itiTni?iTnin]if[niniTiiiU!inTiUT.i]iiiTintiir ,'m'i wwtamm mm» tt*' 9 i< » \'*m .w ' ! 'f\'' i wmwmt Mif \twp t-***»¥ V'»*'*o=-^ ESSENTIALS Of EXPERIMENTAL FIIYSIOKk;? BRODIE mnuiinTinimmintinnnntiir ^" CORNELL UNIVERSITY. 4^4 ; THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF "^THE N. Y. STATE VETERINARY COLLEQE. 1897 Cornell University Library QP 44.B86 The essentials of experimental physiolog 3 1924 001 040 413 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924001040413 EXPERIMENTAL PHYSIOLOGY A TEXT-BOOK OF CHEMICAL PHYSIOLOGY AND PATHO- LOGY. By W. D. Halliburton, M.D., F.B.S., M.B.O.P., Professor of Physiology in King's College, London ; Lecturer on Physiology at the London School of Medicine for Women. With 104 Illustrations. Svo. 285. ESSENTIALS OP CHEMICAL PHYSIOLOGY. By W. D. HAiiiBURTON, M.D., P.B.S., M.E.O.P., Professor of Physiology in King's College, London ; Lecturer on Physiology at the London School of Medicine for Women. Svo. 5s. *,jf* This is a book suitable for medical students. It treats of the subject in the same way as Prof. Schafbb's * Essentials ' treats of Histology. It contains a num- ber of elementary and advanced practical lessons, followed in each case by a brief descriptive account of the facts related to the exercises which are intended to be performed by each member of the class. AN INTBODUCTION TO HUMAN PHYSIOLOGY. By Augustus D. Waller, M.D., Lecturer on Physiology at St. Mai'y's Hospital Medical School, London ; late. External Examiner at the ^Victorian University. Third Edition, Revife^tJ.i ■'With^Sf4|Ilfustrations. '8voi ^ISs.; f 'i "■ ■ ' ' ■■: LECTURES ON PHYSIOLOGY. By Augustus D. Waller, M.D., Lecturer on Physiology at St. Mary's Hospital Medical School, London ; late External Examiner at the Victorian University, First Series. On Animal Electricity. Svo. 5s. net. EXERCISES IN PRACTICAL PHYSIOLOGY. Part I. Elemen- tary Physiological Chemistry. By Augustus D. Waller and W. Legge Symbs. Svo. Is, net. Part II. in the press. Part III. Physiology of the Nervous System ; Electro-Physiology. Svo. 2«. 6d. net. THE ESSENTIALS OP HISTOLOGY. Descriptive and Practical. For the Use of Students. By E. A. Schafeb, F.B.S., Jodrell Professor of Physiology in University College, London ; Editor of the Histological portion of Quain's ' Anatomy.' Illustrated by more than 300 Figures, many of which are new. Fourth Edition, Bevised and Enlarged. Svo. 7s. 6rf. (Interleavedj lOfi.) LONGMANS, GREEN, & CO., 39 Paternoster Row, London New York and Bombay. THE ESSENTIALS OF EXPERIMENTAL PHYSIOLOGY FOB THE USE OF STUDENTS BY T. G. BEODIE, M.D. LECTUBEB ON FHYSIOLOeY, ST THOMAS'S HOSFITAI. MEDICAI. SCHOOI. LONGMANS, GEEEN, AND CO. S9 PATERNOSTER ROW, LONDON NEW YORK AND BOMBAY 1898 All rights reserved PKEFACE In writing this book my aim has been to give a short account of those experiments which can be carried out by students during classes, together with a selection of experiments suitable for class demonstra- tions. In the selection of the experiments I have been largely guided by the course of Advanced Prfictical Physiology given by Professor Hallibueton at King's College, which was based upon the ' Syllabus of Lectures ' published by Professor J. Buedon Sandbeson in 1879, though in several respects I have modified and added to this course. The illustrations are for the most part new. For permission to reproduce several of the figures of instruments I wish to thank Professors McKbndeick, Yeo, Hallibueton, and Wallee. The source of these figures is indicated in each case. The reproductions of the tracings are aU new and taken from tracings specially prepared for the purpose. With very few exceptions they are all reproduced the same size as the originals, so that the measurements indicated in the text directly apply to the figures. Those modifications of many of the usual forms of apparatus figured in the text have been made for me by Mr. C. F. Palmbe, and are especially designed for class work. The plan of the book varies slightly from that adopted by Professor Schafbe and Professor Hallibueton in their ' Essentials.' I have VI EXPEKIMENTAL PHYSIOLOGY made use of three different types : a small type employed in describing apparatus or the method of carrying out an experiment ; a medium type forming the main body of the text ; and a heavy type used in the accounts of the more fundamental experiments which are fitted for elementary classes. It seemed better to mark off these elementary experiments in this way rather than to separate the book into an elementary and an , adv9,nced,, course. The number of elementary experiments given is only small, and a detailed list of them will be found on p. xiv. , To ]?rof esser BAtijiiiEH^ON and to ' Professor Scbafee my best tjianks. are due for the many suggestions and criticisms with whiph they have aided me. 'during the preparation of the book. To Dr. A. E. EussELL, Medical Registrar, St, Thomas's Hospital, I am especially indebted foi;' inariy valuable suggestions and alterations, and for his assistance in ireading and correcting, the proofs.. ' ■ ' T. G. BEODIB. St. Thomas's Hospitax, December 1897. CONTENTS CHAPTER I. II. III. IV. V. VI. VII. VIII. IX. X. XI. XII. XIII. XIV. XV. XVI. XVII. XVIII. XIX. XX. XXI. XXII. PAGE Some Physical Instkuments in Constant Use in PhysiologioaIi expekiments . . 1 Pkeparation op a Fbog's Muscle. Its Response to Stimula- tion. The Gbaphic Method 16 A Single Contraction of a Frog's Muscle. Its Modification UNDER Changes in the External Conditions . . 30 Summation op Muscular Contraction. Tetanus . . 56 Fatigue op Muscle . . 66 The Thickening op a Muscle on Contraction. The Muscle Wave 71 Independent Muscular Excitability. Excitation op Muscle by the Constant Current. Polarisation of Electrodes. . . 76 Some Experiments to Determine the Functions op Nerves . 85 Examination op the Fbog's Heart. The First Stannius Ligature 97 The Action op Heat and Cold upon the Frog's Heart . . 112 The Nerves op the Frog's Heabt and Their Functions . . 120 Action op Drugs upon the Frog's Heart 130 Some Further Methods foe Examining the Activity of the Frog's Heabt 134 Demonstration op the Movements of the Mammalian Heart. The Cabdiogbafh 138 Some Experiments in Electro-physiology 146 Schema op the Circulation. The Sphygmograph . . 157 Demonstration of Blood Pressure and its Nervous Eegulation 168 The Kidney. Demonstration of an Oncometer Experiment . 189 Demonstration of the Nervous Begulation of Bespibation. The Stethometeb and Pneumograph 201 Demonstration op the Secretion op Saliva from the Submaxil- laby Gland op the Dog 209 Eeplex Action as Studied upon the Spinal Cord op the Frog 214 Some Experiments in the Physiology of the Eye. Accommoda- tion, Ophthalmoscopy, Coloub Sense, Perimetry . . . 218 LIST OF ILLUSTEATIONS VIS. Plate I. Becobd of a Sebies of Sdccessive Twitches of A Htoglossus Muscle Stimulated, by Make Shocks, once EACH Second Tofacep. 70 Plate II. Becord of the Blood Pbessuke and Eespibation IN A Babbit dubinq Asphyxia „ 182 1. The Daniell Batteey (MoKendbick) page 2 2. The Gbenet Batteey (MoKendbick) 2 3. The Bunsen Batteey (MoKendbick) 3 4. The Gbove Batteey .... 3 5. The LECLANCnfi Batteey (MoKendbick) . .... 4 6. The Induction Coil (MoKendbick) .4 7. DiAOBAM op the Cuebents Induced in the Secondaby Coil . . 6 8. Abbangement of Appaeatus foe Equalising the Make and Break Shocks 7 9. To Illustrate the Action of Neef's Hammeb 8 10. To Illustrate the Action of Neef's Hammeb with the Helmholtz Modification 9 11. Two Forms op Mercury Key ]^ ^^ 12. Two Forms of Meecuby Key i 13. Simple Fobm of SpRma Key 10 14. Two Forms of the Du Bois Key 1 ,- 15. Two Forms of the Du Bois Key J 16. Plan of the Abbangement of the Du Bois Key as a Shobt-cibcuit- ING Key 11 17. Aebanged as a Simple Beeak Key. Not to be used aftee this Method in a Secondary Cieouit . . . . . . .11 18. Pohl's Commutatoe ; ... 12 19. A Fobm of Cut-out Key 13 20. Arrangement of Apparatus for Making Use of Single Induced Shocks 14 21. Arrangement of Apparatus to Show the Beeak Extba-oubbent . 14 22. Leg Muscles of the Frog seen from the Inner Side . . . . 17 23. Leg Muscles of the Frog seen from the Outer Side ... 17 24. Gasteocnemius-scutic Preparation 18 25. Abbangement of Appaeatus fob Showing Make Extba-cuerent . 19 26. The Belations of the Hyoglossus in the Frog 20 27. Two Records of the Vibeations op a Toning-foek Vibeating at the Bate op 10 pee sec 22 28. A TiME-MAEKEB OE Cheonogbaph (McKendrick) 23 29. A Spring Chronograph 24 30. Lower Part op Drum to show Method op Deiving the Cylindee at Diffebent Bates 24 X EXPERIMENTAL PHYSIOLOGY MS. PASE 31. Muscle held in Muscle-fokceps and attached to Simple Levek . 25 32. Simple Form op Wike Electkodes 26 33. Heights ot .Contraction, of a Muscle with Diffebent SskenGths of Stimuli ' . . 27 34. Maeet's Fokm of Eecordino Tamboub (McKendkick) .... 28 35. A Second Fokm of Eecokding Tamboub ... ... 29 36. A Break Key 30 37. Plan op the Aeeangement op the Appabatus foe Eecoeding a Simple Twitch 31 38. Isotonic Twitch op a Htoglossos Muscle 34 39. To Illustbate the Meaning op the Cubve of Fig. 38 . . . . 35 40. Simple Twitch op a Gastbocnemius . 36 41. Twitch op a Hyoglossus ^eooeded by a Heavy Levee . . . . 38 42. The Peinciple of the Isotonic Method ... . . 39 43. The Peinciple op the Isometric Method 40 44. Muscle Attached to an Isometric Lever 40 45. Three Isometric Twitches with Dipfeeent Initial Tensions . . 41 46. Aeeangement of Simple Levee foe Eecoeding by the Method op Aftee-load ............ 43 47. Twitches Taken undeb the Peinciple op Apier-loading . . . 44 48. Apparatus for Varying the Tempeeatubes of a Muscle by Immebsion 45 49. Twitches op a Hyoglossus at Diffebent Tempeeatubes ... 46 50. Twitches of a Gastbocnemius at Diffebent Tempeeatubes . . . 47 51. Twitches op a Hyoglossus with Diffebent Loads .... 48 52. Twitches of a Gastbocnemius with Diffebent Loads . . . . 48 53. Two Twitches given by a Muscle Poisoned with Veeateine . . 50 54. Wobk-diaqeam op a Gastrocnemius fob Single Twitches - . . 51 55. Simple Form of Pendulum Myograph 53 56. Teigger Key 54 57. Simple Twitch of Hyoglossus Muscle recorded by the Pendulum Myograph . . . . 55 58. Arrangement of Upper Part op Drum foe applying Two Stimuli to A Muscle 57 59. Effect op Two Successive Stimuli, with Geadually Diminishing Intervals, upon a Gastbocnemius 58 60. Mode of Fitting up a Vieeating Eeed 60 61. Eeed aeeanged to Vibbate in a Hobizontal Plane . . . .61 62. The Gradual Peoduction op Tetanus as the Bate op Stimulation was Inceeased 62 63. The Genesis of Tetanus with Slow Eotation op Eecoeding Sueface 64 64. A Seeies op Twitches op the Hyoglossus made to Contbact eveey half-second to show the ALIEB.iTION IN THE TwiTOH AS THE MuSCLE becomes Fatigued . . . .68 65. Prolonged Tetahisation op a Hyoglossus showing Eelaxation as THE Muscle became Fatigued 70 66. Method op Recording the Thickening op a Muscle as it Conteacts 71 67. Curve I the Shortening, and Curve II the Thickening of a Semi- membranosus AND GEAcn-is Preparation 72 68. Diagram to Illustrate Wave Movement 73 LIST OF ILLUSTRATIONS XI FIG, PAGE 69. Apparatus fob Becobding the Thickening op a Muscle ai Two Points, FOB THE PTJEPOSE OP STUDYING THE MuSOLE WaVE .... 74 , 70, The Thickening op a Muscle 75 .71. Method op Studying Polab Excitation of a Muscle .... 80 72. Method op Aebanging the Apparatus to Show Polarisation op Elec- trodes 82 73. Several Models of .Unpolabisable Electrodes (Waller) ... 83 74. Simple Form op Uijpolarisable Electrodes . . . .... 83 75. Plan op Apparatus fob Studying the Changes op Excitability op Electbotonus ■ . . .88 76. Diagram Indicating the Changes op Excitability of a Nerve in Electbotonus 90 77. To Illustrate the Principle op the Monochord . . . . 91 78. A Second Form op Monochord 92 79. The Eheochobd as Arranged for Varying the Direction and Stbenqth op a Current thbough a Nerve 92 80. Arrangement op Apparatus fob Studying the Velocity of a Nervous Impulse ............. 95 81. Two Twitches op a Gastrocnemius when the Sciatic was Stimulated 95 82. Antbbiob and Postebiob Suepaces op the Fbog's Heabt . . .97 83. Appabatus for Eecording the Heart Beat by the Suspension Method 99 84. Eecoed op the Movements op the Frog's Heart by the Suspension , Method 100 85. Application op the First Stannius Ligature to the Frog's Heart 104 86. Electrical Stimulation op the Ventricle op the Frog's Heart in Standstill by the Stannius Ligatuee to Show the ' Staiecase ' Effect 106 87. A Simple Form of Flexible Electrodes 106 88. A Single Contbaction op the Fbog's Ventbicle .... 107 89. A Single Contbaction op the Fbog's Ventbicle 108 90. A Eepetition of the Tbacing op Fig. 89 with a Sloweb Movement OP the Eecording Surface 108 91. The Effect of Two Successive Stimuli upon the Ventricle of the Frog's Heart 109 92. Tetanisation of a Frog's Ventricle in Standstill by the Stannius Ligature ..... 110 93. Apparatus fob Varying the Temperature op a Frog's Heart . . 112 94 a. Tracings Obtained by Immersing an Excised Feog's Heabt in Diluted Blood at Dipfeeent Tempeeatuees 114 94 B. Tracings Obtained by Immersing an Excised Frog's Heart in Diluted Blood at Dipfeeent Temperatures 115 95. Single Contractions of the Fbog's Ventbicle at Vaeious Tempeea- tuees 117 96. DiAGEAM of the Vabiations op the Dueation op a Single Ventbicle Contbaction at Dipfeeent Tempeeatuees 118 97. DiAGBAM of the Vabiations in Height of Contbaction op the Frog'^s Ventricle at Different Tempeeatuees . . . . . . Hg 98. To Show the Couese of the Vagus in the Frog. .... 120 99. The Course op the Sympathetic in the Frog 121 XU EXPERIMENTAL PHYSIOLOaY FIG. PAGK 100. Effects of Tetanisisg the Vagus with Different Strengths of Stimum ... 123 101. The Effect of Tetanisation of the Vagus 126 102. Stimulation of the Sympathetic 127 103. The Effect of Muscarine and Atropine on the Frog's Heart . 131 104. The Effect of Applying a Weak Solution op Nicotine directly TO THE Heart ........... 132 105. Tracings Eeooeded by a Lever Resting upon a Frog's Heart . . 134 106. Eoy's Tonometer (Halliburton) 135 107. ScHiFER's Prog-heart Plethysmograph 136 108. Frog-heart Plethysmograph by which the Pressure Changes can also be Eecorded by a Small Manometer 137 109. A Simple Form of Apparatus for Artificial Respiration . . . 139 110. Arrangement op Levers for Recording the Movements op the Mam- malian Heart by Attaching Threads to the Auricle and Ventricle respectively 140 111. Tracing Obtained prom the Rabbit's Heart, Employing the Levees OF Fig. 110 . . 141 112. Result of the Stimulation of the Left Vagus 142 113. Result of the Injection of 1 c.c. of a 4 per cent. Solution of Caffeine Citbate ... 143 114. The Cardiograph ... 144 115. A Cardiogram taken upon a Man 145 116. KiJHNE's Experiment op Contraction without Metals . . . . 148 117. Arrangement of Apparatus for Showing Secondary Contraction . 148 118. Side View of Galvanometer and Shunt, Lamp and Scale (Waller) . 149 119. Course of Current through Galvanometer (Waller) . . . 150 120. Plan of Du Bois-Reymond's Method op Measuring the Muscle Currents . . 152 121. Lippmann's Capillary Electrometer (Waller) . . . 154 122. Currents op Frog's Heart (Waller) 155 123. Arrangement op Apparatus to Show the Paradoxical Contraction . 156 124. Schema op the Circulation 158 125. Apparatus for Studying the Passage of a Pulse Wave along an Elastic Tube . .163 126. Marey's Sphygmograph (Halliburton) .... . . 164 127. Diagram to Show the Arrangement op the Levers in Marey's Sphygmograph . . . 