volume of the 
 diluted blood, and from the count obtained, calculating the number 
 in one cubic millimeter of undiluted blood. 
 
 Obtaining the Blood. Qeanse the tip of the finger or the 
 lobe of the ear with soap and water and then wipe it well with a 
 piece of absorbent cotton wet with alcohol. With a sterilized 
 needle or haemospath prick the cleaned finger or lobe of the ear and 
 allow a good sized drop of blood to form without pressure. Then 
 insert the point of the larger, erythrocyte, pipette, and very carefully 
 draw up in the manner shown you the blood to the mark 0.5. 
 Wipe off all blood adhering to the outside of the pipette with absorb- 
 ent cotton. If the blood is drawn in beyond the mark it may per- 
 
19 
 
 haps be possible to bring it back to the mark by carefully touching 
 the end of the pipette to the filter paper. 
 
 Diluting the Blood. Place the end of the pipette in Hayem's 
 solution and by suction draw in fluid up to the mark 101. Be care- 
 ful not to allow the blood to escape from the end of the pipette 
 in so doing. Close both ends of the pipette and shake it well to 
 thoroughly mix the blood and the diluent. 
 
 Filling the Counting Cell. After the blood has been well mixed, 
 allow several drops to escape, wipe off the end of the pipette and 
 then catch a small drop upon the center of the glass disk in the 
 counting cell without allowing the diluted blood to overflow into 
 the moat. Cover quickly and carefully and press down gently upon 
 the cover until Newton's rings are seen. Should they not appear, 
 cover and cell must be first carefully cleaned and the work must 
 be repeated from the beginning. Allow the corpuscles time to 
 settle and then proceed to count them. 
 
 Counting. It will be seen that the field contains areas of 25 
 squares in which the bounding squares are divided by a line. Count 
 the number of corpuscles in each small square, counting all the 
 corpuscles that are upon the upper and left hand bounding lines 
 and disregarding all those upon the lower and right hand lines. 
 Count in this way 100 small squares and calculate the number per 
 cubic millimeter. It will help you to count them in the blocks of 
 16 small squares. If preferred, all the corpuscles within the block 
 of 25 small squares formed by the bisecting line (16 full squares, 
 16 half squares and 4 quarter squares) counted and then count 4 such 
 blocks. 
 
 Calculation. Each small square is 1-400 of a square milli- 
 meter and the cell is 1-10 millimeter deep; each square, therefore, 
 represents 1-4,000 of a cubic millimeter of diluted blood. The 
 dilution is 1 :2co and 100 squares are counted. The number of 
 corpuscles in a cubic millimeter of blood, therefore, equals the num- 
 ber counted multiplied by 4,000 and 200 but divided by 100 or the 
 number of cells counted. 
 
 Control Count. Rinse off the cover and counting cell with 
 distilled water and dry them carefully by means of lens paper or 
 gauze. Shake up the pipette and as before after letting 2 or 3 drops 
 
20 
 
 escape receive a small drop upon the disc in the counting cell and 
 make a second count of ioo squares. 
 
 If the second count confirms the first, submit your results for 
 examination. A second count does not of course obviate ' errors 
 made in obtaining and diluting the sample of blood. If the instruct 
 tor considers the count incorrect, the experiment must be repeated 
 from the beginning with a fresh drop of blood, the counting cell 
 and pipette being first cleaned and dried in the manner given below. 
 
 Cleaning the Cell. Carefully rinse out the cell with distilled 
 water and dry it with absorbent cotton. Do not use alcohol or 
 other solvent in cleaning it. Rinse off the cover with distilled water 
 and wipe it on a piece of gauze or lens paper. 
 
 Cleaning the Pipette. Rinse out the pipette with saline 
 solution by drawing it into it and shaking it and then forcing it 
 out. After the salt solution wash it out with alcohol and then with 
 ether and dry it by drawing air through it by means of an aspirator. 
 Unless the pipette is kept clean it is valueless. 
 
 Counting the White Corpuscles. The procedure 
 is the same as in counting the red corpuscles except that the other 
 pipette is taken, the entire number of small squares are counted 
 in blocks of 25, and instead of the diluent used in counting red cor- 
 puscles, 4% acetic acid or Toison's fluid must be employed. 
 
 Count the number of leucocytes in the entire number of small 
 squares, or 16 blocks. Calculate the number in a cubic millimeter. 
 The dilution is 1 :20 and the total number counted, therefore, is 20 
 times 4,000, times the number counted divided by 400. 
 
 Make a second count with another drop. If there is a marked 
 error the count must be repeated with a fresh drop of blood. 
 
 When you have finished, pipette and cell and cover must be 
 cleaned as directed above. 
 
 Determination of Amount of Haemoglobin. Demon- 
 stration. 
 
 HAEMOGLOBIN AND ITS DERIVATIVES. 
 
 Haemoglobin. Upon a clean slide place a rather large 
 drop of blood from your finger. Around it place a ring of natural 
 
21 
 
 Canada Balsam and place upon it a cover glass so that the drop 
 is sealed in by the balsam. Set the specimen aside for a day or so 
 and examine it with a microscope for crystals of oxy-hemoglobin. 
 Note forms and color. 
 
 Co-haejnoglobin. Pass some illuminating gas through a test- 
 tube full of defibrinated blood for a few minutes until Co-haemo- 
 globin has been formed, and then add, drop by drop, pure ether 
 until the blood has become laked. Allow it to stand in the cold, on 
 the window sill or in the cold room in an open beaker for a day 
 or two. Examine then and crystals of haemoglobin will probably 
 be found. Some of these may be removed by means of a pipette 
 to a slide and examined under the microscope. Reducing the 
 alkalinity by the cautious addition of a weak solution of acid sodium 
 phosphate tends to hasten crystallization (Hermann's Practicum.) 
 
 The derivatives of haemoglobin are of considerable importance 
 when we remember that the blood is continually undergoing decom- 
 position in the body normally and especially in conditions of internal 
 haemorrhage. In certain diseases (e. g., malaria) there is a great 
 destruction of red corpuscles. All fevers are attended by a more or 
 less marked dissolution of the erythrocytes. 
 
 Hematin. Oxyhemoglobin, treated with acids and alkalies, h 
 decomposed into Hematin and a proteid constituent of haemoglobin 
 which has been termed Globin. 
 
 Experiment 30. In a test-tube add to some defibrinated blood 
 a few drops of strong caustic potash solution and warm. The solu- 
 tion turns to a greenish red, indicating the formation of alkali-hem- 
 atin. Neutralize it by the cautious addition of HCL. drop by drop 
 and the hematin is thrown down together with the proteid present 
 as a dirty-brown precipitate. 
 
 Experiment 31. — To some dried blood in a test-tube add several 
 cubic centimeters of strong acetic acid and warm. A brown color 
 is assumed due to Acid-hematin. Neutralization of the acid by 
 means of ammonia or other alkali will cause precipitation as before. 
 Hematoporphyrin. This is derived from the hematin by a 
 spliting off of the Fe. It is apparently closely related to, — isomeric 
 with, — Bilirubin of the bile which is undoubtedly the form in which 
 the hemoglobin waste leaves the body. It is likewise closely related 
 
22 
 
 to Hematoidin which was described by Virchow as occurring in 
 old blood-clots within the body. Bilirubin and hematoidin appear 
 to be identical. 
 
 Experiment 32. Place a small amount of dried blood in a test- 
 tube and add concentrated sulphuric acid. The pigment is decom- 
 posed and hematoporphyrin goes into solution. The solution in 
 sulphuric acid may be filtered through an asbestos filter and to it 
 added distilled water until the hematoporphyrin is thrown down as 
 a precipitate. Cautiously add NaOH until the solution is slightly 
 alkaline, when it will again dissolve. 
 
 Hemin, or Hydrochloride of Hematin. (Histology labora- 
 tory work.) 
 
 THE SPECTRA OF THE BLOOD PIGMENTS. 
 
 Oxy-haemoglobin. To a few drops of defibrinated blood in a 
 test-tube add distilled water and shake. Place some of the solution 
 in a watch glass and examine it by means of the spectroscope employ- 
 ing the solar comparison spectrum. Note the two . characteristic 
 absorption bands and their relative width and location. There is 
 also absorption at the two ends of the spectrum. 
 
 Haejnoglobin. To the diluted blood in the test-tube add ammo- 
 nium sulphid until the oxyhemoglobin is reduced to hemoglobin. 
 Place some of the Hb. solution in a watch glass upon the stand of 
 the spectroscope and note that the two absorption bands are replaced 
 by one band. Compare the spectra of Hb and HbO. Shake thor- 
 oughly the solution of hemoglobin which you formed by the reduction 
 of the oxy-hemoglobin and observe that the bright red color of 
 oxy-hemoglobin is regained. Examination under the spectroscope 
 would again show the characterstic two absorption bands. 
 
 The Spectra of Co-hemoglobin, hematin, and hematoporphyrin 
 and hemochromogen will be demonstrated to you. 
 
MUSCLE AND NERVE. 
 
 I. Irritability, Conductivity, Contractility. 
 
 II. Stimuli. 
 
 Chemical, thermal, mechanical, electrical. 
 
 III. The Irritability of Muscle. 
 
 IV. The Galvanic and Faradic Currents. 
 V. The Contraction of Muscle. 
 
 (a) The Simple Twitch. 
 
 (b) Minimal and Maximal Stimuli. 
 
 (c) The Summation of Contractions. 
 
 (d) Incomplete and Complete Tetanus. 
 
 (e) Summation of Subminimal Stimuli, i 
 
 VI. Electricity as a Stimulus. 
 
 (a) Regulation of Electricity as a Stimulus. 
 
 (b) The laws of Electrical Stimulation. 
 
 (c) Electrotonus. 
 
 (d) Pfliiger's Law. 
 
 (e) Stimulation of Human Nerves. 
 
 (f) Irritability and Conductivity in Nerves Compared. 
 
 VII. The Responses to Stimulation. 
 
 (a) Mechanical. 
 
 (b) Thermal. 
 
 (c) Chemical. 
 
 (d) Electrical. 
 
 VIII. The "Work of Muscular Contraction. 
 
 (a) Work done. 
 
 (b) Absolute Work. 
 
 (c) Isometric Contraction. 
 
 IX. Fatigue. 
 
 It is advantageous to consider next the physiology of Muscle 
 and Nerve. The application of exact methods is here the simplest 
 and the general features of life phenomena are here well represented ; 
 further, it is necessary in later work to have the physiology of muscle 
 and nerve as a back ground for the study of the special physiology 
 involved. 
 
 Three properties which seem to be fundamental in living matter 
 wherever found are here developed to a high degree of specialization 1 : 
 Irritability, (excitability) common property of all protoplasm; Con- 
 ductivity, pre-eminently characterise of nerve; Contractility, pecu- 
 liarly the property of muscle. 
 
24 
 
 By irritability is meant the power of setting free energy in 
 response to some disturbing influence, the amount of energy set 
 free being often out of all proportion to the influencing cause. The 
 external and internal influences that are effective are known as 
 Stimuli. The Responses to stimulation with which we meet in living 
 matter are various. Muscle responds by a transformation of energy 
 which appears largely as mechanical movement (contraction) and 
 heat. A gland responds by increased formation of secretion; the 
 electrical organ of the Electric fishes, (e. g., Torpedo) gives a strong 
 electrical response, etc. It should be remembered that the law of 
 the Conservation of Energy holds in the phenomena of the living 
 as well as of the non-living world, and each response represents a 
 transformation of energy and never a creation of energy. 
 
 There are, then, three sides of the physiology of muscle and 
 nerve which are to be considered, (i) Stimuli and the phenomena 
 of stimulation, (2) The properties of Irritability and Conductivity, 
 (3) The Responses to stimulation. 
 
 Irritability and Conductivity may be demonstrated on the mus- 
 cular and nervous tissues of many animals. Cold-blooded animals 
 are easier to work with, for obvious reasons. The frog is especially 
 suited for experimental work on muscle and nerve and will be used 
 here in this course. It will be necessary, therefore, to facilitate 
 later work, that you become somewhat familiar with the anatomy 
 of the frog and the methods of "making muscle and nerve prepara- 
 tions. Four muscles, or groups of muscles are suitable for this 
 work: (1) The Gastrocnemius muscle, (2) the Semimembranosus- 
 gracilis preparation, (3) the double semimembranosus-gracilis prepa- 
 ration, and (4) the Sartorius. 
 
 Before making the muscle preparations from the living tissue, 
 dissect them out carefully in a preserved specimen according to the 
 directions that follow. 
 
 I. The Gastrocnemius Muscle-Nerve Preparation. 
 This is the one that will be usually employed. It is to- 
 be prepared in the following manner. Kill the frog by pithing. 
 For this, take the frog in the left hand with the head of the frog 
 between the index and middle fingers, the thumb upon the back 
 of the frog. Bend the head down and the articulation between the 
 
25 
 
 Fig. 1. 
 
 Muscles of the Leg. Frog. Dorsal Aspect. 
 
 1 = M. ilio-fibularis. 
 
 2 = M. semimembranosus. 
 
 3 = M. gastrocnemius. 
 
skull and vertebral column becomes evident. With a slender scalpel 
 or fine scissors cut the atlan'to-occipital ligaments and the medulla 
 oblongata at this point and insert a tracer into the cranial cavity 
 destroying the brain. The destruction of the spinal cord cause* 
 contraction of the muscles of the legs which are thereby rigidly 
 extended. The contraction of the muscles soon passes off and the 
 legs become limp and relaxed. 
 
 Place the frog dorsal side up on a glass plate and remove the 
 skin carefully from the leg and thigh. The tendo Achillis is thus 
 exposed, divided below the sesamoid bone and the gastrocnemius 
 muscle freed up to the knee. The leg. is carefully disarticulated at 
 the knee and cut away, care being taken not to injure the nerve 
 where it enters the dorsal side of the upper end of the muscle. 
 
 The sciatic nerve from which the Gastrocnemius muscle receives- 
 its innervation is dissected as follows : — Upon the dorsal side of the 
 thigh (Fig. i) carefully separate the M. gluteus maximus and M. 
 ilio-fibularis (Biceps) from the M. semimembranosus, thereby dis- 
 closing the sciatic nerve. The lower (caudal) end of the urostyle 
 is next carefully lifted and the muscles adjoining it cut on each side 
 close to the urostyle exposing higher up the sciatic nerve and its 
 three component nerves. Carefully remove the urostyle. Cut the 
 spinal column across between the sixth and seventh vertebrae and 
 bisect the 7th and 8th vertebrae in the middle plane. 
 
 Grasp the section to which the nerve-roots are attached, lift it 
 with the scissors free the sciatic nerve down to the knee, taking care 
 not to cut it or stretch it. Lay the nerve along tihe side of the 
 Gastrocnemius muscle. Cut the femur across about one centimeter 
 above its condyles. For attachment to a muscle lever, a bent pin as 
 a double hook is inserted into the tendon of Achilles. 
 
 Before making the preparation, the necessary apparatus must 
 be first set up and in working order. When not to be used imme- 
 diately, however, the muscle-nerve preparation should be stored 
 within the abdominal cavity of the frog or covered over with the 
 ovary (if the frog is a female), or with cotton wet with physiological 
 salt solution. Muscle and nerve must at every step be kept moist, 
 if necessary by the use of physiological salt solution. 
 
a? 
 
 Fig. 2. 
 
 Muscles of the Leg. Frog. Ventral Aspect. 
 
 3 = M. gastrocnemius. 
 
 4 = M. sartorius. 
 
 5 = M. gracilis. 
 
28 
 
 It is often of advantage to retain the skin of the leg as a sleeve 
 over the gastrocnemius preparation. To do this, cut the skin around 
 (in a circle) at the ankle and strip it free up to the knee, turning it 
 wrong side out like 'the finger of a glove. Cut the tendon of Achilles 
 below the sesamoid bone and free it up to the knee. Remove the 
 tibia at the knee and pull the skin sleeve back down over the gastroc- 
 nemius muscle. Then dissect out the sciatic nerve in the mannei 
 directed above, removing the skin down to the knee. In many 
 instances it would not be necessary to dissect out the entire length of 
 the sciatic nerve. 
 
 Gastrocnemius Muscle-Nerve Preparation for Demon- 
 stration. When it is not important to record the con- 
 tractions, the sciatic nerve may be dissected out down to the 
 knee, the skin being left intact upon the leg and foot. After the 
 entire length of the nerve has been dissected out, the femur is cut 
 
 Fig. 3. , 
 
 Method of clamping Muscle-nerve 
 Preparation for demonstrating ac- 
 tion of stimuli. 
 
 across above the knee and the leg fastened in the clamp at the knee 
 up side down, the foot and toes serving as an indicator or lever. 
 (Fig- 3)- Care must be taken that the nerve is not caught in tftve 
 clamp. 
 
 The Semimembranosus-Gracilis Preparation. The 
 
 relations of these muscles is seen from the figures. The fascia 
 
20 
 
 bordering them is to be cut away with the scissors and from the 
 ■dorsal side, the blunt scalpel handle inserted between these muscles 
 and the M. ilio-fibularis or Biceps, freeing them from the femur and 
 the remaining muscles of the thigh. If the M. semitendinosus, a 
 •double-bellied muscle, is found to be included with them, it should 
 be cut near its distal end. The distal attachment of these muscles 
 is to the head of the tibia, so that cutting the femur just above the 
 knee and the tibia just below the knee leaves the bones at the knee 
 in a convenient form to hold in the femur clamp ; a hook also, may 
 be easily passed through the articulation. Cut away the muscle mass 
 and disarticulate the upper end of the femur. Cut through the long 
 ■slender ilium (Consult figure of skeleton) near the acetabulum and 
 witb the scalpel separate the pubic bones at the symphysis pubis. A 
 hook can be inserted through the cartilage of the acetabulum or the 
 fragment of bone held in a clamp. 
 
 The Double Semimembranosus-Gracilis Preparation. This is 
 made in the same way as the single Semimembranosus-gracilis 
 preparation, except that the preparation is made at both sides and 
 after disarticulating the femurs at the hip and cutting away the 
 muscle mass, the symphysis pubis should be cut transversely just 
 above the attachment of the semimembranosus and gracilis muscles 
 leaving them thus joined by a thin layer of bone. 
 
 The Sartorius. Upon the ventral side of the thigh of the frog 
 (Fig. 2) is a long thin muscle whose origin is from the symphysis 
 pubis and whose distal attachment is to the fascia of the leg tlve 
 capsule of the knee and to the tibia. It is a delicate muscle, at first 
 not easily separated from the neighboring muscles. The muscle 
 fibers are parallel, running the entire length of the muscle, and this 
 relation makes the muscle valuable for demonstration of certain 
 ifacts. The nerve enters the muscle at about its middle. 
 
 STIMULI AND THEIR ACTION. 
 
 The stimuli which cause nerve and muscle to react may be 
 ■grouped as chemical, thermal, mechanical and electrical. In the 
 body, the "normal stimulus" for the muscle is the Nervous impulse. 
 This name but masks our ignorance, as the nature of the real 
 •change that constitutes the stimulus is unknown; possibly chemical 
 
3° 
 
 processes underlie it ; if not, certainly molecular changes. Glands also- 
 are excited to activity by the nervous impulse as a stimulus. In the 
 nerve fiber the nervous impulse is originated normaHy either by' a 
 sense-cell, or another nerve fiber influences its nerve-cell, or "The 
 Will" in some way starts an impulse. 
 
 The irritability of a motor nerve and the action of a stimuli 
 upon it are most easily determined by the contraction of the muscle- 
 to which the nerve goes, — the muscle thus acting as an indicator to 
 show the state of activity of the nerve. 
 
 Mechanical Stimuli. Make a sciatic-grastrocnemius prep- 
 aration of the kind shown in Figure 3 as directed in the text,, 
 the femur-clamp being attached to an iron stand by means of a 
 double clamp. With the scissors clip the end of the nerve and observe 
 the resultant contraction of the muscle. The scissors have given 
 the nerve a mechanical stimulation. Other more elaborate experi- 
 ments might be performed and special apparatus has been devised 
 for studying the effect of mechanical stimulation (Demonstration.) 
 Accidental mechanical stimulation of nerves, sensory or motor, will 
 doubtless occur to you (e. g., hitting the "crazy bone.") 
 
 Thermal Stimuli. Heat a needle red hot and apply it 
 cautiously to the end of the nerve. Usually the heat of the needle 
 will cause contraction of the muscle; however, the hot needle kills 
 the portion of the nerve with which it comes in contact and some- 
 times without first stimulating it. 
 
 Chemical Stimuli. With the same preparation test the 
 stimulating value of a number of chemical solutions. To do thU, 
 place in a watch glass a drop of the solution to be tested and bring 
 the drop in contact with the end of the nerve as it hangs down ; its 
 stimulating action is shown by the movements of the frog's foot. 
 Drying, as you will see, itself irritates the nerve, so that it is nec- 
 essary to moisten the nerve now and then by allowing physiological 
 salt solution to drop over it. It will probably be necessary to take 
 a second muscle-nerve preparation to complete the list of chemicals 
 to be tested. 
 
 After one solution has been tested, cut off the portion of the 
 nerve that came in contact with it, wipe out the watch glass and 
 test another solution. 
 
3t 
 
 Test the following solutions of chemicals. They will not all 
 have the same value as nerve stimulants. Record your results. 
 
 Ammonia. 
 
 Potassium hydroxid, 5%. 
 Zinc chlorid, %% 
 Mercuric chlorid, 5%. 
 Acetic acid, strong solution. 
 Nitric acid, 10%. 
 
 Magnesium sulphate, saturated solution. 
 Glycerin. 
 
