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Full text of "The essentials of experimental physiology, for the use of students"



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EXPERIMENTAL PHYSIOLOGY 



A TEXT-BOOK OF CHEMICAL PHYSIOLOGY AND PATHO- 
LOGY. By W. D. Halliburton, M.D., F.R.S., M.R.C.P., Professor of Physiology 
in King's College, London ; Lecturer on Physiology at the London School of 
Medicine for Women. With 104 Illustrations. 8vo. 28s. 

ESSENTIALS OF CHEMICAL PHYSIOLOGY. By W. D. 

Halliburton, M.D., F.R.S., M.R.C.P., Professor of Physiology in King's College, 
London ; Lecturer on Physiology at the London School of Medicine for Women. 
8vo. 5s. 

*»* This is a book suitable for medical students. It treats of the subject in the 
same way as Prof. Schafeu'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 INTRODUCTION TO HUMAN 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. Third 
Edition, Revised. With 314 Illustrations. 8vo. 18s. 

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 Anuual Electricity. 8vo. 5s. net. 

EXERCISES IN PRACTICAL PHYSIOLOGY. Part I. Elemen- 
tary Physiological Chemistry. By Augustus D. Waller and W. Leoue Symes. 
8vo. If. net. Part II. in the press. Part III. Physiology of the Nervous 
System ; Electro-Physiology. 8vo. 2s. 6rf. net. 

THE ESSENTIALS OF HISTOLOGY. Descriptive and Practical. 

For the Use of Students. By E. A. Schafer, F.R.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, Revised and Enlarged. 8vo. 7s. 6<7, (Interleaved. 10s.) 



LONGMANS, GREEN, & CO., 39 Paternoster Row, London 
New York and Bombav. 



THE ESSENTIALS 



OF 



EXPERIMENTAL PHYSIOLOGY 



FOB THE USE OF STUDENTS 



BY 

T. G. BRODIE, M.D. 

LECTURER ON PHYSIOLOGY, ST THOMAS'S HOSPITAL MEDICAL SCHOOL 



LONGMANS, GREEN, AND CO. 

39 PATERNOSTER ROW, LONDON 
NEW YORK AND BOMBAY 

1898 

A.11 rights reserved 



PREFACE 



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 Practical Physiology given by Professor 
Halliburton at King's College, which was based upon the ' Syllabus 
of Lectures ' published by Professor J. Burdon Sanderson 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 McKendrick, Yeo, Halliburton, and Waller. The 
source of these figures is indicated in each case. The reproductions 
of the tracings are all 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. Palmer, and 
are especially designed for class work. 

The plan of the book varies slightly from that adopted by Professor 
Schafer and Professor Halliburton in their ' Essentials.' I have 

i i 



1 11 



vi EXPERIMENTAL 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 advanced course., The number of elementary 
experiments given is only small, and a detailed list of them will be 
found on p. xiv. 

To Professor Halliburton and to Professor Schafer my best 
thanks are due for the many suggestions and criticisms with which 
they have aided me during the preparation of the book. To Dr. 
A. E. Eussell, Medical Eegistrar, St. Thomas's Hospital, I am 
especially indebted for many valuable suggestions and alterations, and 
for his assistance in reading and correcting the proofs. 

T. G. BRODIE. 

St. Thomas's Hospital, December 1897. 



CONTENTS 



CHAPTER 
I. 



II. 
III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XL 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

XXI. 
XXII. 



PAGE 

Some Physical Instruments in Constant Use in Physiological 

Experiments .......... 1 

Preparation of a Frog's Muscle. Its Response to Stimula- 
tion. The Graphic Method 16 

A Single Contraction of a Frog's Muscle. Its Modification 

under Changes in the External Conditions .... 30 

Summation of Muscular Contraction. Tetanus . . . . 56 

Fatigue of Muscle 66 

The Thickening of a Muscle on Contraction. The Muscle Wave 71 
Independent Muscular Excitability. Excitation of Muscle by 

the Constant Current. Polarisation of Electrodes. . . 76 

Some Experiments to Determine the Functions of Nerves . 85 

Examination of the Frog's Heart. The First Stannius Ligature 97 
The Action of Heat and Cold upon the Frog's Heart . .112 

The Nerves of the Frog's Heart and Their Functions . . 120 

Action of Drugs upon the Frog's Heart 130 

Some Further Methods for Examining the Activity of the 

Frog's Heart 134 

Demonstration of the Movements of the Mammalian Heart. 

The Cardiograph 138 

Some Experiments in Electro-physiology 146 

Schema of the Circulation. The Sphygmograph . . • 157 

Demonstration of Blood Pressure and its Nervous Regulation 168 

The Kidney. Demonstration of an Oncometer Experiment . 189 
Demonstration of the Nervous Regulation of Respiration. 

The Stethometer and Pneumograph 201 

Demonstration of the Secretion of Saliva from the Submaxil- 
lary Gland of the Dog .....••• 209 
Reflex Action as Studied upon the Spinal Cord of the Frog 214 
Some Experiments in the Physiology of the Eye. Accommoda- 
tion, Ophthalmoscopy, Colour Sense, Perimetry . . . 218 



LIST OF ILLUSTRATIONS 



TO. 

Plate I. Eecord of a Series of Successive Twitches of 
a Hyoglossus Muscle Stimulated, by Make Shocks, once 
each Second To face p. 70 

Plate II. Eecobd of the Blood Pbessuee and Eespiration 

in a Rabbit dubing Asphyxia „ 182 

1. The Daniell Battery (McKendrick) i*age 2 

2. The Gbenet Batteby (McKendeick) 2 

3. The Bunsen Batteby (McKendbick) 3 

4. The Gbove Batteby 3 

5. The Leclanche Battery (McKendrick) 4 

6. The Induction Coil (McKendrick) 4 

7. Diagram of the Currents Induced in the Secondary Coil . . G 

8. Aeeangement of Appaeatus fob Equalising the Make and Bkeak 

Shocks 7 

9. To Illusteate the Action of Neef's Hammee ..... 8 

10. To Illustrate the Action of Neef's Hammee with the Helmholtz 

Modification 9 

11. Two Foems of Mercury Key | .„ 

12. Two Forms of Meecuey Key j 

13. Simple Form of Spring Key 10 

14. Two Forms of the Du Bois Key i . , 

15. Two Forms of the Du Bois Key J 

16. Plan of the Arrangement of the Du Bois Key as a Short-circuit- 

ing Key 11 

17. Aeranged as a Simple Break Key. Not to be used aftek this 

Method in a Secondaey Ciecuit 11 

18. Pohl's Commutatoe ........... 12 

19. A Foem of Cut-out Key ......... 13 

20. Aeeangement of Apparatus foe Making Use of Single Induced 

Shocks 14 

21. Arrangement of Apparatus to Show the Break Extra-current . 14 

22. Leo Muscles of the Frog seen from the Inner Side . . . . 17 

23. Leg Muscles of the Frog seen from the Outer Side ... 17 

24. Gasteocnemius-sciatic Peepabation 18 

25. Aeeangement of Appaeatus for Showing Make Extea-cubbent . 19 

26. The Relations of the Hyoglossus in the Fbog 20 

27. Two Records of the Vibrations of a Tuning-fork Vibrating at the 

Rate of 10 per sec 22 

28. A Time-marker or Chronograph (McKendrick) 23 

29. A Spring Chronograph 24 

30. Lower Part of Drum to show Method of Driving the Cylinder 

at Diffeeent Rates 24 



x EXPERIMENTAL PHYSIOLOGY 



i ii. 