164 128. Sphyomogram Taeen by Marey's Sphygmograph . . . . 165 129. Richardson's Modification op Dudgeon's Sphygmograph . . 166 130. Plan op the Levers in Dudgeon's Sphygmograph . . . 166 131. Two Sphygmogeams Taken by a Dudgeon's Sphygmograph . . . 167 132. Arrangement of Apparatus for a Blood-pressure Experiment . . 169 133. Dissection of the Nerves of a Rabbit's Neck 170 .134. Two Forms op CANNULa: 170 135. TraoiSg of the Blood Pressure prom a Rabbit taken by the Mercury Manometer 172 136. Blood Pressure and Respiratory Tracing op a Curabised Cat under Morphia 173 LIST OF ILLUSTRATIONS XUl FIG. PiQE 137. Stimdlation op the Depressor Nebve in a Rabbit . . . . 174 188. Stimulation op the Central End op the dittbed Sciatic . . . 176 139. Pressor Epfeot Produced by Stimulating the Central End op the ScuTic OF A Cuearised Cat under Morphia 177 140. Stimulation of the Peripheral End op the Left Vagus in a Babbit 178 141. Two Successive Stimulations op the Peripheral End of the Eisht Vagus with the Same Strength of Stimulus 179 142. Stimdlation or the Central End op the Left Vagus in a Babbit . 180 143. Bppect op an Injection op Nicotine upon the Blood Pressure . 181 144. To Illustrate the Inertia op a Mercury Manometer . . . . 183 145. Pick's C-Spring Manometer (Yeo) 183 146. Tracing by Pick's Manometer 184 147. HBrthle's Manometer 184 148. Tracings of Blood Pressure op the Babbit by HuRthle's Manometer 185 149. Stimulation of the Peripheral End of the Vagus . . . . 186 150. NoKMAL Blood Pressure and Bespiration 187 151. Ludwig's Stromuhr . 187 152. Two Sizes op Boy's Kidney Oncometer 190 153. To Illustrate the Principle op Boy's Oncometer . . . . 190 154. The Oncograph 191 155. An Air Oncometer for the Kidney 191 156. Simultaneous Tracing op the Volume Changes op the Kidney and of the Carotid Blood Pressure in a Dog 194 157. Kidney Volume and Blood Pressure in a Dog . . . . 196 158. Effect of Caffeine upon the Kidney Volume and Blood Pressure 197 159. Effect of Neurine upon the Kidney Volume and Blood Pressure . 199 160. Alteration in Bespiration on Stimulation of the Superior Laryn- geal Nerve 203 161. Eppeot upon Bespiration of Stimulation op the Glossopharyngeal Nerve 204 162. Besult of Section of the Vagus, the other Nerve having been Previously Divided 204 163. Stimulation of the Central End op the Vagus, both Vagi having -> BEEN Divided .......... 164. Stimulation of the Central End of the Vagus, both Vagi having BEEN Divided .... .^ ... . 168. Mahey's Pneumograph (McKendrick) 206 166. Sanderson's Stethometee 207 167. Mode op Applying the Stethometer to Becord Changes in Trans- verse Diameter of the Chest 207 168. Becord op Changes in the Transverse Diameter of the Thorax DURING Bespiration (Man) 208 169. The Eelation op the Veins to the Submaxillary Gland in the Dog 209 170. Eelations op the Duct and Nerves of the Submaxiliary Gland in the Dog ... 210 171. The Phakoscope (McKendrick) 220 172. The Eeplected Images as seen in the Phakoscope .... 220 173. To Illustrate Scheiner's Experiment .... . . 221 205 XIV EXPERIMENTAIm ; PHYSIOLOGY PIG. PAGE 174. The Couese of the Ljeni pj the Indieect Method of EniPiiO^iNa THE Ophthalmoscope , , , . 223 175. The Course or the Light in Examining the Bye by the Direct Method . . . . . . . . . . . -' ; . 223 176. Pkiestley-Smith's Perimeter (Halliburton) . . . . . .225 177. A Perimetric Chart for the Biqht Eye (Halliburton) ■ , . . 226 The experiments and descriptions of apparatus for elementary- classes will be found in the following positions, and are indicated by being printed in heavy type : — PAGE The Induction Coil 4 DESCRIPTION OF the More 1mpokt.4nt Keys 10 The Nekve-muscle Preparation 16 The Hyoglossus Preparation . . 20 The Simple Levee. 25 Minimal and Maximal Excitation' 26 The Simple Muscle Curve 30 The Work Performed during a Twitch 50 Tetanisation of a Muscle 65 Thickening of a Muscle during a Twitch 71 Independent Muscular Excitability 76 Stimulation op Nerve .... ... . . 86 Eecokd op the Beat of the E'roo's Heart 97 Excision of the Frog's Heart 101 Action of the Vagus upon the Frog's Heart . . ... . . 120 Seflex Action Studied on the Frog 214 THE ESSENTIALS OF EXPERIMENTAL PHYSIOLOGY CHAPTBE I SOME PHYSICAL INSTEUMENTS IN CONSTANT USB IN PHYSIOLOGICAL EXPEBIMENTS Bbpoee undertaking any purely physiological experiments it is necessary to understand the construction and mode of working of certain pieces of physical apparatus which are in constant use ; such, for instance, as batteries, induction coils, keys, &c. The Daniell's Element (fig. 1) is in very general use, on account of the constancy of the current it yields. It consists of an outer vessel of glass or glazed earthenware, in which is placed a cylinder of copper open at both ends. Within the copper cyUnder is a porous pot, and vsdthin this is a roll of zinc. The outer vessel is filled with a saturated solution of sulphate of copper, and an excess of the crystals is kept in the solution. The porous pot is filled with dilute sulphuric acid (1 to 5 of water). Connections are taken from the copper and zinc cylinders. The positive pole of the battery is the copper, the negative the zinc. To prevent local action the zinc cyhnder is previously thoroughly amalgamated by first cleaning its surface with dilute sulphuric acid, and then rubbing metallic mercury well over its surface with a piece of cloth dipped in the acid. When in action the chemical changes in the battery are, solution of zinc and formation of ZnS04 at the zinc plate, and decomposition of the CUSO4, by the hydrogen appearing at the copper plate to form H2SO4 and metallic Cu, which latter is deposited on the copper surface. The E.M.P. (electromotive force) of the battery is 1'072 volts. 2 EXPERBIENTAL PHYSIOLOGY Grenet's Battery (fig. 2) is a single fluid battery. It consists of an amalgamated zinc plate fixed between two carbon plates k, k. The zinc plate is fixed above to a rod b, by means of which it can be lifted from the fluid. The two carbon plates are connected to the binding screw, e, which is therefore the positive pole ; the zinc is Fig. 1. — The Daniell Battebt. Fig. 2. — The Gkenet Battery. connected to d. The fluid is made by adding four parts of a 10 per cent, solution of potassium bichromate to one of sulphuric acid. In action the zinc is dissolved, and the hydrogen set free at the carbon plates is oxidised by the bichromate and thus removed. When freshly made the battery has an E.M.P. slightly above 2 volts, but rapidly falls until it reaches about 1-8 volts. A Bunsen Battery (fig. 3) consists of an outer earthenware pot in which is placed a zinc cylinder. Inside this is a porous pot carrying a square block of carbon, c. The wire connections are made to the carbon, the positive pole, and to the zinc, the negative pole. The porous pot is filled with strong nitric acid, and the fluid surrounding the amalgamated zinc is dilute sulphuric acid (1 to 7). The SO4 appearing at the zinc plate when the battery is in action dissolves the zinc to form ZnS04, and the Hg appearing simultaneously at the BATTERIES carbon pole is oxidised into HjO by the nitric acid, of the battery is 1'9 volts. The E.M.P. Fig. 3. — The Buvsen Battery. (McKendbiok.) The Grove Battery (fig. 4) is similar to the Bunsen battery, but the carbon is replaced by a sheet of platinum. Its E.M.P. is 1-96 volts. The leclanclie Battery (fig. 5) consists of a glass jar containing a saturated solution of ammonium chloride into which an amalgamated zinc rod dips. This forms the negative terminal. The positive consists of a carbon plate fitted into a porous pot packed with small pieces of carbon mixed with manganese dioxide. The porous pot is then filled up with the ammonium chloride solu- tion. Its E.M.E. when freshly prepared is 1'48 volts. It has the disadvantage that it tends to polarise rather quickly, and is therefore only used when a current is required for short periods of time. It is very convenient, as it does not fume ; there are no acids to be spilt, and it does not require much attention. b2 Fig. 4. — The Grove Battery. EXPERIMENTAL PHYSIOLOGY Dry Batteries. — These are of very great convenience in that they are always ready for use, do not give off fumes, and contain no fluid ^'^ to be spilt. One of the most satis- factory of these is the Obach dry battery, manufactured by Siemens. + In principle, they are usually modified Leclanch6 cells. THE INDUCTION" COIL The form of induction coil usually employed by physiologists is Da Bois- Reymond's sledge induotorinm (fig. 6). It consists of a coil, a, of fairly stout insulated copper wire wound on a wooden reel in the centre of which is a core of soft iron wires, c. The number of turns of wire in this, the PRIMARY COIL, varies in different instruments from 200 to 500 or more. The ends of the wire of the primary coil are con- nected to the two binding screws / and h. A second coil of much finer wire is wound round a large wooden bobbin, the whole forming the SECONDARY COIL, b. This is fixed to a wooden foot sliding in a Fig. 5. — The Leclanchb Battebt. , 6. — The IsDncTioN (McKendbick.) grooved base, m, and the central cavity in the wooden bobbin is of such a size that the secondary coil may be pushed home so as to completely cover the primary coil a. The terminations of the wire of the second- ary coil are connected to two binding screws, only one of which, n, THE INDUCTION COIL 5 can be seen in tlie figure. The number of turns of wire in this coil is 5,000 or more. The turns of wire in each coil are carefully insulated from each other. The action of the coil depends upon the fact that if the strength of a current running along a wire be altered, an induced current is set up in a second wire placed near to it. The E.M.P. of the induced current depends upon several factors : 1. It is directly proportional to the intensity of the current change in the first wire. 2. It is directly proportional to the rate of change of the inducing current. 3. It is inversely proportional to the distance between the two wires. 4. It varies with the angle between the two wires, the maximum effect being produced when the wires are parallel to each other, and no effect when they are at right angles to each other. 5. The strength of the induced current may be increased by con- centrating the force of the magnetic field ; as, for instance, by placing a coil of soft iron wires in the interior of the primary coil. Some or all of these various factors are utiUsed in the production of an induced current for physiological purposes ; but as the induced current produced by the induction of one wire upon one other is very small, the induction coil forms a very convenient means by which these weak induced shocks may be multiplied and added to one another. By taking a large number of turns of wire in each coil the effect is greatly increased, because each turn of the primary coil induces a current in each of the turns of the secondary, and all these small effects are added together to produce a single greatly increased effect. We have seen that an induced current is only produced in the secondary coil during a change in the strength of the current in the primary, so that if that change be effected instantaneously, as in breaking the current, the induced current is also instantaneous. The direction of the induced current is such as to tend to oppose the new change, so that if a current be suddenly sent into the primary coil, round which it runs in the direction of the hands of a watch, the induced current in the secondary coil passes along its turns in the reverse direction, i.e. against the direction of the hands of a watch. Conversely, on suddenly breaking the primary current, the induced current is in the same direction as that in the primary. In a consideration of the action of the induction coil, there is a further point of some considerable importance, for just as the wires of the primary can react upon the wires of the secondary coil, so can 6 EXPERIMENTAL PHYSIOLOGY BReA/f each turn of-ithe primary induce currents in each neighbouring turn of the coil. If we consider two neighbouring turns when the current is suddenly increased, the increase in the one wire will induce a current in the second, and this induced current will be in the reverse direction to that of the main current, and as the direction of the current in two neighbouring turns is the same it tends to diminish the amount of the increase in the second -wire. As the duration of this induced current is very short its effect is soon exhausted, but not before it has produced the result that more time is required for the current to reach its full strength than would have been the case if the wire had been perfectly straight. On breaking the circuit the circuit of the primary is broken, so that no induction currents can be set up in the primary. The fall in potential is therefore instantaneous. These effects are diagrammaticaUy represented in fig. 7. In this figure, lines written hori- zontally indicate time, and vertical lines strength of current. At the instant a a current whose amount is represented by the vertical line A c is suddenly thrown into the primary, but in- stead of instantly reaching its full intensity, when the course of events would be represented by the line a c, time is occupied before it attains its full strength. Thus the gradual rise of strength of the current is represented by the curved line ab. At the instant g the current is broken, and there occurs an instantaneous fall in strength to zero, which is thus represented by the line f g. The induction effect produced in the primary on making the circuit is spoken of as the make, extra-current. The result of this upon the current induced in the secondary coil is of very great importance. One of the chief factors varying the intensity of the induced current is the rate at which the change is effected, and as the make takes an appreciable time while the break is instantaneous, it follows that the induced secondary current at make is of less E.M.P. than that at break, but lasts longer. This is indicated in the lower half of fig. 7. The line K B indicates zero current, and the curved line k l m the current induced in the secondary by the change of current A b in the primary. The intensity of the change at any instant is indicated by the vertical height of the curve for that instant, and is drawn below the line k m, P/t/MA/tY SECONDAKY Fig. 7. THE INDUCTION COIL 7 iDecause the current is in the reverse direction to that of A b. The Une EPS indicates the current induced in the secondary by the sudden change p g in the primary : it is above the line k e because it is in the same direction as the inducing current, and is of greater height than that representing the current induced on make. Von Helmholtz ■showed how we might approximately equalise the two induced ■shocks by the introduction of a deri-ving circuit into that through the primary. Pig. 8 shows how to arrange the apparatus to demon- ■strate this. A battery is connected to the two terminals of the primary •coil, and to these are two further ■wires connected to a key and forming the derived circuit. It is seen that there is always some •current passing through the primary both when the key is Pig. 8.