 Sodium chlorid, saturated solution. 
 Finally, allow the nerve to become dry. 
 r~ 
 
 For more exact experimental work it would be advisable to 
 employ only standard solutions, and take greater precautions to pre- 
 vent drying out of the nerve. Much remains to be done before the 
 action of chemical stimuli is understood. Cases of stimulation of 
 sensory nerves by chemical agents will doubtless be remembered by 
 you (cuts, raw surfaces, burns, toothache sometimes, etc.) 
 
 Electrical Stimuli. The Galvani Experiment. Place 
 a copper plate across a zinc plate at an angle of about 20 degrees and 
 across the gap formed lay the nerve of a muscle-nerve preparation. 
 When the nerve touches both plates the muscle contracts. This 
 experiment is of historical interest as through it,- — accidentally and 
 in modified form, — Galvani in 1786 discovered the form of electricity 
 that bears his name (Galvanic.) 
 
 The salt solutions contained in the nerve coming in contact with 
 the different metals, copper and zinc, forms a small battery cell and 
 completes the circuit. The electric current so caused to flow stimu- 
 lates the nerve and causes the muscle to contract. 
 
 IRRITABILITY OF MUSCLE. 
 
 In the above experiments it has been shown that the nerve rt 
 spond to various stimuli. If the same were applied to a muscle directly 
 it woud be found that the muscle itself responded by contraction to 
 these same forms of stimulation. Such experiments, however, would 
 not be conclusive or of value in proving the independent irritability 
 of muscle, for the muscle is full of nerve fibers passing to each of 
 
32 
 
 the individual muscle fibers, and it is these and not the muscle fibers 
 which would be stimulated first. In order to test the irritability of 
 muscle it is therefore necessary to eliminate the nerve fibers. This 
 may be accomplished by (a) Degeneration, — cutting the motor nerve 
 of the muscle and after some time it will be found to have completely 
 degenerated, (b) Curare injected subcutaneously interrupts the 
 ■communication of the nerve with the muscle by paralyzing the motor 
 end plate. It is this method which will be employed here, (c) The 
 independent irritability of muscle is also shown by stimulating mus- 
 •cle in places where the nerves are absent, such 'as, e. g., — (i) the ends 
 of the sartorius muscle in the frog, (2) the ureter, (3) the apex 
 •of the heart (?). 
 
 Experiment 40. Inject into the dorsal lymph sac of a frog 
 ?4-^2 c - c - of a 1% solution of curare. In 15-20 minutes, the frog 
 will be completely paralyzed. Pith the frog and dissect out one of 
 -the muscles of the leg for stimulation and test (1) the chemical 
 ■stimulation of HC1, NaCl, distilled water, ammonia. Try the Gal- 
 vani experiment with the sartorius (see electrical stimuli above), 
 (c) Suspend the muscle in a vial of physiological salt solution heated 
 to about 45°C; the muscle contracts, passing into a condition of 
 Rigor caloris. (d) The mechanical stimulation of a blow upon the 
 muscle is not so easily seen ; however, it exists and the sartorius is 
 "best suited for demonstrating the efficiency of this form of stimula- 
 tion. 
 
 THE GALVANIC AND FARADIC CURRENTS. 
 
 Electricity, whose stimulating action is thus illustrated in 
 the simple manner given above, as a stimulus possesses several mani- 
 fest advantages over the other forms of stimuli. It does not kill or 
 injure the part stimulated whereas they must do so more or les.-:. 
 The strength of stimulus can be/ more easily regulated than in the 
 •case of the other forms. It can be used on the uninjured intact 
 "body for the stimulation of deeper lying parts and organs, which 
 the other forms of stimuli cannot so well accomplish. These feat- 
 ures of electricity make it a stimulus of great value in physiology 
 and medicine, and it will be necessary to consider in some detail 
 during the course the electrical current, its forms, generation, regu- 
 lation, measurement, detection and application. Before proceeding 
 
33 
 
 to apply it further in the study of physiology of muscle and nerve,, 
 we must examine its forms and their application. 
 
 I. The Galvanic Current. When certain chemical' 
 substances go into solution in water (especially) they are believed 
 to become dissociated into their component acid and metallic radi- 
 cals, negative and positive ions, which on separation become the 
 bearers of opposite charges of electricity. Thus, NaCl in solution 
 becomes separated into Na (positive) and CI (negative.) If there 
 is chemical action such that the positive ions can be drawn toward 
 one side and the negative ions toward the other side, and the two 
 points of attraction connected by a wire or other conductor, an elec- 
 tric current will flow from the positive side through 1 the wire to- 
 the negative side. 
 
 Thus, to take a concrete example; — If a copper plate and a 
 zinc plate be suspended in a dilute solution of sulphuric acid and the 
 two connected by a wire, a current will flow from the copper (posi- 
 tive) through the wire to the zinc (negative,) This depends upon 
 the following chemical reaction: Zn-f-H 2 S0 4 =ZnS0 4 +2H. and we 
 may content ourselves here with the following explanation. The sul- 
 phuric acid dissolved in the water becomes dissociated into its 
 ions (acid and metallic radicals), Hydrogen and S0 4 , the former 
 bearing a positive charge, the latter a negative charge. The S0 4 
 unites with the Zn, depositing, so to speak, its negative charge while 
 H passes off at the copper pole giving to it its positive charge. A 
 more correct explanation or attempt at explanation would lead us 
 into the domain of physical chemistry. The positive charge may be 
 considered to represent a higher degree of electrical intensity which 
 tends to accumulate at the copper plate (See Difference of Potential), 
 to be equalized by the flow of current through the wire from the 
 copper to the zinc. 
 
 Battery Cells. The principles illustrated by the above- 
 example have been made use of in the construction of many forms of 
 battery cells as a source of electricity. T!he cells which will be 
 demonstrated to you and whose construction and chemical actien you 
 should understand are : Dcmiell cell, Bunsen cell, Grenet cell, Edison 
 cell, Leclanche cell, dry cell. Preserve a copy of the table given 
 you. These, and similar types of battery cells, are used in physiology 
 
34 
 
 and medicine as a source of electricity. Daniell and Edison cells 
 have a more constant E.M.F. (voltage) ; Bunsen cells possess a 
 fairly constant voltage and a higher current (Amperage), while 
 the Grenet cells have a high efficiency but it is of short duration. 
 
 Keys. Appliances for opening and closing an electric cir- 
 cuit. The following keys may be used : (a) Simple Keys, for open- 
 ing and closing a circuit, (b) Short-circuiting Keys, arranged to 
 short circuit an electric current; they may also be used as simple 
 keys, (c) Pole-changing Keys, to reverse the direction in which the 
 current is flowing, (d) Switches, to transfer the current from one 
 circuit to another. 
 
 The Commutator, Pole-changer, or Rocking- Key, 
 combines keys (c) and (d). The rocking key with metal contacts 
 may also be used as a short-circuiting key. They can of course, 
 all of them, mercury or metal contact commutators, be employed as 
 simple keys. Examine the mercury or metal commutator assigned 
 to you ; understand and diagram the three or four ways in which this 
 piece of apparatus may be used. 
 
 Electrodes. Metal or other terminals conveying the elec- 
 tricity to the tissue or part of the body to be stimulated and thus 
 completing the circuit. The electrode connected with the positive 
 pole of the battery cell is called the Anode; the one connected with 
 the negative pole, the Kathode. Two forms will be used by you, — 
 The Platinum Electrodes and the N on-polarizable Electrodes. 
 Understand the reasons for employing these forms of electrodes; 
 the method of preparation of the non-polarizable electrodes will be 
 demonstrated to you. 
 
 II. The Induced or [Faradic Current. In addi- 
 tion to the galvanic current, the induced current is often used for 
 stimulation. It is formed by electro-magnetic induction, and depends 
 upon the following facts whose explanation cannot be attempted 
 here (Demonstration). 
 
 (a) When a wire which is part of a completed circuit is moved 
 in a magnetic field across the lines of force ( an electric current is 
 generated' — induced — in the wire so moved. If the wire is moved 
 back in 'the direction opposite to that first employed, the current in 
 the wire is reversed in direction. 
 
35 
 
 {b) When an electric current is passed through a coil of 
 wire, it develops around it a magnetic field — converting the coil into 
 a magnet, an electro-magnet. If a wire or coil of wire is moved 
 across this field, a current is induced in the second coil while it is 
 "being moved, the direction of the current being reversed when the 
 direction of movement is reversed. 
 
 (c) Making and breaking (closing and opening) the current 
 in the first or primary coil has the effect of movement, so that 
 when the current in the primary coil is made and broken, two cur- 
 rents are formed in the secondary circuit which are of opposite direc- 
 tion. Upon these facts depends the construction of the 
 
 Inductorium. This is a form of induction coil used in physi- 
 ology and medicine. A current is formed in the secondary circuit 
 each time the primary circuit is made and broken. Of these, the 
 break current is the stronger. The nearer the secondary coil is to 
 the primary, the stronger the current induced in the secondary coil. 
 Likewise, when the secondary coil has its axis at right angles to the 
 axis of the primary coil, no current will be induced, and as it is 
 rotated toward the parallel axis, progressively greater current will be 
 induced. 
 
 The Interrupted Current. It is often desirable to stimulate by 
 means of a rapid succession of currents of short duration. With 
 the galvanic current this is accomplished by some form of inter- 
 rupter. The inductorium is provided with a form of automatic 
 interrupter whose action you should understand and be v able to dia- 
 gram. This is called the Wagner Hammer. 
 
 III. The Direct Dynamo Current may of course 
 be used in place of the galvanic current. 
 
 IV. The Alternating Dynamo Current is use- 
 ful in electro-therapeutics less so in physiology. 
 
 V. Static Electricity. Employed in therapeutics : 
 seldom in experimental physiology. 
 
 THE CONTRACTION OF MUSCLE. 
 
 Before proceeding farther in the examination of electricity as 
 . a stimulus, let us examine one of the Responses which muscle shows 
 - when subjected to stimulation, i. e., Contraction. 
 
36 
 
 The Simple Twitch. This you have already seen as the 
 result of mechanical, thermal and chemical stimulation. In order to 
 study it in more detail the graphic method will be employed. 
 
 The Graphic Method. The plotting of curves is largely 
 employed in the sciences (e. g., physics, physiology, medicine, etc.) 
 when it is desired to obtain a record of a variable in terms of two 
 functions of that variable. In medicine (fever cures, urine secre- 
 tion, respirations, pulse rate, etc.) and in physiology time is one 
 function, and therefore in physiology a moving surface is employed 
 upon which the other function, the amount of vital activity, records 
 itself. 
 
 Often, as in the case of the contraction of a muscle, the amoun: 
 of movement (activity) is so small that it is advantageous to have 
 it amplified by means of a magnifying lever. 
 
 Experiment 41. Connect a dry cell with the inductorium for 
 single shock, with a simple key and a signal magnet in the primary 
 circuit. From the binding posts of the secondary coil, pass fine 
 wires to the binding post on the femur-clamp and to the binding 
 
 Fig. 4. 
 
 Simple Twitch. 
 
 post on the lever which should be connected with the muscle prepa- 
 ration by a short coiled wire (Fig. 4). Employ a Semimembranosus- 
 gracilis preparation suspended from a femur clamp and attached to 
 a light muscle lever. Choose a position of the secondary coil at which 
 the muscle responds only to the break current. Bring the signal 
 magnet to write on the smoked surface of the drum immediately 
 below the writing point of the muscle lever. Revolve the drum by 
 hand to form a base line. Then spin the drum rapidly by hand and 
 when it is running smoothly, quickly make and break once the 
 
37 
 
 primary current. The muscle records its contractions as a simple 
 curve in which you may recognize these three parts : a latent period 
 intervening between the moment of stimulation and the beginning of 
 contraction, the period of increasing contraction, the period of relax- 
 ation. In the frog muscle, under ordinary conditions, these periods 
 have about the value of i-ioo second, 4-100 second and 5-100 sec- 
 ond respectively. Their relative and absolute duration, however, 
 depend upon various factors (Demonstration). 
 
 Experiment 42. The strength of stimulus has a great deal to 
 do with the response obtained. Perform the following experiment 
 to demonstrate this : A dry cell with a simple key is connected with 
 the inductorium for single shock. Wires from the secondary coil 
 are connected with the femur clamp and muscle lever (Fig. 4). The 
 drum is to be revolved by hand. Draw a base line. With the posi- 
 tion of the secondary coil giving the weakest possible current, make 
 and break the primary current. No contraction will result. Record 
 the stimulation upon the drum by a dot and rotate the drum about 
 5 millimeters and repeat the experiment . employing slightly stronger 
 stimulus. Continue to increase the strength of stimulus, indicating 
 each stimulation by a dot, and rotating 5 millimeters after each trial. 
 Soon a strength of current will be reached which will cause con- 
 traction, — a Minimal Stimulus. Gradually increase the strength of 
 current until at last a height of contraction is reached which is not 
 exceeded with further increment in the strength of stimulus, — a 
 Maximal Contraction. 
 
 Subminimal Stimuli, although by themselves not causing 
 contraction, must not be assumed to be without effect. Examination 
 of another form of response than the chemical, — the electrical re- 
 sponse (see below), would show that this is not true. , , 
 
 Experiment 43. Connect a dry cell through a simple key with 
 the inductorium for single shock. From the binding posts of the 
 secondary coil pass wires to the binding posts of the moist chamber 
 and connect them with the platinum electrodes in the moist chamber 
 (Fig. 5). Dissect out a muscle-nerve preparation and fasten it m 
 the moist chamber with the tendon attached to the muscle lever, 
 arranged to record the contractions on the drum. Place the nerve 
 over the electrodes. Put in the moist chamber a piece of blotting 
 
38 
 
 or filter paper wet with water, and cover. Find a position of the 
 secondary ooil that will give the weakest stimulus which is effective. 
 Choose a stimulus just subminimal in strength. Prepare to record 
 contractions as in experiment 42. Draw a base line. At intervals 
 of 4 seconds stimulate the muscle indicating each stimulation by 
 a dot upon the drum rotating it at its slowest rate, 5 millimeters 
 
 Fig. 5. 
 
 iimitLx 
 
 between each trial. Afer repeating the stimulation several times, 
 the muscle will respond by contractions of increasing height. There 
 is here the effect of a summation of stimuli which are individually 
 subminimal. 
 
 Therefore, every time we stimulate with a break induction 
 shock, we must remember that there is a make shock which, though 
 subminimal may yet have some effect on the succeeding contraction. 
 For exact work it is well to "cut off" in some way the make current 
 and prevent it from reaching the tissue. 
 
 Summation of Contractions. When two or more stimuli are 
 given to nerve or muscle, the result will depend upon the time rela- 
 tions of the stimuli, and the character of the contractions resulting 
 under these circumstances will be demonstrated to you. You will 
 see, however, that when the second stimulus falls within the period 
 of contraction or relaxation from the effects of the first stimulus, 
 the second contraction is, as it were, piled on top of the first, the 
 muscles not stopp'ng to finish the first contraction but starting off 
 straightway on the second contraction. 
 
 Incomplete Tetanus. If a series of stimuli are sent in one after 
 .another at a rate such that each succeeding stimulation will cause tha 
 
39 
 
 muscle to contract again before it has fully relaxed from the pre- 
 ceding contraction the muscle will remain in a state of contraction 
 in which, however, the individual component contractions can still 
 be seen, v 
 
 Experiment 44. Connect a dry cell with the inductorium for 
 single shock with a simple key in the primary circuit. Connect the 
 platinum electrodes of the moist chamber with the terminals of the 
 secondary coil (Fig. 5). Make the muscle-nerve preparation and 
 place it in the moist chamber connected with the writing lever so 
 that it may record its contractions on a drum. Have the recordng 
 drum set to revolve at a rapid rate. Choose a position of the second- 
 ary coil giving just a break contraction. Start the drum and draw 
 a base line ; then by means of the key make and break the current 
 at the rate of 4-5 times a second. (A watch ticks 5 times a second.) 
 
 Repeat the experiment making and breaking the current by 
 means of the key as fast as you can. How fast can you do it? 
 
 Experiment 45. Change the wires in the primary circuit to the 
 binding posts of the inductorium. for interrupted shock, and repeat 
 the experiment holding the key closed for several seconds. There 
 results a complete fusion of response Complete Tetanus. 
 
 ELECTRICITY AS A STIMULUS. 
 
 It is necessary for you to know more about the stimulus which 
 you have been us'ng; how it may be regulated and how it acts, as 
 it is- of considerable practical importance. 
 
 Regulation of Electricity as a Stimulus. 
 
 Electromotive Force (E. M. F) ; Difference of 
 
 Potential. In a battery cell the intensity of energy upon 
 
 which the flow of current depends is called the E.M.F. At the 
 copper or carbon pole in the batteries studied by you the intensity 
 may be spoken of as greater than at the zinc or negative pale. This 
 difference is known as the "difference of potential" between the two 
 poles. When the two poles are connected by a conductor permit- 
 ting it, there is a flow of current which would equalize the difference 
 of potential were it not that the chemical activ'ty in the cell tends 
 continually to maintain it. The E.M.F. then is equal to the difference 
 
40 
 
 of potential existing between the two poles of the circuit. Between 
 any two points in the circuit there is a difference of potential which 
 is greater the farther they are apart. The E.M.F. represents the sum 
 of the differences of potential existing bctwe«;ji all the different 
 points in the circuit. 
 
 Determine the E.M.F. in volts for the dry cells assigned to you, 
 number them and keep a record of their voltage. 
 
 Resistance. Understand the analogy of the "flow" of 
 the electric current and the flow of a current of water in pipes. In 
 order that an electric current flow, it is necessary that there be a 
 certain amount of E.M.F. to overcome the "resistance" in the cir- 
 cuit. In the flow of water through pipes the smaller the pipe and 
 the longer the pipe, the greater is the resistance to its flow, and analo- 
 gous conditions prevail in the case of the electric current : the longer 
 the wire and the smaller its caliber, the greater the resistance. A third 
 factor upon which resistance depends is the character of the con- 
 ducting substance, and from the resistance substances offer to the 
 flow of the electric current they may be grouped an non-conductors 
 or insulators, poor conductors and good conductors. Examples of 
 each will doubtless occur to you. In the case of the batteries already 
 mentioned the resistance to the flow of current when the two poles 
 are connected, lies not only "in the wire" but in the cell as well so 
 that it is convenient to speak of the resistance here as external and 
 internal. The internal resistance may be considerable and if the 
 external resistance is small it must be considered in applying Ohm's 
 law given below, since the R there represents the entire resistance 
 internal and external. If the external resistance is great, however, as 
 when the current is passed through the tissues of the body the 
 internal resistance may be neglected. 
 
 Measurement of Current. The amount of current 
 then varies with the E.M.F. and inversely as the Resistance. The 
 relation of E.M.F., R. and Intensity of current is formulated as 
 Ohm's law, I=E-^-R, — the amount of current equals the E.M.F. 
 divided by the resistance. The Ampere is the unit of measurement 
 for the strength of current. In the case of any of the batteries exam- 
 ined the resistance, internal and external, is so slight when they are 
 connected up by means of a short wire of large caliber that the am- 
 
41 
 
 perage will probably exceed the amount measureable by the ammeter 
 available. If, however, the resistance is increased by (Ohm's law) 
 by placing in the circuit a longer and finer wire, it may then be meas- 
 ured, and if the internal and external resistances are known the 
 amperage can be calculated. 
 
 Place in the circuit of the dry cell whose voltage is known, as 
 a known resistance, i meter of resistance wire (resistance about — 
 ohms) and measure the amperage by means of the ammeter. Can 
 you calculate the internal resistance of the cell? 
 
 Measurement of Resistance. It will not be neces- 
 sary for you to do this yourselves. In cases where it is necessary, 
 it will not be measured directly but indirectly by comparison with 
 known resistances by means of Resistance Boxes or the Wheatstone 
 Bridge. 
 
 The unit of resistance is the Ohm. According to Ohm^s law 
 then a battery giving an E.M.F. of i volt with i ohm resistance in 
 the circuit would produce a current of i ampere. 
 
 The Regulation of the Amount of Current. 
 From Ohm's law, it is evident that the current may be regulated 
 either (a) by regulating the voltage, or (b) regulating the resist- 
 ance, — increased resistance causing decreased current, increased 
 E.M.F. increased current and vice versa. 
 
 Practically, three ways offer themselves (a) Joining cells 
 together to increase the E.M.F. or current, (b) Regulating Resist- 
 ance, (c) By a Shunt. 
 
 Joining Cells Together. This may be done either 
 by joining them positive pole to positive pole, or positive pole to 
 negative pole, the two ways being indicated as joining them 'in par- 
 allel" and "in series." 
 
 If you were to join two or more cells first in series and then in 
 parallel and by means of voltmeter and ammeter test the voltage and 
 amperage of each combination, it would be seen that when they 
 are joined in series the voltage is increased while the current remains 
 practically the same, while when they are joined in parallel, the 
 current is increased while the E.M.F. remains practically the same. 
 In physiology we usually join cells in series. Joining the cells in 
 Multiple, is grouping them in series and then combining these groups- 
 
42 
 
 in parallel, thus accomplishing increase in both amperage and voltage. 
 For a given number of cells an arrangement of groups may be found 
 that will give the greatest efficiency. 
 
 Regulation of Resistance. As stated above, in- 
 creased resistance will cause decreased current. Special instruments 
 for introducing resistance into a circuit are the Rheostat, Resistance- 
 Box, Rhecchord. 
 
 The Shunt. If an electric current is divided and led through 
 two wires, the fraction of current flowing through each branch will 
 be inversely proportional to the resistance in each branch. Since 
 the resistance varies with the length of wire, it is easy to closely 
 regulate the amount o'f current. 
 