PAGE 

31, Muscle held in Muscle-forceps and attached to Simple Lever . 25 

:',-2. Simple Form of Wire Electrodes 26 

83. ELeights of Contraction of a Muscle with Different Strengths of 

Stimuli 27 

34. Marey's Form of Recording Tambour (McKendrick) .... 28 

35. A Second Form of Recording Tambour 29 

3G. A Break Key 30 

37. Plan of the Arrangement of the Apparatus for Recording a Simple 

Twitch 31 

38. Isotonic Twitch of a Hyoglossus Muscle 34 

39. To Illustrate the Meaning of the Curve of Fig. 38 . . . . 35 

40. Simple Twitch of a Gastrocnemius 36 

41. Twitch of a Hyoglossus recorded by a Heavy Lever . . . . 38 

42. The Principle of the Isotonic Method ...... 39 

43. The Principle of the Isometric Method 40 

44. Muscle Attached to an Isometric Lever ...... 40 

45. Three Isometric Twitches with Different Initial Tensions . . 41 

46. Arrangement of Simple Lever for Recording by the Method of 

After-load ............ 43 

47. Twitches Taken under the Principle of After-loading . . . 44 

48. Apparatus for Varying the Temperatures of a Muscle by Immersion 45 

49. Twitches of a Hyoglossus at Different Temperatures ... 46 

50. Twitches of a Gastrocnemius at Different Temperatures . . . 47 

51. Twitches of a Hyoglossus with Different Loads .... 48 

52. Twitches of a Gastrocnemius with Different Loads . . . . 48 

53. Two Twitches given by a Muscle Poisoned with Veratrine . . 50 

54. Work-diagram of a Gastrocnemius for Single Twitches . . . 51 

55. Simple Form of Pendulum Myograph 53 

56. Trigger Key ............ 54 

57. Simple Twitch of Hyoglossus Muscle recorded by the Pendulum 

Myograph ... ......... 55 

58. Arrangement of Upper Part of Drum for applying Two Stimuli to 

a Muscle 57 

59. Effect of Two Successive Stimuli, with Gradually Diminishing 

Intervals, upon a Gastrocnemius 58 

60. Mode of Fitting up a Vibrating Reed 60 

61. Reed arranged to Vibrate in a Horizontal Plane .... 61 

62. The Gradual Production of Tetanus as the Rate of Stimulation 

was Increased 62 

63. The Genesis of Tetanus with Slow Rotation of Recording Surface 64 

64. A Series of Twitches of the Hyoglossus made to Contract every 

half-second to show the Alteration in the Twitch as the Muscle 

becomes Fatigued 68 

65. Prolonged Tetanisation of a Hyoglossus showing Relaxation as 

the Muscle became Fatigued ........ 70 

66. Method of Recording the Thickening of a Muscle as it Contracts 71 

67. Curve I the Shortening, and Curve II the Thickening of a Semi- 

membranosus and Gracilis Preparation 72 

68. Diagram to Illustrate Wave Movement 73 



LIST OF ILLUSTRATIONS XI 

KIG. PAG K 

69. Apparatus for Becording the Thickening of a Muscle at Two Points, 

for the purpose of studying the muscle wave .... 74 

70. The Thickening of a Muscle 75 

71. Method of Studying Polar Excitation of a Muscle .... 80 

72. Method of Arranging the Apparatus to Show Polarisation of Elec- 

trodes 82 

73. Several Models of Unpolarisable Electrodes (Waller) ... 83 

74. Simple Form of Unpolarisable Electrodes 83 

75. Plan of Apparatus for Studying the Changes of Excitability of 

Electrotonus 88 

76. Diagram Indicating the Changes of Excitability of a Nerve in 

Electrotonus 90 

77. To Illustrate the Principle of the Monochord .... 91 

78. A Second Form of Monochord 92 

79. The Eheochord as Arranged for Varying the Direction and 

Strength of a Current through a Nerve 92 

80. Arrangement of Apparatus for Studying the Velocity of a Nervous 

Impulse ............. 95 

81. Two Twitches of a Gastrocnemius when the Sciatic was Stimulated 95 

82. Anterior and Posterior Surfaces of the Frog's Heart ... 97 

83. Apparatus for Recording the Heart Beat by the Suspension Method 99 

84. Record of the Movements of the Frog's Heart by the Suspension 

Method 100 

85. Application of the First Stannius Ligature to the Frog's Heart 104 

86. Electrical Stimulation of the Ventricle of the Frog's Heart in 

Standstill by the Stannius Ligature to Show the ' Staircase ' 

Effect 106 

87. A Simple Form of Flexible Electrodes 106 

88. A Single Contraction of the Frog's Ventricle .... 107 

89. A Single Contraction of the Frog's Ventricle 108 

90. A Repetition of the Tracing of Fig. 89 with a Slower Movement 

of the Recording 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 for Varying the Temperature of a Frog's Heart . . 112 
94 a. Tracings Obtained by Immersing an Excised Frog's Heart in 

Diluted Blood at Different Temperatures . . . . . 114 
94 b. Tracings Obtained by Immersing an Excised Frog's Heart in 

Diluted Blood at Different Temperatures . . . . .115 

95. Single Contractions of the Frog's Ventricle at Various Tempera- 

tures 117 

96. Diagram of the Variations of the Duration of a Single Ventricle 

Contraction at Different Temperatures 118 

97. Diagram of the Variations in Height of Contkaction of the Frog's 

Ventricle at Different Temperatures 118 

98. To Show the Course of the Vagus in the Frog .... 120 

99. The Course of the Sympathetic in the Frog 121 



x ii EXPERIMENTAL PHYSIOLOGY 

eaaB 
no. 

100. Effects or Tetanisino the Vagus with Diefkkext Strengths ok 

Stimuli 12i * 

101. The Effect of Tetanisation oe 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 of Nicotine directly 

to the Heart 1^2 

105. Tracings Eecorded by a Lever Besting upon a Frog's Heart . . 134 
10G. Roy's Tonometer (Halliburton) 135 

107. Sen a fee's Frog-heart Plethysmograph 136 

108. Frog-heart Plethysmograph by which the Pressure Changes can 
also be Recorded by a Small Manometer 137 

109. A Simple Form of Apparatus for Artificial Respiration . . . 139 

110. Arrangement of Levers for Recording the Movements of the Mam- 

malian Heart by Attaching Threads to the Auricle and Ventricle 

■ respectively ............ 140 

111. Tracing Obtained from the Rabbit's Heart, Employing the Levers 

of Fig. 110 14 1 

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 Citrate 143 

114. The Cardiograph 144 

115. A Cardiogram taken upon a Man 145 

116. Kuhne's Experiment of 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 of Measuring the Muscle 

Currents ............. 152 

121. Lippmann's Capillary Electrometer (Waller) 154 

122. Currents of Frog's Heart (Waller) 155 

123. Arrangement of Apparatus to Show the Paradoxical Contraction . 156 

124. Schema of 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 of the Levers in Marey's 

Sphygmograph 164 

128. Sphygmogram Taken by Marey's Sphygmograph 165 

129. Richardson's Modification of Dudgeon's Sphygmograph . . . 166 

130. Plan of the Levers in Dudgeon's Sphygmograph .... 166 

131. Two Sphygmograms Taken by a Dudgeon's Sphygmograph . . . 167 

132. Arrangement of Apparatus for a Blood-pressure Experiment . . 169 

133. Dissection of the Nerves of a Babbit's Neck 170 

134. Two Forms of Cannula 170 

135. Tracing of the Blood Pressure from a Babbit taken by the Mercury 

Manometer 172 

136. Blood Pressure and Respiratory Tracing of a Curarised Cat under 

Morphia 173 



LIST OF ILLUSTRATIONS Xlll 

FIG. PAGE 

137. Stimulation of the Depressor Nerve in a Rabbit . . . . 174 

138. Stimulation of the Central End of the divided Sciatic . . . 17G 

139. Pressor Effect Produced by Stimulating the Central End oe the 

Sciatic of a Curarised Cat under Morphia . .... 177 

140. Stimulation of the Peripheral End oe the Left Vagus in a Rabbit 178 

141. Two Successive Stimulations of the Peripheral End of the Right 

Vagus with the Same Strength of Stimulus ..... 179 

180 
181 
183 
183 
184 
184 



142. Stimulation of the Central End of the Left Vagus in a Rabbit 

143. Effect of an Injection of Nicotine upon the Blood Pressure 

144. To Illustrate the Inertia of a Mercury Manometer . 

145. Fick's C-Spring Manometer (Yeo) 

146. Tracing by Fick's Manometer 

147. Hurthle's Manometer ......... 

148. Tracings of Blood Pressure of the Rabbit by Hurthle's Manometer 185 

149. Stimulation of the Peripheral End of the Vagus . . . . 186 

150. Normal Blood Pressure and Respiration 187 

151. Ludwig's Stromuhk 187 

152. Two Sizes of Roy's Ktdney Oncometer 190 

153. To Illustrate the Principle of Roy's Oncometer . . . . 190 

154. The Oncograph 191 

155. An Air Oncometer for the Kidney 191 

156. Simultaneous Tracing of the Volume Changes of 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 Respiration on Stimulation of the Superior Laryn- 

geal Nerve 203 

161. Effect upon Respiration of Stimulation of the Glossopharyngeal 

Nerve 204 

162. Result of Section of the Vagus, the other Nerve having been 

Previously Divided 204 

163. Stimulation of the Central End of the Vagus, both Vagi having \ 

been Divided 

r 20') 

164. Stimulation of the Central End of the Vagus, both Vagi having 



tsa j 



been Divided 

165. Marey's Pneumograph (McKendrick) 206 

166. Sanderson's Stethometer 207 

167. Mode of Applying the Stethometer to Record Changes in Trans- 

verse Diameter of the Chest 207 

168. Record of Changes in the Transverse Diameter of the Thorax 

during Respiration (Man) 208 

169. The Relation of the Veins to the Submaxillary Gland in the Dog 209 

170. Relations of the Duct and Nerves of the Submaxiliary Gland in 

the Dog 210 

171. The Phakoscope (McKendrick) 220 

172. The Reflected Images as seen in the Phakoscope .... 220 

173. To Illustrate Scheiner's Experiment 221 



xiv EXPERIMENTAL PHYSIOLOGY 

MO. PAGE 

174. The Course of the Light in the Indirect Method ok Employing 

the Ophthalmoscope 223 

175. The Course of the Light in Examining the Eye by the Direct 

Method 223 

17(1. I'uikstlky-Smith's Perimeter (Halliburton) 225 

177. A Pebimetbic Chart for the Right 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 Important Keys 10 

The Nerve-muscle Preparation ......... 16 

The Hyoglossus Preparation 20 

The Simple Lever 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 of Nerve 86 

Record of the Beat of the Frog's Heart 97 

Excision of the Frog's Heart 101 

Action of the Vagus upon the Frog's Heart 120 

Reflex Action Studied on the Frog 214 



THE ESSENTIALS 



OF 



EXPERIMENTAL PHYSIOLOGY 



CHAPTER I 

SOME PHYSICAL INSTRUMENTS IN CONSTANT USE IN 
PHYSIOLOGICAL EXPERIMENTS 

Before 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 cylinder is a porous 
pot, and within 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 
cylinder 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 ZnS0 4 at the zinc plate, and decomposition of the C11SO4, 
by the hydrogen appearing at the copper plate to form H 2 S0 4 and 
metallic Cu, which latter is deposited on the copper surface. The 
E.M.F. (electromotive force) of the battery is 1-072 volts. 

B 



2 EXPERIMENTAL 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 Dakiell Battery. 



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.F. 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 S0 4 
appearing at the zinc plate when the battery is in action dissolves 
the zinc to form ZnS0 4 , and the H._> appearing simultaneously at the 



BATTERIES 

carbon pole is oxidised into H 2 by the nitric acid, 
of the battery is l - 9 volts. 



The E.M.F. 




Fig. 3. —The Bunsen Battery. (McKendrick.) 

The Grove Battery (fig. 4) is similar to the Bunsen battery, but 
the carbon is replaced by a sheet of platinum. Its E.M.F. is 1'96 
volts. 

The Leclanche 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.F. 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 (trove 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 
Leclanche cells. 



THE INDUCTION COIL 

The form of induction coil usually 
employed by physiologists is Du JBois- 
Xteymond's sledge inductorium (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 Leclanche Battery. 




Fig. 6. — The Induction Coil. (McKkndrick.) 

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 the 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.F. 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 Qr all of these various factors are utilised 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 



each tarn of^the 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 diagrammatically represented in fig. 7. In this 

figure, lines written hori- 
^AffE break 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 w T ould 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 a b. 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 ?nake 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.F. than that at break, 
but lasts longer. This is indicated in the lower half of fig. 7. The 
line k r indicates zero current, and the curved line klm 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, 




PR/MARY 



SECONDARY 




P c. 