— Aruangement of Appakaxus ■open and closed. When the key ^o" Equalising the Make and . , T ,, , , ., Break Shocks. IS closed the current from the battery on reaching the first terminal of the coil divides into two parts, one passing through the coil, the other through the deriving circuit. The amount of current passing through" either circuit is inversely proportional to the total resistance in that circuit. If then the resistance of the deriving circuit be small in comparison with that of the coil, only a small proportion of the total current passes through the coil. On opening the key, the whole of the current is thrown through the coil and, as pre'viously explained, an extra-current is produced which for a time delays the establishment of the current to its full intensity. On closing the key, there is a fall of current which produces an extra-current running in the same ■direction as that of the main current ; and as the circuit through the primary is stiU closed, this extra-current can act in delaying the fall of strength of the current. The result is that the current induced in the secondary is considerably diminished and made approximately equal to that of the make. These results are indicated in the diagrams ■of fig. 7. The current passing through the primary when the key of the derived circuit is closed is indicated by a d. On opening the key the current rises in value to a c, but its course is delayed and takes the course represented by the dotted line d e. If the key be opened at F, the fall in strength to the line d h is not instantaneous, but takes time and is represented by the curved line F h. The effects on the induced currents in the secondary circuit are represented by the interrupted lines k n o and e t v respectively. For very many purposes it is essential to have a rapid series of 8 EXPERIMENTAL PHYSIOLOG Y induction shocks, wMch can of course be obtained by a rapid make and break of the circuit through the primary. To obtain this in an auto- matic way the induction coil is always fitted with an arrangement termed the NEEF'S HAMMER. This is represented in fig. 6, and consists of a pillar d carrying a steel spring to which is attached an iron armature k. In the centre of this spring is a small platinum plate for making contact with l=PP ^ L l I the platinum point of a screw adjustable in a brass plate con- nected to the binding screw /, and therefore with one terminal of the primary. Fixed under k is a double electromagnet i, one end of the wire of which is con- nected to h, the second terminal of the primary coil, and the other end to a central pillar Z. The mode of action is illustrated by fig. 9, A battery is connected by one pole to the pillar a and by the other to the pillar b, using a mercury key k. If th& platinum point of the screw Si be in contact with the platinum plate on the upper surface of the spring v, then on closing the key k the circuit is closed, and if we suppose the positive pole of the battery to be in connection with the pillar a the course of the current is from the battery to a, then along the spring v to the screw Si, thence through the primary coil to the electromagnet, and from this to the second pillar b, and so through the key k back to the battery. As soon as the circuit is thus closed the electromagnet acts upon the armature and pulls down the spring v, thereby separating the two platinum surfaces. The current is at once broken, and the electro- magnet therefore ceases to attract the armature, which is carried up by the spring v ; a new contact is thus made by the platinum surfaces, and the whole cycle of events is repeated. In this way the circuit through the primary is made and broken automatically at a rate which depends solely upon the rate of oscillation of the steel spring v. At each make and at each break of the circuit induced currents are pro- duced in the secondary circuit, which, as previously explained, are of very unequal intensities. —To Illustrate the Action OF Neef's Hammeb. Von Helmholtz showed how the Neef s hammer might be arranged to give shocks of about the same intensity. All that is necessary is to THE INDUCTION COIL connect the piUar d (fig. 6) with the binding screw / by a stout wire and screw up the screws s, and s^ (fig. 10) until s, is removed from contact with the spring v, and Ss hes just below it, but not touching it. Fig. 10 illustrates the action of the hammer with this arrangement. The connections to the battery remain the same. On closing the key K the path of the current is now from the battery to the piUar a, and from this by the stout wire to the screw Si, and thence to the primary coil p c. From the primary coil it passes to the electromagnet b, thence to the pillar b, and so through the key k back to the battery. Immediately the current is closed the electromagnet at- tracts the armature of the spring V, and as it pulls it down brings the platinum plate on its lower surface into contact with the platinum point of the screw S2, the result of which is that the derived circuit from the pillar A through the spring v to the pillar b is closed. The current is now divided, and in- stead of all passing through the primary coU and electromagnet most travels through the derived circuit, because the resistance of this is much less than that of the coU and electromagnet. The current of the electromagnet becoming so much weaker is now unable to resist the upward pull of the spring v, which therefore recoils, and thus breaks its contact with the screw Sj. The derived circuit is broken and the whole current again sent through the coil, the cycle is repeated, and so on continuously. Just as in the previously described case where a simple derived circuit was used to equalise the make and break shocks this arrange- ment attains the same end, and is to be used when it is necessary that the two shocks should be nearly equal. One of the great conveniences of the sledge induotorium is the ready manner in which the strength of the induced shock can be varied by simply altering the distance of the secondary coil from the primary. It must, however, be remembered that the strength of the induced current is by no means inversely proportional to the distance of the secondary coil from the primary, but that the strength of the induced current increases at a far greater rate than the diminution of ^^_^K Fig. 10. — To Illdsteate the Action or Neep's Hammee with the Helmholtz MODiriOATION. 10 EXPERIMENTAL PHYSIOLOGY distance between the two coils. The value of the induced current may be determined empirically by use of the galvanometer. Some forms of coil are already graduated in this manner. Another plan which is at times adopted for varying the strength of the induced current is to have the secondary coil so fitted that it can be rotated and its long axis set at any angle to the axis of the primary. The induced current, with a fixed alteration in the primary, is then proportional to the cosine of the angle between the two axes of the coils. SOME FORMS OF KEYS FOR OPENING AND CLOSING- A CIRCUIT The MERCURY KEY. — This key is used for making and breaking a current by hand, and is constructed in various forms (see figs. 11 and 12). In fig. 11 there are two cups, c', c^, hollowed out in a vulcanite base and with two binding screws, b' and b^, entering them from the B Inst. Co. Ltd. qams. Pigs. 11 and 12 Two Fokms or METiOUE-r Key. The cups are nearly filled with mercury, and can be connected by means of the stout bent copper wire w w which hinges through a piece of vulcanite e. In fig. 12 there is a single mercury cup into which a wire dips to make contact with the binding screw. The SPRING or CONTACT KEY (fig. 13) consists of a metal spring connected to a binding screw A. At its movable end there Fig. 13. —Simple Fokm oi' Spuing Key. is a vulcanite knob c by which it can be depressed, and thus a platinum point on its lower surface brought into contact with a platinum plate THE DU BOIS KEY 11 on the brass plate d, wMch is connected by the strip of copper e to the second binding screw b. When interposed in the course of a circuit, the circuit will only be closed when c is depressed to lie in contact with D. DU BOIS-EEYMOND'S FRICTION KEY (figs. 14 and 15) consists of two metal blocks a and b (fig. 14), each carrying two binding screws, fixed on an insulating base. The two blocks can be connected Figs. 14 asd 15.- Inst. Co. ltd. Cmmb. -Two FoBMs OF THE Dc Bois Key. by a metal cross-bar c, which thus closes the key. This key is of very great service, and is employed in two ways indicated in the two ac- companying figures (16 and 17), where it is represented as being used in the secondary circuit of an inductorium. In fig. 16 is shown the -Fio. 16. — Plan of the Arbangement of THE Dn Bois Key as a Shobt-oik- cditing Key. Fig. 17. — Akeanged as a Simple Beeak Key. Not to be used afteb this Method in a Seoondaby CiKoniT. arrangement in which it is used as a short-circuiting key. The two terminals of the secondary coil are connected by wires to two of the binding screws on the blocks, one to each block, and to the remaining two binding screws are connected the wires of a pair of electrodes, e, 12 EXPEEIMENTAL PHYSIOLOGY lying under a nerve or other structure to be stimulated. When the key K is open any current in the secondary coil can travel through the electrodes. If the key be closed, a current in the coil divides when it reaches the key, passing either through the key or to one electrode, thence through the nerve to the other electrode, and so back to the key. As the resistance of the key is very low compared to the high resistance of the piece of nerve, practicaUy the whole of the current passes that way, or, in other words, the secondary coil is short-cir- cuited. A Du Bois key is always to be used in this manner when in a secondary circuit. The second method of using the key is shown in fig. 17, where it is used as a simple key. The electrode wires e, are represented connected to one terminal of the coil and to one block of the key k,. The other terminal of the coil is connected to the second block of the key. When the key is closed any current in the coil can pass through the electrodes, but when the key is opened the secondary circuit is broken. The key can be used after this plan for making- and breaking any battery circuit, but should not be thus employed in a secondary circuit. POHL'S COMMUTATOR (fig. 18) consists of a wooden or vulcanite base in which are six mercury cups, to each of which a binding screw is connected. A rocker made of a vulcanite axis h, to which two curved wires k and two ver- tical ones L are joined so that the vertical and curved wires of the same side are connected together, is so arranged that the two straight wires are supported in the cups a and B, and the curved wire may ■y*"" be made to dip into either -• pair of the four remaining Fig. 18.— Pohl's Commutatob. "ups. Two cross wires are also provided which connect c to F and d to e. Supposing now that the positive pole of a battery is connected with a and the negative with b, and the key is turned over so that the curved wires k dip into the cups c and d, and if c and D are connected by wires to any circuit, then the current enters at a, passes up l along k to c, thence through the circuit to d, and so to B and back to the battery. If now the rocker be turned over so as tp rest in the cups e and f, as shown in the figure, then the current enters at a, passes to e, thence by one cross wire to d, through the external circuit to c, by the second cross wire to f, and so back to b. In the first position of the rocker the current in the external circuit A CUT-OUT KEY 13 was from c to d, in the second position from d to c, i.e. by moving the rocker the direction of the current in the external part of the circuit has been reversed. This key can also be used in a second way by removing the cross- wires, when two circuits can be closed by it, either from c to d or from E to p. Suppose, for instance, that the two ends of a muscle were connected by wires to b and f, and the wires of a pair of electrodes . upon which the nerve is lying to c and d, then if the key be in the position of the figure a current entering at a and leaving at b is sent through the muscle, whilst if the rocker be rotated into the cups c and p the current through the muscle is broken, and instead is sent through the nerve. For the mode of connecting the key for such a purpose, see fig. 80, p. 95. A KEY FOR OUTTIHG OUT EITHER THE MAKE OR BREAK SHOOK This consists (fig. 19) of two spring keys, one between p' and p', closed when the spring b is brought into contact with the metal piece d, and the other one between s^ and s^. The contact is made in each case between two platinum Fig. 19. — A Pobm of Cni-OTji Key. sitrfaces, one under B and the other projecting up from D, and similarly in the other key. These keys are closed automatically by two vulcanite sectors, v' and v^, which are carried on an axis which can be rotated by hand or driven by a ru n n in g cord round the coned pulley. These sectors can be rotated into any position on the horizontal axis, and clamped by screws. Fit up the key p' p- to make and break a current through the primary, and s^ s', so that it short-circuits the secondary when it is closed. Thus the two terminals of the secondary are connected, one to s^ and the other to s^, and the two electrode wires 14 EXPERIMENTAL PHYSIOLOGY are connected to the same binding screws. If now the pulley be rotated in the direction of the hands of a watch, and the sectors are in the position drawn in the figure, the sequence of events is : — ^i. the spring a is brought into contact with c, and therefore the secondary coil is short-circuited ; ii. the spring B is brought into contact with d, thus closing the primary ; a make shock is therefore induced in the secondary, which is, however, short- circuited because the spring A is stiU depressed ; iii. the sector v' glides off the spring a, which flies up, and the secondary coil is no longer short- circuited ; iv. the sector v^ leaves the spring b, which flies up and breaks the primary circuit, and the break shook now passes to the electrodes and through a nerve or muscle laid upon them. By fixing the sector v^ a little in advance of v', only make shocks would be sent through the electrodes. "When a more rapid series of stimidi is required, two notched wheels are provided to replace the sectors ; these close and open the keys six times in each revolution, and one, as with the sectors, may be set a fittle in advance of the other, and so either make or break shocks sent through the electrodes as desired. Fit up the key as directed, and placing the electrodes upon the tongue, rotate the key, and show that the one or other shock can be cut out as required. Experiment 1. — Show that the break shock Is g:reater than tbe make sbock in the following way. Connect the primary coil with a battery and mercury or spring key as in fig. 20. To the secondary coil attach a pair of wires, and remove the coU to some distance from the primary. Hold the two PC. Fio. 20. — Akbangement of Appaeatus for Making Use of Single Induced Shocks. iree ends of the wires on the tip of the tongue, and make and break the primary circuit by opening and closing the mercury key. At first nothing is felt. Now gradually move up the secondary coil, testing each new position by opening and closing the key in the primary circuit. At last a position wiU be found at which a shock is perceived at break and none at make. Make a note of the posi- tion of the secondary coil with respect to the fixed scale. Move up the secon- dary still farther, noting that the break shock becomes progressively stronger, and at last a position is reached at which a shock is felt on making the current. This position is to be noted and contrasted with that previously observed for the break shock. The experiment also clearly shows how convenient the coil is for modifying the strength of stimtdus to any required degree. Experiment 2. — To demonstrate the break extra-current arrange the apparatus as in fig. 21, applying the Fig. 21. — Akbangement op Appabatus to electrodes E to the tongue. First close Show the Bbeak Extba-oubkent. the key Kj ; on now closing the key K, the current is short-circuited, and none passes through the tongue ; on opening k^ all the current passes through BREAK EXTRA-CURRENT 16 the tongue. Neither on opening nor closing the key k, is any distinct shock felt unless the' battery is very strong. Now open the key k^ and again open and close K2. Each time the key Kj is opened the current is sent through the tongue, and the resistance being very high there is a sudden fall in strength of the current. On opening a distinct shock is felt. This is due to the extra-current brought about by the sudden fall in strength, inducing currents in the turns of wire of the primary coil p c. 16 EXPERIMENTAJ. PHYSIOLOGY CHAPTBE II PEEPAEATION OF A FEOG's MUSCLE. ITS EESPONSE TO STIMULATION. THE GEAPHIC METHOD PITH A FROG. — Pass your nail along the back of a frog's skull until the groove between the skull and the first vertebra is felt, and then insert the point of a fine scalpel between these two, and so divide the central nervous system transversely at about the level of the medulla. Now insert a blunt-pointed seeker into this aperture and pass it forward into the skull cavity, so as to destroy the brain, and then downwards into the vertebral canal, and thus destroy the spinal cord. MAKE A NERVE MUSCLE PREPARATION.