 By this means, also, any fraction of a voltage may be obtained 
 by "leading off" from any two points in a circuit; the nearer the 
 points* are together the less the E.M.F. (difference of potential) 
 obtained. Compare Electromotive Force above. 
 
 The Rheocord. This instrument applying methods (b)- and (c) 
 given above shouid be well understood and the three ways in which 
 it may be used, appreciated and diagramed. 
 
 The Induced Current. Review the structure of the 
 inductorium. It is important that you understand the generation of 
 the opening and closing secondary currents, their differences as to- 
 strength, and duration and why these differences exist; i. e., con- 
 sider the size of the wire and the number of turns in the primary and 
 secondary coils, self-induction and its effects. 
 
 The break induced current is thus of shorter duration and 
 greater intensity than the make induced current. It is important that 
 you have a clear idea of the differences between the galvanic and 
 induced electrical currents for understanding their value and action 
 in the stimulation of muscle and nerve. Compare a graphic repre- 
 sentation of the induced currents with that of the galvanic currents. 
 
 The manner of regulating the strength of the induced current 
 is already understood by you. 
 
 The I/aws of Electrical Stimulation. 
 
 The following so-called "laws" are helpful generalizations but 
 not absolute in their application, nor are they necessarily peculiar to- 
 
43 
 
 electrical stimulation but are doubtless fundamentally more or less 
 universal in their application ; the first, for example, is demonstrable 
 though not with the same facility for other forms of stimulation. 
 
 I. Change and not Intensity of Current Stimu- 
 lates. This is not absolutely true for there are several 
 known exceptions to the general rule. 
 
 Experiment 47. Join two dry cells in series and connect the 
 positive pole with the O-post of the rheochord placing in the circuit 
 a simple key. Prepare itwo non-polarizable electrodes and connect 
 them with the O-post and slider of the rheocord. Prepare a sartorius 
 
 Pig 6. Pig. 7. 
 
 muscle and put a non-polarizable electrode against each end. Place 
 the slider close to the O-post and close the key. Practically none of 
 the current passes through the muscle but all through the rheochord. 
 Gradually, slowly and evenly move the slider along the wire without 
 lifting it, to the other post of the rheochord. If this is carefully done 
 there will be no contraction of the muscle. Open the key and con- 
 traction takes place. Again place the slider about 20 centimeters 
 from the O-post. Close the circuit; contraction results; open the 
 circuit and again the muscle contracts. From this, it appears that 
 it is not the flow of the current that stimulates but the sudden change 
 of the closing and opening of the current. 
 
 Experiment 48. Connect up the dry cells* as before, but place 
 in the circuit of one of them a short-circuiting key with "the key 
 closed (Fig. 7). Place the slider about 50 centimeters from the 
 O-post; close the simple key; contraction occurs. Open the short- 
 circuiting key thus placing the second cell in the circuit and the mus 
 cle again contracts. This law of sudden change having a stimulating 
 
44 
 
 value was first formulated by DuBois-Reymond. Consult your text- 
 book upon this point. 
 
 II. Kathode Stimulates at Make, Anode at Break. 
 
 (Experiment 49.) To demonstrate this, cauterize a frog 
 and when it is entirely under, pith it and dissect out the sartorius 
 muscle. Slit one end of the muscle longitudinally forming legs, and 
 place it upon ice from which it is protected by paraffined paper. 
 Against each leg place a non-polarizable electrode (Fig. 8). Con- 
 nect up two cells as in experiment 47, with the simple key rheochrod 
 and non-polarizable electrodes. Place the slider about 50 centimeters 
 from the O-post. Close the key, the kathode leg contracts. Open 
 the key ; the anode leg will contract. 
 
 We may find apparent exceptions to this later when we stimu- 
 late deep-lying nerve and muscle. It is necessary to keep in mind 
 that the points where the current enters and leaves the irritable tissue 
 are of real importance, so that it will be necessary to remember the 
 distinction between the physical and the physiological anode and 
 kathode, since they may not be, in fact never are, precisely the same. 
 
 III. The Kathode Stimulation is the Stronger. 
 (Experiment 50). Arrange the cells, rheochord, key and non- 
 polarizable electrodes as before (Fig. 8). Dissect out the sartorius 
 
 of the other leg, slit it and place it 
 upon ice as before with paraffined pa- 
 per between the muscle and the ice. 
 Let the two divisions of the muscle be 
 against the two non-polarizable elec- 
 trodes (Fig. 8). With the slider next 
 the O-post, open and close the key. 
 , Repeat, having the slider y 2 centi- 
 meter farther away from the O-post 
 each time, noting at which electrode 
 contraction first appears, and at what 
 
 position of the slider. Repeat the experiment for confirmation. 
 
 We have chosen to have you demonstrate these peculiarities of 
 
 electrical stimulation with muscle and with the galvanic current. 
 
 Were you to test it, you would find that these same laws hold also 
 
 for nerve and when induced current is employed. 
 
 m^ajas^^ l 
 
45 
 
 Electrotonus. 
 
 The passage of the electric current modifies markedly the irrita- 
 bility and conductivity of nerve and muscle, and this fact is at the 
 basis of "laws" II and III. The following statement may be illus- 
 trated by the experiments 51 and 52 that follow. 
 
 When an electric current is passed through a nerve or muscle, 
 irritability and conductivity during the passage of the current are 
 increased around the kathode and decreased around the anode. 
 When the current is broken the conditions are reversed. Very strong 
 currents also decrease the irritability and conductivity in the neigh- 
 borhood of the kathode as well, while the current is made. 
 
 Experiment 51. Connect up three cells in series with a rocking 
 key and rheochord in the circuit (Fig. 9). Place the slider about tc 
 centimeters from the O-post of the rheochord. Connect the slider and 
 O-post of the rheochord with the rocking key which is also to be con- 
 nected with the non-polarizable electrodes in the. moist chamber and 
 arranged for reversing the current. 
 
 Connect up a dry cell with the inductorium for single shock with 
 a simple key in the primary circuit. From the binding posts of the 
 secondary coil wires are to connect with the platinum electrodes 
 which are to be nearer the muscle than the non-polarizable electrodes 
 but as close to the one non-polarizable electrode as possible. Place 
 a piece of blotting paper in the moist chamber wet with water. Cover 
 the moist chamber. 
 
 Arrange a muscle-nerve preparation, securing as long a stretch 
 of nerve as possible, and place it in the moist chamber attached to 
 the muscle lever for writing on the drum. Let the lever be just 
 afterloaded with a 20-gram weight. The drum should be set to 
 revolve at its slowest rate. 
 
 With the key of the polarizing circuit open, test the stimulating 
 electrodes and choose a strength of current such that only break con- 
 tractions occur and these as weak as possible. Then record the upon 
 the drum revolving at its lowest rate, groups of five contractions, as 
 follows : 
 
 (1) With the polarizing current open. (2) Close the polar- 
 izing current and again stimulate. (3) Open the polarizing current 
 again stimulate. (4) By means of the rocking key reverse the 
 
46 
 
 polarizing current, so that the anode is next the muscle ; close it and 
 again stimulate. (5) Open the polarizing current and again stimu- 
 late. It may be necessary to increase the strength of the stimulating 
 current after (3). If after (3) the response is entirely lost, if one 
 waits long enough, and tests it again it will return. 
 
 Record your results. Do they justify the statements made above 
 concerning the changes in irritability caused by the passage of the 
 current? The name Electrotonus given to these changes in irrita- 
 bility and conductivity caused by the electric current is a poor name 
 but it has gained a hold. The change around the anode is called 
 Anelectrotonus; that around the kathode, Katelectrotonus. Do these 
 experiments throw light on the reason for the second law of stimula- 
 tion given above? The change in conductivity can be examined by 
 means of another experiment. 
 
 Fig. 0. 
 
 Fig. 10. 
 
 Experiment 52. As in the last experiment, arrange a polarizing 
 current with three dry cells, rheochord, rocking key and simple key 
 but do not use the platinum electrodes (see Fig. 10). Have the 
 non-polarizable electrodes in the moist chamber half an inch or 
 more apart. With the same or, — better, — a fresh muscle-nerve 
 preparation in the moist chamber prepare to record contractions upon 
 a drum revolving at its slowest rate. Arrange to use about 1-3 of 
 the available polarizing current. 
 
47 
 
 Start the drum, arrange the writing lever, which should be just 
 afterloaded with 10-20 grams, and then drop upon the nerve between 
 the non-poiarizable electrodes a drop or two of saturated salt solution. 
 The muscle soon begins to undergo the irregular tetanus of salt 
 stimulation. With the polarizing electrode between the muscle and 
 the salt the kathode, make the polarizing current. Open it. Reverse 
 the current so as to make that electrode the anode and again cloie 
 and open the current. Results and their explanation. 
 
 Repeat the experiment employing about two-thirds of the avail- 
 able polarizing current. 
 
 Repeat the experiment using the full available polarizing current. 
 What bearing do the results have on the verification of the state- 
 ment made at the beginning under Electrotonus ? 
 
 Were you to test the change in rate of conduction, you would 
 find that the rate also is diminished and increased around the anode 
 and kathode respectively. 
 
 Pflueger's law. 
 
 As a result of the changes in irritability and conductivity around 
 the kathode and anode, the response to stimulation varies under 
 different conditions, the direction and strength of the current modi- 
 fying the result. 
 
 Experiment 53. Arrange one pair of non-polarizable electrodes 
 in the moist chamber, connecting them with three dry cells in series 
 with a simple key, fheochord and commutator in the circuit, connected 
 as shown in Fig. 10. Trace the course of the current and ascertain 
 in which position of the rocker the anode is next the muscle, — i. e., 
 the current ascending. Prepare a muscle-nerve preparation and con- 
 nect to record its contractions on a drum revolving at its slowest 
 rate. 
 
 With the ascending current, and with the slider next the O-post, 
 make and break the current. No contraction will result. Move 
 the slider y 2 centimeter from the O-post and again make and break 
 the current. Repeat, moving the slider J4 centimeter at a time until 
 finally contractions are secured. Note whether make or break con- 
 tractions appear first and at what position of the slider. After both 
 make and break contractions have been secured, larger intervals on 
 
4 8 
 
 the rhebchord may be chosen between successive trials. When the full 
 available current is reached continue adding cells in series until an 
 intensity of current is reached such that there is no closing con- 
 traction. 
 
 Repeat the experiment using a descending current. 
 
 Record your results in the following table : 
 
 Ascending current. Descending current. 
 Make Break. Make. Break. 
 
 Weak current || | || | 
 
 Medium current jj | || ( 
 
 Strong current || | || 
 
 Very strong current... |j | || | 
 
 Examine the results and see how they are to be explained by 
 the altered conditions of irritability and conductivity around the 
 anode arid kathode which we have considered under electrotonus. 
 
 Stimulation of Human Nerves. 
 
 When one turns to the stimulation of nerves within the body, 
 there is met a result apparently different from what would be 
 expected from Pflueger's law- Such, however, is not the case. In 
 order to understand the "law of contraction" here, there is to be 
 considered (a) the resistance offered by the body to the electric cur- 
 rent (b) the difference between the physical and the physiological 
 electrodes, (c) the advantages of unipolar stimulation, and finally, 
 (d) that the density of the current where it enters and leaves the 
 nerve or muscle is an important factor in its efficiency as a stimulus. 
 
 Motor Points. The points where individual muscles caii 
 best be stimulated. They are usually the points of entrance of the 
 motor nerves of the muscles. Consult Figs. 12, 13 and 14. 
 
 Nerve Points. Places where the nerves of the body, can 
 best be stimulated. 
 
 Experiment 54. Connect up three dry cells in series. Place a 
 simple key in the circuit and attach 1 to the inductorium for single 
 shock (Fig. 11). Connect long wires to the secondary coil and ascer- 
 tain if possible which is the kathode at the break current. Connect 
 the indifferent electrodes with the other wire and place it on the back 
 of the neck. Have both electrodes well wet and covered with cotton 
 
49 
 
 cloth. With a sufficiently strong current, find out the motor points 
 on tLe forearm (Figs. 13 and 14) for (1) supinator longus (brachio- 
 radialis), (2) Flexor pollicis longus, (3) Adductor minimi digiti. 
 (4) Dorsal interossei, (5) Flexor sublimis digitorum. Find the 
 ulnar nerve at the elbow, the ulnar and median nerves at the wrist. 
 
 Fig. 13 
 
 Motor Points of the Head. 
 
 = M. frontalis. 
 
 = M. orbicularis palpebrarum. 
 
 = M. Levator menti. 
 
 = M. zygomaticus. 
 
 Fig. 13. 
 
 Motor Points, Arm, Flexor Aspect. 
 
 1 = M. supinator longus. 
 
 2 = M. flexor pollicis longus. 
 
 3 = M. Adductor minimi digiti. 
 
 5 = M. flexor sublimis digitorum. 
 
 6 = N. medianus. 
 
 7 = N. ulnaris. 
 
 Fig. 14. 
 
 Motor Points, Arm, Ex- 
 tensor Aspect. 
 1 = M. supinator longus. 
 4 = M. interossei. 
 
 (What muscles of the hand do they innervate?) Find also the motor 
 points for the following muscies of the face (Fig. 12). (1) Frontalis. 
 (2) Orbicularis palpebrarum (oculi), (3) Levator menti (Mentalis), 
 (4) Caninus (Lev. ang. oris) (5) Risorius. Other muscles may be 
 tried if desired. Consult Figs. 12, 13 and 14. 
 
 Experiment 55. The Law of Normal Contraction. 
 Connect up 8 dry cells in series. Place in the circuit a rocking key 
 and a simple key. Connect the brass electrodes with the rocking key 
 and make the kathode the stimulating electrode. Place the indiffer- 
 
5© 
 
 ent electrode upon the back of the neck with the stimulating electrode 
 over the ulnar nerve at the elbow, make and break the current. If 
 there is no contraction of the muscles innervated by the ulnar nerve., 
 add cells in series one at a time until there appears contraction at 
 the make of the current. Is there contraction at the break ? Reverse 
 
 the direction of the current by means of the rock : ng key so as to 
 make the stimulating electrode the anode ; there will be no contrac- 
 tion. Add cells until there is anodic contraction and note which is 
 first attained, contraction on closing or opening. Make the stimulat- 
 ing electrode the kathode and continue adding cells until contraction 
 occurs upon opening the current, or closing tetanus is secured;- Note 
 that the order in which the contractions appear is the following: 
 
 cells, weak current, K. C- C. 
 
 cells, stronger current, K. C. C, A. C. C, A. O. C. 
 
 cells, strong current, K. C. C, A. C. C, A. O. C, K. O. C. 
 
 cells, very strong current, K. C. Tetanus, which may ap- 
 pear before K. O. C. 
 
 F ! ll in the table. 
 
 This normal order in which the contractions appear with increas- 
 ing strength of current is important, since in conditions of degenera- 
 tion of the motor nerves, the order in which K.C.C. and A.C.C. (or 
 
5i 
 
 A.O.C) appear is often reversed, thus; — A.C.C., K.C.C., A.O.C., 
 K.O.C. 
 
 Relative Irritability of Muscle and Nerve to 
 the Faradic and Galvanic Currents. Both galvanic 
 a.nd faradic electricity have been used in the work so far, and 
 in many cases they might have been used interchangeably. Were 
 there time experiments could be performed to show that they have 
 a different value for the stimulation of muscle and nerve, muscle 
 requiring currents of longer duration as effective stimuli than does 
 nerve. Nerve is also more irritable than muscle. 
 
 Reaction of Degeneration. When the normal muscle is 
 stimulated', it is of course the nerve fibers in the muscle that are 
 stimulated. In cases of degeneration of motor nerves, it is the muscle 
 fiber itself which responds. The difference of reaction of muscle to 
 the galvanic and faradic currents in cases of nerve and muscle degen- 
 eration is known as the Reaction of Degeneration. 
 
 RESPONSES OF MUSCLE AND NERVE TO STIMULATION. 
 
 As a result of stimulation, the muscle responds by contraction, 
 which you have already studied. The mechanical response, however, 
 is not the only one, and is accompanied by (a) thermal, (b) chemical, 
 and (c) electrical changes- These will be studied in the laboratory 
 and in demonstrations. 
 
 When nerve is stimulated, the change, — which may be called 
 ■excitatory state, is propagated along the nerve fiber to its termina- 
 tion. In contrast to muscle, it has very little that is demonstrable, — 
 no mechanical response, no clearly proven chemical change, or eleva- 
 tion of temperature that can be detected. There is, however, a marked 
 electrical change. 
 
 Experiment 56. The Demarcation, Current or Cur- 
 rent of Injury. As carefully as possible remove tihe skin 
 from the tlrgh of a pithed frog and dissect out carefully with 
 out injuring the surface, any muscle of the thigh or leg, — for ex- 
 ample, the gracilis-semimembranosus. Prepare two non-polarizable 
 electrodes and by means of a fine wire, connect them up with a gal- 
 vanometer (Fig. 16). If you do not know how the instrument 
 responds to the direction of current, test it by means of a battery 
 
cell and a rheochord arranged to have a difference of polential of 
 not more than 1-200 of a volt (Have the whole resistance of the 
 20 meters of wire in the circuit, and take off from it with the slider 
 at, say, 7 centimeters). Test the non-polarizable electrodes after 
 they have been prepared, by bringing them in contact with each 
 other ; there should be no deflection of the galvanometer needle. 
 
 Place both electrodes upon the uninjured (natural) surface 
 of the muscle ; there will be no, or only a very slight deflection of the 
 needle. Now cut the muscle across with a clean smooth cut. 
 Place one electrode upon the cut surface and the other upon the 
 natural surface. There is a marked deflection of the needle. Note 
 the deflection and which electrode it is that is in contact with the 
 cut surface. Place both electrodes upon the cut surface. Result. 
 Gradually move one electrode toward the edge of the cut surface 
 and onto the natural surface. Result. Explanation of results. 
 
 Fig. 16. 
 
 Fig. 17. 
 
 Muscle tissue, uninjured and at rest, seems to show no differ- 
 ence in electrical condition. The explanation of the demarcation 
 ■current will be discussed elsewhere. 
 
 Nerves show also in the same way a current of injury which 
 you can demonstrate for yourselves in the carefully prepared sciatic 
 nerve. 
 
53 
 
 The Action Current. When nerve or muscle is active 
 it undergoes an electrical change forming a difference of potential 
 negative at the active part as compared with the resting part 
 through a galvanometer. When thus connected up so as to permit 
 it, a flow of current takes place, from the active part through the 
 tissue to the resting part, and through the galvanometer back to 
 the injured part. This is the action current. (See demonstration.) 
 
 Secondary Contraction. By means of two muscle- 
 nerve preparations carefully prepared, you can demonstrate your- 
 self the current of action by using one muscle as an indicator whose 
 nerve is stimulated by the action current of the first muscle (fig. 17). 
 
 Experiment 57. Arrange one^ cell and inductorium with a sim- 
 ple key in the primary circuit and attach the platinum electrodes to 
 the binding posts of the secondary coil. Carefully prepare two 
 muscle-nerve preparations and arrange them so that the nerve of 
 the one lies across the muscle of the first preparation (Fig. 17). 
 With a single induction shock, stimulate the nerve of the first prepa- 
 ration; the muscle contracts and practically simultaneously with it 
 the muscle of the second preparation. The nerve of the second 
 preparation is stimulated by the action current of the first muscle. 
 
 Secondary Tetanus may be induced in the second mus- 
 cle accompanying tetanus of the first when a number of rapidly 
 repeated stimuli are employed. 
 
 The action current is an important indication of the activity in 
 the muscle, and is quite a delicate test, as can be judged from the 
 above experiments and demonstrations. 
 
 The activity of nerve is also accompanied by an action current. 
 Activity in the central nervous system, in sense-organs, in glands,, 
 is also accompanied by an electrical change, which in fact thus 
 affords us our most sensitive test of the activity in living matter 
 everywhere. We will have occasion to refer to the Action Current 
 in later work. 
 
 Electrotonic Currents. A third form of electrical change will 
 be merely considered in the demonstrations. It should be under- 
 stood that the demarcation current and electrotonic currents are in- 
 cluded here for convenience and not because they are directly con- 
 nected with the electrical change in nerve or muscle during activity. 
 
54 
 
 Che,mical Response. The electrical change is to be regarded as 
 an accompaniment of the chemical change which must be consid- 
 ered fundamental, underlying all the forms of response. This will 
 be considered in the demonstrations. In nerve the evidence of 
 chemical change is practically lacking. 
 
 Thermal Response. Demonstration only. This is an important 
 accompaniment of the chemical change and the mechanical change 
 of form. Heat formation and contraction are the most important 
 forms in which the energy of muscular activity appears. In the 
 case of nerve, again, there is no evidence of heat formation during 
 activity. 
 
 Mechanical Response. See pages . 
 
 THE WORK OF MUSCULAR CONTRACTION. 
 
 It is necessary to consider some of the results of muscular con- 
 traction. The two chief forms in which the energy of the response 
 to stimulation appears are, as has been said, heat and movement. 
 When a muscle contracts and lifts a load (or in the body, moves a 
 bone attached to its tendon of insertion), it performs work, giving 
 to the weight an energy of position which when the muscle relaxes, 
 is "given back" to the muscle in the form of heat. Increase in the 
 amount of load may even occasion at first an increase in the height 
 of contraction. The real test, however, is the amount of work 
 done, which is found by applying the following equation : — W=hw., 
 where W equals the work done, and h equals actual distance through 
 which the weight is lifted, w equals the weight lifted. The actual 
 height is found by dividing the recorded height by the magnification, 
 which is found by the direct proportion, a :b : :c :d ; where a equals 
 actual height, b equals recorded height, c the distance of point of 
 attachment of muscle to fulcrum of lever, and d is the total length 
 ■of lever. 
 