THE INDUCTION COIL 7 

because the current is in the reverse direction to that of A b. The line 
R p s indicates the current induced in the secondary by the sudden 
change fg in the primary : it is above the line K r 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 deriving circuit into that through 
the primary. Fig. 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 Fig. 8.— Arrangement or Apparatus 
open and closed. When the key F0R Equalising the Make and 
.11,1 j. ,i 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 previously 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 still 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 de. 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 kno and rtv respectively. 

For very many purposes it is essential to have a rapid series of 



h EXPEKIMENTAL PHYSIOLOGY 

induction shocks, which 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 /» . In the centre of this spring is a small platinum 

plate for making contact with 
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 /, 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 /. 
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 the 
platinum point of the screw s , 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 s lf 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. 




Fig. 9. — To Illustrate the Action 
of Neef's Hammer. 



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 



9 



connect the pillar d (fig. 6) with the binding screw / by a stout wire 
and screw up the screws Sj and s 2 (fig. 10) until S] is removed from 
contact with the spring v, ands 2 lies 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 pillar A, and 
from this by the stout wire to the screw s,, and thence to the primary 
coil p c. From the primary coil it passes to the electromagnet e, 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 
s 2 , 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 coil and electromagnet 
most travels through the derived 

circuit, because the resistance of this is much less than that of the coil 
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 S 2 . 
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 inductorium 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 




Fig. 10. — To Illustrate the Action of 
Neef's Hammer with the Helmholtz 
Modification. 



10 



EXPERIMENTAL PHYSIOL' )Q Y 



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 1 , c 2 , hollowed out in a vulcanite 
base and with two binding screws, b 1 and b 2 , entering them from the 




B Inst. Co. Ltd. <Af>M3. 

Figs. 11 and 12. — Two Forms of Mercury Key. 

side. 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 
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 




Fig. 13. —Simple Form of Spring Key. 



THE DU BOIS KEY 



I 1 



on the brass plate d, which 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-REYMOND'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 




Inst. Co. Ltd. Umb, 
FlGS. 11 AND 15. — TWO FORMS OF THE Du 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 




Fig. 16. — Plan of the Arrangement of Fig. 17. — Arranged as a Simple Break 
the Do Bois Key as a Short-cir- Key. Not to re used after this 

cutting Key. Method in a Secondary Circuit. 

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, 



L2 



EXPEE I M KNTA L PHYSIOLOGY 



lying 1 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, practically 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 
be made to dip into either 
pair of the four remaining 
cups. 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 to 
rest in the cups e and p, 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 




Fig. 18. — Pohl's Commutator. 



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 f. Suppose, for instance, that the two ends of a muscle were 
connected by wires to e 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 
d 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 CUTTING OUT EITHER THE MAKE OR 
BREAK SHOCK 

This consists (tig. 19) of two spring keys, one between p 1 and p 2 , closed when 
the spring b is brought into contact with the metal piece D, and the other one 
between s 1 and s 2 . The contact is made in each case between two platinum 




Fig. 19. — A Form of Cut-out Key. 

surfaces, 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 1 and V s , which are carried 
on an axis which can be rotated by hand or 
driven by a running 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 1 p 2 to make and 
break a current through the primary, and s 1 s'-', so that it short-circuits 
the secondary when it is closed. Thus the two terminals of the secondary 
are comiected, one to s 1 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 still depressed ; iii. the sector v 1 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 shock 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 1 , only make shocks would be sent through the electrodes. When a more 
rapid series of stimuli 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 little 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 greater tban the make 
shock in the following way. Connect the primary coil with a battery and 
mercury or spring ke}' as in fig. 20. To the secondary coil attach a pair of 
wires, and remove the coil to some distance from the primary. Hold the two 



PC 




Fig. 20. — Arrangement of Apparatus 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 will 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 further, 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 
stimulus to any required degree. 

Experiment 2. — To demonstrate 
the break extra-current arrange the 
apparatus as in fig. 21, applying the 
Fig. 21. — Arrangement of Apparatus to electrodes e to the tongue. First close 
Show the Break Extra-current. the key K, ; 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 15 

the tongue. Neither on opening nor closing the key k. 3 is any distinct shock 
felt unless the battery is very strong. Now open the key k } and again open 
and close k.,. Each time the key K 2 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 EXPERIMENTAL PHYSIOLOGY 



CHAPTER II 

PKEPARATION OF A FROG'S MUSCLE. ITS RESPONSE TO 
STIMULATION. THE GRAPHIC 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 ana/tomical 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 laying 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, km, 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 line 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. — Leg Muscles of the Frog 
seen from the inner slde. a, 
Gracilis, s, Sartorius. v, Vastus 
Lvi'ernus. g, Gastrocnemius. 



Fig. 23. — Leg Muscles of the Frog 
seen from the Outer Side, t, 
Triceps, b. Biceps. s»;, Semimem- 
branosus, g, Gastrocnemius. 



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 
k the knee-joint ; g is the gastrocnemius and t the tendo Achillis with 
its sesamoid bone s. The nerve n stili remains attached to a piece of 
the vertebral column v, which serves as a convenient means of 
handling the nerve. At n, 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 



EXPEEIMENTAL PHYSIOLOGY 



the tendon, or this is pierced by a bent pin, and thus the lower end 
attached 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. — Gastrocnemius-sciatic Preparation. 



ing the electrodes first to the nerve 

sending an induced current through the electrodes. 



THE MOIST CHAMBER 

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 
break shock is stronger than the make shock. 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 coil as in the preceding experiment, it 
will now be found that the strength of the break 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 shock caused 
a twitch of the muscle was 26i cm. A make shock was first effective 
when the coil was brought up to 1(H 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 9^ 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 coil and elec- 
trodes arranged in parallel and with a Du Eois key k 2 interposed so that both 
may be short-circuited. Interpose a 
friction key k 1 and a resistance-box r 
in the main circuit. Also place a key 
k :; in the electrode circuit. The cur- 
rent on reaching the key k 2 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 ' 1 B^T 

circuit. Close the key k 1 and open _, „_ . . 

-, • , J i r . , Fig. 25. — Arrangement of Apparatus 

k-, and now interpose enough resist- „ „ „ , „ 

... 1 . i °i • ■? for Showing Make Extra-current. 

ance at R until opening and closing K A 

gives no contraction of the muscle. Next, with k 1 and k 3 closed, open and 
close k-. Each time k 2 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 r, 
been reduced until it no longer was able to stimulate on make. On closing 
the key k 2 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 2 . The break of the current through the nerve is not 
sufficient to stimulate, and the muscle does not contract. 

If the key K 2 be kept open and k 1 closed and opened, a contraction occurs 
both at make and break. This arrangement thus demonstrates both make 
and break extra-currents. 

MAKE A GRACILIS AND 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, carefully cutting 
through the fibres of the rectus interims minor, which are inserted into the 
skin 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 interims minor. The gracilis, or rectus interims major, a, is to be seen 
from the front of the thigh, being in relation on its outer edge with the 

c2 




20 



EXPERIMENTAL PHYSIOLOGY 



adductor brevis, adductor magnus and sartorius, s. The semimembranosus, 
s///, is seen on the posterior surface with its outer border in relation with the 
|i\ i iioiniis above and the biceps, b, below. Both muscles arise above from 
the symphysis pubis, and below are inserted by tendinous aponeuroses into 
the tibio-fiimla. 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 ami 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 easily separated right up to the 
symphysis. The semitendinosus usually tends to separate with them, and 
may he 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 
he 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 passing 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- 




Fig. 26. — The Relations of the 
Hyoglossus, h g, in the Fkog. 



THE HYOGLOSSUS PREPARATION 2L 

cisions 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 
from 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 GRAPHIC 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 ii we wish 



22 



EXI'EIM.M KNTAL 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, lines measured parallel to the direction 
of motion indicated time, and that to determine the value of those 
lines all that was necessary was to fix a very light 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 Records of the Vibrations of a Tuning-fokk Vibrating at 
the Rate of 10 per sec. The Tracing a b was taken while the Record- 
ing Surface was Moving more Rapidly than during the Record 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 



RECORDING TIME 



23 



shape of surface which is most generally useful is that of a cylinder 
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 & 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-marker or Chronograph. (McKendrick.) 



(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 
frequently 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 



L>4 



EXPERIMENTAL PHYSIOLOGY 



that the spring s does not touch the writing surface. With \v in the position 
drawn, the oscillations are at the rate of two per second. When w is moved 




Fig. 29. — A Spring Chronograph. 



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. —Lower Part of Drum to show Method of Driving the Cylinder at 

Different Eates. 



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. 87). 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 drum 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 e which is placed in 
contact with a bar f screwed into the drum- spindle A. F and e are kept in 
contact by a brass spring, so that the drum is rotated by the brass disc. The 
coned prdley c is driven by a running cord, and on the same axis is a smaller 
coned pulley K and a brass ring r covered with rubber. "When R 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 pulley 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 r 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, R 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. 31. — Muscle held in Muscle-forceps f and attached to Simple Lever 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- 



26 EXPERIMENTAL PHYSIOLOGY 

tion then varies inversely as the distance of the point of attachment 
from the axis. Fig. 31 represents such a SIMPLE LEVER l, which 
is represented as arranged for recording the movement of a muscle m, 
whose upper end is held firmly in the MUSCLE FORCEPS p. 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 CRANK 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 bv 




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 the wires firmly. Near 
the ends of the wires a drop of 
Fig. 32.-Si.iple Form of Wire'' me ! te ? filing-wax w is fixed, so 

Electrodes as *° hold the wires parallel to one 

another and about 1 mm. apart. 
The wires are then cut off about 4 mm. beyond the wax, and these projecting 
pieces bared by scraping off the silk 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 EXCITATION 

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 in the primary and a Du Bois key 
in the secondary. The muscle may he stimulated either directly or 
indirectly. Arrange the electrodes accordingly. Remove 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 in the primary. 
No contraction residts 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 line on the drum. Now turn 
the drum by hand through about *5 cm. Move up the secondary coil 1 cm. 
and stimidate as before. Repeat gradually, increasing the strength of the 
stimulus and moving the drum after each contraction has been recorded. 
At a certain position the make shock will be found to cause a contraction as 
well 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 



^^■l«JH£^BL : flilU<~BKEJ*U<>lMt9H Mltia— :»«T: 



Fig. 33. — Heights of Conteaction of a Muscle with Different Steengths of 
Stimuli. The Numbers Eefer to the Distances of the Secondary Coil. 
The Interrupted Line above Shows the Instants at which the Prima by 
Cubeent was Made and Bboken. A Eise in this Line indicates Make, a 
Fall Beeak. 