— The simplest and one of the most convenient muscles to isolate for experiments is the gastrocnemius. Its anatomical relations are shown in figs. 22 and 23. To prepare it together with its nerve, pith a frog, and cutting through the spinal column one vertebra above the sacrum, remove all the soft parts in front down to the pubis, including the viscera, taking care not to injure the branches of the sciatic plexus lying on the pos- terior wall of the abdominal cavity. If the sacrum be now firmly held, the skin over the back of the iliac bones can be drawn down, and the whole of it drawn off the two legs, thus lajring bare the muscles of the thigh and leg. The tendo Achillis is cut across below the ankle-joint, and with its sesamoid bone dissected free up to the belly of the gastrocnemius, which is then isolated from the tibia and fibula right up to its insertion into the femur. The head of the tibia is then cut through just below the knee-joint. Next proceed to isolate the sciatic, which will be found lying between the biceps, b, fig. 23, and semi- membranosus, sm, on the posterior surface of the thigh. Carefully separate these muscles, and follow up the nerve to the pelvis, cutting through its branches as they are laid bare. The nerve should not be touched with metal instruments, and in its separation should not be allowed to be covered with blood from the vessels which accompany It. Next cut through the muscles attached to the urostyle, and divide THE GASTROCNEMIUS PREPARATION 17 the vertebrae in the mid liae into two symmetrical halves. Lift up the muscles which have been cut from the urostyle, and turn them outwards, so as to expose the sciatic, which can then be completely isolated up to its three constituent cords, and so to the vertebrae. Cut through the joint between the vertebrae and the ilium, and the vertebrae can then be picked up, and by this means the nerve lifted and its isolation completed down to the lower end of the femur, where it divides into two branches. It is then laid on the gastrocnemius while the muscles are separated from the femur, the triceps from the outer side, and the adductors from the inner. The femur is then cut through at Fig. 22. — Leo MnsoLBS or the Fboo SEEN FKOM THE InNEK SidE. a, Gbacilis. s, Saktoeius. V, Vastus InTEBNUS. G, GASTEOONEMinS. Fig. 23. — Leo Muscles of the Fbog SEEN FEOM THE OuTEE SiDE. T, Teiceps. b, Biceps, sm, Semimem- BEANOSUS. G, GABTBOONEMroS. about its upper third and the preparation is complete. Fig. 24 is a drawing of such a nerve-muscle preparation, where f is the femur and E the knee-joint ; a is the gastrocnemius and t the tendo Achillis with its sesamoid bone s. The nerve n still remains attached to a piece of the vertebral column v, which serves as a convenient means of handling the nerve. At Nj is the branch of the nerve to the gastro- cnemius. The femur can be clamped in the muscle forceps, and thus a rigid support is given to its upper end. A fine thread is tied round c 18 EXPEEIMENTAL PHYSIOLOGY the tendon, or this is pierced by a bent pin, and thus the lower end attachsd to the lever of a myograph (see fig 31, p. 25). If a crank lever is to be used it is not necessary to thoroughly isolate the femur, but its lower end can be directly fixed to the cork plate of the myograph by a needle which is passed through the bone. In many cases, too, it is not necessary to completely iso- late the nerve up to the vertebrae. DIRECT AND INDIRECT EXCITATION OF MUSCLE. A muscle may be made to contract by a stimulus applied to the muscle mass itself, when the excitation is termed direct, or it may be caused to contract by a stimulus applied to its nerve, which stimulus then travels down to the muscle. This is indirect ex- citation. Test this by apply- and then to the muscle, and Fig. 24. — Gasteocnemius-sciatic Pbepabation. ing the electrodes first to the nerve sending an induced current through the electrodes. THE MOIST OHAMBEE, In all instances in which we are experimenting upon an excised muscle and nerve, it is of the greatest importance that they should be protected from drying. To secure this it is necessary either to im- merse them in some fluid which exerts no harmful effect upon them, such as defibrinated ox-blood, or to place them in an enclosed air- chamber in which the air is kept moist. This latter is termed a moist chamber, and is of different form according to the myograph employed. It consists of a glass cover to the myograph, in which is an aperture through which a thread may pass to connect the muscle to the record- ing lever. The air in the chamber is kept moist by placing in it a few pieces of blotting-paper wetted with normal saline solution. Experiment 1. — Utilise this nerve-muscle preparation to prove that the 1>reak sbock is stronger tban tbe make sbock. Arrange the apparatus in the same way as in Experiment 1, p. 14 (see fig. 20), placing the nerve upon the pair of electrodes. Gradually decrease the distance between the two coils as in that experiment, and make notes of the positions of the secondary coil when a twitch occurs — (1) at break of the primary circuit, (2) at make. Experiment 2. — By using the arrangement previously described and shown in fig. 8, p. 7, show that, by the introduction of a deriving circuit of THE EXTRA-CURRENTS 19 low resistance in parallel with the primary coil, the induced shocks are rendered of nearly equal value. Test this on the nerve-muscle preparation. On varying the position of the secondary coU as in the preceding experiment, it will now he found that the strength of the hreak shock has become nearly ■equal to that of the make shock, which has also been somewhat reduced. Thus in one experiment it was found that the farthest position of the secondary coil from the primary at which a break shook caused a twitch of the muscle was 26^ cm. A make shock was first effective •when the coil was brought up to 10^ cm. With the deriving circuit of low resistance as in experiment 2 the break shocks first produced a twitch when the coil stood at 10 cm., and the make shock was •effective when the coil stood at 9f cm. Experiment 3. — Demonstrate upon the nerve-muscle preparation the •existence of the break extra^current, arranging the apparatus as in Experi- ment 2, p. 14 (fig. 21). Experiment 4. — Demonstrate the make extra-current, arranging the apparatus as in fig. 25. A current is sent through the primary coU and elec- trodes arranged in parallel and with a Du Bois key v? interposed so that both may be short-circuited. Interpose a friction key k^ and a resistance-box k in the main circuit. Also place a key k' in the electrode circuit. The cur- rent on reaching the key K- divides, And as the resistance of the piece of nerve across the electrodes is very high, most passes through the primary coil, which therefore acts as a deriving ' — t^ circuit. Close the key k^ and open t^ ^^^ . > „2 J „ ;„*„ ^„„„ \, „;„* Fig. 25. — Abeangement of Apparatus K^ and now interpose enough resist- g^ jj^^^^ Extba-ouekent. ance at r until opening and closing k^ gives no contraction of the muscle. Next, with k^ and k' closed, open and close ¥?. Each time k* is opened the muscle contracts, stimulated by the make extra-current in the primary coil, for the strength of constant current at the same time sent through the nerve has, by increasing the resistance e, been reduced until it no longer was able to stimulate on make. On closing the key k^ the currents through both primary and nerve are short-circuited, a break extra-current is produced in the primary, which, however, is short- circuited by the key k'. The break of the current through the nerve is not sufficient to stimulate, and the muscle does not contract. If the key k^ be kept open and k' closed and opened, a contraction occurs both at make and break. This arrangement thus demonstrates both make and break extra-currents. MAKE A GRACILIS AJSTD SEMIMEMBRANOSUS PREPARATION" First study the relations of these muscles as given in figs. 22 and 23. Pith a frog and dissect away the skin from the thigh, carefolly cutting through the fibres of the rectus internus minor, which are inserted into the ^kin on the adductor surface of the thigh. The muscles can then be readily made out on the inner side of the thigh separated from one another by the rectus internus minor. The graciUs, or rectus internus major, a, is to be seen from the front of the thigh, being in relation on its outer edge with the c2 20 EXPERIMENTA.L PHYSIOLOGY adductor brevis, adductor magnus and sartorius, s. The seniimembranosuSf wm, is seen on the posterior surface with its outer border in relation with the pyriformis above and the biceps, b, below. Both muscles arise above from the symphysis pubis, and below are inserted by tendinous aponeuroses inta the tibio-fibula. Cut through the aponeurosis at the outer border of each muscle, and then separate each from the subjacent muscles, viz. the adductors and semitendinosus. Isolate the muscles right down to their lower insertion and cut through the tibio-fibula just below this, and then divide the femur a little above the knee-joint. By holding the piece of bone thus isolated the two muscles can now be easUy separated right up to the symphysis. The semitendinosus usually tends to separate with them, and may be removed later by cutting through its lower attachment, then dissect- ing it away from the gracilis, or finally dividing its two heads of attachment, to the pelvis. The other muscles attached to the symphysis are now cut through, and the head of the femur disarticulated from the acetabulum. In many cases it is convenient to make a second preparation in a similar manner from the opposite leg ; but if this be not required, the whole leg may be removed, disarticulating at the acetabulum. The great advantage of this preparation is that we have a mass of muscle in which the fibres are very nearly straight, and are of a good length. With a double preparation the muscles can hang side by side, and so the tranverse section is doubled. The upper end can be conveniently fixed by passiag a strong needle through the acetabula. With the two preparations dissected out they can also be hung one below the other, being united by a piece of the symphysis, and thus a muscle of double length is obtained. MAKE A HYOGLOSSUS PREPARATION .—One of the simplest and most convenient muscle prepara- tions that can be obtained from a frog is the hyoglossus muscle. Fig. 26 shows the general course and arrange- ment of the muscle. It is attached to the anterior edge of the body of the hyoid cartilage, and from this the fibres run forwards to meet in the mid line with the muscle of the oppo- site side. The two then run forward as two bands to the apex of the lower jaw, and thence into the substance of the tongue. In the tongue the fibres run towards the tip and the muscle gradually ends by becoming inserted into the submucous connective tissue of that organ.' It is supplied by the hypoglossal nerve (h, fig. 26). To utilise the muscle when we wish to stimulate directly, all that is necessary is to lift up the lower jaw and cut through the joint between the two jaws on either side, extending the in- Fia. 26. — The Belations of the Hyoglossus, h g, in the Fbog. THE HYOGLOSSUS PREPARATION 21 tsisions down to the shoulder girdle. The lower jaw is then pulled slightly forwards, and by a single transverse incision at the upper edge of the shoulder girdle the whole of it is removed. It is now placed mucous surface upwards, the tip of the tongue lifted up and either transfixed with a hook, or a fine thread is tied round it. The tongue is then turned forwards and extended out of the mouth. The body of the hyoid cartilage now stands out clearly, and this may be transfixed by a pin, and in that way fixed to the cork of a myograph, or the cartilage may be directly clamped in a muscle forceps. The thread or hook may then be attached to the writing lever. The great advantage of the preparation is that the muscles are composed of long fibres strictly parallel to one another, which are completely protected from any injury during the preparation, because the muscle itself is not exposed. Remaining in situ the whole time, they are protected froin drying by the mucous membrane of the tongue and mouth, and on the ventral side by the skin of the jaw. If we wish to stimulate indirectly, the two hypoglossal nerves can be easily isolated and laid upon electrodes. The only disadvantage lies in the small size of the muscle, but the many advantages which it possesses give, in the greater number of experiments, full compensation for that disadvantage. THE GEAPHIO METHOD Most of the movements carried out by the different parts of the body, and which it is our object to study, are performed at so rapid a rate that the unaided eye is only able to give us a judgment of the broad outlines of the movement. By it alone we are quite unable to gain any accurate knowledge of the details of a particular movement. For instance, if we expose the heart of a recently killed frog, and watch it beating, it is difficult to be certain that the auricular beat precedes the ventricular, and in many cases it is quite impossible to determine with any certainty whether the contraction be carried out at a faster or slower rate than the dilatation, or, if there be a difference, to determine the amount of that difference. Still more is the difficulty perceived if we turn our attention to a more rapid movement, such as a single twitch of a frog's muscle, where the whole cycle of movement is so rapid that we are quite unable to accurately judge of its amount, or of any variation in the rate of its contraction or relaxation. We require, then, some means of obtaining a permanent record of each movement which we may afterwards study at our leisure ; and this means is afforded us by what is termed the graphic