 Experiment $8. Record upon a drum revolved by hand the 
 lieights of contraction of a semimembranosus-gracilis muscle prepa- 
 ration stimulated directly with a uniform submaximal induction 
 shock, the muscle being loaded with 10, 20, 50, 100, 150, 200, 250, 
 300 grams in the successive trials. Unless you are expeditious, it 
 
55 
 
 will be better to use the moist chamber in performing this experi- 
 ment. 
 
 Avoid stretching the muscle by having it just afterloaded, i. e., 
 let the weight and lever be just supported by the screw when the 
 muscle is relaxed. 
 
 Calculate the actual work done and plot it in the form of a 
 curve having on the abscissa the intervals representing 50 grams 
 each, the intervals on the ordinates being gram-millimeters. It 
 thus appears that increased resistance creates in muscle an increase 
 in effort. 
 
 Experiment 59. Obtain a record of the amount of word done 
 by a muscle (semimembranosus-gracilis preparation), the muscle 
 being just afterloaded with 50 grams, the contractions being re- 
 corded upon a drum revolving at its slowest rate, maximal break 
 induction shocks being sent in at intervals of 4 seconds. Continue 
 the stimulation until the muscle is exhausted. Fix the record and 
 calculate the total amount of work done by measuring the recorded 
 heights of contraction, adding them together and reducing to the 
 actual height, recording final results in terms of gram-millimeters. 
 
 Other phases of the work done by muscle when it contracts 
 will be taken up in demonstration. 
 
 Isometric Contractions. In the preceding experi- 
 ments the ' resistance (weight) has remained nearly uniform 
 throughout the contraction (inertia excepted) and the muscle has 
 been free to contract its full extent. Such conditions are termed 
 isotonic conditions. Conditions occur, however, in which the con- 
 traction is resisted with an ever-increasing resistance, and the mus- 
 cle is prevented from contracting to any great extent. Such con- 
 tractions are known as Isometric contractions. This is the case 
 when a muscle contracts against a stiff spring. The energy in this 
 case is during contraction stored in the spring as tension to appear 
 as heat when the muscle relaxes. 
 
 Experiment 60. Record the isometric contraction of a muscle 
 by means of a spring lever. It is necessary first to find the value of 
 the spring against which the muscle will act. 
 
 Graduation of the Isometric Spring. To the spring is at- 
 tached a writing lever. Fasten the spring with the hook down and 
 
56 
 
 bring the writing lever point against the drum. Turn the drum 
 around once by hand to record a base line. Place ioo grams in the 
 scale pan attached to the spring. When the spring is bent, again 
 revolve the drum once. Repeat, for each ioo grams up to 500 
 grams. Fix and preserve the record for reference. 
 
 The Isometric Contraction. Make a muscle-nerve preparation 
 and clamp the femur in the jaws of the femur clamp. By means of 
 a double hook, connect the Achilles tendon of the gastrocnemius 
 muscle with the spring turned hook side up. Bring the writing 
 point against the drum revolving at its fastest speed and by means 
 of a single maximal break induction shock stimulate the nerve. 
 An isometric muscle curve will be written. 
 
 Disconnect the muscle from the spring and connect it to the 
 ordinary writing lever which should be of the same length as the 
 isometric lever and just after load it with 20 grams. Stimulate the 
 muscle with a break induction shock of the same strength as before, 
 and aim to have the contraction recorded on the drum revolving 
 at the same rate of speed as nearly under the isometric curve as is 
 possible. 
 
 Compare the two curves as to (a) form, (b) work done. It 
 will probably be found that the isometric contraction took place more 
 rapidly and the summit of contraction (extreme contraction) was 
 longer held. 
 
 Measure the height of the isometric contraction in comparison 
 with the record of the spring's tension, reduce it to the absolute 
 height of contraction and calculate the work done by the muscle 
 (W = w. h -=- 2). Measure'the height of the isotonic contraction 
 in comparison and determine the amount of work done. The iso- 
 metric contraction will doubtless be found to represent several 
 times the amount of work done during the isotonic contraction. 
 This shows that to increased tension muscle responds by increased 
 force of contraction. This should be borne in mind later when 
 the contraction of the heart muscle is considered. 
 
 FATIGUE. 
 
 Experiment 61. Prepare a semimembranosus-gracilis prepara- 
 tion and attach it to the femur clamp and muscle lever. Just after- 
 
57 
 
 load it with 20 grams. Pass fine wires from the terminals of the 
 secondary coil to the two ends of the muscle and by means of break 
 induction shocks of such strength that the make current contrac- 
 tions do not appear, stimulate the muscle at intervals of 2 seconds 
 and record the contractions on a slowly moving drum. When the 
 muscle has been exhausted, so that it no longer contracts, permit it 
 to rest for 5 minutes and again stimulate as before. A short period 
 of recovery is shown. It is possible to employ the time-marking 
 circuit as the primary circuit of the inductorium and obtain auto- 
 matic stimulation at the stated interval. 
 
 Experiment 62. Arrange the ergograph to record the contrac- 
 tions of the abductor indicis in the manner shown you. Place the 
 point of the adjustable rod in the middle hole of the spring. Bring 
 the writing point against a drum revolving at the slowest rate. Con- 
 tract the muscle voluntarily every 2 seconds until exhaustion sets in. 
 How does muscular fatigue in the body differ from fatigue of a 
 muscle removed from the body? Where are the possible seats of 
 exhaustion in muscular fatigue? What points become fatigued first? 
 
PI,AIN MUSCI,B AND GI,AND. 
 
 I. Plain Muscle. 
 
 Spontaneous Rhythmic Contraction. 
 Response to stimulation: its peculiarities. 
 II. Reflex Action. 
 
 Reflex response; reflex time. 
 
 III. The Sympathetic Nervous System. 
 
 IV. Inhibition and Excitation. 
 V. Visceral Movement. 
 
 Intestinal Movements, Influence of Nerves. 
 VI. Secretion. 
 
 Salivary Secretion. 
 Secretory Nerves. 
 
 PLAIN MUSCLE. 
 
 You have seen that skeletal muscle is dependent on the central 
 nervous system (i) for its contraction, (2) for its nutrition (lecture 
 and recitations) and (3) for the co-ordination of action by which 
 the purposiveness of the movement is expressed. In skeletal mus- 
 cle, each muscle fiber receives its own nerve fiber ; the contraction 
 can only exceptionally pass from muscle-fiber to muscle-fiber and 
 the contraction of the muscle is the sum of the contractions of its 
 component muscle cells. 
 
 In the contraction of plain muscle which is the basis of most 
 visceral movement (ex. esophagus) and in the heart beat, the rela- 
 tions that nerve and muscle have to each other are more difficult of 
 analysis. 
 
 I. Plain and cardiac muscle seem to possess an inherent capac- 
 ity for rhythmic contraction. The part : cipation of a nervous mechan- 
 ism in carrying it out has not been excluded. 
 
 Experiment 63. Pith a frog, toad or Necturus and dissect out 
 the full length of the esophagus. Tie threads around both ends, at- 
 taching one to the holder in the moist chamber, the other to a light 
 muscle lever. 
 
 Bring the pointer to bear lightly against a smoked drum re- 
 volving at the slowest rate. You may obtain an idea of the rate, by 
 marking on the drum and keeping' time by your watch, or arranging 
 
59 
 
 a signal magnet to record minutes on the drum below the muscle 
 record. 
 
 Intestine might also be tried and found to contract rhyth- 
 mically. Is a local nervous mechanism at the basis of these rhyth- 
 mic contractions? 
 
 II. Late histological work tells us that plain muscle cells and 
 heart cells are probably connected together by "intercellular bridges'' 
 so that it is possible that the impulse passes from cell to cell. 
 
 III. Plain or non-striated muscle may be designated physio- 
 logically as slozv muscle ; whereas cross-striated muscle is quick in 
 in its contraction. 
 
 Experiment 64. From the stomach of a N.ecturus cut a ring 
 near the pylorus and suspend it between two pin hooks suitably bent, 
 the head of one of the pins clamped in a flat-jawed clamp, the 
 other bent again so as to hook' into the muscle lever. To this 1 nst 
 pin wire is attached the other end going to the binding post of the 
 muscle lever clamp. Connect wires from the lever and clamp with 
 the rheochord in shunt, the source of electricity being 6 fresh dry 
 cells of high amperage connected in series. Arrange the writing 
 lever to record on a drum revolving at a medium rate. Below it let 
 a signal magnet in a parallel series record the moment of making 
 and breaking the current while a second signal magnet records sec- 
 onds. Use a fresh ring of stomach for each experiment and prove 
 the following: 
 
 (1) The galvanic current stimulates at make and break. (2) 
 The amount of contraction is affected by the duration of the flow 
 of current. Measure the latent period, the period of contraction 
 and the period of relaxation in a typical curve. Is it necessary that 
 a current have an appreciable duration in order to cause plain mus- 
 cle to contract? Will a single break induction shock cause plain 
 muscle to contract? Why not? How is it with skeletal muscle? 
 Nerve ? 
 
 Reflex Action. The activity of plain muscle and gland 
 are largely occasioned or influenced reflexly; that is, by peripheral 
 stimuli acting through the central nervous system. The reflex arc 
 by which this is accomplished consists of the afferent impulse, the 
 
6o 
 
 efferent impulse and the reflex center which "reflects" the incoming 
 into the outgoing impulse. The time it takes a nervous impulse to 
 pass over a given length of nerve is known to you; the reflex time 
 is longer because of a delay occuring within the central nervous 
 system in the translation of the afferent into the efferent impulse. 
 
 Experiment 65. With a sharp-pointed scalpel cut through the 
 spinal cord at the atlanto-occipital articulation and with a tracer 
 destroy the brain. Allow the frog to remain upon the glass, plate 
 covered with a damp cloth for a time that the shock may pass off. 
 Then clamp the head through the upper and lower jaws and hang it 
 up. The legs will soon hang down. 
 
 Pinch one foot sligthly with the coarse forceps. The foot is 
 drawn up reflexly. Pinch the foot hard: both legs may be moved. 
 Moisten a piece of filter paper with strong acetic acid and place it 
 upon one thigh. Observe and record the reflex responses occa- 
 sioned by the chemical stimulus. Remove the filter paper and rinse 
 off the spot with distilled water. Immerse one foot up to the ankle 
 in a breaker of 1-10% sulphuric acid and count the number of sec- 
 onds intervening between the moment of immersion and the reflex 
 response. The time is greater, however, than the true reflex time. 
 
 Experiment 66. The Reflex Time. With the reflex 
 frog employed in the above experiment or with another if neces- 
 sary, take the reflex time by the following procedure : 
 
 To the longest toe of one foot, tie a thread and connect it with 
 a muscle lever, arranged to write upon a rapidly revolving drum. 
 Wrap two loops of bared fine wire around the foot and ankle =md 
 connect them with the secondary coil of an inductorium arranged 
 to give interrupted shock. Have a key, signal magnet, and two dry- 
 cells in the primary circuit. Have a time marker for 1-5 or 1-4 
 seconds intervals and the signal magnet writing immediately below 
 the muscle lever and in the same vertical line. Start the drum and 
 with a strong interrupted shock send in a short stimulus. Both 
 legs will contract and the gastrocnemius muscle give the reflex 
 time. Compare your result with the velocity of the nervous impulse. 
 
 A more exact method is the following : Cut the skin along the 
 front of the Tibia and circularly at the ankle and free it up to the 
 
6i 
 
 knee. Dissect out the Achilles tendon and gastrocnemius muscle 
 up to the knee. Tie the remaining muscles and Tibia tightly to 
 prevent bleeding and remove the foot and leg below the ligature. 
 Clamp the Tibia near the knee. Connect the Achilles tendon with 
 the muscle lever: wrap the fine wire from the secondary coil bind- 
 ing post about the skin that was dissected free, and obtain the reflex 
 time as above. 
 
 Inhibition of Reflex Action. Demonstration. 
 
 The Sympathetic Nervous System. While in the 
 case of skeletal muscle a single nervous element carries the impulse 
 from central nervous system to muscle, a second element is found 
 in the path to plain muscle and gland, the cells and fibers which be- 
 long to it making up the Sympathetic System. The Ganglia are 
 where the cell bodies are located and their extensive and varied dis- 
 tribution causes the relation and interrelation of the cerebro-spinal 
 and sympathtic systems to be exceedingly complex. 
 
 The elements of the sympathetic system, however, seem simply 
 to be interpolated in the path from central nervous system to peri- 
 pheral structures innervated and to have no independent action or 
 control (exceptions?). The structures innervated comprise: vis- 
 ceral muscle (e.g., — stomach, intestines) ; glands (e.g., — the salivary 
 glands, gastric glands, etc.) ; blood vessels, ducts and capsules; hair 
 muscle ; intrinsic eye muscle. The nerve fibers concerned in the in- 
 nervation of plain muscle and gland have been by Langley dis- 
 tinguished as preganglionic and postganglionic. 
 
 Motor (Augmentor) and Inhibitory Impulses. In 
 many cases plain muscle and gland receive impulses producing- 
 opposite effects, — contraction or relaxation, increased or decreased 
 secretion, and probably there is in every case a corresponding dou- 
 ble nerve supply. In the case of both the kinds of fibers, however, the 
 path consists of two nervous elements in series, of which the sec- 
 ond belongs to the sympathetic system. 
 
 The double innervation is especially found in the glands and 
 muscle belonging to the alimentary tract and respiratory system, 
 and in a portion of the circulatory system. The phenomenon of 
 inhibition is very puzzling and is found as well in the central nervous 
 system where we shall have occasion to consider it again. 
 
62 
 
 VISCERAL MOVEMENT. 
 
 Experiment 67. Intestinal Movements. Anaesthetize 
 a dog, cat or rabbit* and open the abdominal cavity under 
 warm (38°) physiological salt solution, exposing the intestines. Ob- 
 serve their movements and try to detect 2 kinds ; so-called "Sivay- 
 ing" movements of the entire intestine, and Peristaltic movements, 
 — rings of contraction traveling slowly down the intestine. Examine 
 these : how many per minute ? Does a region of relaxation precede 
 the contraction? If you were to experiment further, you would find 
 (a) that peristaltic movements would continue after the cerebro- 
 spinal nerves going to the intestines were cut (splanchnics and 
 vagus) and (b) that drugs paralyzing nerves (nicotine, atropine,, 
 and cocaine) would check the peristalsis. What would be your 
 conclusion from these two facts? Compare with the peristalsis the 
 swaying movements. 
 
 Experiment 68. Inhibition of Peristalsis. Remove 
 
 the animal temporarily from the bath of physiological salt solution 
 covering the abdominal organs with a cloth wet with warm physio 
 logical salt solution and search out and cut the splanchnic nerves on 
 both sides. Return the animal to the warm bath. What change is 
 there in the peristalsis ? Explanation. 
 
 SECRETION. 
 
 Experiment dp. The Secretion of the Submaxillary 
 gland. Anaesthetize a cat or dog and perform the follow- 
 ing operation to expose the submaxillary gland and its duct an<J 
 secretory nerves. Tie the animal out ventral side up and fasten the 
 head. Make a cut through the skin parallel with the border of the 
 lower jaw 1 centimeter from it within it, extending from within 
 half an inch of the symphysis to the angle of the jaw. The cut may 
 be lengthened later if necessary. Be very careful not to cut any of the 
 
 ♦Rabbits are best anaesthetized by the use of chloral hydrate or 
 urethane. Give a rabbit of 2 kilograms weight a rectal injection of 
 10 c. c. of a 10% solution of chloral hydrate 20 minutes before it is 
 needed, and supplement the narcosis by the administration of ether. 
 
63 
 
 large superficial veins. Any vein so cut must be ligated to prevent 
 hemorrhage. 
 
 Cut away the superficial fascia and platisma muscle. Retract 
 the cut edges of the muscle: There are exposed the submaxillary 
 gland, a portion of the parotid gland, the digastric and mylohyoid 
 muscles, the external jugular, posterior facial, anterior facial, man- 
 dibular and communicating veins. Cut the digastric muscle near i'.s 
 insertion on the jaw and carefully dissect it up and turn it back, 
 double ligating the veins if necessary. Next, with the scissors care- 
 fully cut through the mylohyoid muscle and turn it back over the 
 jaw- There are now exposed (a) the lingual and hypoglossal nerves, 
 (b) the ducts of the sub (retro-) lingual and submaxillary glands 
 coursing parallel to the jaw and crossed by the lingual nerve the 
 duct of the submaxillary gland being the larger; (c) leaving the 
 lingual nerve before it crosses the ducts, the Chorda tympani run- 
 ning back to the submaxillary gland parallel to the ducts. 
 
 Dissect out the submaxillary gland removing its capsule and 
 turn it back toward the base of the ear. The external carotid artery 
 and its external and internal maxillary branches are exposed in the 
 depths under the digastric muscle and crossed by the hypoglossal 
 nerve. From a branch of the external maxillary artery the gland 
 receives its blood supply. Veins from the gland empty into the 
 external jugular near its origin. 
 
 Ligate the submaxillary duct near the point where it crosses 
 the lingual nerve. Place under it another thread,. When the duct 
 swells with saliva make a v-shaped cut in it with fine sharp scis- 
 sors and insert a fine glass cannula. Tie the duct upon it. The saliva 
 issues from the cannula. Catch and count the drops. 
 
 Very carefully isolate the chorda tympani near the lingual 
 nerve and place guarded electrodes under it. Stimulate it with in- 
 terrupted induction shocks and note (a) the appearance of the 
 gland, (b) the effect on the amount and character of secretion. If 
 the isolation of the nerve failed, stimulate it nearer the gland to- 
 gether with the ducts. Tie a cannula into the external jugular 
 vein after having ligated the facial veins. Catch the blood as it 
 flows. Stimulate the chorda tympani and observe the change in 
 color and amount of blood. 
 
6 4 
 
 Perform the operation given in experiment number 83 for ex- 
 posing the vagus nerve. The nerve lies beside, the carotid artery. 
 Vagus nerve and sympathetic are in the same sheath. Take the 
 nerve on the ball of one finger and with a tracer carefully tear the 
 sheath and separate the nerves; the smaller nerve will be the sym- 
 pathetic. Place guarded electrodes over the nerve and stimulate. 
 If the isolation of the sympathetic nerve fails, place the electrodes 
 upon the external maxillary artery and stimulate thus the sympa- 
 thetic fibers that reach the gland by following the artery. Observe 
 any changes in the gland and the secretion. 
 
 You should take advantage of the opportunity of stimulating 
 the sympathetic nerve to observe the effect upon the pupil of the 
 eye. Explain or reserve explanation until you are studying vision. 
 
 The submaxillary gland may be taken as a type of glands in 
 general. Write a concise statement of the results of the experiment, 
 with an explanation of the results. Compare the innervation of 
 plain muscle and gland. 
 
HEART AND CIRCULATION. 
 
 I. The Heart. 
 
 (a) As a Rhythmically contracting Hollow Muscle. 
 
 1. Rate, Systole, Diastole. 
 
 2. Cause of the Contraction. 
 
 3. Peculiarities of the Contraction. 
 
 4. Effects of Heat and Cold. 
 
 5. The Work of the Heart-beat. 
 
 6. The Thermal and Electrical Responses. 
 
 (b) The Nervous Regulation of the Heart-beat. 
 
 1. Inhibition. 
 
 2. Augmentation. 
 
 (c) The Heart as a Pump. 
 
 Character and Efficiency of the Valves. 
 
 (d) The Human Heart. 
 
 Topography, Heart-sounds, Apical-Impulse. 
 
 II. The Blood Pressure. 
 
 (a) In Animals. 
 
 1. Measurement. 
 
 2. The Vagus Nerve in relation to Blood Pressure. 
 
 3. Influence of sensory nerves. 
 
 (b) In Man. 
 
 III. The Pulse. 
 
 (a) The Volume Pulse. 
 
 (b) The Velocity Pulse. 
 
 (c) The Pressure Pulse. 
 
 The constant chemical change called Metabolism which is :xi 
 the basis -of all life phenomena demands the presence of the nece.3 
 sary chemical substances, food stuffs, the presence of oxygen and 
 the removal as waste of the end products of the chemical action. 
 The surface of the body, however modified, must be the source of 
 the former and the point of elimination of the latter. In the very 
 small forms of animal and plant life (e.g., protozoa), it is near 
 enough to all parts of the living substance so that a special circula 
 tory mechanism is not necessary. In all animals of larger size, 
 however, some special circulatory system must be present and we 
 
66 
 
 find the need met in various ways.* Not always do we find the oxy- 
 gen and food stuffs conveyed to the tissues by the same path (In- 
 sects) nor do we always have the circulating fluid confined in dis- 
 tinct vessels. Usually, however, there is as in ourselves a heart 
 acting as a pump together with definite channels, — blood vessels. 
 In the Vertebrata, also, there is in addition to the closed circulation a 
 supplementary open lymphatic circulation. 
 
 The demands on the circulatory system are satisfied if a suf- 
 ficient capillary flow is maintained. The finer tubes, capillaries and 
 arterioles, offer as we shall see considerable resistance to the flow 
 of the blood. To overcome this a high arterial pressure is necessary 
 which in turn is kept up by the heart's action. The conditions 
 which are met with in the circulatory system are first of all physical, 
 the forcing of a fluid through a system of closed tubes by a pump 
 the heart ; secondly, "vital" factors ; the heart is a hollow muscle con- 
 tracting rhythmically, the rate and strength of whose contractions 
 are under nervous control. The caliber of certain of the tubes is 
 also controlled by the nervous system for the regulation of the 
 capacity of the vascular system, the arterial blood pressure, and the 
 blood supply of the various organs and regions of the body. 
 
 THE HEART. 
 
 The Heart as a Rhythmically Contracting Muscle. 
 