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. 



L'eS 



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 offer 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. 



UNIPOLAR 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 will 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 way 
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 Form of Recording Tambour. 



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-tisrht. A tube leads 



TAMBOURS 



29 



into the interior of each, and the two tambours are through these connected 
by a piece of rubber 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 b, 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 magnification 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 R 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 1 . The advantages of this form are that the 




Fig. 85. — A Second Form of Becokmng Tambour. 



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 1 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 



CHAPTEE III 



A SINGLE CONTRACTION OF A FROG S MUSCLE. ITS MODIFICATION 
UNDER CHANGES IN THE EXTERNAL 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. — Record 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 coil p c, and the second terminal of 
this to the mercury key k, and thence to the special break key k 1 , from the 
second terminal of 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 1 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 2 . The free 
extremity of b is slightly notched to 
receive the rod a, and the two are kept 
firmky in contact by a screw, part of 
which is seen in the figure under the 
vulcanite base, which tends to force b 
upwards. If a current be made to 
enter at b 1 it will 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 a 
(fig. 37), fixed to a collar fitting on the axle of the cylinder, is brought into such 
a position that there is a well-blackened smooth piece of paper at the front of the 
drum, when the arm a touches the rod of the break key k 1 . The two terminals 
of the secondary coil sc are connected to the two blocks of the Du Bois friction 
key k 2 , 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 
to 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 
timing-fork f, or a chronograph, is arranged to write its tracing vertically 




Fig. 36.— A Break Key. 



A MUSCLE TWITCH 



31 




82 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 coil is now brought into such a 
position thai 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 1 is closed and 
then k 2 is opened. The drum is next very slowly rotated by hand until 
the arm a breaks the key k 1 and the shock thus produced in the secondary 
coil causes a twitch of the muscle, which is recorded as a vertical line on the 
smoked surface. The key K 3 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 1 and open K-. Set the drum revolving by switching the friction 
wheel below the coned pulley p into contact with the wheel h, the arm a 
breaks the contact of K 1 , 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 from the 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, 1 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 b, 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', b b', c c', and clcV, written while the smoked surface 
was stationary, are taken for the purpose of making the time measure- 
ments more accurately. The curve is seen to fall naturally into three 
parts : — 

1 A very convenient varnish consists of 250 c.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'U shows 
that this occupied ^fu ths of a second, i.e. 01 sec. This method does 
not give accurately the true measurement of muscle latency. It is too 
high. More accurate measurements by specially designed methods 
show it to vary from 003 to -008 sec. for frog's muscle. There are 
several reasons why a measurement by the above method cannot give 
the true result. In the first place, a muscle does not contract simul- 
taneously all over, but the contraction starts at some one spot and 
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 
rather to a stretching of the remainder of the fibre both above and 
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. This 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 toe, as shown by the piece of time tracing V c', was 
^fyths of a second, i.e. -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 PII YSIOLOG Y 



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'df, to be oV^ths of a second, or 



i 



Fig. 38. — Isotonic Twitch of a Hyoglossus Muscle. Time Tracing, 200 per sec. 
Magnification, 3 (i.e. the Vertical 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 
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 
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 

o 

20 1 

28 mm. Consequently the muscle contracted x-. , i.e. nearly a 

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 



of the load lifted into the height through which it is moved, or w 
=l7?. In this experiment the load, including the lever, was adjusted 

20 

to be 2 grms. Hence the total work was 2 x -= 1333 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 

- . = 178 grm. mm. per sec. 
075 & * 

The load was not, however, retained at the highest point, but 

pi p» F 3 p* p3 pS F ? p« p9 




A B D 

Fig. 39. — To Illustrate the Meaning of the Curve of Fig. 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 fig. 38. All measurements along a d represent 

d2 



36 



EXPERIMENTAL PHYSIOLOGY 



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 1 has been drawn at right angles to ad and of 
three times that length (78 mm.) because the recording lever in tracing 
the curve magnified the shortening three times. FjFg has been drawn 
parallel to ad and divided at f,, f 2 , f 3 ... by a series of points 
which follow one another at intervals of four vibrations of the tuning- 
fork. Hence f, f 2 , f 2 p 3 , . . . &c. each represent -^th of a second. 
Then f 2 g 2 , f 3 g 3 . . . f 9 d have been drawn parallel to a f, to cut 
the curve in g 2 , g 3 . . . . In this way we are able to state that at the 
instant a, at which the muscle was stimulated, its length was ^ a f. 

gLth of a second later its length was £ f 2 g 2 
5^ths ditto ditto ^ f 3 g 3 

/oths ditto ditto ^ f 4 g 4 

5 %ths ditto ditto 3 F 9 D 

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 




Fig. 40, 



-Simple Twitch of a Gastrocnemius. Time Tracing, 
Magnification, 5. 



200 per sec. 



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 introduced. 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 0-01 sec. ; the 
period of contraction 005 sec. ; and that of relaxation 0-1 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 follow 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 will 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 pulling 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 



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, 
Fick 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 Fick 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 ihe muscle is attached to the point p of the 
lever, 10 cm. from the axis. This part of the lever consists of a light 
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 ^th of the 
weight w. The movement of the 
weight upwards is also only o^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 

the physical manifestations of the FlG - 42 -- The Principle of the Iso- 

., , . n 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 Mis 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 a c. When the 
muscle is stimulated it tends to contract and lift 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 muscle 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 



merits of the writing point are previously determined experimentally, 
any position of the writing point will be known to be caused by the 



Fig. 43. — The Principle of the Isometric 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. — Record an isometric twitch 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 2 . 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 an Isometric Lever. 



by the screw s 1 , 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 know 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 applied 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 choose 
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. Record 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 writing 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. — Three Isometric Twitches with Different Initial Tensions. The 
Numbers on the Left indicate the Number of Grams required to Bring 
the Lever to the Level of the Corresponding Horizontal 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 twitch, but measurement shows a few important 
differences. 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 

Grams 


Latent 

Period 

in Sees. 


Apex Time Total Time 
in Sees. in Sees. 


I 

II 

III 




5-7 
16-7 


30-4 
55-6 
66-7 


•005 
•006 
•007 


•057 -117 
•06 -142 
•065 -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 approxi- 
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 wave 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 AFTER-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 circum- 
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 runs 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. — Arrangement of Simple Levee for Eecording by the Method of 

After-load. 

by 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 
from this position another curve. It will be found that 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. 

Fig. 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 
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, 



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 



MMHHH^^^^^^^Hl^^H 





























Fig. 47. — Twitches Taken under the Principle of After-loading. 

more important, it is gradually increasing its tension until it is able 
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 
shortening is then registered. 

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 
hollow so that water at different temperatures can be circulated 
through it. In another a stout metal wire 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 hollow 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- piece 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 tension 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 pulls 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 for Varying the 
Temperatures of 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 until 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. 

Repeat 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 

Twitch in 

mm. 


Mean Elate 
of Work 


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 o/^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 



EXPERIMENTAL I'll YSIOLOG Y 




The mean rate of work is given in grm 
mm. per second in the last column. 

From 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 15° C, though still 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 with 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 cases 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. 

For 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. SO. — Twitches of a Gastrocnemius at Different Temperatures. 
Tracing, 200 per sec. Magnification, 5. 



Time 



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 twitch 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 tempei'a- 
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. 4'2. The writing lever 
should be made as light as possible. The ordinary crank myograph lever 
could 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 muscle, 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. 

Fig. 51 shows a tracing obtained in this way. The muscle was 
the hyoglossus. The loads in grams additional to the weight of the 




Fig. 51. — Twitches of a Hyoglossus with Different Loads. Time Tracing, 
200 per sec Magnification, 3. 

lever are written over the curves. Fig. 52 is a similar figure taken 
from a gastrocnemius. 




Fig. 52. — Twitches of a Gastrocnemius 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 VERATEINE 49 

This is better seen in fig. 52, obtained from a gastrocnemius, than in 
fig. 51, from a hyoglossus. 

3. The period of relaxation 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. 

III. THE INFLUENCE 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 stimidated 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 will be found that the muscle 
has again retmned to its previous state and the contraction is greatly pro- 
longed. 

The most satisfactory preparation to use for this experiment 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 lies. 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 n 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 n 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 

E 



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. 




Fig. 



53.— Two Twitches given by a Muscle Poisoned with Veratrine. 
Time in Seconds. 



THE WORK 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 
making 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 will 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. 1 

1 The load chosen must depend on the size of the muscle. That of 40 grrns. 
as here given is the most convenient for a medium-sized gastrocnemius. 



WORK PERFORMED DURING A TWITCH 



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 




Fig. 54. — Work-diagram of a Gastrocnemius for Single Twitches. The 
ordinates above x are heights of twitch j the rectangles below repre- 
SENT the Amounts of Work. 

fig. 54 was drawn was carried out in this way. Distances measured 
along o x represent loads. Lines drawn parallel to o v represent 
heights of contraction, and in this experiment they are magnified 
five-fold. Each cm. measured along o x from o represents 40 grams. 
The work performed during one of the contractions, e.g. b d, is I u d 
x 160 grm. mm., b d to be measured in mm. As o b represents the 

E 2 



52 EXPERIMENTAL PHYSIOLOGY 

load and b d the height of contraction, the work is represented by 
o b x b d, i.e. by the rectangle obdk, and similarly for all the other 
contractions. These rectangles are not, however, readily comparable ; 
therefore proceed in the following manner. Determine the number of 
grm. mms. of work performed in each contraction and divide this by 
10 ; measure off on the squared paper a line equal to the number 
obtained vertically under the contraction. Thus for the contraction 
b d, the work was Job x b d grm. mms. = \ x 160 x 18 = 576. 
Therefore a line b l 57-6 mm. was drawn as a continuation of d b. 
Then complete the rectangle b l m n, which then contains 576 
sq. mms., and therefore represents the total work performed, 1 sq. mm., 
representing 1 grm. mm. of work. It will of course be f of the 
rectangle o d. In a similar manner the other rectangles were drawn 
and represent the other amounts of work for each contraction. The 
aim of this has been to represent each successive work by rectangles 
upon equal bases of 10 mm., and therefore the heights are a measure 
of the work done and at once appeal to the eye. 