method, the general principle of which is that the part in movement is made to record its movement by writing it upon a surface. Thus if we wish 22 EXPEEIMENTAL PHYSIOLOGY to record the amount of contraction of a frog's muscle we may fix one end to some rigid support and to the free end attach some form of writing-point, which is made to record its movement upon a piece of paper so placed that the point, during its movement, is always in contact with the paper. Where the amount of movement to be recorded is small, it is readily magnified by some form of lever such as one of those represented in figs. 31 and 37. "We in this way obtain a straight or curved line which gives us at once a permanent record of the amount of movement performed, or of some multiple of it. We still have one important point to determine in the consideration of any movement, viz. the time occupied. Thomas Young was the first to show how we might obtain measurements of time with very consider- able accuracy. He pointed out that if a surface be moved in a given direction at a constant rate, Unes measm^ed parallel to the du-ection of motion indicated time, and that to determine the value of those hnes all that was necessary was to fix a very hght style or marker to a vibrating rod, held so that the style was in contact with the moving surface and its movements at right angles to the direction of motion of the surface. If the time of oscillation of the rod be known, the rate of movement of the surface is directly determined. This time measure- ment was perfected by Duhamel by employing a tuning-fork to one prong of which a light writing-point is fixed. The rate of vibration of the tuning-fork can be determined with very great accuracy, and hence the rate of movement of the surface can be determined with the same accuracy. The recording surface, which is most convenient and which is usually employed, consists of a smooth and highly glazed surface of paper, which is covered with a thin deposit of carbon, obtained by holding it in a smoky flame of burning gas, camphor, turpentine, or some other substance. The writing-point is made of metal, glass, or moderately stiff paper cut to a sharp point, which is Fig. 27. — Two Eecords of the Vibrations of a Tuninq-fobk ViBKATiNa at- THE Bate of 10 peb sec. The Teacino a h was taken while the Eeookd- ING SUKFACE WAS MoVING MOKE EapIDLY THAN DUKING THE EeCOED C d. then made to scratch the smoked surface, and so remove some of the black deposit and bring the white surface of the paper into view. The EECOEDING TIME 23 shape of surface which is most generally useful is that of a cyUnder which can be set rotating about its long axis by clockwork or some other means. In fig. 27 are reproduced two tracings taken by a tuning- fork, which vibrated at the rate of ten per second, the cylinder being made to rotate at two different rates. The distance between the summit of one curve and that of the next curve represents the space travelled over by the surface in ^ second. This distance in the tracing a 6 is 2'85 cm., or in one second the surface travelled 28"5 cm. In the lower tracing the rate is found to be 4'8 cm. per second, if we measure the distance between one summit and the tenth following. The recording of time by means of a tuning-fork possesses the dis- advantage that the vibrations soon cease, especially if the rate of vibration be rapid. To obviate this, a method commonly employed is to record by means of a chronograph (fig. 28), actuated by an electrical current made and broken at some definite known rate by a special piece of apparatus. The chronograph Fig. 28. — A Time-mabkek ok Chbonogeaph. (MoKendrick (fig. 28) consists of a small electromagnet and a movable armature, to which is attached a writing-point. Each time the current is closed the armature is attracted and the writing-point moves downwards. The rate of vibration of the writing-point thus depends upon the rate of make and break of the current employed. The current may be automatically closed in a regular manner in several ways. "Where the rate required is slow a pendulum clock is very firequently used ; when a more rapid rate is required, a tuning-fork, to one prong of which a platinum wire is attached, so that with each vibration the wire completes a circuit either by touching a platinum surface or by dipping into mercury. The tuning-fork is kept vibrating indefinitely by means of an electromagnet. A very convenient time-marker is shown in fig. 29. It consists of a stiff steel band s firmly clamped at one end by the metal cross-bar c. Attached to it is a heavy weight w, by altering the position of which we are able to modify, to a certain extent, the rate of oscillation. The oscillation of the spring is communicated to the vertical bar e, and thus to a lever b e, to which a writing lever l is attached. The writing lever l makes an angle with b e, so 24 EXPERIMENTAL PHYSIOLOGY that the spring s does not touch the writing surface. With w in the position drawn, the oscillations are at the rate of two per second. "When w is moved Fig. 29. — A Spbing Chkonogeaph. to the transverse mark a the rate becomes four per second, and when at d eight per second. As the weight is heavy, when once the spring is started vibrating it keeps on for a sufficient length of time for most experiments. In a recording cylinder such great differences of speed are required for Fig. 30. — Lowek Pakt of Dkdm to show Method op Dbiving the Cylineer at Different Bates. different purposes that it is often difficult on the same drum to obtain suf- ficient variations. For rapid rates of movement a common plan is to drive a THE SIMPLE LEVER 25 friction wheel, by means of clockwork or a running cord, which can be thrown into contact with a second wheel on the axis of the drum (see fig. 37). For slow rates the most satisfactory method is to rotate the drum by means of a tangent screw. The drum represented in fig. 30 combines these two, so that one or the other plan can be used by simply changing the position of a lever h. The figure represents the base of the druru only, the cylinder and upper fittings being the same as those seen in fig. 37. The axis of the drum rests on the steel point of a short vertical rod round which a brass disc d rotates in a collar. On the disc is a little upright B which is placed in contact with a bar f screwed into the drum-spindle a. f and b are kept in contact by a brass spring, so that the drum is rotated by the brass disc. The coned pulley c is driven by a running cord, and on the same axis is a smaller coned pulley k and a brass ring e covered with rubber. "When k is brought into contact with the edge of the disc d the latter is set in movement, and thus gives a rapid movement to the drum. The coned puUey k by an endless cord drives a second pulley g on a second axis, the end of which is a screw. The screw fits into a toothed projection on the rim of the wheel d, so that when s and D are in contact, as in the figure, the rotation of s gives a slow move- ment to the disc d. These two axes are fixed on a base pivoting about a point hidden in the drawing by pulley c. When the handle h is carried over to the left, the rubber disc k comes into contact with the disc d, and the screw s is removed. When, on the other hand, the handle h is to the right, e is removed and s brought into contact with the disc. As a general rule, the various movements we have to record are small in extent, and it therefore becomes necessary to magnify them at the time we record them. This is usually effected by employing some form of lever, the extremity of which is made of a writing-point, ^>- Fig. 81. — Muscle held in MnscLE-roKOEPS p and attached to Simple Levek l. and which is fixed, at a point near its axis, to the muscle or other tissue whose movements are to be recorded. The degree of magnifica- ae EXPERIMENTAL PHYSIOLOGY tion then varies inversely as tlie distance of the point of attachment from the axis. Fig. 31 represents such a SIMPLE LEVEE l, which is represented as arranged for recording the movement of a muscle m, whose upper end is held firmly in the MUSCLE FORCEPS f. All recording levers should be made as light as possible, consistent with sufficient rigidity to prevent distortion of the record by vibrations set up in the lever itself The question of lightness is of the greatest importance when rapid movements are to be recorded. Another form of lever which is also very commonly employed is the CRANE LEVER. This consists of a lever with two arms fixed at right angles to each other. It is represented in fig. 37, p. 31, as being used for recording a simple twitch of a muscle. One of the two arms is long, and when used is fixed horizontally. This is the writing lever. The other is fixed vertically, is much shorter, and is the lever to which the muscle is attached. The muscle in this instance lies horizontally, so that with a crank lever the movement of the writing point is at right angles to the direction of the movement recorded. When we wish to excite a muscle electrically it is necessary to have a pair of electrodes by which the shock may be carried to the muscle or nerve to be excited. There are very many forms of these which can be employed. A simple form, readily made, is shown in fig. 32. Two very thin and flexible copper wires, a and b, covered with silk are taken and twisted together at d and e. A small cork c is taken transfixed by a pin p and two shallow cuts made in it. The wires are then forced into the cuts, as seen in the figure. This holds tlae wires firmly. Near the ends of the wires a drop of Fig. 32.-SIMPLE Fokm of Wibe'' "pelted sealing-wax w is fixed, so Electrodes. ^^ *" ■"°'^^ *°^ wires parallel to one another and about 1 mm. apart. The wires are then out off about 4 mm. beyond the wax, and these projecting pieces bared by scraping off the sUk insulation. In many cases it is a further advantage to imbed the uncovered points in wax, and only expose the wires for about 1 mm., and on one surface only. This tends to prevent escape of the current to surrounding parts. MINIMAL AND MAXIMAL EXOITATIOM" If the strength of the excitation be varied, it is found that the response of the muscle varies in amount. This should be studied in the following way. Experiment 5. — Cover and blacken a drum. Dissect out a muscle and attach it either to a simple-lever or to a crank-lever myograph. Fit up the MAXIMAL AND MINIMAL STIMULI 27 exciting apparatus with a contact key ia the primary and a Du Bois key in the secondary. The muscle may be stimiilated either directly or indirectly. Arrange the electrodes accordingly. Eemove the secondary coil to some distance from the primary. Bring the writing-point to the drum surface, and while the latter is at rest close and open the key ia the primary. No contraction results either on make or on break. If one occur move the secondary further from the primary. Gradually move the secondary up to the primary, when a position will be found at which a slight twitch will occur at break. This is recorded as a vertical hne on the drum. Now turn the drum by hand through about -5 cm. Move up the secondary coil 1 cm. and stimulate as before. Eepeat gradually, increasing the strength of the stimulus and moving the drum after each contraction has been recorded. At a certain position the make shook will be fotind to cause a contraction as weU as the break. After a time it will be found that a further increase of the strength of the stimulus does not lead to an increase in the height of the contraction. Fig. 33 records an experiment carried out in this way. It was obtained from a gastrocnemius with indirect stimulation, and a magnification of 5. The first indication of a contraction was on break with the secondary coil at 17 cm. of the scale. This strength of stimulus is called the MINIMAL STIMULUS, and the contraction is i^mis^mM^m^^mK^mB^mK^mi^^u^mss^^^^^^i^^ Fia. 33. — Heights of Conteaotion of a Muscle with Diffeeent Steengths of Stimuli. The Numbebs Eefee to the Distances of the Seoondaky Coil. The Interrupted Line above Shows the Instants at which the Primary Current was Made and Beoken. A Rise in this Line indicates Make, a Pall Break. also termed minimal ; any strength of stimulus lower than that was for this muscle sub-minimal. As the stimulus was increased it is seen that the contractions on break increased at first rapidly, and then more slowly, but that beyond 9 cm. the height did not increase. The stimulus at 9 cm. was therefore a MAXIMAL STIMULUS, All strengths of stimulus below this were SUB-MAXIMAL. A con- traction on make was first obtained when the secondary coil stood at 13 cm,, and this rapidly increased in amount till it reached a maxi- mum at 9 cm. 28 EXPERIMENTAL PHYSIOLOGY The tracing also shows one other point of some importance. It is to be noticed that the heights of the break contractions do not show a perfectly uniform gradation, but oifer some irregularities. This is due mainly to irregularities in the strength of the stimulus, for the induced shock at break is in reality compound, and caused mainly by the break of the current, and also by the break extra-current which sparks across in quite an irregular manner at the instant the break is effected. triSriPOLAE, EXCITATION" Experiment 6. — Set up the coil to give single shocks, and at first only attach one wire to the secondary coil. Excise a nerve muscle preparation, and placing it upon a dry glass plate put the single wire from the secondary coil under the nerve. On opening or closing no contraction occurs. Next insert a second wire in the remaining terminal of the secondary coil and attach its other end to a gas pipe and so to the earth. A contraction wiU now occur both on opening or closing the primary circuit. Thus it is seen that, in the latter case, the amount of current ■which passes through the earth and the glass plate is sufficient to stimulate the nerve. It is in order to avoid excitation in this v^ay that the Du Bois key is used as a short-circuiting key in the secondary circuit. RECORDING MOVEMENTS BY MEANS OF TAMBOURS In recording movements of different parts of the body, it is often necessary to be able to transmit that movement to some little distance because the part cannot be conveniently brought sufficiently near to Fig. 34 Makey's Fokm or Eecoeding Tambouk. the recording surface to be able to write its movements directly upon the surface. When this is the case, one of the most convenient methods is to employ a pair of tambours, one of which is termed the receiving tambour and the other the recording tambour. Each tambour consists of a shallow circular metal box -whose upper surface consists of a rubber membrane so that it is air-tight. A tube leads TAMBOURS 2& into the interior of each, and the two tambours are through these connected by a piece of jnxbber tubing. When thus connected a pushing-in of the membrane of the receiving tambour causes a corresponding rise of the membrane of the recording tambour, and to the same extent if the two tambours are of the same size. The form of the receiving tambour varies according to the purpose for which it is intended. The form of the recording tambour is shown in fig. 34. The flat metal box, provided with a side tubular /, is represented at a. This is covered above by the rubber membrane 6, to the centre of which is attached a metal disc c with a vertical jointed rod which moves the recording lever d. The amount of maguiiioation may be varied by altering the position of the jointed rod with respect to the axis of the writing lever. Another form of tambour is represented in fig. 35. It consists of an oblong vulcanite base on whose upper surface is a shallow circular cavity into which the metal tube t opens. This is covered with thin rubber membrane, which is attached to the vulcanite with a little Canada balsam. The upper surface of the rubber is covered by a brass plate p with a central circular aperture through which the rubber e is seen. The movements of the mem- brane are transmitted by the cork c to the writing lever l. The axis of this lever is held on a rod, which can be clamped in any position by the screw r, and adjusted to any height by a vertical rod passing through the vulcanite base and fixed by the screw s\ The advantages of this form are that the Fig. 35. — A Seconu Form of Eecoeding Tambgub. rubber membrane is very quickly replaced, and is easily made air-tight. The metal plate p is held on by two stout rubber bands, b' and b', and by changing this for one with a larger or smaller central aperture the sensitiveness of the tambour can be at once decreased or increased. 