 Experiment 70. Examine the beating heart of (a) the frog or 
 Necturus, (b) the turtle. The alternating periods of contraction 
 and relaxation, systole and diastole, are distinguished by changes 
 in color and size (shape and position) the heart being smaller and 
 paler in systole, larger and redder in diastole (why? changes in 
 mammals?) Closer examination shows that not all parts contract 
 
 * "In Cyclops a flow is caused by movements of the alimentary 
 canal. In Daphnia, the lymph enters a hollow muscle and is then ex- 
 pelled." (Porter.) Among the Crustacea, are also found Circulatory 
 Systems of other degrees of complexity. 
 
r, 7 
 
 at the same time but that the sinus venosus** contracts first then 
 the auricles, next the ventricle and finally the bulluis arteriosus (fig. 
 18). In other words, a wave of contraction passes over the heart 
 
 Pig. 18a. 
 "Frog's Heart, Dorsal Aspect. 
 
 Fig. 18b. 
 Frog's Heart, Ventral Aspect 
 
 from the venous end to the arterial end. When we remember that 
 the heart is a modified tube (Embryology), the heart's contraction 
 resolves itself into a peristaltic contraction wave traversing the tube 
 from end to end. Further, it is not a continuous progression but 
 an apparent pause occurs where the wave passes from sinus to 
 -auricle, from auricle to ventricle, and from ventricle to bulbus. 
 
 In regard to what is the cause of the heart's contraction, what 
 -starts the heart beat, how it spreads throughout the heart, the mean 
 ing of the pause between auricle and ventricle, nothing definite cpu 
 be said at present. Much points to a purely muscular or myogenic 
 
 **The hrart of the frog and other Amphibians, contains two com- 
 partments or chambers not present in our heart as distinct chambers. 
 The veins empty into a Sinus Venosus which in turn opens into the 
 right auricle. The ventricle is not divided into right and left ven- 
 tricles, this only occuring in higher animals with the development of 
 .« distinct Pulmonary Circulation. From the ventricle the blood passes 
 into the Bulbus Arteriosus from which the aortic arches sprang. 
 
68 
 
 origin and propagation of the contraction wave. There is some 
 evidence in favor of a nervous mechanism underlying the rhythmic 
 contraction of the heart. If the latter view is true, the nervous 
 mechanism must be purely intracardiac since the heart can beat 
 for hours or days outside the body. 
 
 Experiment /i. Cut out the frog's heart and place it in a 
 watch-glass with some Ringer's solution. Leave it there to beat to 
 exhaustion (?). 
 
 Intracardiac Ganglia and nerve fibers in connection with them 
 exist and their discovery was hailed as proof of the nervous origin 
 of the heart beat. In the frog, groups of ganglion cells are located 
 in the sinus venosus (Remak's Ganglion), in the interauricular 
 septum (v. Bezold's Ganglion) and at the auriculo-ventricular 
 groove (Bidder's Ganglion). 
 
 Experiment 72. The Stannius' I/igatures, / and II 
 (Fig. 19). Carefully place a ligature (Ligature I) around the 
 heart in the sino-auricular junction and draw it tight: the auricle 
 and ventricle stop beating. Now carefully ligate the heart in the 
 auriculo-ventricular groove (Ligature II). Usually after the liga- 
 ture has been drawn the ventricle begins to beat again. 
 
 II. 
 Stannius Ligatures. 
 
 Experiment 73. Remove the hearts from two frogs and place 
 them in a watch glass of Ringer's solution. In the one heart cut 
 off the ventricle just to the ventricular side of the auriculo-ventricu- 
 lar groove. In the other heart, make the cut just to the auricular 
 
6 9 
 
 side of the groove. Contraction of the ventricle in the two cases? 
 Comment and suggested explanation. 
 
 How can the above experiments be interpreted as indicating 
 the correctness of the neurogenic view? It is necessary, however, 
 to be cautious and this interpretation cannot be accepted without 
 proof. The following two simple experiments bring evidence in 
 favor of the myogenic view. 
 
 Experiment 74. Bernstein's ligature. With a liga- 
 ture drawn tight, compress the middle of the ventricle of a frog"s 
 heart in situ strongly enough to break the physiological continuity 
 of the apex with the rest of the 1 heart, but without severing the phy- 
 sical connection. Release the ligature. The apex has stopped beat- 
 ing. It is still irritable and can be made to give isolated beats by 
 stimulating it. Now compress the bulbus arteriosus thus increasing 
 the intraventricular pressure; the apex will probably begin to beat 
 again. Microscopic examination would probably show that there 
 were no nerve cells present in the apex ; if so, the heart beat must 
 be of muscular origin. (Compare, however, statements of Bethe, 
 
 '03- ) 
 
 Experiment 75. Cut off the bulbus arteriosus from the frog's 
 heart and cut it up into fragments and place them in a watch glass 
 with some. Ringer's solution and examine them under the low powei 
 of the microscope. Some will probably be found undergoing rhyth- 
 mic contraction. If you were to imbed these pieces and make serial 
 sections of them you would again undoubtedly fail to find nerve cells, 
 present. (Caution.) 
 
 The Effect of a Constant Stimulus upon the 
 Heart Muscle. 
 
 Experiment 76. Twist the ends of two fine wires around pins 
 to form electrodes and connect them up with a dry cell having a 
 simple key in the circuit. 
 
 Pith a good-sized frog. Expose the heart from the ventral 
 side and separate most of the ventricle by a cut a little to the ven- 
 tricular side of the auriculo-ventricular groove, thus making a so- 
 called "Apex preparation." It stops beating when severed from 
 
7° 
 
 the rest of the heart. Place the apex preparation upon a cork and 
 stick the pin electrodes into the cork so that the anode is against the 
 cut surface and the kathode in contact with the apex of the heart. 
 Cover the preparation. Close the key: the preparation begins to 
 contract rhythmically. Open the key: it stops beating. Try the 
 experiment with the current passing in the opposite direction. Here 
 the galvanic current, a constant stimulus, causes the heart muscle 
 to respond by rhythmic contractions. Certain chemical stimuli at 
 least, can produce a similar result. 
 
 Experiment .77. Place a crystal of common salt upon the apex 
 preparation: it may start rhythmic contractions in the heart. The 
 constant mechanical stimulation of increased intracardiac tension 
 will also cause rhythmic beats. This you have already shown under 
 experiment 74 and it will be again demonstrated to you. 
 
 There are anions and kations (salts) in the blood which are 
 believed by some to play an important part in causing the rhythmic 
 heart-beat. Test the influence of isotonic solutions of sodium, po- 
 tassium and calcium salts by means of the following experiment. 
 
 Experiment 78. Prepare three heart strips by cutting longi- 
 tudinal rings 2-3 millimeters wide from the ventricle of a turtle and 
 severing the ring. Attach small loops of thread to the two ends of 
 the strips so formed. Attach one end to heart levers and the other 
 end to glass hooks and suspend the strips in vials containing re- 
 spectively: (a) 0.7% NaCl (ji normal), (b) 0.9% KC1, and (c) 
 1.0% CaCl; (d) Have ready a fourth vial and a bottle of Ring- 
 er's solution (NaCl 0.7%; KC1 0.01%; CaCl, 0.026%). Have 
 Ringer's solution (NaCl 0.7%; KClo.01%; CaCl, 0.026%). Have 
 the writing levers nearly balanced and bring them lightly in contact 
 with the smoked surface of a recording drum or drums revolving 
 at their slowest speed. Below the writing levers arrange signal 
 magnets to record 1 minute intervals. 
 
 After a shorter or longer interval, the strip in sodium chlorid 
 solution will begin to contract rhythmically, but after a time the 
 contractions will become weaker and stop. Neither of the other 
 strips will contract. Compare the calcium and potassium strips. 
 Replace the solutions, bathing the strips by Ringer's solution. After 
 
7 1 , 
 
 an interval they will probably begin to contract rhythmically. Re- 
 sults and their explanation. Review the problem of the cause and 
 nature of the rhythmic heart-beat. 
 
 Experiment /p. Recording the Heart-Beat. Employ 
 either method given below, A or B, and obtain a record of 
 the contraction of the frog's heart. 
 
 A. Vertical Suspension. Attach a thread about 2 inches long 
 to the heart lever, the other end of the thread bearing a small bent 
 pin. Pith a frog and fasten it to the frog board ventral side up. 
 Expose the heart and fasten the bent pin into the apex of the ven- 
 tricle. Cut the fraenum or ligament attached to the dorsal side of 
 the heart, raise the lever so as to slightly stretch the heart and 
 record the heart-beat upon a drum revolving at a moderate rate 
 of speed. Have a time-marker record seconds upon the drum. 
 Both auricular and ventricular contractions should record them- 
 selves. 
 
 B. Horizontal Suspension. Pith a frog and pin it out ventral 
 side up upon the special frog-board. Under the frog- board, in the 
 manner shown you, clamp the right-angled lever furnished you and 
 nearly counter-balance it by means of a lead weight. Expose the 
 heart. Connect the apex with the arm of the lever by means of a 
 pin hook and thread tied to the lever by means of a slip-knot so 
 that it may be easily adjusted. Stick a pin through one of the aortic 
 arches to furnish a fixed point against which the heart may con- 
 tract. Cut away the body wall enough to permit the heart and 
 thread to have free action. Record contractions as under method 
 A. Both auricular and ventricular contractions should record them- 
 selves. 
 
 Note the character of the curve. Open the auricle by slitting it 
 with the fine scissors so as to render the heart bloodless. Note 
 and explain, if possible, changes in the form of the curve. Note 
 relative time of (a) the pause, (b) contraction, (c) relaxation. 
 What is the rate? 
 
 Peculiarities of the Heart's Contraction. 
 Experiment 80. All Contractions Maximal. Pith 
 a frog. Fasten it out ventral side up upon the frog board. Place a 
 
7 2 
 
 Stannius ligature I about the heart at the sino-auricular junction; 
 the auricle and ventricle stop beating, but are still irritable and may 
 be made to contract by stimulating them. Substitute for the thread 
 in experiment 79 a fine copper wire. Connect a dry cell with a 
 simple key in the circuit with an induction coil for single shock. 
 From the binding posts of the secondary coil pass one wire to the 
 stand bearing the heart lever, the other wire, with a broad terminal 
 plate may be inserted in the abdominal cavity of the frog. Prepare 
 to record the contractions on a drum revolving at a slow rate. 
 
 Begin with the position of the secondary coil, giving the weak- 
 est current, and make and break the primary current. Gradually 
 increase the current until at length an efficient stimulus is obtained 
 and the heart contracts. Continue to increase the strength of stim- 
 ulus and record the contractions. Note that the contractions ob- 
 tained by means of the weakest efficient stimulus was a great as 
 that obtained with the strongest stimulus. With an effective break 
 shock (make shocks being excluded) stimulate the heart at inter- 
 vals of 5 seconds. Compare the contractions. Compare response 
 of the heart muscle with that of skeletal muscle. 
 
 Experiment 81. The Refractory Period and Com- 
 pensatory Pause. Arrange the apparatus as in the preced- 
 ing experiment but place in the primary circuit a signal magnet 
 to record the stimulation and have it write on the drum immediately 
 below the writing point of the heart lever. Arrange the drum to 
 revolve at a moderate speed. 
 
 Pith a frog and expose the heart from the ventral side. Place 
 a first Stannius ligature about the heart. Attach the hook to the 
 apex of the heart and raise the clamp so as to slightly stretch the 
 heart. Place the large electrode in the abdomen of the frog. Have 
 their wires connected with the secondary coil as in experiment 80 
 so that the pin hook is the kathode at the break current. Record 
 the heart-beat upon a drum revolving at a moderate speed. The 
 signal magnet should record immediately below the writing point 
 of the heart lever as before. 
 
 Stimulate the heart by means of single break shocks and choose 
 an efficient stimulus: The heart responds to each stimulation by a 
 
73 
 
 single contraction. Now group stimuli together in pairs and vary 
 the interval between the two stimuli so that the second stimulus falls 
 (a) after the relaxation from the first contraction, (b) during re- 
 laxation, (c) at the end of contraction (d) during contraction, 
 (e) at the beginning of contraction. The signal magnet records 
 the time of stimulation. Results and your conclusions there- 
 from. 
 
 The experiment may be repeated if desired with the rhyth- 
 mically beating heart. 
 
 Tetaniform Contractions. Make and break the primary cur- 
 rent as rapidly as possible. Result. 
 
 Change the primary circuit wires so as to stimulate with the 
 interrupted current, and repeat. Can you obtain a tetanus of heart 
 muscle ? 
 
 Experiment 82. Effect of Heat and Cold upon the 
 Heart. Prepare two lots of physiological salt solution, 
 one cooled to nearly freezing (Ca. 5" C), the other heated to about 
 40° C. Pith a frog and expose the heart from the ventral side. 
 Connect it as in experiment 79 and obtain a record of the heart beat. 
 
 (1) Allow the heart to record the normal beat during one 
 revolution of the drum. (2) Raise or lower the drum and imme- 
 diately below or above the normal record obtain a second record 
 while cold salt solution is allowed to drop over the heart, care being 
 taken not to ailow the pipette to touch the heart or lever. (3) Finally. 
 below this record obtain a tracing recorded while hot physiological 
 salt solution is dropped over the heart. Fix and preserve the rec- 
 ord. Do you consider that the increased temperature of blood in 
 fever has an influence upon the rate of the heart-beat? 
 
 The Work of the Heart. 
 
 Save in the peculiarities brought out in the above experiments 
 the heart muscle agrees with other striated muscle. Temperature 
 as you have just seen modifies the result. Load, in the form of 
 intracardiac pressure, also influences the strength of contraction 
 (Demonstration). This last is especially important to keep in mind 
 in connection with 1 ithe pathology of the circulation. The rule of in- 
 creased tension causing increased response within a limit, holds 
 
74 
 
 good here as in the case of skeletal muscle. You have already 
 touched on this in experiment 74. 
 
 Thermal Response. There is a direct response, about 1-25 of 
 the body's heat coming immediately from the heart-beat. All the 
 heart's energy appears finally as heat and another fraction is thus 
 derived indirectly from the heart's contraction. 
 
 Electrical Response. This will be demonstrated to you in the 
 frog or turtle and if possible also in man. The theoretical impor- 
 tance of the action current of the heart's contraction will then be 
 explained to you and emphasized. 
 
 The Nervous Regulation of the Heart Beat. 
 Experiment 83. The Inhibitory Action of the 
 VaguS. Turtle. The inhibitory action of the vagus is simply- 
 studied in the turtle. Examine figure 20, showing the course and 
 relations of the vagus in the neck of the turtle, or yourself make a 
 dissection of a preserved specimen. The vagus is easily found and 
 
 Relations of Vagus Nerve in the . 
 Neck. Turtle, 
 a = Sphincter colli, 
 b = Ventral Neck Muscle, 
 c = Trachea, 
 d = Dorsal Neck Muscle, 
 e = Carotid Artery, 
 f = Cervical Sympathetic, 
 g = Vagus Nerve. 
 
 Mg 20. 
 
 identified as it accompanies the carotid artery. Pull out the head 
 of the turtle and with the bone cutters, by one quick cut, from the 
 dorsal side, break the neck and cut the spinal cord close to the 
 
75 
 
 skull. With a piece of wire, break up the brain and as much of 
 the spinal cord as is possible. By means of the bone cutters remove 
 the plastron and expose the heart. Tie a thread about the ligament 
 which is attached to the apex of the heart. Expose the vagus nerve 
 in the neck upon either side, isolate it carefully and place a small 
 piece of sheet rubber under it. Connect a dry cell with the induc- 
 torium for interrupted shock with a simple key and signal magnet 
 in the primary circuit. Connect the platinum electrodes with the 
 secondary coil. 
 
 Lift the apex. Connect the thread attached to the apex of the 
 ventricle to the heart lever and record the contraction upon a 
 smoked drum revolving at a slow rate of speed, the signal magnet 
 being arranged to trace its record immediately beneath the writing 
 point of the heart lever. 
 
 Allow the heart to record a number of normal beats and then 
 stimulate the vagus nerve with an interrupted induction shock (a) 
 of such strength that the heart is slightly slowed, (b) use a greater 
 strength of current and stop the heart. (c) Stimulate with a 
 strength of stimulus sufficient to give complete inhibition, but con- 
 tinue the stimulation a long time in order to secure "vagus escape." 
 
 Experiment 84. The Inhibitory Action of the Vagus 
 Frog. Prepare to record the contractions of the frog's heart by 
 either suspension method given in experiment 79, and also 
 to stimulate the vagus nerve with the interrupted induced current, 
 a signal magnet being in the primary circuit. 
 
 Examine figure 21 and then make a preliminary dissection 
 upon a preserved frog before exposing the heart and vagus in the 
 frog to be experimented upon. Place the preserved frog upon its 
 back and expose its heart. Pull the arms well apart and pin them 
 out. Insert a test tube into the esophagus of the frog and carefully 
 remove structures covering the petrohyoid muscle. From the re- 
 lations shown in the figure identify the three nerves, glossopharyn- 
 geal, hypoglossal, and vagus with its laryngeal branch. 
 
 For stimulating the vagus nerve, pith a frog and fasten it out 
 on its back with its arms stretched apart. Expose the heart and 
 find the vagus nerve where it lies near the lower border of the 
 
7 6 
 
 petrohyoid muscle. Carefully isolate it upward toward Hie angle 
 of the jaw and at that point pass a thread under it and tie it. ( ut 
 the nerve on the central side of the ligature. Place a piece of thin 
 
 Flo. 196.— Scheme of the Dissection of the Frog's Vagus. SM. Submentalis ; LU. Lung; 
 V. Vagus: GP. Glossopharyngeal ; Ug. Hypoglossal; L. Laryngeal; Pit, SH, GU, 
 OH. Petro-, Sterno-, Genio-, Omo-hyoid ; BB. Hyoid ; BO. Hyoglossus; H. Heart; 
 BR. Brachial plexus. 
 
 Fig. 21. 
 
 sheet rubber under the nerve. Connect the heart to the recording 
 lever. Arrange the writing lever and signal magnet to write im- 
 mediately under each other. 
 
 Allow the heart to record a number of normal beats and then 
 stimulate the vagus nerve with an interrupted induction shock (a) 
 of such strength that the heart is slightly slowed, (b) Use a greater 
 strength of current and stop the heart, (c) Stimulate with a 
 strength of current sufficient to give complete inhibition, but con- 
 tinue the stimulation a long time in order to secure "vagus escape." 
 
 Results and their explanation. 
 
 The Augtnentor Nerves of the Heart. Dog, cat or 
 rabbit. Demonstration. 
 
77 
 
 The Heart as a Pump. 
 Experiment 85. The Character and Efficiency of 
 the Valves. For this demonstration a fresh sheep's heart 
 will be used. If there is much fat on the heart, it must first be 
 carefully removed by dissection so that the roots of the aorta and 
 pulmonary artery are laid free. 
 
 A. Carefully introduce a glass tube about y 2 inch in diameter 
 but tapering at the end, through the aorta into the ventricle, taking 
 pains not to puncture or injure the aortic valves in so doing. Tie 
 the aorta firmly around it. With the scissors, dissect away the left 
 auricle nearly down to the auriculo-ventricular ring. After having 
 done this, fill the glass tube with water so as to distend the ventricle 
 and close the bicuspid valves. Observe the two main and the minor 
 flaps of the valve and note how completely, competently, they close 
 the auriculo-ventricular orifice. Next open the ventricle without in- 
 juring the aorta or its semilunar valves and examine the chordae 
 tendineae to recall their relations and function in connection with 
 rendering the valves competent. Note the consistency and flexi- 
 bility of the curtains forming the valves. 
 
 B. Carefully remove the glass tube from the heart and attach 
 the aorta close to the end of the bent glass tube furnished you. 
 Carefully cut away the ventricle to within a short distance of the 
 aortic valves so that they may be easily seen from the ventricular 
 side. Pour water into the other end of the glass tube and observe 
 that it issues from the cardiac arteries. Tie these. The valves 
 should now support a column of water without leakage. Note their 
 appearance when closed. Insert a probe so as to render them in- 
 competent. See how the corpora Arantii assist in rendering the 
 closure complete. It is of considerable interest to examine the tri- 
 cuspid valves and pulmonary valves as you did the mitral and 
 aortic valves under A. and B. above. 
 
 Gad's Ox Heart Demonstration furnishes a good 
 idea of the valves and their action. 
 
 The Human Heart. 
 
 Obviously our knowledge of the human heart cannot be gained 
 by direct observation as in the experiments above. The actual 
 
7 8 
 
 beating human heart has been touched or seen in relatively few 
 cases. We rely then upon analogy, here perfectly safe, and upon 
 the evidences that the heart can give us- through the chest wall 
 or indirectly through the peripheral circulation. This evidence in- 
 cludes : 
 
 (a) The size and location of the heart as ascertained by Percus- 
 sion. 
 
 (b) The heart sounds; their character, relative strength, etc. 
 
 (c) The apical beat. 
 
 (d) Indirect evidence coming through the peripheral circulatory- 
 
 system, such as: — 
 1, the pulse; 2, blood pressure; 3, abnormal circulation in parts, 
 producing conditions of congestion, cyanosis or anaemia, etc. 
 
 The Topographical Relations of the heart and their 
 determination by percussion rightly belong in courses of top- 
 ographical anatomy and physical diagnosis and not here. How- 
 ever, you should have for the following experiment knowledge of 
 the position of the heart in relation to the chest wall and the general 
 location of the valves. From your text-book of anatomy make a 
 diagram for future reference indicating these topographical rela- 
 tions. 
 