We see directly that the amount of work performed at first 
increased rapidly as the load was increased, and reached a maximum 
at a load of 160 g. From that point it decreased, but at a less rapid 
rate than it had increased, and at 320 g, although the height of lift 
was only § mm., the amount of work performed was considerable. At 
360 g. the muscle only gave a scarcely perceptible lift. 

This experiment also gives us a means of determining one other 
point in a muscle twitch, viz. the amount of load it is just able to lift 
when it is stimulated. In order, however, to get comparable results it 
is necessary to expresss this weight in a form for a definite amount of 
muscle. As it depends directly upon the transverse sectional area of 
the muscle, it is usual to express it in grams per sq. cm. of sectional area, 
and it is then spoken of as the ' ABSOLUTE FORCE ' of the muscle. 

We may gain this approximately from the preceding experiment if 
we know the length and transverse section of the muscle. In order to 
obtain these, the weight, specific gravity, and length were measured. 
These were : W = 329 g. S.G. = 1104, I = 2125 mm. The load it 
was just unable to lift was 360 g. Its volume (r) is given by 

W "329 

- - = = -298 cub. cm. = 298 cub. mm. Therefore its average 

transverse section - = n . rt _ = 1402 sq. mm. Hence the absolute 
L 21-25 

360 
force per sq. mm. of transverse sectional area was = 25-6 grms. 

Hence the absolute force per sq. cm. of sectional area was 2,560 
grams. 



PENDULUM MYOGRAPH 



53 



The absolute force of a muscle varies considerably in different 
muscles and in different animals. For mammalian muscles it is much 
higher than in the case of the frog's muscle. Determinations made 
upon the gastrocnemius have given results of as much as 8,000 to 
10,000 grams per sq. cm. 



THE PENDULUM MYOGRAPH 

A form of recording surface which has been largely employed for 
recording a single twitch of a muscle is the pendulum myograph, a 
simple form of which is shown in fig. 55. 




Fig. 55.— Simple Form of Pendulum Myograph. 

It consists of a sheet of plate glass which is covered with glazed paper, 
and its surface is then smoked. This glass is held in a aupport at the end of 



54 



EXPERIMENTAL PHYSIOLOGY 




Fig. 56. — Trigger Key. 



a wooden, pendulum swinging on two steel points at the upper angle of a large 
triangular frame. Clips are provided at either side of the frame by which 
the pendulum may be held at either side. Projecting from the lower end of 
the middle of the pendulum is a tongue of metal which breaks the contact 
of a special trigger-key the details of which are shown in fig. 56. It 

consists of a brass trigger d fixed 
on an axis on which there is a 
sector j which is in contact with a 
brass spring a, connected to a 
binding screw B-. The trigger is 
represented in the figure in an un- 
stable position, so that if its upper 
end is moved slightly to the right, 
the spring a will bring it into con- 
tact with the end of the screw s. If, 
on the other hand, it is moved a little 
to the left, the spring will make it 
move downwards. The screw s 
fits in a pillar p connected by a strip 
of brass c to a binding screw b 1 . 
The screw is tipped with platinum 
and comes into contact with a platinum plate let into the surface of the 
trigger d. If a current be sent through the key by the binding screws, it 
is closed only when the trigger d is in contact with the screw s. In that 
position the trigger is kept in contact by the spring. As soon as d is knocked 
to the left, the contact is broken and is not again closed if the trigger be carried 
beyond the neutral point in which it is drawn in the figiue, being prevented 
from returning by the spring a. 

Experiment 8. — Take a simple muscle curve with this myograph. In- 
sert the trigger key in the circuit of , the primary coil, and place a Du Bois 
key in the secondary. Make a hyoglossus preparation and fix it to the 
recording lever, with electrodes for stimulating it directly. Close the trigger 
key, and with the pendulum hanging vertically bring the writing point to 
the surface ; next bring the contact at the bottom of the pendulum to touch 
the trigger key while this is still pressed tightly to the screw s. Make a 
little vertical mark with the writing lever at this spot. This marks the 
point of stimulation. Now lift the pendulum until it is caught in the catch 
on the right, and having opened the Du Bois key, release the pendulum, 
which will then swing across and be caught in the catch on the opposite side. 
At the middle of the swing it will knock over the trigger, and the break shock 
in the secondary will thus excite the muscle. Finally draw a zero abscissa 
line moving the pendulum by hand, and take a time tracing underneath. 

Fig. 57 shows the form of curve thus obtained. The zero abscissa 
line is, of course, an arc of a circle of radius equal to the length of the 
pendulum. 

The form of the curve is identical with those already studied in 
previous experiments. Time measurements should be made of the 
curve. 




H W 



^U 



Se4 



56 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE IV 

SUMMATION OF MUSCULAR CONTRACTION. TETANUS 

In order to study the nature and the production of a prolonged tetanic 
muscular contraction it is necessary to first examine the effect of 
applying a second stimulus to a muscle before the contraction caused 
by the first has ceased. This may be done by using some form of 
apparatus of the general principle of that described in the following 
experiment. 

Experiment 1. — To the upper end of the shaft of the drum are fixed two 
brass collars, s 1 , s 2 , which can be clamped in any position by means of screws. 
Held in the collars are two brass rods, R 1 , R 2 , terminating in flexible strips of 
brass, m 1 , m 2 . To the upright of the drum is clamped an insulating vulcanite 
base, on which is fixed a stiff brass rod, x, to which a binding screw, b 1 , is 
connected. A second binding screw, b 2 , is attached at any convenient position of 
the metal stand of the drum. The arm r 2 is now adjusted in the collar, so that 
the spring m 2 just touches the tongue x, and the collar is rotated until a smooth 
piece of the blackened paper is opposite the writing point when the two are 
in contact. The second arm r' is similarly adjusted. The primary circuit 
is now arranged so that the current passes from the battery to one terminal 
of the primary coil, from the second terminal of this to the binding screw b 1 , 
and from the binding screw B 2 back to the battery. Whenever either arm 
R-, R 1 touches the metal x the circuit is then closed and travels through 
the coil to b\ through the metal x to the arm r 2 , and so up the shaft of the 
drum to its stand, and then through the binding screw b 2 back to the battery. 
As the drum is rotated a little further the spring m- is bent until it slips off 
the metal-piece x and the circuit is broken. 

Make a nerve-muscle preparation (the muscle may be stimulated directly, 
in which case the nerve need not be prepared) and fit it to the myograph. 
Place the electrodes under the nerve (or so that the stimulus is sent through 
the whole length of the muscle) and move the secondary coil until the break 
shock will give a maximal contraction while the make shock is still ineffec- 
tive. Bring the writing point to the surface and mark the two points of 
stimulation by very slowly rotating the drum by hand. As the first spring 
touches the metal-piece an induced shock is produced in the secondary circuit, 
which, however, is not sufficient to stimulate the nerve or muscle. When 
rotated a little further the spring leaves the metal-piece x, the cmrent is 
broken, and the induced shock stimulates the nerve or muscle, the muscle 
contracts, and so records the point of stimulation. In a similar way the 
second point of stimulation is also recorded. 

At first the second contact m 1 should be fixed at some little angular distance 



EFFECT OF TWO STIMULI 57 

from the first, so that the contraction caused by the first shall have had time 
to be completed before the second stimulus is sent in. The necessary 
angular distance will of course depend upon the rate of rotation of the 
drum. This need not be very rapid — about 10 to 15 cm. per second 
at the circumference. The contraction will then extend over about 1 cm. 




Pig. 58. — Arrangement of Upper Part of Drum for applying Two Stimuli to 

a Muscle. 

of the paper. The double contraction may now be recorded with the drum 
in motion. Next move the second contact a little nearer the first and lower 
the myograph, so that it will record at a fresh level of the smoked surface. 
Mark the two points of stimulation as before, and then record the two con- 
tractions. Repeat this several times, on each occasion moving the second 
contact a little nearer to the first. 

In this manner a series of curves will be recorded similar to those 
of fig. 59. In 1 and 2 the first contraction was finished before the 
second stimulation reached the muscle. The effect of the second stimu- 
lation is therefore a repetition of the first. A closer examination, how- 
ever, shows certain differences. In the first place the second contrac- 
tion is higher than the first, 9 - 75 mm. and 9 mm. for 1 ; 10 mm. and 
9 mm. for 2. Secondly, the total duration of the twitch is longer in 
the second than the first, 13 - 5 mm. and 11 mm. for 1 ; 15 mm. and 
13 mm. for 2. In tracing 3 the second excitation fell at about the com- 
mencement of the last third of the relaxation period of the first contrac- 
tion and the commencement of the second contraction just before the 
lever reached the abscissa line. In 4 and 5 excitation occurred during 
the relaxation period of the first contraction ; in 6 at about the apex 
of the first, and in 7 during the early part of the period of con- 



58 



EXPERIMENTAL PHYSIOLOGY 



traction. We see that in these last five curves there is a summation 
of effect. The second apex is at a higher level than the first, and 




Fig. 59. — Effect of Two Successive Stimuli, with Gradually Diminishing 
Intervals, upon a Gastrocnemius. 



SUMMATION OF STIMULI -09 

the maximum summation effect occurred in curve 6, where the height 
of the second apex is 17 cm. as compared with 16'5 for the second 
apex of 5 ; 14-25 cm. for that of 4 ; 13 cm. for that of 3 ; and 9 cm. 
for that of the first apex. As a general statement, it is found that the 
height of the second contraction is greatest when the instant of stimu- 
lation falls at the commencement of the last third of the period of 
contraction of the previous twitch. In connection with the height of 
the second twitch it is seen from curves 3 and 4 that when the com- 
mencement of the second contraction falls in the lower half of the re- 
laxation of the first the height of the second contraction, as measured 
from the level at which it starts, is higher than the height of the 
first. 