30 EXPERIMENTAL PHYSIOLOGY OHAPTEE III A SINGLE CONTRACTION OP A FEOG's MUSCLE. ITS MODIFICATION UNDBE CHANGES IN THE EXTEBNAL CONDITIONS If a single stimulus of very short duration be applied to a muscle or its nerve, the muscle responds by giving a contraction of very short duration. This is termed a simple twitch, and is to be studied as in the following experiment. Experiment 1. — Eeoord a simple twitch of a muscle setting up the apparatus in the following way (see fig. 37). Connect one terminal of a battery B to one terminal of the primary coO. p c, and the second terminal of this to the mercury key k, and thence to the special break key k', from the second terminal'bf which a wire is connected to the battery. The details of construction of the break key are shown in fig. 36. A brass pillar d rotates about a vertical axis upon two bearings, and to it is fixed a bent brass rod a. To the metal bearings of d a binding screw b' is connected, and this is fixed in an insulating base of vulcanite. A brass tongue b slightly curved upwards at its free end, is also fixed to the vul- canite base, and is connected to the second binding screw b^. The free extremity of b is slightly notched to receive the rod a, and the two are kept firmly in contact by a screw, part of which is seen in the figure under the Beeak Key. vulcanite base, which tends to force B upwards. If a current be made to enter at b^ it wUl pass to d, thence along a to b, and so out from b'*. If now a be knocked on one side the current is broken directly a and b are separated. The drum having been covered and smoked is placed in position, and the arm ^ (fig. 37), fixed to a collar fitting on the axle of the cylinder, is brought into such a position that there is a weU-blackened smooth piece of paper at the front of the drum, when the arm A touches the rod of the break key k'. The two terminals ,■ of the secondary coil sc are connected to the two blocks of the Du Bois friction key k'', and to the remaining two terminals are connected the two wires of the elec-'" trodes e. A gastrocnemius-sciatic preparation is now excised, the femur fixed 1)0 the cork plate of the myograph, and a fine thread tied to the tendon of the muscle, thus connecting it to the vertical arm of the crank lever. A small weight w is attached to the horizontal arm at a point near its axis, and the muscle so fixed that the writing lever is horizontal or points slightly downwards. The nerve is now laid across the wire electrodes, the key k' being kept closed. A tuning-fork f, or a chronograph, is arranged to write its tracing vertically A MUSCLE TWITCH 31 \ 32 EXPERIMENTAL PHYSIOLOGY under the myograph lever. Before either writing-point is allowed to touch the smoked surface, the drum should be set in motion to see that the front of it rotates from right to left. The secondary coU is now brought into such a position that maximal contractions are obtained when the key k is opened. The drum is now rotated until the rod a is a little in front of the arm of the break key k'. Adjust the writing-point of the lever l'' to touch the drum surface whilst the tuning-fork f is not in contact. The key k' is closed and then k'* is opened. The drum is next very slowly rotated by hand until the arm A breaks the key k' and the shock thus produced in the secondary coU causes a twitch of the muscle, which is recorded as a vertical line on the smoked surface. The key k- is again closed. We now know that, no matter at what rate the drum be rotating, at the instant at which the arm a breaks the primary circuit the writing-point must be exactly opposite the vertical line just recorded. In other words, this vertical line represents the instant at which the stimulus will be sent into the nerve, i.e. it is the point of stimula- tion. Now rotate the drum through about a half-revolution, set the tuning- fork vibrating, and bring its writing-point in contact.with the surface. Close the key k' and open k'. Set the drum revolving by switching the friction wheel below the coned puUey p into contact with the wheel h, the arm a breaks the contact of k', a stimulus is sent to the nerve, and the muscle con- tracts. As soon as the writing lever has returned to rest, the drum is stopped. This takes as a rule about half a revolution. The key k'^ is closed and the writing-point of the tuning-fork removed from the surface. The writing- point of the lever is once more brought accurately on to the abscissa line, and the drum rotated so that a horizontal line is recorded on the drum. This is the zero- abscissa line. The drum is again rotated till the writing-point is brought to the line marking the point of stimulation, when the lever is depressed until it cuts the time tracing. In a similar way vertical arcs are drawn opposite the following three points : (1) the point at which the tracing leaves the zero- abscissa line ; (2) the highest point of the curve ; and (3) the point when it regains the abscissa line. One or two of such curves should be taken, and the curves given by different muscles should also be recorded. A tracing by a hyoglossus preparation is especially useful. This may be stimulated directly, for which purpose one electrode wire is wound round the pin fixing the hyoid cartilage to the cork plate, and the other may be attached to the bent pin passing through the tip of the muscle, or it may be passed directly through the tongue from side to side. This wire should be very fine. The paper may now be removed firomthe drum, a note of the nature of the experi- ment may be written upon it by a finely pointed pen, and it may then be fixed by drawing it through a dish of varnish,' afterwards allowing it to dry. In this way the curve of fig. 38 was obtained. The point of stimu- lation is marked at a, and h, c, d are the other three points mentioned above. The rate of vibration of the tuning-fork is 200 per second. The muscle from which it was obtained was a hyoglossus, and the writing-point magnified the movement of the muscle three times. The curved lines a a', h V, c c', and dd', written while the smoked surface was stationary, are taken for the purpose of making the time measure- I ments more accurately. The curve is seen to fall naturally into three ( parts : — 1 A very convenient varnisli consists of 250 o.c. of best white-hard varnish to which 1 litre of methylated spirit and 10 c.c. of castor oil are added. This dries quickly and gives a dull surface to the tracing. THE SIMPLE MUSCLE CURVE 33 (i.) From the point of stimulation, a, to the point of commencing ^ contraction, b. This is the LATENT PERIOD. During this time there is no change of length. The chronograph tracing a'l/ shows that this occupied ^^ths of a second, i.e. -01 sec. This method does not give accurately the true measurement of muscle latency. It is too liigh. More accurate measurements by specially designed methods show it to vary from 003 to -008 sec. for &og's muscle. There ard several reasons why a measurement by the above method cannot give the true result. In the first place, a muscle does not contract simul- j taneously all over, but the contraction starts at some one spot and I ^ then spreads in a wave-like manner over the rest of the muscle. ^ Following an excitation at one spot, the fibres in that position contract, ' but do not at first lead to a movement of the recording lever, but jrather to a stretching of the remainder of the fibre both above and-i below the point contracting. This is because the parts which have to be moved possess some inertia, and the part whose earliest movement we wish to record is not united to the lever by a rigid connection, nor is its upper end rigidly fixed, but at both ends muscle tissue is interposed. As muscle is elastic the first result of the contraction of a part of a fibre is a stretching of the neighbouring parts, and movement will only be communicated to the lowest extremity when either the whole of the fibre has commenced to contract, or when the increase of tension by the stretching has been transmitted through the elastic fibre to that extremity. (ii.) From the point of commencing contraction b to the highest point of the curve c. ^his is termed the PERIOD OF CONTRACTION . The curve is for about the first third convex to the abscissa line, which means that the rate of the contraction is gradually increasing. This rate of contraction is at first very slow, as seen by the acute angle which the first part of the curve makes with the abscissa ; it then rapidly increases, as shown by the increasing inclination to the abscissa, and very soon reaches a maximum rapidity. From this, again, there is another change in rate, this time in the reverse direction, for the curve becomes con- cave to the abscissa line, and gradually, shortening becomes slower until at last it ceases, when the tangent to the curve becomes parallel to the abscissa line. The time occupied by the writing point in travelling from b to c, as shown by the piece of time tracing V c', was ■^ ths of a second, ie. -075 sec. (iii.) The third portion of the tracing is from the highest point c to the point d, at which the lever again reaches the abscissa line. This part is called the PERIOD OF RELAXATION. The terminal point, d, is often a difficult one to determine with any accuracy, because the lever does not come instantly to rest ; but, as it always possesses some 34 EXPERIMENTAL PHYSIOLOGY inertia, it oscillates for a time about a mean position which it ultimately reaches. The difficulty therefore is purely instrumental,, and should be reduced to a minimum by working with as light a lever as possible. It is particularly marked when the relaxation process is. carried out very rapidly, and is completely absent when, from any cause, the time is prolonged. An examination of this part of the curve shows practically the same changes as the preceding portion,, though in the reverse order. It is at first concave, and then, after an intermediate portion in which the change of curvature is but slight, it becomes convex to the abscissa line. These changes mean that at first the rate of relaxation increases slowly, then more rapidly, until a maximum rate is attained, and from this gradually diminishes until relaxation ceases. The length of time occupied by this process, in the curve of fig. 38, is seen, by measuring c' d!, to be ^^ths of a second, or Fig. 38. — Isotonic Twitch of a Htoglossus Muscle. Time Tbacino, 200 per sec. Magnification, 3 (i.e. the Vektical Ordinate represents 3 times the AMOUNT OF shortening AT THAT INSTANt). ■075 sec. ; but this time measurement is not to be regarded as quite so ac- curate as the two preceding— it is probably estimated a little too high. By adding up these three time measurements it is seen that for this twitch the total time, occupied was -16 sec. So far we have been mainly occupied in a study of the curve with regard to its^^time relations, but there are other points which the curve f can teach us. In the first place the height of the curve will tell us the amount of the shortening that took place. The height of c from i the abscissa line is found to be exactly 20 mm. ; and as the magnifica- tion of the movement was 3, the amount the muscle contracted was 20 ^mm. The length of the muscle when loaded by the lever was 28 mm. Consequently the muscle contracted^ x-g^, i.e. nearly a o 28 quarter of its whole length. We may in the] next place estimate the amount of work per formed by the muscle during its twitch. This is given by the product; THE SIMPLE MUSCLE CURVE 35 of the load lifted into the height throngh which it is moved, or w =z.h. In this experiment the load, including the lever, was adjusted 20 to be 2 grms. Hence the total work was 2 x -^ = 13-33 grm mm. o This work was effected by the muscle in the time -075 sec. Hence the mean rate at which the muscle worked during its contraction was 13'33 -^^-^ = 178 grm. mm. per sec. ■075 The load was not, however, retained at ttie highest point, but F' F> F3 F* F' F« F' F» F» Fig. A B 39. — To Illcsteate the Meaning of the Cubte of Pig. 38. was allowed to fall again, and the lever ultimately came to rest at exactly the same level as at the start. Therefore, in falling, the load performed exactly the same amount of work upon the muscle as had been previously performed by the muscle upon the load. Moreover as in this particular example the time occupied in the relaxation happens to be identical with that of the contraction, the mean rate at which it was performed was identical with that of the former. The exact meaning of the curve of fig. 38 or of any other curve taken upon the same principle by the graphic method will be rendered very evident by a study of fig. 39. In this figure a b c d is an exact repro- duction of the curve of fier. 38. All measurements along a d represent d2 36 EXPERIMENTAL PHYSIOLOaY time, and ordinates at right angles to this indicate for this particular example changes in length of the muscle. The muscle was 26 mm. long ; consequently a f^ has heen drawn at right angles to a d and of three times that length (78 mm.) because the recording lever in tracing the curve magnified the shortening three times. f,F9 has been drawn parallel to ad and divided at Fi, Fj, Fj ... by a series of points which follow one another at intervals of four vibrations of the tuning- fork. Hence f, Fj, f^ f.,, . . . &c. each represent n^th of a second. Then f^ a^t F3 G3 . . . Fg d have been drawn parallel to a f, to cut the curve in Gj, Q3. . . . In this way we are able to state that at the instant a, at which the muscle was stimulated, its length was ^ a f. ^th of a second later its length was ^ f^ Gj ditto ditto ditto ditto T^uis ditto ditto It should be remembered that in a great number of these graphic records the true interpretation to be placed on the curves is one similar Aths ^ths Aths 3 F3G3 Fig. 40. — Simple Twitch of a Gastkoonemius. Time Tbacinq, 200 peb sec. Magnification, 5. to the above. As a rule, however, we shall find it sufficient to take into account only changes in length, width, &c., according to the move- ment which is being recorded. For purposes of comparison fig. 40 is iutroduced. This is a curve obtained in the same way, but given by a gastrocnemius. It shows the same features as those of fig. 38. The latent period is 001 sec. ; the period of contraction 0-05 sec. ; and that of relaxation O-l sec. The magnification in this case was five-fold. In recording a single muscle contraction by the method