 Experiment 86. The Heart Sounds. Apply your ear 
 to various parts of the chest wall in the person examined and note 
 to what an extent you can hear the cardiac sounds. The heart 
 sounds have at least the following components: The first sound; 
 (i) the muscle sound, (2) the closing of the mitral valves, (3) the 
 closing of the tricuspid valves : The second sound ; ( 1 ) the closing 
 of the aortic valves, (2) the closing of the pulmonary valves. 
 While the heart sounds may be heard over widely separated points 
 on the chest wall (and other regions) there are definite localities 
 where their component elements may best be heard. These points 
 are : For the aortic valves ; the second intercostal space to the 
 right of the sternum or over the sternal ends of the second costal 
 cartilage ; for the pulmonary valves, the second intercostal space 
 to the left of the sternum. For the mitral valve, over the apex of 
 the heart, less well in other places to the left of the sternum (e.g., 
 
79 
 
 the 3rd and 4th intercostal spaces). For the tricuspid valves, over, 
 the lower portion of the sternum and to the right of it (over the 
 sternal ends of the 5th and 6th costal cartilages). 
 
 Make an outline sketch of the chest wall and mark on it these 
 areas, lettering them with the appropriate letters. Think a moment 
 and say why one would expect to hear the various valvular sounds 
 best in these places. 
 
 With a stethoscope listen carefully to the heart sounds at these 
 localities noting the relative and absolute loudness of the first and 
 second sounds and the character of the tone. Identify the first 
 sound by (a) placing a finger on the apical impulse (apex) while 
 listening to the heart beat, (b) placing the finger on the carotid pulse. 
 The sound travels best when the direction of the sound coincides 
 with the blood current. Compare the distinctness of the 1st and 2nd 
 sounds at the apex and in the second intercostal space. Listen to 
 the heart sounds over the carotid and to the right of the sternum. 
 Can you state pathological conditions in which the blood current is 
 reversed? Do you understand how insufficiency and stenosis in the 
 different valves might change the points where the sound (or mur- 
 mur) would be best heard? Compare the strength of the second 
 sound at the aortic and at the pulmonary area. Can you imagine 
 conditions in which the second sound would seem louder in the pul- 
 monary area? 
 
 The Apical Beat or Impulse. View the chest wall 
 and abdomen and see if the heart beat is shown as movement. Nor- 
 mally this occurs only in the 5th intercostal space about one and 
 one-half inches inside the mammary line. Locate the apical beat 
 and place your fingers over it to determine the point of strongest 
 impact. Is the location normal? 
 
 Experiment 87. The Cardiogram. The graphic record 
 of the apical beat may be obtained by means of receiving and re- 
 cording tambours. Connect up a receiving tambour by means of 
 inelastic (white) rubber tubing with a recording tambour whose 
 lever is arranged to record upon a drum revolving at moderate 
 speed. 
 
 If the receiving tambour must be held by hand, take pains to 
 
8o 
 
 hold it still. The person whose apical beat is being recorded must 
 also be in the position in which the apical beat is most strongly felt 
 (probably sitting) and must, of course, remain quiet. Fix the rec- 
 ord and examine it to see whether there are indicated both auricular 
 and ventricular systole. 
 
 Place a finger over the carotid artery in the neck and with the 
 other hand take the apical beat. Compare the carotid pulse with the 
 apical beat as to the relative time of occurrence. With the stethoscope 
 listen to the heart over the sternum and at the same time place a 
 finger over the apical beat. With which heart sound is the apical 
 beat synchronous? 
 
 Clinically, the apical beat is of importance: — (a) for determin- 
 ing which is the first heart sound, (b) for locating the apex of the 
 heart (in hypertrophy or displacement), (c) in certain cases it is 
 lost, exaggerated or modified in character. 
 
 Experiment 88. The Rate of the Heart Beat. Bring 
 in a record of the pulse rate (rate of the heart's contraction) 
 in 6 persons, taken sitting, standing and lying flat. Give their age 
 and the time of day. Be able to discuss results. 
 
 BLOOD PRESSURE. 
 
 The following experiments are to be performed in the Blood 
 Pressure room in groups of four by special appointment. There 
 will be a division of duties and sincere earnestness and strict atten- 
 tion to the work in hand must be maintained. Number i will do the 
 operating, No. 2 give the anaesthetic, No, 3 take charge of the re- 
 cording pens, and No. 4 preside over the stimulation and the motor. 
 No. 1 is to have the general direction of the experiment. Each 
 operation or stimulation should be recorded upon the paper. Each 
 record is to be worked over and properly labeled and fully under- 
 stood after which they are to be submitted to the Instructor for 
 examination. 
 
 Experiment 8p. The Measurement of Blood Pressure. 
 Take a blood pressure tracing through the carotid artery 
 of the dog or cat. While 1 and 2 are anaesthetizing the animal, 
 3 and 4 should see that the apparatus is in good working order: — 
 
8i 
 
 (a) that the motor and kymograph run smoothly, (b) that the writ- 
 ing pens are clean and in position (the blood pressure pen, the signal 
 pen and the respiration pen should write in the same vertical line. 
 The respiration and blood pressure pens should have red ink, the 
 time and signal pens black ink), (c) That the induction coil and 
 signal magnet work well, (d) that there is on hand plenty of 10% 
 magnesium sulphate solution. Fill the pressure bottle, and flush 
 out and fill the manometer and lead tube. 
 
 Dogs should be given a hypodermic injection of about 1-2 c. c. 
 of a 5% solution of morphine sulphate about 20 minutes before 
 they are anaesthetized. With them chloroform may be used. Cats 
 should be anaesthetized with ether in an animal box. 
 
 When the animal is well under the influence of the anaesthetic, 
 place it ventral side up on the animal board and fasten down the 
 arms and legs. From the manubrium sterni nearly to the larynx, 
 with a sharp scalpel cut the skin in the middle line. Divaricate' the 
 cut edges of the skin, exposing the sternothyroid and sternohyoid 
 muscles over the trachea. Cut these in the middle line exposing the 
 trachea. Isolate this and pass a thread under it a short distance 
 below the larynx. Cut a transverse slit in it between the cartilages 
 and insert the tracheal cannula. Tie it with the thread securing 
 it by tying the thread again over the transverse limb of the T-tube. 
 The anaesthetic should now of course be administered through the 
 tracheal tube. Draw to the side the cut sternohyoid and thryoid 
 muscles on the right side, exposing the carotid artery, internal 
 jugular vein, and vagus and sympathetic nerves (in a common 
 sheath), lying between the trachea and the sterno-mastoid muscle. 
 
 Isolate the carotid artery for an inch or so and under it pass 
 two threads. Choose an artery cannula of the right size. Clamp 
 the carotid artery as far down as possible and about an inch above 
 ligate it with the upper one of the threads. Make a V-shaped 
 cut in the artery, fill and insert the cannula: tie the artery firmly over 
 it and secure k as you did the tracheal cannula. Fill the tip of 
 the cannula. Attach the monometer tube to the cannula and fill 
 it, washing out all air through the side tube. Lower the pressure 
 
82 
 
 bottle to find the O-level and set the time marker to write at that 
 level. Raise the pressure bottle and clamp it off. 
 
 All is now ready. Start the motor and the time marker, loosen 
 the clamp on the respiratory tube and when the pens are writing 
 well, remove the clamp from the artery. Note and explain the pul- 
 sations, respiratory fluctuation. Calculate the maximum, minimum 
 and mean arterial pressure in terms of mm. of mercury. 
 
 With the same animal as a continuation of this experiment 
 perform 
 
 Experiment 90. The Vagus Nerve and Blood Pres- 
 sure. The operator should begin the isolation of the vagus 
 nerve immediately after the above experiment has been well started. 
 Employ the shielded electrodes and with an interruptel induced 
 •current, 2 dry cells in the primary circuit and the secondary coil at 
 8 centimeters, stimulate the right vagus nerve, the time of stimula- 
 tion being recorded upon the drum by the signal pen in a parallel 
 •circuit. 
 
 Stimulate, the vagus nerve several times, with increasing 
 strength of current, obtaining first slowing of the heart beat and 
 then total arrest of the heart. 
 
 Place two ligatures about the vagus nerve 5 millimeters apart 
 and cut the vagus nerve in between the ligatures. Record upon the 
 drum the moments of ligating and cutting. Stimulate the peri- 
 pheral end of the vagus: stimulate central end of the vagus. If 
 total arrest of the heart is not produced, increase the strength of 
 stimulus. Expose and stimulate the left vagus. Double ligate and 
 cut the nerve as before. Stimulate the peripheral end: stimulate 
 the central end. Continue the experiment as 
 
 Experiment 91. Reflex Influence of Sensory Nerves 
 on Blood Pressure, (a) Sciatic Nerve. Expose and stimu- 
 late the sciatic nerve at the hip. Nets relation to res- 
 piration and blood pressure- Cut the sciatic nerve and stimulate 
 central end: stimulate peripheral end. 
 
 (b) Splanchnic Nerve. Upon the left side, locate the last rib. 
 Just below and parallel to it make an incision about 4 inches long 
 through the skin and then successively the muscles of the abdom- 
 
83 
 
 inal wall and the peritoneum. The incision should begin well to- 
 ward the back. Divaricate the cut edges and insert a piece of 
 gauze and hold back and up the viscera (stomach, omentum, intes- 
 tine), exposing the root of the mesentery. Locate the coeliac artery 
 and the semilunar ganglion. With the tracer tear away the perito- 
 neum over the Coeliac artery and find the splanchnic nerve (great 
 splanchnic) where it crosses it. Isolate the nerve for a distance, 
 (a) Stimulate the semilunar ganglion: (b) Stimulate the splanch- 
 nic nerve. If possible, (c) ligate the splanchnic nerve and cut it 
 peripherad of the ligature and stimulate the central end, and finally, 
 (d) again stimulate the semilunar ganglion. Note and explain 
 effects upon blood pressure and respiration. Finally, — 
 
 Experiment 92. Kill the animal under anaesthetic either Ca) -> 
 by asphyxiation caused by clamping the trachea, (b) asphyxiation 
 from the administration of CO gas, (c) Opening the femoral vein 
 and permitting the animal to bleed to death. Note and explain 
 where possible the effect upon the blood pressure. 
 
 Experiment 93. Reflex Regulation of Blood Pres- 
 sure and Heart. With . a second animal take the blood 
 pressure and respiration tracings as in the preceding experiments 
 (90, 91, 92), and test the influence that the stimulation of the fol- 
 lowing nerves has upon the heart and blood pressure: 
 
 (a) Ammonia: Stimulation of nasal branches of trigeminus. 
 With a pipette introduce into each nostril a drop of ammonia. 
 
 (b) Try also electrical stimulation of the nasal mucosa by 
 placing one electrode against the septum the other against the lateral 
 wall of the nasal cavity. 
 
 (c) Expose and stimulate the Superior Laryngeal Nerve. 
 
 (d) Expose and stimulate the Lingual Nerve. 
 
 (e) Expose and stimulate the Splanchnic nerves and Semi- 
 lunar ganglion. 
 
 (f) Expose and stimulate the Sciatic nerve. 
 
 (g) Insert a probe down the trachea through the respiration 
 cannula and stimulate mechanically the mucous membrane near the 
 bifurcation. 
 
 You tried (e) and (f) after both the vagus nerves were cut; 
 
8 4 
 
 compare the present results with those then obtained. Work up 
 the record calculating the change in heart rate and blood pressure 
 which the stimulation caused in each case. 
 
 Kill the animal in one of the three ways (a, b, or o) given un- 
 der experiment 92. 
 
 Experiment 94. Blood Pressure in Man. The direct 
 measurement of blood pressure in ourselves is,, of course, not possi- 
 ble save in exceptional cases. It has been done. An indirect method 
 must be resorted to whenever in clinical work it is desirable to take 
 the arterial pressure. Such methods are necessarily inexact for 
 reasons that you will readily appreciate. 
 
 Of the instruments devised for the purpose of obtaining meas- 
 urement of the blood pressure in ourselves, there are available; — 
 (1) the Riva-Rocci Sphygmonanometer, (2) the Hill & Barnard 
 Sphygmomanometers, (c) the Basch Sphygmomanometer, (d) the 
 Oliver Haemodynamometer, (e) Janeway's Sphygmomanometer. 
 
 With the Hill & Barnard instrument and also with either the 
 Riva-Rocci, Oliver, v. Basch, or Janeway apparatus, find the ap- 
 proximate arterial pressure in your right fore-arm, arm or radial 
 artery according to the demands of the instrument used. You 
 should appreciate the sources of error in these pieces of apparatus. 
 The development of more accurate methods would be welcome. 
 
 The Clinical Application of these methods of estimating arterial 
 pressure is found in certain cases of heart and kidney disease, dis- 
 eases involving the vasomotor mechanism, etc. ; also occasionally 
 in ' administering an anaesthetic. 
 
 THE PULSE. 
 
 The rhythmic activity of the heart forces at intervals of systole 
 a certain volume of blood (about no c. c.) into the arterial system 
 and so passes on to it its periodicity of action. This has three sides 
 to be considered. The injection at systole of such a quantity of 
 blood into the arteries increases the velocity of flow throughout the 
 arterial system. This rhythmic increase in velocity constitutes the 
 Velocity Pulse (The tachograph and its demonstration). 
 
 Corresponding to the increase in the amount of blood which 
 the heart forces into the arterial system at systole there is a per- 
 
85 
 
 iodic increase and decrease in the volume of blood in each organ, 
 or part of the body. This is the Volume Pulse (The Plethysmo- 
 graph and its demonstration). The condition of dilation or con- 
 traction of the arteries greatly affects it. 
 
 The amount of blood in a part, the distribution of the blood 
 in the body, is under the control of the vasomotor nerves. It is 
 quite important that you understand the mechanism on which the 
 regulation of the blood supply depends. 
 
 The sudden addition of the systolic output to the blood already 
 in the aorta causes an increase in pressure which is transmitted 
 throughout the arterial system as a wave of increased pressure, 
 the Pressure Pulse, or the pulse as commonly known. 
 
 Experiment 95. Feeling the Pulse. Place the balls of 
 the volar surface of the last phalanges of the first three fingers over 
 the radial artery in the wrist, located between the spinous process 
 of the radius and the tendon of the flexor carpi radialis, and note ; — 
 (a) the Regularity of the heart's action, (b) the Rate of the heart- 
 beat: this you have already done (Exp. 88), (c) the Tension, dis- 
 tension of the artery, whether the pulse' is soft or hard; (d) the 
 Character of the pulsations, — whether large or small, whether quick 
 or slow ; that is, whether the distension and relaxation takes place 
 quicklv or not. Combinations of these characters partly determine 
 the description of the pulse as strong, weak, contracted, full, 
 empty, etc. 
 
 Examine faithfully the radial pulse in the right and left arms 
 of three individuals setting down your characterization of the pulse 
 in each case and have the instructor verify them. A correct judg- 
 ment of the pulse comes only after long practice. 
 
 Experiment 96. Sphygmography. Obtain by means 
 ■of the sphygmograph assigned you a graphic representation of the 
 radial pulse in your right or left arm. Be careful to adjust the in- 
 strument as exactly as possible so that the pelotte rests over the 
 artery at the radial tuberosity, and that your arm and hand rest 
 •easily and relaxed and that you avoid movement while the tracing 
 is being taken. Identify in the pulse curve so taken (a) the pre- 
 dicrotic notch, dicrotic notch and postdicrotic notch, (b) can you 
 
86 
 
 determine whether the pulse is celer, tardus, durus, or mollis? 
 Have you any criticism to make of the method? 
 
 Experiment 97. Influence of Amyl Nitrite. Prepare 
 to make a second pulse tracing, and when all is ready, breathe 
 in two drops of Amyl nitrite placed on a cloth. When you begin 
 to feel the effects, take the pulse tracing. Amyl nitrite paralyzes 
 the musculature of the arterioles, causing dilation. Observe and 
 explain: — (a) the decreased tension, (b) the exaggerated dicrotic 
 notch or the occurrence of a dicrotic pulse. When a marked dicrotic 
 notch occurs in the pulse, what condition of the vascular system is 
 suggested ? 
 
 The Velocity of the Pulse Wave. Demonstration. 
 
 The length of the Pulse "Wave may be calculated 
 from the above. 
 
 The Pulse taken in connection with other features, gives val- 
 uable information as to the heart action, the condition of the peri- 
 pheral vessels and the tension in the arterial system, the arterial 
 pressure, which you have already studied. 
 
RESPIRATION. 
 
 The close relation of the Respiratory and Circulatory systems 
 is indicated by the work above (the pulse, heart rate, blood pres- 
 sure). Many of the facts of respiration, however, involve such 
 careful and exact work in the field of gas analysis that they are 
 not suited for general laboratory work, but must be given in specia' 
 demonstration. 
 
 The following outline presents an analysis of Respiration am! 
 the factors involved. 
 
 RESPIRATION DEPENDS UPON 
 I. The Mechanical Factors. 
 II. The Chemical and Physical Factors. 
 III. The "Vital" Factors. 
 I. The Mechanical Factors are 
 
 A. The Elasticity of the Lungs, and 
 
 B. Respiratory Movements, involving 
 
 (a) The Muscles of Respiration and their action. 
 
 1. The Diaphragm. 
 
 2. The Intercostals. 
 
 3. The accessory muscles of inspiration. 
 
 4. The muscles of expiration. 
 
 (b) The Nervous Regulation of Respiration, by 
 
 1. The Respiratory Center, through 
 
 2. The condition of the blood and reflexly, 
 
 3. The vagus nerve, also through 
 
 4. Other sensory nerves and likewise 
 
 5. Higher Centers, — -"psychic" control, etc. 
 The Result of A. and B. is 
 
 (a) The Inspiration and Expiration of air (amount?).' 
 
 (b) Diffusion of gases in the lungs, 
 
 (c) Change of pressure in the lungs, altering 
 
 (d) The Partial Pressure of O, and CO. which are im- 
 
 portant for II. 
 II. The Chemical and Physical Factors include 
 
 A. Partial Pressure and Tension of On and CO... 
 
 (a) In the alveolar air, 
 
 (b) Their tension in the blood, 
 
 (c) Their tension in the tissues. 
 
 B. Chemical affinity of Hb. for O,. 
 
88 
 
 C. Chemical affinities of C0 3 . 
 
 D. Diffusion and Osmosis. 
 III. The "Vital" Factors. 
 
 A. In addition to the above, there is probably an action of 
 the capillary and pulmonary epithelium. 
 
 Experiment 98. The Respiratory Movements. 
 
 By means of some form of pneumograph or stethograph and a tam- 
 bour, record on a drum revolving at a moderate rate of speed your in- 
 spirations and expirations. Determine the rate at which the drum 
 is revolving and have it indicated on the tracing. 
 
 Record the respiratory movements occurring under the follow- 
 ing conditions: 
 
 (a) Lying flat on the back. 
 
 (b) Sitting. 
 
 (c) Standing. 
 
 (d) After having run up stairs or otherwise exercised. 
 
 (e) Record a laugh, 
 (f) A cough. 
 
 (g) A sneeze. 
 
 Set down on the tracing age and time of day. At typical places 
 in the curve measure the relative time of expiration and inspiration. 
 Note the character of the inspiratory and expiratory portions of 
 the curve. 
 
 Experiment pp. The Volume of the Air Inspired and 
 Expired. By means of a spirometer, determine in yourselves: — 
 
 (a) The volume of tidal air (approximately). 
 
 (b) The volume of complemental air. 
 
 (c) The volume of supplemental air. 
 
 (d) The entire vital capacity. 
 
 Record your results. 
 
 The Elasticity of the I^ungs and Intrathoracic and 
 Intrapulmonary Pressure. Demonstration. 
 
 The Gases of Inspired and Expired Air. Demon- 
 stration. 
 
 The Blood Gases. Demonstration. 
 
 The Respiratory Center. In experiments 90, 91, 92, 
 and 93; you have tested the influence of a number of sensory 
 
8 9 
 
 ..erves upon the respiratory center. Examine the records and un- 
 derstand the effect of stimulating the nasal branches of the trigem- 
 inus, the lingual, the superior laryngeal, vagus, sciatic and 
 splanchnic. 
 
 The Respiratory Center and the Vagus Nerve. 
 Head's experiment. Demonstration. 
 
 The Phenomena of Hyperpnoea, Dyspoea, Asphyxia, 
 CO-Poisoning. Study the phenomena of asphyxiation in 
 those records in which the animal was killed by this means, 
 keeping- in mind the influence of the bloo'd on the respiratory 
 center. 
 
 Respiratory Center and Anaemia. See the records in 
 which the animal was killed by bleeding', hemorrhage, 
 
 Respiration and Blood Pressure. In experiment 89, 
 note the respiratory fluctuations of the blood pressure and 
 make an analysis of the factors that serve to cause them. 
 
 Respiration and the Heart Rate. Examine rec- 
 ords of experiments 89-93 and note and explain (?) the relation 
 of the pulse rate to the respiratory phase. 
 
 Experiment 100. Respiration and the Pulse. 
 Valsalva's Experiment. This experiment may be performed if the 
 Instructor permits. Arrange to take a pulse tracing and while it is 
 being traced, close the glottis and make a forced expiration. Note 
 the effect upon the pulse. The explanation. 
 
 Experiment 101. Muller's Experiment. If the Instructor per- 
 mits, make a sphygmographic ; record of the radial pulse and while 
 the tracing is being taken, close the glottis and make a forced in- 
 spiration. Again note the pulse curve. 
 
 Experiment 102. Prepare to take a pulse tracing and when all 
 is ready, breathe in two drops of amyl nitrite on a cloth. When 
 you begin to feel the effects take the pulse tracing making the 
 while deep inspirations and expirations. Let the one working with 
 you note and indicate on the record the periods of inspiration and 
 expiration. Observe and explain effect of respiration on (a) the 
 tension of the pulse (arterial pressure), (b) the pulse rate. 
 