With regard to the time of the second contraction one other point 
of interest is found, viz. that the apex time of the second contraction 
is less than the apex time of the first, where by apex time is meant 
the total time elapsing from the instant of stimulation till the highest 
point of the curve is reached. 



THE GENESIS OF TETANUS 

A study of the effect of applying two stimuli to a muscle or its 
nerve, the time interval between the two being varied, naturally 
leads to a consideration of the effect which will be obtained by ex- 
tending the number of stimuli. 

To gain an answer to this it is necessary to have some form of apparatus 
which will give a series of stimuli at regular intervals, and further allow of 
an alteration of that interval. There are many forms of apparatus that will 
effect this, but the simplest consists of a flat steel spring which can be clainped 
in different positions, and whose free end is provided with a platinum wire 
by means of which a circuit may be closed with each vibration of the spring. 
The rate of vibration with a given spring depends, solely, upon the length of 
spring which is allowed to vibrate, and increases as the spring is shortened. 
To keep up the vibration of the spring it is usual to introduce an electromagnet 
which attracts it as soon as the circuit is closed. The method of fitting up 
the apparatus is shown in fig. 60. A c is the flat steel spring which can be 
firmly held in any position by the clamp c. At a a platinum wire is soldered 
to the free end of the spring, and this can close a circuit by dipping into the 
mercury m held in a vulcanite cup. e is an electromagnet held above the 
vibrating reed. In order to get regular vibration of the reed the electromagnet 
should be fixed at a point about two-thirds of the length of the spring away 
from the clamp {i.e. nearer to a than its position, as shown in tbe figure). To 
fit up the apparatus connect one terminal of the battery b with the mercury 
cup by means of the binding screw t 1 . Connect the clamp of the reed by its 
binding screw t to one terminal, E 1 , of the electromagnet and the second, 
T 2 , to one terminal, p 1 , of the primary coil. The second terminal of the coil 
is then connected to the battery. Supposing now that the platinum wire a 



60 



EXPERIMENTAL PII YSIOLOG Y 



dips into the mercury, the circuit is closed, and consequently the electromagnet 
attracts the 'iron reed, the point of which is thus lifted from the mercury, and 
the circuit is broken. The reed then falls, the current is again made, and the 
cycle repeated indefinitely. Note that the general principle of the whole 
arrangement is precisely the same as that of the Neef's hammer attached to 
the inductorium. The only difference that we have is, that the length of the 
reed, and consequently the rate at which it vibrates, is easily adjustable, 
whereas in the Neef s hammer the rate of vibration is permanently fixed. 
In some ways it is rather more convenient to fix the reed so that it vibrates 
horizontally instead of vertically, as in fig. 61. The platinum point is then 
bent downwards and the mercury cup overfilled, and so adjusted that the 
platinum point makes contact by touching the side of the mercury. By 
using it in this position there are fewer adjustments to be made when the 




IZ3EZ 1 '. . '. IS :iSE L.' J L ; l Hi 15 

Fig. 60. — Mode of Fitting dp a Vibrating Reed. 



spring has to be changed to a fresh position, and it will be found that the spring 
vibrates rather more regularly. The wire connections are the same as in the 
previous case. 

In using the reed each time the platinum dips into the mercury, a make 
shock is produced in the secondary ; and each time it is lifted from the 
mercury a break shock is produced, so that there are two stimuli for each 
complete vibration, which are, moreover, of unequal value. This is a great 
disadvantage in the employment of the vibrating reed which can, to a certain 
extent, be overcome by so regulating the position of the secondary relatively 
to the primary that only the break shocks are effective in producing a twitch. 
Even then, however, we must not consider the make shock as producing no 
■effect, for it is found that a shock which in itself is insufficient to cause 
a contraction can produce an alteration in the nerve or muscle, which is 



SUMMATION OF STIMULI 



61 



shown in a difference in effect produced by a second stimulus which rapidly 
follows it. 

The make shock (or break shock) may be cut out by using the key shown 




Fig. 61. — Reed arranged to Vibrate in a Horizontal Plane. 

in fig. 19, and fitting in the two notched wheels instead of the sectors. 
Alteration in the rate at which the stimuli are sent in can then be effected by 
altering the rapidity at which the key is driven. 

Experiment 2. — Adjust the vibrating reed as just described, at first clamping 
it quite at the end, so that it vibrates two to three times per second. Make 
a nerve muscle preparation and fix it in a simple lever or crank lever 
myograph, and having covered and smoked the drum arrange it so that it 
rotates at the rate of 8 cm. per second. Adjust the secondary coil, using a 
Du Bois key as a short-circuiting key and placing the coil in such a position 
that it gives maximal shocks on break while the make shocks do not stimulate. 
Close the key in the secondary circuit, set the vibrating reed in action, 
bring the writing point up to the smoked surface, and allow the drum to 
rotate. Open the key in the secondary for about one to two seconds, and thus 
allow the shocks to reach the nerve. The muscle contracts and its movements 
are recorded. Stop the drum and next shorten the length of vibrating reed, 
and take a second tracing in the same manner as before. Take a series of 
tracings in this way, between each, making the reed vibrate a little faster 
by shortening it. When the reed has been sufficiently shortened the effect 
at last produced is a complete tetanus. 

In an experiment carried out as thus described the series of 
tracings shown in fig. 62 were obtained. The time tracing in all cases 
was eight per second. The preparation was the gastrocnemius stimu- 
lated indirectly, and the magnification was threefold. In curve 1 the 



62 



EXPERIMENTAL PHYSIOLOGY 



mm 




Fig. 62.— The Gradual Production of Tetanus as the Rate of Stimulation was Increased. 



GENESIS OF TETANUS 63 

rate of stimulation was four per second, and it is seen that each 
contraction is distinct. On measuring the heights of the twitches 
it will be found that the second is a little higher than the first, and 
the third a trace higher than the second, the last four ail being of 
the same height. This ' staircase ' effect, very slightly marked in this 
particular instance, is usually to be observed, especially if the pre- 
paration be very fresh and has not been injured during its removal. 
It shows that by a contraction a muscle is brought into such a 
state that an immediately following stimulus of the same strength 
evokes a more powerful response. That it is a question of increased 
capacity of performing work rather than an increase of excitability 
is indicated by the fact that it is to be observed when maximal 
stimuli are employed. 

In curve 2 the rate of stimulation was increased to ten per 
second. "We see that the first contraction was nearly complete 
before the second stimulus led to a fresh contraction. The lever did 
not reach the zero abscissa line, and some summation occurred. The 
third stimulus effected a contraction before relaxation was complete, 
and a fresh summation occurred ; and so on for the later contractions, 
though after the fourth the maximum height of contraction did not 
increase. 

In curve 3 the rate of stimulation was further increased to sixteen 
per second, and a much greater summation of effect is recorded. The 
second apex lies well above the first, the third above the second, but to 
a less extent, and the fourth above the third, though here the increase 
of shortening was only slight. From this the apices remained at practi- 
cally a uniform level. An interesting point is to be noticed in this 
curve, viz. that the lowest points of the undulations of the curve 
become progressively at a higher level as stimulation proceeds. This 
effect is due to fatigue brought about by the number of contractions 
the muscle has been made to give. One of the effects of fatigue (see 
chap, v.) is found to be a marked slowing of the rate of relaxation, 
so that as this was produced in this instance the later stimuli began 
to produce their effects on the muscle before relaxation had proceeded 
quite as far as in the preceding contraction. 

In curve 4 the rate was increased to 18 - 5 per second, and in 5 to 
22 per second. The curves show practically the same points as those 
already described for 3. The only difference, apart from the lesser 
excursion of the oscillations, is that there is more summation, and 
therefore both upper and lower apices are at a higher level than in 
the preceding curves. 

Curve 6 shows a similar condition, though carried to a further 
degree. The line joining the upper apices is approximated to that 



64 



EXPERIMENTAL PHYSIOLOGY 



joining the lower, and in addition one other feature is observed, viz 
that the amount of contraction progressively increases throughout. 

In these last four curves it is to be noticed that the relaxations of 
the first few contractions progressively increase. In curve 5, for 
instance, the first relaxation is practicaily nil, the second 2 mm., the 
third 3 mm., the fourth 3 mm., and at a later stage when fatigue 
begins to set in, they again diminish in amount, due to the cause 
already explained. The meaning of this increase in relaxation 
receives a certain degree of explanation in the light of the fact already 




Fig. 63.— The Genesis of Tetanus with slow Rotation of Recording Surface. 



studied, that the apex time of the second twitch in a summation 
series is less than that of the first. The diminution of apex time in a 
series has also been found to extend to the third, and in favourable 
cases to a fourth or later contraction. 

In the last curve (7) a practically complete tetanus is recorded 
which was produced when the rate had reached thirty per second. It 
is seen that the upper line of the whole curve very gradually ascends. 
There are slight wavy oscillations on this fine, which, however, are 
not synchronous with the series of stimuli. 



TETANUS 65 

In a similar manner repeat the experiment upon a hyoglossus. 
The experiment may be further modified by reducing the rate of 
rotation of the drum to 1 cm. per second. In this way fig. 63 was 
obtained, the magnification being twofold. The figure brings out 
clearly the same points as those we have already studied in the pre- 
ceding instance. With the slower rate of recording surface the way 
in which the lines joining the apices or bases of the successive 
contractions ascend is very clearly seen. 

Take a tracing of complete tetanus employing the Neef's hammer 
of the coil for the purpose, when a tracing similar to curve 7, fig. 62, 
p. 62, will be obtained. 

Experiment 3. — To effect this, attach the two poles of a battery to the two 
pillars of the coil, and adjust the vibrating hammer until it works continu- 
ously. Insert a Du Bois key in the secondary circuit as a short-circuiting 
key. Excise a nerve-muscle preparation and fit it in a myograph, laying the 
nerve across the electrodes. Upon a slowly moving surface record the result 
of stimulation of the nerve for a short time. Repeat, varying the strength of 
the stimuli. 