we have just employed, there is one factor in the method which causes an inaccuracy in the result we are aiming at, and as it leads to several im- portant considerations we must examine into it with some detail. This is that the recording lever must possess a certain amount of mass, and, as a consequence, is unable to foUow alterations in length in an absolute manner, more particularly when those alterations are THE EFFECT OF INERTIA 37 effected at some speed. That the mode of action of this factor may be made more clear, let us consider what happens during the twitch of a muscle to which a weight is directly attached. The force exerted by the muscle during its contraction acts directly on the weight, which it sets in motion, and produces an acceleration in it directly proportional to the force and inversely proportional to the mass moved. The result is that the weight gains a certain amount of kinetic energy by virtue of which it wiU continue to move upwards, even though the muscle force ceases to act upon it, until that kinetic energy is neutralised by the constantly acting force of gravity. This is exactly the condition, then, when the force of the contraction begins to diminish ; and if, as is usually the case, we are actually recording the movement of the weight, the record of the true alteration of length is distorted by the operation of this acceleration. But the acceleration introduces another alteration which is even of greater influence, for as the acceleration upwards increases, so more and more of the weight ceases to pull directly upon the muscle, i.e. its tension diminishes. The result of a diminution in tension is that the elastic force of the muscle comes into play and produces a shortening which thus interferes with the shortening process we are attempting to record. The greater the load pulUng upon the muscle the more will the action of acceleration interfere with the record. In the second process, that of relaxation, acceleration again comes into play. At first the tension diminishes because the weight does not follow the rapid relaxation instantaneously, but with a certain delay. When the relaxation is, however, becoming slower, the weight is moving down- wards with a certain velocity imparted to it by the action of gravity, and a time is reached when the weight is moving downwards with a velocity greater than the rate of lengthening of the muscle. The result is it acts upon the muscle and the tension begins to rise, increasing until it is equal to the weight plus that force necessary to stop the acceleration. The muscle is therefore stretched beyond its initial length, and then, when the acceleration of the weight is stopped, the excess of tension over load acts upon the weight which is once more lifted, acceleration imparted to it, and the whole process is once more repeated, until with a few more oscillations the weight at last comes into equilibrium. These final oscillations are to be observed in all tracings, and fig. 41 is reproduced especially in order to show them. The muscle recording was the double hyoglossus and the magnification five times. The only load attached to the muscle was the recording lever, in this case made of a light straw of about 25 cm. in length. The preparation was the same one that had been previously employed 38 EXPERIMENTAL PHYSIOLOGY to give the tracing of fig. 38, where we note that these oscillations are much less. To diminish the effects of acceleration we must always aim at employingrecording levers of as small a mass as is compati- ble with the neces- sary rigidity. The lever used for fig. 38 was much lighter than that used for fig. 41. It is, however, necessary for many experiments to study the contrac- tion when the mus- cle is loaded. We have seen that if we apply the load directly under the muscle, acceleration must come into play with the result that the tension does not remain constant, but during the earliest part of the contrac- tion period is in- creased, and during the later part and most of the period of relaxation it is below that of the weight, and at the end of relaxation it rapidly rises, and after a few oscilla- tions ultimately reaches the initial tension. The part w ■«! ft O w EH I s THE ISOTONIC AND ISOMETRIC METHODS 39 of the curve most markedly affected is the apex. Acceleration pro- duces a greater distortion the greater the rapidity of the movement we are attempting to record. In order to be able to record twitches under different tensions, and yet ensure that the tension remains practically constant throughout, Pick introduced what is known as the isotonic method. The end aimed at is to prevent acceleration of any part to be moved which possesses mass. This Pick obtained approximately by the arrange- ment shown in fig. 42. The weight w is not applied directly beneath the muscle m, but to a small pulley on the axis a, and therefore much nearer the axis than the point of attachment of the muscle. In the particular lever drawn the muscle is attached to the point p of the lever, 10 cm. from the axis. This part of the lever consists of a hght flat aluminium band, so that it is rigid in the direction in which move- ment takes place. The pulley has a radius of 5 mm. Hence the tension on the muscle is ^V^h of the weight w. The movement of the weight upwards is also only ^th of the muscle movement, and con- sequently the bad effects of acce- leration are diminished twenty- fold. The curves of figs. 38 and 40 are taken with this lever. There is a second important aspect from which we can study thephysicalmanifestations of the ^'•*- 42.-The Pkinciple of the Iso- '■ •' -, 1 . , TONIC Method. processes underlying a muscle contraction. This lies in answers to the questions : What happens if a muscle is prevented from shortening when it is stimulated ? What variation in tension, if any, takes place ? To investigate this problem Fick invented the isometric method, in which change of tension is re- corded and change of length is practically prevented. The principle of the method is illustrated by fig. 43. The muscle m is attached above to a rigid support and below to a lever, c a, at a point near its axis, A. The lever is continued behind a in the form of a stiff spring, A B, which rests on a rigidly fixed knife edge at b. A light writing point,' c, is attached to record the movements of ac. When the muscle is stimulated it tends to contract and hft up a c, but this is resisted by the spring a b, which is chosen of such a strength that the movement is very nearly prevented. The small upward move- ment of the lower rnuscle end is highly magnified by the long lever A D, and records the amount of bending of the spring a b. If now the forces required to bend the spring so as to produce definite move- 40 EXPERIMENTAL PHYSIOLOGY ments of the writing point are previously determined experimentally ^ any position of the writing point will be known to be caused by the-. B Fia. 43. — The Pbinoiplb op the Isomeieio Method. exertion of a certain force by the muscle. In this way, then, we may record variations in the force exerted by the muscle at different, instants of its contraction. Experiment 2. — Becord an isometric twitcb by means of the apparatus shown in fig. 44. The upper end of the muscle is to be fixed in the muscle forceps. The lower end by means of an S-shaped hook is attached to the lever x at a point near its axis. This axis consists of a stiff steel wire, w, which can be clamped at any position by the screw s''. About 2 mm. from the end of the axis the lever x is rigidly fixed perpendicular to it, and the project- ing piece fits loosely into a small socket in the brass support a. The brass arm b carrying the axis can be adjusted horizontally and clamped in any position Muscle Attached to ak Isometbio Lever. by the screw s', so that the free end of the axis just rests in its socket. Any rotation of the lever now produces a torsion in the steel axis, and this torsion is proportional to the amount of rotation of the lever. By hanging weights on the lever and observing the torsions produced we shall then &iow that when that same displacement is produced by a muscle the tension exerted, which is exactly opposed by the torsion of the wire, is to be measured by the previously appUed weights. Arrange the recording and stimulating apparatus. THE ISOMETRIC TWITCH 41 as for a simple twitch, p. 30, and then dissect out a muscle preparation. This should be the semimembranosus and gracilis (see p. 19). If we ohoosfr a small muscle which will only exert a small tension, a long piece of the torsion wire must be taken ; if a powerful muscle a short piece. The muscle may be stimulated directly or indirectly. Beoord the twitch and tuning-fork tracing as before, and then determine the point of stimulation and draw an abscissa line. Next remove the muscle and to the lever attach a thread, which passes over a pulley held in the muscle forceps and to its free end hang a weight. This pulls up the lever and the writmg point. By rotating_ the drum draw a line parallel to the zero abscissa. Now hang on a larger weight,, and so obtain a second line, and by a series of these evaluate the movements of the writing point. The form of curve obtained by this method is seen in fig. 45. These curves were all taken from the same double semimem- FiG. 45. — Thbee Isometeio Twitches with Different Initiaii Tensions. The KUMBEBS ON the LeFT INDICATE THE NuMBEB OF ObAMS BEQUIBED TO BeING the Leteb to the Level of the Coebesponding Hobizontal Line. branosus and gracilis preparation with maximal stimuli, the only alteration in the conditions of the three experiments being with regard to the initial tension of the muscle. The horizontal lines indicate the amount of displacement of the lever by given weights, which are expressed in grams. The general form of the curve is seen to closely correspond to that of an isotonic tvritch, but measurement shows a few important dififerences. There is a latent period, a period of rising tension, and one of falling tension. The apex of the curve is seen to be rounded. 42 EXPERIMENTAL PHYSIOLOGY ■The rise of tension is seen to be, on the whole, fairly uniform in rate, being slow at the commencement, and near the apex. Undula- tions on the curve are instrumental in character, and are due to the extremely disadvantageous position from which the lever is moved. The measurements of such curves should be arranged in tabular form, as in the following table : — Initial Tension in Grams Maximum Tension in (jrrams Latent Period in Sees. Apex Time in Sees. Total Time in Sees.' I II III 5-7 16-7 30-4 55-6 66-7 •005 ■006 •007 •057 •06 •065 •117 •142 •170 From this table it is seen that the maximum tension attained during a twitch becomes greater when the initial tension is raised. With rise in initial tension the latent period, apex time, and total time all increase, but the greatest increase is in the period of falling tension. By comparing these three measurements with those given for an isotonic twitch (pp. 33-36) it is seen that the apex time for an isotonic twitch is longer than for an isometric, but that the period of relaxa- tion is practically the same as the period of decreasing tension: The aim of an isometric twitch is to be able to record the tensions a muscle is able to exert at each instant of a twitch carried out, when it is prevented from shortening. It is important to recognise that the methods employed for this purpose can only give us an apiproxi- mate result. This is due to the fact that we cannot prevent the muscle fibres from shortening, at any rate in part. When a muscle is stimulated the whole length of each fibre does not commence con- tracting at the same instant, but one part is first affected, and from this, as a centre, a w&,ve of contraction travels along the whole fibre. As a result the part which first contracts exerts an increased tension upon the rest of the muscle fibre, which it stretches, and at the same time this extension allows it to contract. We could get a better solution to the problem if we could simultaneously stimulate the whole length of each muscle fibre, so that all its parts commenced contracting at the same instant. THE METHOD OF AETER-LOAD In our study of the muscle twitch up to this point we have mainly been dealing with contractions carried out whilst the load on the muscle was as nearly as possible constant. There is, however, another AFTER-LOAD - 43 method which very commonly obtains in many of our bodily move- ments, in which the muscle is under a low tension until it commences to contract, and then, only, experiences a rise of tension. We can imitate such a process by the plan of supporting the weight, and only allowing it to act on the muscle when it has already begun to con- tract. This is called the method of after-loading. Experiment 3. — To examine the nature of a twitch under such ciremn- stances arrange the apparatus as for taking a simple twitch. Prepare a gastrocnemius and attach it to the modified simple lever shown in fig. 46. This consists of an ordinary simple lever, but to the frame carrying the axis is fitted a stout brass plate, b, which nms parallel to the writing lever but not vertically under it. The end of this plate has a piece which projects under the lever and carries a screw, s. This can be screwed up so that the tip of -the screw can support the metal part of the writing lever at any level. Load the muscle, e.g. with a load of 20.g'., which, preferably, should be applied Fig. 46. — Abbangement of Simple Leveb for Eecokding by the Method of Aftek-load. hy a proportionately heavier weight attached nearer to the axis. Screw down the screw so that the whole load is carried by the muscle, and bring the writing lever to a, horizontal position. Now record a simple twitch. Next screw up the screw to support the writing lever, so that the writing point is placed at the level of the apex of the curve just taken. Record firom this position another curve. It will be found thai the muscle still raises the lever. Raise the screw s once again until the level of the writing point is at the summit of this second curve, and again record a twitch. Repeat the process two or three times more. Pig. 47 gives a series of curves obtained in this way. They are taken from a gastrocnemius in the manner described. The very striking and highly characteristic feature of these curves is that j though the weight is supported at a level which it just reached at : the height of a previous contraction, yet it is further raised when the ' muscle is again stimulated. Under such conditions, then, the muscle | contracts to a greater degree than when freely loaded. As was to be •expected, the latent period is longer in this second case, and, as the \ tracings show, becomes still further prolonged as the height of sup- port of the weight is increased. The time measurements show for the four successive curves here reproduced '01 sec, '035 sec, '042 sec. 1 44 EXPERIMENTAL PHYSIOLOGy and '065 sec. respectively. Two things are happening in these later twitches which account for this difference. In the first place, the muscle is taking in any ' slack ' there may be. Secondly, and Fig. 47. — Twitches Taken undeb the Pbinoiple of Aftek-loading. ! more important, it is gradually increasing its tension until it is able I to lift the load. The first part of such a twitch is therefore isometric ; \ but beyond a certain point it suddenly becomes isotonic, and its 1 shortening is then registered. I ALTERATIONS IN THE SIMPLE TWITCH BROUGHT ABOUT BY VARIOUS