 Experiment 103. The Respiratory Sounds. By means 
 of a stethoscope, listen to the sound of the quiet breathing- 
 
go 
 
 a,nd forced breathing over the right lung (say, about 5th or 6th 
 rib). 
 
 The Vesicular Breathing which is heard is a soft, purring, 
 sound, peculiar, hard to characterize and recognize at first. It is 
 not explained in the same way by all. Its recognition and distinc- 
 tion from abnormal respiratory sounds will, be a matter of impor- 
 tance in your clinical work later. Note the relation of the sound 
 to the expiration and inspiration. During forced breathing, an- 
 other crackling sound may be heard. 
 
 Bronchial Breathing. With a stethoscope listen to the breath- 
 ing in front over the trachea and the upper part of the sternum; 
 behind, at the vertebra prominens, above and below. This sound, 
 likewise, is peculiar and important. Note the character of the 
 sound and the differences in inspiration and expiration. Compare 
 it with the vesicular breathing. 
 
 The Vocal Fremitus. Place your hands upon various regions 
 of the chest wall while the person experimented on says, "33," 
 "99," or counts, "1, 2, 3, etc.," etc. The vibrations can be distinctly 
 felt by the hand. Place your ear over various portions of the chest 
 wall while the person counts and note the character of the trans- 
 mitted sound. 
 
 Percussion. Demonstration. 
 
 ANIMAL HEAT. 
 
 Experiment 104. Upon three successive days, by means of a 
 thermometer placed in the axilla or under the tongue, determine 
 your own body temperature at the hours of, 7 A. M. (or upon aris- 
 ing), 10 A. M., 3 P. M. and 9 P. M. (or upon retiring). Record 
 your results. Be prepared to explain or discuss them. 
 
 The Source of Body Heat. The chief source of the 
 
 body heat is the skeletal musculature which furnishes about 40%. 
 The circulatory system furnishes about 5% ; Glands large percent- 
 age. 
 
 The Heat Value of the Food Stuffs. The heat value 
 of one of them will be demonstrated to you- 
 Calorimetry. Demonstration. 
 
THE PHYSIOLOGY OF VISION. 
 
 I. The Eye as an Optical Instrument. 
 
 A. (a) Laws of Optics. 
 
 (b) The Constants of the Eye. Cardinal Points. 
 
 (c) Images on the Retina. 
 
 1. Sensory Regions: Macula, Blind-spot, Peripheral 
 
 Boundary. 
 
 2. Sensory Layer: Purkinje's Figures, etc. 
 
 3. Visual Acuity. 
 
 B. Optical Defects. 
 
 (a) Lost Light. 
 
 (b) Acentricity of Refracting Surfaces. 
 
 (c) Spherical Aberration. 
 
 (d) Chromatic Abberation. 
 
 (e) Optical Defects of Refraction. 
 
 1. Myopia. 
 
 2. Hyperopia. 
 
 C. Accommodation: Lens changes, range. 
 
 3. Correction of Myopia and Hyperopia. 
 
 4. Astigmatism. 
 
 D. Clinical Examination of the Eye. 
 
 (a) Ophthalmoscopy. 
 
 (b) Skiascopy. 
 
 II. The Nutrition of the Eye. 
 
 III. The Response of the Retina to Stimulation. 
 
 . (a) The Limits of Vision. 
 
 (b) The Changes in the Retina. 
 
 1. Visual Purple. 
 
 2. The Movement of the Pigment. 
 
 3. Electrical Changes. 
 
 (c) The Course of Excitation. 
 
 1. It is gradual. 
 
 2. Exhaustion and Recovery. 
 
 3. Adaptation. 
 
 IV. The "Psycho-Physiology" of Vision. 
 
 (a) Color Vision. 
 
 (b) Complementary Colors. 
 
 (c) Color Induction. 
 
 (d) The Theory of Color "Vision. 
 
 (e) The Function of the Rods and Twilight-Seeing, 
 (f ) Color Blindness. 
 
9 2 
 
 V. Binocular Vision. 
 A. 
 
 (a) The Movements of the Eye. 
 
 (b) Convergence and Accommodation; the Eye-reflexes. 
 
 (c) The Visual Fields. 
 
 (d) The Corresponding Regions of the two Retinas, 
 (f) The Visual Fields and the Brain Centers. 
 
 B. 
 
 (a) Perspective. 
 
 (b) Stereoscopy. 
 
 VI. Visual Illusions. 
 
 I. THE EYE AS AN OPTICAL INSTRUMENT. 
 
 The Fundamental I,aws of Optics. In order to 
 understand the eye as an optical instrument the fundamental laws 
 of optical physics must be well understood and it will be best to 
 review them at the beginning. From the stand-point of the eye 
 it is advantageous to approach the phenomena of refraction in a 
 somewhat different way from that usually given in courses of 
 physics. The following enumeration of topics will assist you in 
 the necessary review. Comment and explanation are given in fine 
 type. 
 
 i. Refraction and the law of sines. The index of refraction. 
 
 2. The law of reflection. 
 
 3. Reflection at a curved surface. Center of curvature, prin- 
 
 cipal and conjugate foci, vertex and the derivation of the 
 formula I -f- p 4- I -f- p' = I -4- F. 
 
 4. The formation of an image by a plane mirror. 
 The formation of an image by a concave mirror. 
 
 5. Refraction at a spherical surface; the center of curvature, 
 
 principal point and plane, principal foci, conjugate foci. 
 The formula: F' -=- f + F" -=- f" = -1. 
 
 6. The formation of an image by refraction at a spherical sur- 
 
 face. Effect of location of object upon the location and 
 size of image. 
 
 7. Refraction by a series of spherical surfaces: conjugate 
 
 planes, the principal foci, conjugate foci, principal points, 
 and planes, the nodal points. 
 
93 
 
 8. The special cases of the biconvex and biconcave lenses : The 
 
 formula : I -=- f + I -^ f" = i ^- F. 
 
 9. Combination of lenses. The formula : - 1 -4- F' + 1 -=- F" 
 
 = 1 -f- F'". 
 
 Note 1. Refraction and the law of sines may be found well pre* 
 sented in almost any text book of physics. 
 
 Sin. \_a _ V_ 
 
 Sin. L/ 3 = V 77 ' 
 where V = Velocity in medium 1 and V" is velocity in medium 2. Tha 
 index of refraction of a medium is the velocity of light in that medium 
 compared to the velocity in a vacuum: n' = V -f- V. for one medium, 
 and n" = V -3- V" for the second medium. 
 
 V^ __ 
 
 V" n' ' 
 
 velocity of light in air is so nearly that in a vacuum (1.00029 in air as- 
 compared to 1.0 in vacuum) that 
 
 V Sin. U 
 
 V^V' = n' = land^ 7 - = n"= slir ^ 
 
 Note 2. The angle of incidence equals the angle of reflection^ 
 Consult a good text book of physics. ^ 
 
 Note. 3. Make a diagram locating the 5 points mentioned. The 
 derivation of the formula you will find given in any good text-book 
 of physics. Appreciate that it applies only when the reflecting sur- 
 face is very small as compared with the radius of curvature. It shows 
 you that object and image always have a constant relation to each other 
 such that for each position of object there is but a single position of 
 image. The formula you will see is the same as the one given under 9. 
 The same fundamental laws underly both reflection and refraction. 
 
 Note 4. "What is the relative position of object and the imag& 
 formed by reflection at a plane surface? Can a real image be formed 
 by a plane mirror? Why or why not? Under what conditions does a 
 concave mirror form a real image? Construct a figure to determine- 
 the size and location of an image of a given object. (Employ, from the 
 two end points of the object, rays parallel to the axial ray and rays- 
 passing through the center of curvature) . 
 
 Note 5. Make a diagram locating the principal point and center 
 of curvature. Take cognizance of the law of sines and locate the- 
 principal foci. There are two, one in each medium. Their location is 
 determined by the radius of curvature and the indices of refraction of 
 the two media concerned. The principal focal distances are propor- 
 tional to the indices of refraction of the two media as is shown in the 
 following derivation of the formula P' -v- f + P" -7- f" = 1. Choose- 
 one conjugate focus and locate the second. 
 
94 
 
 Derivation of F' -=- f + F" -=- f" = 1. (Adapted from Tigerstedt.J 
 In figure 22, o is a point without the principal focus, the rays proceed- 
 ing from which are refracted at the spherical surface whose center of 
 -curvature is C. Ray ov which passes through C is unrefracted; ray 
 
 Fig. 22. 
 
 •oa, any other ray, is refracted (according to the law of refraction) 
 and point i is the conjugate image-point of o. With the radius and 
 normal ca, the incident and refracted ray forms the angles a and p. 
 In triangles CAO and CAI, 
 
 Si n, \_oac oc 
 W SinTL^r = ~^ and 
 
 . . sin. LP _ _EL ("Law of Sines" in trigonometry; the sides 
 v ' sin. \_aic ac ' 
 
 «of a triangle are proportional to the sines of. the opposite angles), but 
 
 \_a = 180° — \_oac, and sin \_oac f= sin ]_a (Trigonometry). 
 
 Dividing (1) by (2)*ind since oc = f + r and ic = f" — r, and 
 
 ac = r, — ™ - 
 
 sin La sin \_aic f -\-r. 
 
 (3) 
 
 sin L^ jin \aoc f — r. 
 
 sin La n" sin \-aic sin \-aio ao. 
 
 Slnce sTn~T^ = V and sin \-aoc = sin Laoi == ~ai.' ' 
 
 {V n' ai f" — r. 
 
 If we consider only a small part of the spherical surface, in other 
 words, take av relatively small in proportion to the radius of curva- 
 ture, ao will approach f and ai t", and may be considered as equal to 
 :them t]ien 
 
 n" V _ V + i. 
 (5) n , f „ — f „ _ r 
 
 Multiply by the denominator and divide by f I", gives 
 
 //:■. — i — 1 r- which shows that o and i are con- 
 
 \°> fi t pi — r 
 
 jugate points, for eacli value of f there is but one value of f". If now 
 f be taken as infinitely large you obtain the second principal focal 
 •distance, 
 
95 
 
 (7) ^; = and'F" = " r , In the same manner f" being 
 
 t t n" — n' ' 
 
 infinitely large, P' =• "' r , > 
 n"-n' (8 >- 
 
 The principal foci depend upon the radius of curvature and the in- 
 dices of refraction. Multiplying (6) by r is obtained 
 
 n" — n' 
 
 . . n' r 1 n"r 1 
 
 ( 9 ) n " _ n / " {>' + n n „/ ' ~pr,= 1 an<i substituting F' and F" for 
 
 F' F" " 
 
 their values, (10) -p- + ,„ = 1. 
 
 Dividing (8) by (7), there is obtained the equation Zl _?!_ 
 
 F" - n" ' 
 The principal focal distances are proportional to the indices of refrac- 
 tion of tne media. 
 
 Note 6. The laws governing the refraction of rays of light eman- 
 ating from point o apply as well to any other point, and if it is 
 equally distant (e. g., s.) from the center of curvature, C, its image point 
 will also lie at an equal distance behind C and the surface of refraction. 
 An object made up of points lying in a spherical surface with its 
 
 Fig. 23. 
 
 center at C will have its image occupying also part of a spherical sur- 
 face with its center at C. The size of object and image are in direct 
 
 proportion to their distance from the center of curvature; _££___!?£.. 
 
 i/i ic 
 oc and ic ne can represent by letters g' and g". g' = f + r and 
 g" = f" _ r . 
 
 The usual method of constructing object and image (Note 4), may 
 be applied to refraction at a spherical surface only in certain cases, 
 it being of course often impossible to draw a line parallel to the optical 
 axis. (Why?) 
 
 Consider a case of refraction at a spherical surface and starting 
 with the object at infinity in the first medium, move it in through 
 the principal focus, principal point (vertex), center of curvature and 
 second principal focal point, to infiinity in the second medium and 
 
9 6 
 
 follow the changes in size and location of the image. At two points 
 object and image will be found to coincide. These points are the 
 Principal Point and the Center of Curvature, which is called the Nodal 
 Point. Refraction take® place at the Principal Plane. All rays passing 
 through the nodal point are unrefracted. 
 
 Note 7. If instead of a single spherical refracting surface there is- 
 a series of concentric spherical refracting surfaces the course of the light 
 is rendered very complex, it (being refracted at each successive surface. 
 However, no matter how many the refracting surfaces the laws estab- 
 lished for refraction at a single surface and the formation of an image 
 hold good here. There are two principal focal points (Fig. 24); for 
 
 Fig. 24. 
 
 each position of object there is a single position of image; but instead 
 of a single nodal point, principal point and principal plane conjugate 
 points and planes may be determined, related to each other as object, 
 and image, and may.be made use of in locating the image. The Princi- 
 pal Focal Points, Principal Points, and Nodal Points constitute the six 
 Cardinal Points of the system. To the principal planes is referred all 
 the refraction; a ray which in the first medium seems to pass through 
 a point in the first principal plane, in the last medium appears to come 
 from the corresponding (conjugate) point in the second principal plane. 
 From the principal point the principal and conjugate focal distances 
 are measured. 
 
 The Nodal Points are optical centers. A ray of light which in 
 the first medium appears to pass through the first nodal point, in the 
 last medium appears to come from the second nodal point and its 
 course is parallel to that in the first medium. From the nodal points, 
 distances of object and image are measured. 
 
 Figure 24 shows the use of these cardinal points in the construc- 
 tion of object and image. From it, by the method of similar triangles- 
 
 (Geometry) it can be shown that the formula 
 
 F 
 
 + 
 
 f" 
 
 = 1 holds as. 
 
 in the case of a single refracting surface. 
 
 Note 8. Lenses are optical systems in which the first and last of 
 three (or more) madia are the. same and usually of less refractive 
 
97 
 
 index than the second medium, the distance between the refracting 
 surfaces being less than the radii of curvature. 
 
 The focal distances therefore "are the same and the equation 
 becomes 1 -i- f + 1 v f = 1 + F. (F" = P" = F.) 
 
 In the biconvex and biconcave lenses, the nodal points have fused 
 with the principal points. Usually lenses are regarded as relatively 
 thin so that the principal (nodal) points may be reduced to one and 
 called the Optical Center. 
 
 Note 9, The shorter the focal distance the greater the refracting 
 power of a lens. The refracting power varies then with the reciprocal 
 of the principal focal distance, 1 -r- F. The power of a combination 
 of lenses is the sum of the reciprocals of their principal focal distances 
 .as expressed by the equation 1tF + 1tF' = 1t F"', which may 
 be easily derived from the formula 1 -r- V + 1 -r f" = 1 — F. Can 
 .you show this to be so? 
 
 The Diopter. Since the power of a lens increases by the 
 reciprocal of the principal focal length and may be represented by 
 it, and since the power of a combination of two (or more) lenses 
 is the sum of the reciprocal focal lengths, it is customary to take 
 the reciprocal focal distance, under the name Diopter as the unit of 
 measurement. Thus, a lens with one meter principal focal distance 
 16 a lens of I diopter, (i -f- I = l). A lens of 2 meters principal 
 focal distance is a lens of y 2 diopter and a lens of l / 2 meter P.F.D a 
 lens of 2 diopters, etc. 
 
 Experiment 105. By means of a gas flame, a metric scale and a 
 piece of ground glass, test up the value of the lenses given you by 
 finding the conjugate focal distances. Remember that object (gas 
 flame) and image are related as given in the formula I -=- f -f- 
 i -i. f" = i -h F. From this the P.F.D. can be calculated and its 
 value in diopters found. 
 
 Combinations of I/enses. In accordance with the 
 last formula I -f- F' + i -=- F" = I -f- F", to find the value of com- 
 binations of lenses, we simply add (or subtract if the lens is concave) 
 their diopters. 
 
 Test as in the experiment above the value of the following com- 
 binations : 5 D and io D, 6 D .and 4 D. A concave lens of 5 D and 
 a convex lens of 10 D. A concave lens of 20 D and a convex lens 
 of 15 D. As indicated above, concave lenses may be determined by 
 
9 8 
 
 combining them with a stronger convex lens. Determine the value 
 of the concave lenses given you. 
 
 The Schematic Eye. 
 
 The laws of optics considered above find immediate application 
 to the conditions in the human eye. 
 
 The Optical Constants of the Eye, which determine 
 the refraction and formation of the image, are: — 
 
 (a) The indices of refraction of the different media, 
 
 (b) the radii of curvature of the different (chief) refracting 
 surfaces, namely, I . the anterior surface of the cornea, 2. the anterior 
 surface of the lens, and 3. the posterior surface of the lens. 
 
 (c) The distances these refracting surfaces are apart also 
 modifies the result. 
 
 The Cardinal Points might be determined from the 
 optical constants by a somewhat complicated calculation ; they are ( see 
 fine print above), (1) The Principal Foci, (2) The Principal Points 
 (and Principal Planes), and (3) The Nodal Points. The eye, it 
 should be remembered, in accommodation for near or far vision, 
 changes its optical constants and hence the cardinal points also change 
 their position. 
 
 The following distances in millimeters will. 'help you in locating 
 the cardinal points of the schematic eye. The point from which the 
 measurements are taken is where the principal axis cuts the anterior 
 corneal surface. As taken for distant vision : — 
 
 The anterior principal focal point, — 13.75 mm. 
 
 The posterior principal focal point 22.79 mm - 
 
 The first principal point, 1.75 mm. 
 
 The second principal point, 2.09 mm. 
 
 The first nodal point, 6.95 mm. 
 
 The second nodal point, 7.29 mm. 
 
 (Schenk) 
 
 Experiment 106. With the following dimensions assumed as 
 normal, make a diagram, magnified 4 times (x 4) locating the car- 
 dinal points and optic axis of the eye. 
 
 ( 1 ) The Anterior-posterior diameter of the eye 24.0 mm. 
 
99 
 
 (2) Distance, upon the optical axis, of the anterior 
 
 corneal surface from the retina 23.0 mm.. 
 
 (3) Distance from the anterior corneal surface to 
 
 the anterior surface of the lens, 3.6 mm.. 
 
 (4) Distance from the anterior surface of the cor- 
 
 nea to the posterior surface of the lens, 7.2 mm. 
 
 (5) Thickness of the cornea, 1.0 mm. 
 
 The Reduced Eye. 
 
 Experiment 107. Make a second diagram, also X4, but indi- 
 cate a single principal plane, a single principal point and a single 
 nodal point, locating them half way between the first and second. 
 
 Experiment 108. The Formation of a Real Image by 
 the Eye. Construct in accordance with the rules of optics,, 
 a figure showing the course of rays of light from a distant object 
 to form an image upon the retina. 
 
 Experiment 109. Refraction in the Eye Accommo- 
 dated for Near Objects. Make a diagram also X4, show- 
 ing the course of light from an object 40 centimeters distant 
 through the eye to the image on the retina. When the eye is accom- 
 modated for near objects, the anterior surface of the lens is approxi- 
 mately 0.4 mm. nearer the cornea, the posterior principal focal point 
 is located at 20.95 instead of 22.79, the anterior principal focal point 
 is — 12.132 instead of — 13. 75, while the nodal point (in the reduced" 
 eye) is at 6.76 instead of 7.12. The principal plane is about 1 mm. 
 nearer the lens. 
 
 The Formation of an Image on the Retina. 
 The Regions of the Retina Sensitive to I*ight. 
 
 Experiment no. Direct your attention to a page of printed 
 matter and note that when you are looking at a particular letter and 
 it is distinctly seen, neighboring letters and words, though seen, are 
 not distinct and in order to see them distinctly, you must turn your 
 eye and "look at them," i. e., have their image fall on the fovea 
 centralis in the macula lutea. There exists, then, direct (when the 
 image falls upon the fovea) and indirect (other parts of the retinal 
 field) vision. 
 
loo 
 
 The Visual Axis makes an angle of about 3.5 degrees in the 
 -vertical and 3.5-7 degrees in the horizontal, with the optic axis of the 
 eye. 
 
 The Blind Spot. Draw upon a piece of white card board a 
 black disc about one-half inch in diameter and about 6 inches from 
 it, make a cross % inch square. Hold the card about 1 foot from 
 the eye and fix the cross (i. e., look at it). Move the card nearer or 
 farther away until the black disc disappears by its image falling upon 
 the blind spot. 
 
 Experiment 111. The Fields of Vision. The Peri- 
 pheral Extent of the Available Sensitive Retina. By 
 
 means of a perimeter, map out carefully for both eyes the 
 visual fields for white, red, yellow, blue and green. Compare the 
 extent of the visual fields upon the temporal and nasal sides and for 
 the different colors. 
 
 Experiment 112. The Sensative I<ayer of the Retina. 
 Purkinje'S Figures. In a dark room, by means of a 
 biconvex lens of moderate power (18 D) concentrate the light upon 
 the sclera as far from the corneal margin as possible and attempt at 
 the same time to shade the pupil of the eye. To do this best, have 
 the one experimented upon look inward toward the nasal side and 
 -concentrate the light from the temporal side. Either immediately 
 or upon moving the lens slightly there will be seen the branching of 
 the blood vessels which course in the inner layer of the retina. This 
 shows that the sensitive layer lies outside the layers containing the 
 "blood vessels. By means of careful measurements of the relative 
 •change of position of the projected image of the blood vessels upon 
 moving the lens which concentrates the light, the distance that the 
 .sensitive layer must be from the blood vessels has been calculated. 
 The circulating blood in the retina may be shown by a simpler experi- 
 ment. 
 
 Experiment 113. Look through light blue glass at the sky and 
 there will be observed numerous bright spots that come and go. By 
 confining the vision to one spot, it will be found that these bright 
 points recur in the same position. They are due to the temporary 
 dogging of the blood vessels ( ?) by the blood corpuscles as thev 
 
101 
 
 pass through them casting their shadows upon the sensory layer of 
 the retina. 
 