66 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE V 

FATIGUE OF MUSCLE 

A perfectly fresh rnuscle possesses in itself a certain store of 
potential energy in the form of chemical substances by whose decom- 
position the muscle is able to perform a definite amount of work, or 
exert a definite force. If the muscle be caused to contract and produce 
either a series of twitches or a prolonged tetanic contraction, this 
chemical energy becomes more and more used up, and the muscle 
passes into a state in which it becomes more and more difficult for it 
to respond to the stimuli sent to it. This difficulty is due primarily 
to the using up of the initial store of chemical energy, and secondarily 
to the accumulation of chemical bodies of the nature of waste 
products which obstruct the action of the physico-chemical processes 
which are the basis of a muscle's activity. In this state a muscle 
is said to be fatigued. We can study this condition of fatigue, from 
a chemical standpoint, and again we may study it by contrasting its 
performances while in this state with its bebaviour under similar 
conditions when in a normal state. 

To show how a single twitch becomes modified as the muscle 
passes into fatigue proceed in the following way. 

Experiment 1. — Fit up the apparatus in a similar manner to that 
employed when studying the effect of two successive stimuli upon muscle 
(fig. 58), but remove the second contact M 1 , so that only a single stimulus is 
sent into the muscle with each revolution of the drum. The rate of rotation 
of the drum should be arranged so that a complete revolution occupies about 
two-thirds of a second. In this way the contact m- by touching x closes the 
primary circuit three times in two seconds, and the induced shocks of the 
secondary circuit are at this rate. A muscle preparation is now got ready 
and fitted into a myograph, and the electrodes fixed in position. The 
secondary coil is so placed that make shocks are ineffective. The point of 
stimulation and an abscissa line are now drawn. It is of great importance 
that the writing point should in this experiment only draw a very fine line. 
The drum can now be set in rotation. With each revolution a twitch is 
caused which is recorded. After about ten to fifteen minutes the drmn may 
be stopped, and the record examined. During this time from 1,000 to 1,500 



FATIGUE OF MUSCLE 67 

twitches will have been recorded, and unless the original contractions were 
great, and the writing point very fine, the lines will be found to have 
in many places largely obliterated one another. To obviate this it is best to 
only record each tenth or twentieth contraction, moving the writing point 
free from the surface during the intermediate twitches. In bringing it once 
more in position it is necessary that it should be brought back exactly to its 
first position, so that the point of stimulation is correctly placed. To carry 
this out with complete accuracy requires some mechanical means of adjust- 
ing the writing point to the surface. 

Fig. 64 reproduces a series of curves obtained in this way. The 
first six curves are numbered in the order in which they were taken. 
No. 1 was the first twitch ; 2 the sixth ; 3 the eleventh ; 4 the twenty- 
first ; 5 the thirty-first ; 6 the forty-first ; and the remainder at 
intervals of ten twitches. Curve No. 1 gives a typical simple twitch. 
Curve 2 is seen to differ from this in a few points : — (i.) It starts from 
a rather higher level. This is not of great importance in this instance 
for this difference is chiefly of instrumental origin, (ii.) Both the 
period of contraction and that of relaxation in 2 are rather longer 
than in 1. (hi.) On measurement the height of the twitch in 2 is 
found to be slightly higher than in 1. On contrasting 3 with 2 these 
differences come out even more clearly. 

After curve 3 the heights begin to gradually decrease, and the times 
of the different periods to increase. Thus the latent period gradually 
increases from '017 second to - 03 second. The contraction time 
increases, though not'very greatly ; but the chief change is in the period 
of relaxation, which is seen to become very greatly extended, so much 
so that the drum has revolved and a fresh stimulus been received 
before relaxation is complete, as seen by the fact that the next con- 
traction starts with the lever at a higher level than in the previous 
curve. This condition of more or less permanent contraction is 
spoken of as contractur. If the experiment be carried on for a longer 
time it is found that the relaxation process to a certain degree 
recovers itself. Eelaxation time slowly diminishes after about four 
or five thousand twitches, but never attains the previous speed seen 
when the muscle was fresh. 

The condition of fatigue, then, is chiefly characterised by a slowing 
of the usual processes of a twitch, a diminution in height, i.e. in the 
total work performed, but most prominently by the prolonged time 
required for relaxation. The series of changes observed in fatigue 
may be to a considerable extent modified by variations of the external 
conditions. Thus, heat markedly accelerates the onset of fatigue. 
Load also hastens the production of fatigue ; but as it aids the relaxa- 
tion the condition of contractur is not so clearly seen. 

F 2 




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73 _i 



" rv L» 

K r = 



= Oz 



H s 






CHANGES OF HEIGHTS OF TWITCH IN FATIGUE 69 

Next study the effect of fatigue in producing alterations in the 
height of contraction, i.e. in the amount of work it is able to perform 
with constant load, by the following method : — 

Experiment 2. — Drive the cut-out key, fig. 19, from the shafting em- 
ployed to drive the drum, so that it gives two shocks per second. Connect 
it with wires to give make shocks only. Fit up a chronograph to give a 
seconds time tracing. Dissect out the gastrocnemius or hyoglossus, and 
having fitted it to the myograph lever attach the electrode wires to stimulate 
directly, and then bring the secondary coil up to the primary until the con- 
tractions produced on each make of the primary circuit are maximal. Gear 
down the drum until it rotates at about the rate of 10 cm. per minute. Bring 
the writing point to the recording surface, start the drum, and then open the 
short-circuiting key in the secondary circuit and record the contractions for 
about five minutes. 

In this manner the tracing of fig. 1, pi. 1, was obtained. The 
tracing was given by a hyoglossus preparation which was loaded by 
the weight of the lever only. The heights of twitch only are recorded. 
It is seen that the first ten twitches give a typical ' staircase ' effect, 
and from that point onwards, the heights gradually diminish to the end 
of the tracing, at first rapidly and then more slowly. The second point 
of interest is with regard to the line joining the basal points of the 
twitches. This is seen to gradually leave the zero abscissa line, as 
fatigue sets in, which is to be explained by the fact we have already 
studied in the previous experiment, viz. that elongation becomes 
greatly prolonged, and hence a new stimulus reaches the muscle 
before it has had time to completely relax. The time at which the 
succeeding stimulus reaches the muscles falls progressively at earlier 
stages of the relaxation. There is produced therefore a condition of 
contractur. On stopping the stimulations the muscle is seen to 
slowly relax, but had not regained its initial length when the traeing 
was stopped. 

The muscle should now be allowed to rest for about ten minutes, 
and the experiment once more repeated, when a result similar to that 
of fig. 2, pi. 1, will be obtained. It gives as it were an epitome of the 
changes observed in the previous tracing. The changes in the 
twitches are brought about very rapidly instead of slowly, as in the 
first tracing. If this tracing be carried on for a very long time it will 
be found that gradually almost complete fusion is obtained, and then 
again the undulations become much more marked. This last change 
occurs when the late stage is reached in which the relaxation process 
begins to shorten again. 

Experiment 3. — Study the effect of fatigue upon the tetanus curve by 
arranging the rate of the vibrating reed to just give complete fusion and 
record a tetanus by means of this, keeping the stimulation up until complete 
fatigue sets in. 



ro 



EXPERIMENTAL PHYSIOLOGY 



It will be found (fig. 65) that the contraction soon begins to 
diminish, at first with some rapidity and then more slowly as fatigue 
sets in. At a, fig. 65, the stimulation was stopped, and it is seen that 




there is no sudden fall of the lever, but only a gradual fall at almost 
the same rate as during the latter part of the period of stimulation. 
The muscle has passed into a marked degree of contractur. 



v *sVf*>. <*£* 



\^M^mxMJMMmyu^y)^ 




glossuion fivefold. Shows the alterations in the character of the twitch as the 




c 



71 



CHAPTEE VI 

THE THICKENING OP A MUSCLE ON CONTBACTION. 
THE MUSCLE WAVE. 

When a muscle shortens during a twitch it also thickens, and this 
thickening may be studied in the following experiment, whose object is 
to magnify and record the changes in a transverse diameter at some 
convenient spot. 

Experiment 1. — Take a tracing of the thickening- of a muscle during a 
contraction by means of the apparatus shown in fig. 66. Arrange the apparatus 




Fig. 66. — Method or Kecording the Thickening of a Muscle as it Contracts. 



in the same way as for a simple twitch, but use the recording apparatus 
shown in the figure. Make a gastrocnemius preparation from a curarised 
frog, 1 and to its tendon attach a length of indiarubber, R. The muscle 
is laid upon a narrow wooden support, h, whose upper surface is covered 
with cork. The upper end is fixed to this base by two pins, to which two 
fine wires are soldered, thus forming a pair of electrodes. The end of the 
strip of rubber is pinned down to the cork base by a pin, so as to put the 
muscle slightly on the stretch. Resting on the muscle at a point near the 
electrodes is a light wire of aluminium, w, in the form of a hoop, the part 
touching the muscle being hammered out flat. This wire is connected 
below to a recording lever, l. 

1 The frog is previously curarised in order to prevent excitation of the muscle 
through its nerve (see pp. 76, 77). 



72 EXPERIMENTAL PHYSIOLOGY 

A tracing obtained by this arrangement is shown in curve n, fig. 
67, and for purposes of comparison a simple twitch taken immediately 
after, under precisely the same conditions, by attaching a thread from 
the tendon to a crank lever is reproduced in curve i. The two curves 
show the following points of difference. 

(i.) The latent period in the case of n is less than in i. The 
measurement given by the curve of thickening is just under -005 sec. 
This method is the one commonly employed for determining the latent 
period, the points to be especially observed being (a) to make all 




Fig. 67 Curve I the Shortening, and Curve II the Thickening of a Semi- 
membranosus and Gracilis Preparation. Time Tracing, 200 per Sec. 

moving parts of the lightest possible character, and (b) to stimulate 
the muscle exactly at the spot on which the recording lever rests. 

(ii.) The amount of movement is very much less in the second 
tracing. This follows as a necessity when we remember that in the 
first instance the curve is a summation of the movements along the 
length of the whole muscle. The second is a summation of the 
different thickenings over one transverse section ; and as the length 
is much greater than the thickness, that of itself explains the 
main difference. Further thickening is not proportional to the 
amount of shortening, which therefore further accentuates the dif- 
ference. 