CONDITIONS I. The Influence of Temperature. — The differences in a simple twitch, brought about when the same muscle is at different tem- peratures, may be studied in many ways. If we are recording the twitches by a crank lever the muscle may be laid upon a metal base arranged so that it can be heated. Thus, in one form, the base is hoUow so that water at different temperatures can be circulated through it. In another a stout metal •mre is soldered to it, which is immersed in water at different temperatures, and so its temperature raised or lowered as required. In another form the muscle is sus- pended in a small moist air chamber made of hoUow metal walls through which water is circulated. The chamber is completely closed except by a small orifice at the bottom through which the thread passes, attaching the lower end of the muscle to the recording lever. One of the most convenient forms is shown in fig. 48. This is to be employed for the purpose in the following experiment : — Experiment 4. — ^Arrange the apparatus as for taking a simple twitch. Fit a cork c (fig. 48) tightly on to the lower end of the metal L-pieoe a b c. A weight w is hung round the little pulley d of the recording lever, so that it rotates the lever upwards. A muscle preparation is then made and its lower end fixed firmly by a pin to the upper edge of the cork c. The best preparation for the purpose is a hyoglossus or a sartorius, but a gastrocne- mius may also be used. The upper end of the muscle is then fixed by a fine EFFECT OF TEMPERATURE 45 thread to the lever. The tenBion on the muscle may be varied by altering the weight w. The electrode wires from the secondary coil are connected (1) to the pin fixing the lower end m, and (2) by a very fine light wire, n, passing through the upper end of the muscle. With this apparatus each twitch of the muscle piillB the lever downwards. The magnification should be about threefold or a little higher. The temperature of the muscle can now be altered at will by bringing up a small beaker containing a fluid at the required temperature, so as to immerse the muscle and the vertical limb of the L-piece. The immersion fluid may be normal saline made with tap water instead of distilled water, though it is bet- ter to employ defibrinated ox-blood which has been diluted with four times its balk of normal saline solution, for it is found that the cha- racter of the contraction is very markedly altered if a muscle be soaked in normal saline for any Fig. 48. — Apparatus fob Varying the Temperatures op a Muscle by Immersion. length of time. Having set up the muscle immerse it in fluid at about 0° C. for three or four minutes, and then remove the fluid and record a twitch in the usual way. Without removing the writing point from the surface, again im- merse the muscle, having previously warmed the beaker of fluid by placing it in warm water imtil its temperature has risen to 5° C. In three minutes remove the beaker and, if necessary, accurately adjust the writing point to the level of the previous abscissa, and then record a second twitch. Eepeat this for several higher temperatures, when a tracing similar to that of fig. 49 will be obtained. This tracing was given by a hyoglossus, the drum moving at a rapid rate. The various points in the curves should now be examined and the necessary measurements arranged in tabular form, as has been done in the following table for the curves of fig. 49 : — Temperature Latent Period Contraction Time Relaxation Time Height of Tjritoh in mm. Mean Bate of Worlc 7°C. 10 15 20 25 30 4-5 3-25 3-0 2-75 2-25 1-5 36 20 15 11 9 8-5 37 28 21 14 10 8 14 10-5 9-25 8-5 8-5 100 26 35 41 47 58 78 In this table all the time measurements are recorded in -j-^ths of a second, and for the height of twitch the highest point of the tracing from the abscissa line in millimetres. The amount of contraction is therefore obtained by dividing these last figures by 3, the amount of magnification. As the load was the same in all cases the total work in each case is proportional to the figures of the fifth column. 46 EXPEEIMENTAL PHYSIOLOGY Ph a s m H I I The mean rate of work is given in grm mm. per second in the last column. !Prom the tracing and from the measurements given in the table the fol- lowing points can be induced. 1. As the temperature rises the latent period, as measured by this method, gra- dually decreases, at first with some rapidity and then more slowly. These experiments, however, do not prove that the true latent period is diminished, for, as above explained, there are several factors at play tending 'to make the measurement by this method too high. The differences can probably be entirely accounted for in this experiment by the increase in the rate of propagation of the muscle wave as the temperature rises. 2. The period of contraction becomes markedly shorter as the temperature rises : at first the rate very rapidly increases, but after about 16° C, though stiU in- creasing, its rate of increase is much slower. 3. The period of relaxation varies in the same manner, but to a more marked degree. When the temperature is low relaxation is slower than contraction, in many experiments very much more so than in this particular instance. At higher temperatures relaxation is carried out more rapidly than contraction. 4. Perhaps the most interesting point in the whole series is vnth regard to the height of the twitch. In this case the maximum height was at 7° C, and the height diminished as the temperature rose to 20° C, at which a relative minimum height occurred. When the temperature was still further raised the height of twitch began once more to increase, and tended towards a second maximum at about 30° C. EFFECT OF TEMPERATURE 47 5. As the load was the same throughout the series of twitches, the total work performed in the several oases is proportional to the heights of lift, and therefore shows the same variations as those pointed out in 4. If, however, we examine the work from the point of view of the rate at which it was performed we see from the figures of the last column that there is a progressive increase in the rate of work- ing which is particularly marked when the relative minimum height at 20° C. has been passed. These rates of work are calculated, as previously described (p. 35), by dividing the amount of shortening by the time of contraction and multiplying by the load, which in this instance was one gram. Por purposes of comparison in fig. 50 is reproduced a similar series where the gastrocnemius was employed. The arrangement of the apparatus was slightly different, being the one figured on p. 112, the muscle being fixed in the position at which the heart is there Fig. £0. — Twitches of a Gastkocnemids at Diffekent Tempekatuees. Time Tbaoing, 200 PER SEC. Magnification, 5. attached. The time tracing is 100 per sec, and the drum was moved at a rather slower rate. The general result is the same as in the previous example ; but it is to be noticed that there is no relative minimum of height of twitch at 20° C. To complete our account of the influences of temperature upon the twitph there are one or two other facts known which do not appear in these tracings. It is found that if the temperature be still further lowered the total height of twitch is still further increased, and the relaxation much more markedly prolonged, and, as 0° C. is approached, there is a rapid change in the direction of diminution in the amount of contraction, till at last none is produced. If, on the other hand, the temperature be still further raised the amount of con- traction increases until about 32° C. is reached : from this tempera- ture the height rapidly diminishes, until the muscle goes into heat contraction at 34° C. The twitches at the higher temperature are of the same total duration, although their height is less. 48 EXPERIMENTAL PHYSIOLOGY II. The Influence of Load. — The effect of load upon the characters •of a simple twitch are to be studied in three ways : (1) where the load is applied by the isotonic method ; (2) where it is applied •directly to the muscle ; (3) where the load only acts on the muscle when it begins to contract. Experiment 5. — Arrange the apparatus as for a simple twitch. Prepare A muscle and fix it in the isotonic lever as in fig. 42. The writing lever should be made as light as possible. The ordinary crank myograph lever «ould also be employed, in which case the loads are to be applied at a point near to the axis. First record a simple twitch with the muscle weighted by the lever only. Then hang on a weight to the pulley by a thread. This extends the musclej and the writing point must therefore be brought back to its original level by raising the upper support of the muscle. Now record a second twitch. Increase the weight and bring the lever once more to its original level and record a third contraction. This may also be repeated until the amount of the contraction becomes very small. Eig. 51 shows a tracing obtained in this way. The muscle was the hyoglossus. The loads in grams additional to the weight of the Fio. 51. — Twitches of a Hyoglossus with Dh'fekent Loads. Time Teaoing, 200 PEK sec. Magnifioation, 3. lever are written over the curves. Fig. 52 is a similar figure taken from a gastrocnemius. Fig. 52. — Twitches of a Gastkoonemius with Different Loads. Magnification, 5. The following effects are to be noticed : — 1. The latent period increases as the load increases. 2. The length of the period of contraction also tends to increase. INFLUENCE OF VERATfilNE 49 This is better seen in fig. 52, obtained from a gastrocnemius, than in fig. 51, from a hyoglossus. 3. The period of relaxa,tion is at first markedly decreased. With higher loads it tends to increase again, often to a considerable degree. 4. The heights of the contraction progressively diminish as the load rises. HI. THE INFLUENOE OF VERATEINE Experiment 6. — Destroy a frog's brain by pithing, leaving the spinal cord intact. Inject 5 minims of a 0'005 per cent, solution of veratrine dis- solved in normal saline solution by the aid of a drop of weak sulphuric acid. Arrange the apparatus for taking a single contraction, but with the drum to rotate at a much slower rate (about 6 cm. per minute). After about half an hour pith the spinal cord and dissect out the gastrocnemius and sciatic, and fix the muscle in the myograph.. In the preparation of the muscle care should be taken to avoid stimulating it or its nerve. Adjust the writing point to the blackened surface, and set the drum rotating. At any instant the muscle may be stimulated by opening the break key by hand. Note that the excitability is diminished, and a stronger stimulus than usual is required. The contraction will be effected quickly, but the relaxation is carried out very slowly, occupying some seconds. As soon as the muscle has completely relaxed, stimulate it once more. It will be found that the character of the twitch is completely altered. It is much more rapid. One or two more contractions may also be recorded, and then the muscle allowed to rest for a time. If it be then once more stimulated it wiU be found that the muscle has again returned to its previous state and the contraction is greatly pro- longed. The most satisfactory preparation to use for this experinient is the hyoglossus. This is attached to the lever in the usual way, and then a few drops of a 1 per 100,000 solution of veratrine in normal saline is injected into the large lymph sac in which the hyoglossus hes. If a very weak solution be directly employed in this way the muscle is ready for use almost at once, and the experiment never fails. Fig. 53 represents two curves produced in such an experiment. Curve I is the first twitch, and curve ii the sixth recorded. The first curve shows the characteristic effect produced. The early part of the period of contraction is effected as rapidly as in a normal twitch, but the latter part is very slow, lasting three seconds. The period of relaxa- tion is 46 seconds. In curve ii the total duration of the twitch has greatly diminished, viz. to 18 seconds, and another feature is present which is highly characteristic of veratrine ; namely, that there is a double apex. The first contraction is carried out almost as rapidly as in a simple twitch, and it is then followed by a second con- traction of very slow course, with rounded apex and showing a slow relaxation. The form of such a curve varies considerably in different instances. Sometimes the muscle may almost completely relax before the second contraction sets in, or again the second contraction may^ follow the first when that has reached its apex as in tracing i. If 50 EXPERIMENTAL PHYSIOLOGY the muscle be made to contract more frequently, and has not received too large a dose of veratrine, an almost normal contraction may be produced after a few stimulations. Pio. 53.^Two Twitches given by a Muscle Poisoned with Vekatrine. Time in Seconds. THE "WOEK PERFORMED DURING A TWITCH We have already pointed out how the amount of work performed during a twitch can be determined, and have studied some variations which occur on altering the conditions under which the contraction is carried out. It now remains to examine more completely the variations in the amount of work as the load is increased. The amount of work is represented by the product of the load lifted into the height of lift, so that if we simply require the total work per- formed we need only record the heights of the series of twitches. Experiment 7. — Arrange the primary coil with a spring key for raaking and breaking the circuit by hand. Place a Du Bois key in the secondary with two fine wires for electrodes. Prepare the myograph lever and measure the distances of the point of attachment of the muscle and the end of the writing point from the axis. The writing point should be cut so that the ratio of the two is some simple multiple, e.g. 5. Next prepare a gastro- cnemius and attach one electrode to the fixed end, the other to the movable end of the muscle. Adjust the position of the secondary coil until it just gives maximal stimuli. Load the muscle with a tension of 40 grams, apply- ing the weight at a point nearer the axis than the point of attachment of the muscle. The weight required to produce a tension of 40 grams wUl be found by multiplying 40 by the ratio between distance of muscle attach- ment to axis to distance of weight attachment to axis. This tension will elongate the muscle. The lever must therefore be brought back to the horizontal by altering the position of the fixed end of the muscle. Rotate the same a little to mark the level of the lever. Stimulate with a make shock recording the height of twitch on a stationary blackened surface. Increase the tension to 80 grams and repeat the process. Take a series of heights in this way, each time increasing the load by a fresh 40 grams.^ > The load chosen must depend on the size of the muscle. That of 40 grms. as here given is the most convenient for a medium-sized gastrocnemius. WOEK PERFORMED DURING A TWITCH 51 In this way a series of vertical lines have been recorded which give the heights of the several contractions. Now take a piece of squared paper and mark off these contractions in series, say 1 cm. apart, measuring each contraction from the short horizontal mark to the apex. In this way a series of lines similar to those above o x in fig. 54 will be recorded. Mark above each the weight with which the muscle was loaded at that contraction. The experiment from which Y * 00 „ Q o o o SS l5