 In the fovea centralis practically only cones exist so^ that the 
 sensitive layer must be the rods and cones. The existence of the 
 blind spot shows that the nerve fibers themselves are insensitive to 
 light. 
 
 Experiment 114. In Order that Two Points in an 
 Object be Distinguished, their Images must Stimulate 
 Two Sensory Elements. Place a card with two lines 
 a millimeter thick and a millimeter apart in a well lighted place 
 upon the wall ; cover one eye and by walking backward and for- 
 ward find the position at which you can just resolve the lines. Repeat 
 the experiment using lines two millimeters in diameter and two 
 millimeters apart. From the distance the lines were from your eye 
 (more exactly stated, the nodal point), and from the distance of the 
 nodal point from the retina, calculate the size of the image of tJke 
 two lines upon the fovea of the eye (Fig. 23). Make a diagram 
 illustrating the experiment. The diameter of a cone in the fovea 
 centralis is given at 2-5 //. 
 
 The Visual Angle. This is the angle subtended at the 
 nodal point by axial rays from the extreme points of an object. 
 From the. experiment above, compute the least visual angle whidb two 
 points can subtend and be distinguishable. If your eyes are normal, 
 it will be found to be 1' or less. 
 
 Test Charts for Visual Acuity are usually based upon a normal 
 visual angle of 1'. Such 'are the Snellen charts. Here the letters 
 are of such a size that at the distance at which normal eyes can 
 distinguish them they subtend angles of 5' while their component 
 lines and spaces subtend 1' angles. 
 
 Experiment 115. Place a Snellen or oitflver test chart upon the 
 wall in a well-lighted place and walk towards it from a distance until 
 you can clearly read the letters which should be read at 16 or 20 feet. 
 Is the distance at which you can read these letters greater or less? 
 Test it for both eyes, one at a time. There is more involved here 
 than the simple acuity of vision, however, and we must first consider 
 the optical defects of the eye. 
 
102 
 
 THE OPTICAL DEFECTS OF THE EYE. 
 
 (a) Lost light and Images by Reflection. Tscherning com- 
 putes, that only 3% of the light is lost and six extra images are 
 formed, of which two only, representing about 2-100,000 of the 
 total light would fall on (or near) the retina. 
 
 (b) In an "Ideal Eye," the visual axis and optical axis would 
 be the same. In our eyes they are as has been stated different axes. 
 'Further, the optical axis of the cornea and the lens do not coinside, 
 so that the eye is not a uniaxial system. 
 
 (c) Spherical Abberation. This is partly corrected by (a) the 
 optical refraction of the different layers of the lens, (b) the con- 
 striction of the pupil, '(c) the fact of direct (foveal) vision. 
 
 (d) Chromatic Abberation. This exists, as may be shown by 
 the following experiment: 
 
 Experiment 116. (a) Look at the sky with the window frame 
 in the field of vision. Pass a card before the eye with the edge par- 
 allel to the window frame. If the card is passed from below upwards 
 when it has covered about half the pupil, the frame will appear bor- 
 dered with blue. If the card is passed from above downward, the 
 border will be red. 
 
 (b) Look at an incandescent filament of an electric light. 
 Pass a card across the pupil with the edge parallel to the filament. 
 When the edge of the card nearly covers the filament, it is seen to 
 have a red fringe on the side toward the card and a blue fringe on 
 the other side. 
 
 Experiment 117. (von Bezold's). Place a card with black 
 lines a millimeter wide and a millimeter apart about two feet away 
 and focus on the head of a pin 'held about 8 inches away. The lines 
 will appear greenislh^yellow and the spaces dark red. 
 
 (e) Defects of Refraction. It is assumed as normal that when 
 the eye is at rest, — not accommodating, — parallel rays of light come 
 to a focus upon the retina ; the eye is then adapted for seeing objects 
 at a distance. Such eyes are termed Emmetropic. Eyes in which 
 
 .paraliel rays of light are brought to a focus before the retina are 
 spoken of as myopic; those in which parallel rays of light would 
 r.oive to a focus behind the retina, hyperopic or hypermetropic. 
 
103 
 
 Experiment 118. Make diagrams of emmetropic, myopic, and 
 hyperopic eyes, indicating (a) the point where parallel rays ;of. light 
 would come to a focus, (b) the course rays of light must . haveiin 
 the three types of eyes, to come to a focus upon the retina, accommo- 
 dation being lacking. 
 
 ACCOMMODATION. 
 
 This is the power of altering the refraction of /the eye so that 
 objects at different distances may yet. produce images that fall ttpon 
 the retina. Of the three possible ways in which it might; be ; accom- 
 plished, two only are practical and are found in the Vertebrates. 
 In ourselves it is accomplished by increasing the refraction of ;the 
 eye by changing the convexity of the lens. • ■' •''" 
 
 Experiment up. The Anterior Surface of the I^ens 
 Advances in Accommodation. Have the person experi- 
 mented upon stand in a good light near a window and 
 look at the eye from the side so that the pupil can just be seen when 
 the eye is looking at a far object. Have the person then without 
 moving change the focus to a near point. Usually the pupil becomes 
 visible due to the pushing forward of the edge of the ' iris by the 
 change in the anterior surface of the lens. 
 
 Experiment 120. The Anterior Surface of the I^ens 
 Becomes more Convex in Accommodation. By means 
 of a phakoscope demonstrate that the lens becomes more 
 convex when the eye is accommodated for a near object. Under- 
 stand the experiment. 
 
 Experiment 121. Dispersion Circles. Hold a piece 
 of wire gauze about 25 centimeters before the eyes and look at.it, 
 then through it at some object out the window. The wires arid 
 their intersections which before were sharp are now blurred. When- 
 ever an object is not in focus, the points of light which make up the 
 sharp image are sections of cones and appear as circles which over- 
 lap causing vagueness of detail and outline. 
 
 Experiment 122. The Range of Accommodation : 
 Far Point; Near Point. When the ciliary muscle is re- 
 laxed the emmetropic eye is adjusted for far vision. The far point 
 may be regarded as infinitely remote, i. e., the rays of light are prac- 
 
104 
 
 tically parallel. In practice, however, 20 feet (6 meters) or more 
 may be taken as a normal distance for the far point. (Why?) The 
 Myopic eye will have a far point relatively nearer than Ithe normal 
 distance while the hyperopic eye even when looking at a far object 
 will still be accommodating. The far point in such an eye will be a 
 virtual one and lie behind the eye and have a negative value. 
 
 By means of letters of the correct size, (i. e., those that subtend a 
 visual angle of 4-5' at 20 feet (more or less) determine for each eye 
 separately the distance at which these letters can be read. Hyperopic 
 and emmetropic eyes require a further test. If the letters can still 
 be read at 20 feet or a greater distance, place before the eye a bicon- 
 vex lens of 1 D. Are the letters still distinct? If so, substitute a lens 
 of greater power until one is found with whidh they can still be 
 distinctly read. If your eye is hyperopic this lens so determined gives 
 you' the degree of manifest far-sightedness and also permits you to 
 locate the far point. (How?) 
 
 The Near Point. With letters which subtend an angle 
 of about 5' at about 25 centimeters find the near point. Move the 
 letters toward the eye until a point is reached where they are no 
 longer sharp due to the dispersion circles. Measure the distance 
 ■ from the point so found to the eye ; it represents the distance of the 
 near point. 
 
 The Range of Accommodation. The far point 
 and the near point having been determined for each eye, find the 
 range of accommodation by subtracting the near distance (p) from 
 the remoter distance (r). 
 
 The Change in the I,ens in accommodation is found 
 according to the following formula for subtracting lenses: i-=-A = 
 i-*-P — i-^R. This formula is directly applicable to the myopic 
 eye. In the emmetropic eye the distance R is infinitely large and 
 i-=-A = i-=-P. In the hyperopic eye where R is negative (Exp. 118) 
 
 the formula becomes ih-A = i-=-P — (1 -. R), or i-=-A = ih-P 
 
 + i-f-R. Determine the value of the change of the eye in Diopters' 
 for each eye. 
 
 Experiment 123. The Determination of the Degree 
 of Myopia or Hyperopia and their Correction. Test 
 one eye at a time by means of a reading chart. At a 
 
distance of 16-20 feet, look at the letters that should be distinctly 
 read at that distance. If they are indistinct the eye is myopic (pos- 
 sibly astigmatic). Place before the eye a biconcave lens of 1 D. Are 
 the letters seen more clearly? Replace this by a lens of 2 D. Re- 
 sult? Proceeding in this way, find the weakest lens which will 
 render the letters distinct ait the proper distance. It indicates the 
 grade of myopia. If the letters are seen clearly at the specified 
 distance, the eye is either emmetropic or hyperopic. Place before the 
 eye a biconvex lens of 1 D. Oan the letters still be clearly seen? 
 Test different lenses choosing the strongest one which will still 
 permit the letters to be clearly seen at the proper distance. This lens 
 indicates the degree of manifest hyperopia. If no such lens can be 
 found the eye is emmetropic. 
 
 When the refraction of the eye is such that all the rays of 
 light from a point cannot be brought to a focus in a point, whether 
 on the retina or not, the eye is astigmatic. In a system of lenses 
 three forms of astigmatism are possible (a) one due to the refracting 
 surfaces not being spherical, (b) due to the refracting surfaces not 
 being centered on the same axis, (c) when rays of light fall upon a 
 spherical surface obliquely. Of these three ways the first is the usual 
 form occurring in the eye and in by far the majority of cases the 
 corneal surface is the one of irregular or unequal curvature. A small 
 degree of corneal astigmatism seems to be present normally. In addi- 
 tion a certain amount of irregular antigmatism occurs. When the 
 astigmatism is due to greater or less refraction in meridians at right 
 angles to each other the astigmatism is said to be regular. In most 
 cases they are horizontal and vertical. The result of astigmatism is 
 that all the rays of light cannot be brought to a focus upon the retina 
 at the same time. Consult the model and be able to illustrate by 
 diagrams. 
 
 Experiment 124. The Recognition of Regular As- 
 tigmatism. Employ a figure made up of radiating rays and 
 test each eye. Look at the figure near to and from a greater distance. 
 If your eyes are markedly astigmatic the rays corresponding to the 
 meridians of lesser curvature will become indistinct while at the far 
 point the lines coinciding with the meridian of greater curvature will 
 be vague. 
 
io6 
 
 , Note which these are and whether the astigmatism is regular, — 
 k'e., the planes at right angles and whether fey are vertical ' and' 
 horizontalor' inclined at an angle to the horizontal. 
 
 1 'Examine other charts and figures for detecting astigmatism. 
 The constant change of accommodation and the play of the fixation 
 point over the chart 'prevents a close test of the degree of astigmat- 
 ism. The power of accommodation must first be removed by means 
 of 'atropine or homatropine before the degree can be determined. 
 The method of skiascopy (see below) also is employed for the detec- 
 tion 'and the determination of astigmatism. The astigmatism due 
 to corneal irregularities when of considerable degree, can usually be 
 detected by means of so simple an instrument as the Keratoscope. 
 
 THE CLINICAL EXAMINATION OF THE EYE. 
 
 The methods here considered, Opthalmoscopy and Retinoscopy 
 (or Skiascopy) depend upon the fact that light reaching the fundus 
 of the eye is not all 'absorbed but is or may be reflected. 
 
 ' Ophthalmoscopy. If the reflected rays of light can 
 be brought to a focus again upon the retina of an observer's 
 eye ; , details of the fundus of the observed eye can be seen. The prin- 
 ciple of the construction of the ophthalmoscope and the manner of its 
 use should be well understood. Two methods are available, the 
 direct artd the indirect method. Understand the principles of these. 
 The Refraction of the eye, whether myopic, emmetropic or hyperopic. 
 in bbth the observer and the observed is an important factor in the 
 use of the ophthalmoscope. Be able to make diagrams showing that 
 this is the case. This is especially true for the direct method of 
 ophthalmoscopy. 
 
 Experiment 125. With the above well in mind, examine suc- 
 cessively (a) the eye of an albino rabbit, (b) the eye of a cat, and 
 (c) the eye of a gray or brown rabbit. The method should be per- 
 severed in until the fundus is seen. In the albino rabbit the rich 
 network of choroideal vessels is easily distinguished. The bapetum 
 and entrance of the optic nerve should be sought out in the eye of 
 the cat! In the rabbit the myelinization of the optic nerve fibers 
 extends out some distance onto the retina, — a condition occurring in 
 us only as an abnormality. 
 
107 
 
 Experiment 126. The Fundus of the Human Eye. 
 
 Figures showing what may be seen by the ophthalmoscope are to 
 be found in several text books which are available. Examine these 
 paying attention to the macula lutea, the veins and arteries, and the 
 entrance of the optic nerve. It is the last which you should seek 
 to find. 
 
 In the manner shown you, employing preferably the indirect 
 method of ophthalmoscopy, seek to see the entrance of the optic nerve 
 in the eye of the person examined. A little perseverance will result 
 in your gaining a good view. 
 
 The importance of the method in general diagnosis and in the 
 special ophthalmological work, cannot be emphasized here. The 
 static defects of refraction in the eye (myopia, hyperopia, and astig- 
 matism) may be detected by means of the ophthalmoscope. The 
 determination of the degree, however, belongs under the method of 
 retinoscopy or sciascopy. 
 
 Sciascopy. Proposition 1. If an eye is myopic and the 
 reflection from a plane mirror be allowed to play across the pupil, . 
 the reflection from the fundus of the eye will move in a direction 
 opposite to that of the mirror, — provided the mirror is beyond the 
 focus of the eye observed. If the mirror is within the focus of the 
 eye, the reflection from the fundus moves with the reflection of the 
 mirror. (Why is 'this true? Diagram it). 
 
 Proposition II. If an eye is emmetropic or hyperopic and the 
 reflection from a plane mirror be allowed to play across the pupil 
 the reflection from the fundus will move in a direction coincident 
 ■with that of the mirror (Why? Diagram it). 
 
 Proposition III. Since with the myopic eye the movement of 
 the reflection from the fundus changes when the mirror passes the 
 focus of the eye, it is possible to locate the focus and determine the 
 •degree of myopia in the eye observed. 
 
 Proposition IV. A biconvex lens of known D. may be placed 
 before the hyperopic or emmetropic eye and the focus determined of 
 the short-sighted combination so formed (Prop. III). By subtract- 
 ing the value of the lens, the degrees of hyperopia may be deter- 
 mined. 
 
io8 
 
 The details of the fundus can be made out more or less clearly 
 if the eye is hyperopic; if it is emmetropic, details cannot be dis- 
 tinguished. If a concave mirror be employed, the movement is 
 reversed in each case. The method may also be employed for the 
 detection of astigmatism and the determination of the degree and 
 the angle of axis. 
 
 Experiment 127. In the manner shown you, examine the eyes 
 of short-sighted, far-sighted and normal persons and confirm propo- 
 sitions I and II. The use of the mirror for determining the degree 
 of short-sightedness or astigmatism, involves practice, experience 
 and the skill acquired thereby, and it cannot be applied in this course. 
 
 IV. THE "PSYCHO-PHYSIOLOGY" OF VISION. 
 
 So far, in the work outlined in the schema given on pages 91 and 
 92, you have only considered the eye as an optical instrument, its de- 
 fects and its examination. Of the remaining divisions covering the 
 physiology of vision, most of the points are better illustrated by spec- 
 ial demonstration than in independent laboratory work. Many feat- 
 ures you can demonstrate for yourselves at home. It would be advan- 
 tageous for all who can to take an elementary course in Psychology. 
 If this is impossible, much help would be gained by working over 
 in connection with the physiology of sensation, the corresponding 
 portions of Titchener's Elements of Psychology or his Primer of 
 Psychology. 
 
 COLOR VISION. 
 
 Experiment 128. The Grays. By means of the color- 
 mixing apparatus, and a black and white disc, obtain on rotation 
 a series of grays between black and white by changing the rela- 
 tive proportions of black and white exposed. 
 
 Experiment 129. Shades. Substitute for the white disc, 
 successive red, yellow, green, blue discs and mix the sensation in 
 each case with black, varying the relative amounts of color and black. 
 Results. 
 
 Experiment 130. Complementary Colors. For each 
 spectral color sensation, there can be found another spectral 
 
109 
 
 color sensation which when mixed with it in the right proportions 
 produces the sensation of white. Consult a table giving such com- 
 plementary colors. Try the following combinations and find tie 
 proportions in which they must be mixed to produce a sensation ot 
 white (gray). 
 
 (a) Red and bluish green. 
 
 (b) Yellow and blue. 
 
 (c) Violet and Yellow-green. 
 
 Other complementary combinations might be tried. 
 
 Experiment 131. Neighboring Spectral Colore 
 
 when mixed give intermediate color-sensations. Mix (a) Red and 
 Yellow, (b) yellowish and bluish green, (c) green and violet. Re- 
 sults. By varying the amounts of each,, all intermediate spectral 
 colors may be produced. 
 
 Experiment 132. The End Colors of the Spectrum 
 
 when mixed produce Purples. Mix varying proportions of Red and 
 Violet. Purples varying from a red purple (carmine) to a bluish 
 purple result. 
 
 Since groups of complementary colors may be taken, a sensa- 
 tion of white (gray) may be produced by mixing a large number,, 
 as in the ordinary day light, thus red, orange, yellowish-green,, 
 bluish-green, indigo violet, would, in the right proportions give rise 
 to a sensation of gray. 
 
 Experiment IJJ. Mix red, green and violet, varying the pro- 
 portions until a gray results (about 80 parts R, 124 parts G, and 157 
 parts V). 
 
 The complementary color of green is purple (R and V). Can you 
 mix green and violet in proportions to produce intermediate colors? 
 Red and green? A few (3 or 4) color sensations may be chosen 
 by whose mixture the entire range of spectral color sensations and 
 the purples may be produced. Again, mixtures with white or black 
 will produce all tints and shades. The grouping of colors as com- 
 plementary is fundamental in our sensation of color, as indicated 
 by color induction. 
 
no 
 
 INDUCTION. 
 
 Experiment 134,- Simultaneous Contrast. Place 
 -a gray paper strip or figure upon two adjacent fields of comple- 
 mentary colors, and cover it with a piece of lens paper. Result. 
 How would you attempt to explain it? Repeat with other groups of 
 -complementary colors. 
 
 Experiment 135. Successive Contrast. In a mod- 
 erately bright light look for a minute steadily at a colored disc upon 
 a white surface and then turn the eye so as to look at the white 
 surface and note the color and the persistence of the after-image. 
 
 Try the above experiments with black and white. Review the 
 simple experiments on color vision and contrast from the standpoint 
 •of Thepries of Color-Vision. 
 
 THE FUNCTION OF THE RODS AND DIM LIGHT VISION. 
 
 Experiment 136. Purkinje's Phenomenon. Choose 
 
 by day light a red and a blue which seem to you of equal intensity 
 of brightness, or have the red, if anything, the brighter of the two. 
 Take them into a room so dimly lighted that at first you can see 
 nothing. When your eye has become adapted to the dim light, look 
 at the red and the blue discs. Which is now the brighter? Do you 
 Tiave a sensation of color? Von Kries' explanation of the phe- 
 nomenon. 
 
 Examine a large number of spectral colors arranged in the order 
 of the colors of the spectrum. Pick out the color that appears the 
 brightest in ordinary daylight. Take the series into a dimly lighted 
 room and after adaptation has been obtained, pick out the segment 
 that is the brightest. Did you have any sensation of color ? Which 
 part of the spectrum is the brightest in dim light ? 
 
 Experiment 137. Direct Vision in Dim I/ight. Of 
 the many facts which might be brought out in connecting the rods 
 with twilight vision, the following experiment alone will be tested. 
 
 Choose a spectral color paper of approximately the same tone 
 as that found in the above experiment to be the brightest in dim 
 light, and 'cut the discs of a size such that when placed at the distance 
 of a meter from the eye, the image will fall entirely on the fovea 
 
Ill 
 
 •centralis (Calculation of size ?). Fasten them on a dead black back- 
 ground at intervals of two or three inches. In a room so dark that all 
 sensation of color disappears, look at the discs, picking out one par- 
 ticular disc and looking at it with direct and indirect vision at a 
 ■distance of a meter. Result and its explanation. 
 
 COLOR BLINDNESS. 
 
 Experiment 138. Eash student should have his eyes tested 
 for color blindness by means of Holmgren's colored worsteds. All 
 -cases of red or green color blindness should be reported and carefully 
 tested. 
 
 BINOCULAR VISION. 
 
 The Eye Reflexes. 
 
 Experiment 139. The Pupil; Accommodation; Con- 
 vergence. The Observed should alternately look at a far object 
 
 and at a ringer held a few feet before the eyes, and the Observer note 
 Ihe changes in the pupil. Appreciate further the usual co-ordina- 
 tion of the iridal, ciliary and external eyes muscles employed in con- 
 vergence (which are they? wfcat is their innervation?). 
 
 Experiment 140. The Iyight Reflex. The Observer 
 •should place the Observed facing a window and should cover both 
 the eyes with his hands. Remove the hands quickly (changes in 
 the pupils). Cover again and then remove one hand. The above 
 •experiment can to advantage be repeated in the dark room, the eye 
 being alternately shaded and illuminated by means of a biconvex 
 lens, and the changes in the pupil carefully recorded. 
 
 Experiment 141. The Consensual Reflex. Repeat 
 
 the experiment above, shading but not covering one eye and alter- 
 nately covering and exposing the second eye, at the same time observ- 
 ing the changes in the pupil of the first (shaded) eye. 
 
 Understand the relation of the paths and centers employed in 
 ■carrying out these important eye-reflexes.