(iii.) The total duration of the second is a little less than that of 
the first curve. This is because, in a contraction, the whole length of 
the muscle fibre does not contract simultaneously, but successively, 
whereas in the particular conditions of the experiment thickening 



THE MUSCLE WAVE 73 

occurs simultaneously throughout the section upon which the recording 
lever rests. 

The Muscle Wave. — We have seen that when a muscle contracts, 
it passes through a series of phases, a latent period in which no 
change of form occurs followed by a period of shortening, and this 
again by one of relaxation ; and the same holds true for each fibre and 
further for each constituent part of that fibre. If we, for the time 
being, limit our attention to what is happening in a single fibre, it is 
found that all parts do not pass through the different phases of their 
contraction synchronously, but that the contraction travels along the 
fibre in the form of a wave. A study of fig. 68 will make this clearer. 
a b is supposed to represent a very long muscle fibre, which has been 
stimulated at the point a, and as a result a wave of contraction, 
represented by the bulging of the fibre between c and d, is travelling 
towards B. At a somewhat later instant than the one drawn, the 
condition of the fibre will be represented by the dotted lines, and the 
front of the wave of contraction will have reached the point e. d has 
then passed through about half of its phases, and at c the muscle has 
returned to its initial form. The wave of contraction will in this way 



:b 



travel on until it reaches and has passed over b, when the whole fibre 
will come to rest. In the study of a wave of such a nature we can 
gain a full knowledge of it, if we can determine its following 
characteristics : — 

(1) Its amplitude. 

(2) The rate at which it travels. 

(3) Its length. 

Its amplitude and general course can be ascertained by recording 
the changes in diameter of a section of the fibre as the wave passes 
over it. The method by which this is done has been carried out in 
experiment 1. Next by measuring the time interval between the 
first movement at d and the corresponding change at e we can deter- 
mine its velocity after measuring the distance of e from d. Thus 
suppose the distance d e to be I centimetres, and the time occupied 
by the wave front in travelling from d to e to be t seconds ; then in one 

second the wave travels - cm., or in other words - is the velocity 

t t 

per second in centimetres. Lastly, if we determine the time the wave 
takes to pass over any fixed point, we can determine its wave length 



74 



EXPERIMENTAL PHYSIOLOGY 



A, i.e. the length c d of fig. 68. 



a wave of velocity - will travel - x 

v v 



For if this time be t' during that time 
t' cms. But at the end of the 



measured interval t' the wave is just leaving the fixed point. Hence 

A = - x t cms. 
t 

Actual measurements show that this wave length is great as com- 
pared to the general length of a muscle fibre, so that a single fibre 
cannot present at any one instant all the phases representing a single 
wave of contraction. Referring to our diagram it is as if the part 
d e were the only piece available for observation, and we then had to 
study the wave of thickening as it travelled over that portion. Thus 
if we record the total changes at two positions on the fibre and the 
time relations of those changes, we can then determine all the 
characteristics of the wave. This we can do by the following 
method : — 

Experiment 2. — Arrange the apparatus as for a simple twitch, fitting in 
a pair of pin electrodes. Curarise a frog and dissect out a gracilis and semi- 
membranosus preparation. Arrange this as shown in fig. 69. The prepara- 




Fig. 69. — Apparatus for Becording the Thickening of a Muscle at Two 
Points, for the purpose of studying the Muscle Wave. 

tion m is pinned down to a cork base, at one end a pair of pin electrodes 
being used. Two levers, l 1 and tr, are then arranged as in the figure. Each 
lever consists of a light bar to which is jointed a light vertical bar termi- 
nating in a flattened foot to rest on the muscle. Each lever is held on a 
specially arranged block, a, which slides along a bar, d, and can be fixed in 
any position by a screw, c. The axis of the lever is carried on a plate, b, 



THE MUSCLE WAVE 



75 



which can be rotated round the screw e, and by that screw clamped in any 
position to a. By movement along the horizontal rod d the levers can be 
approximated or separated to suit the length of the muscle. By rotation of 
the block a around the rod d the writing point of the lever can be raised or 
depressed, and finally by rotation of the plate b the writing point can be 
adjusted to the writing surface. By this apparatus we can record the changes 
in thickness of the muscle at two points separated by a distance which can be 
measured in millimetres. One lever is fixed near the pin electrodes, the other 
as far away as is convenient. 

On recording a single twitch the tracing obtained is similar 
to that of fig. 70. In this experiment the vertical levers rested on 
the muscle at two points situated 16 mm. from each other, and 
each therefore records the variations of thickness at those two points. 

The electrodes were placed immediately under the point on which 
the upper lever rested. The time tracing is 200 per second. Hence 




Fig. 70.— The Thickening of a Muscle ; Curve I at 4 mm., and Curve II at 
20 mm. from the spot stimulated. magnification, 8. tlme tracing, 200 
per Sec. 



the measurements of the two latent periods are "0044 second and 
•0094 second respectively. The difference is "005 second. Hence 
the muscle wave travelled from the first lever to the second, a 
distance of 16 mm., in -005 second ; therefore its rate was 3 - 2 metres 
per second. The temperature of the room and hence of the muscle 
was, in this experiment, 18° C. 

The time occupied by the total variation of thickness is seen for 
both curves to be *085 second. Hence the length of the muscle 
wave was - 085 x 3 - 2 metres = 27"2 cm. 



76 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE VII 

INDEPENDENT MUSCULAR EXCITABILITY. EXCITATION OF MUSCLE 
BY THE CONSTANT CURRENT. POLARISATION OF ELECTRODES 

INDEPENDENT MUSCULAR EXCITABILITY 

By this is meant the property a living muscle fibre possesses of 
responding by a contraction to a stimulus applied directly to it. To 
prove that the muscle substance is itself excitable, it is necessary to 
devise an experiment in which the stimulation of the muscle-fibre via 
its nerve is altogether avoided. The experiments commonly adopted 
for this purpose are the following : — 

Experiment 1— BERNARD'S CURARE EXPERIMENT.— Destroy 
the brain of a frog. Cut through the skin at the back of the left 
thigh for about an inch, separate out a short length of the sciatic 
nerve, and pass a stout ligature under it. Bring the ends of the 
ligature to the front of the thigh and tie tightly, thus including the 
whole of the structures of the limb with the exception of the sciatic 
nerve. Now inject a few drops of a one per cent, solution of curare 
(Indian arrow-poison) into the dorsal lymph sac and allow the frog to 
remain for about half an hour. At the end of that time the animal 
has become quite paralysed with the exception of the left leg. Pinch- 
ing the skin of the right leg produces no movement in that limb, but 
pinching the left leg leads to movements of the limb. Now dissect out 
both sciatic nerves right up to the vertebral column. Arrange a 
battery and coil for giving tetanising shocks and place the electrodes 
under the right sciatic nerve. Stimulation of the nerve in any part 
of its course has no effect upon the muscles which it supplies, but 
can produce reflex contraction of the leg muscles on the left side. 
Next place the electrodes under the left sciatic. Stimulation of this 
nerve causes contractions of the leg and foot muscles of the same side 
wherever the electrodes are placed, whether close to the knee where 
it has not been exposed to the action of the poison in the blood, 
or at that part near the vertebral column where the poison has been able 
to reach it. Finally apply the electrodes directly to any of the muscles 
of the right leg. They contract on stimulation. 



EFFECT OF CURARE 77 

The action of the curare has been to destroy the physiological con- 
tinuity of muscle with its nerve fibre. The poison injected is rapidly 
absorbed into the blood, and so carried to all parts of the body with the 
exception of the left leg below the ligature, where the vessels have 
been occluded. The upper part of the left sciatic has been exposed to 
the poison, but is still excitable, showing that the action of the poison is 
not on nerve-fibre ; and as the muscles in any part of the body contract 
when directly excited, it follows that they are not the parts affected 
by the poison. The portion paralysed must therefore be situated at the 
connection of the nerve to the muscle, i.e. the motor end plate or the 
small terminal piece of nerve which is unprotected by a medullary 
sheath. Just at this point, moreover, a very complex net of blood 
vessels is found, so that the part would be freely exposed to any poison 
present in the blood. 

From the same preparation we may also show another fact which 
further tends to the same conclusion. 

Experiment 2. — Using single induced break shocks determine for the 
left nerve the strength of stimulus necessary to just cause a twitch of the 
gastrocnemius, and secondly that which gives a maximum twitch. Having 
done this, apply the electrodes directly to the paralysed gastrocnemius, the 
right, and determine the two corresponding positions for the muscle. 

It will be found that in the latter half of the experiment the stimulus 
must be greater for both cases. This tends to confirm the previous 
result, viz. that it is muscle fibre which is being stimulated, and not 
nerve fibre, and in that case shows that MUSCLE IS LESS EXCIT- 
ABLE THAN NERVE. 

Experiment 3. — Xuhne's Sartorius Experiment. — Carefully dissect 
out a sartorius, and to the tendon which attaches it to the tibia tie a fine 
thread. The upper end of the muscle may be freed from its attachment 
to the symphysis. Suspend the muscle with its upper end hanging down- 
wards, and bring up under it a drop of glycerine in a watch glass until the 
end of the muscle just touches the glycerine. No contraction results. Cut 
off the end which has touched the glycerine, and note that the muscle con- 
tracts under the mechanical excitation. Again touch the cut surface with 
glycerine. If only about 1 mm. of the end has been cut off there is a^ain 
no contraction. Cut off a fresh miUimetre of muscle and repeat as before. 
It will be found that when about 3 to 4 mm. of the upper (pelvic) end has 
been cut away, on contact of the freshly exposed end with the glycerine, the 
muscle shows irregular twitchings, and is at last thrown into a state of incon- 
plete tetanus. This experiment should in the next place be supplemented by 
showing that if a gastrocnemius nerve muscle preparation be made, and the 
cut end of the nerve dipped into glycerine, the gastrocnemius is thrown 
into a similar series of irregular twitchings. Nerve fibre is therefore excit- 
able to glycerine. 

The explanation of the preceding experiment becomes clear by the 



78 EXPERIMENTAL PHYSIOLOGY 

light of a knowledge of the distribution of the nerve fibres in the 
sartorius. Kuhne showed that the upper 4 to 5 mm. of the 
sartorius contained no nerve fibres, nor could nerve-endings of any 
kind be traced in this part. The same holds good for the lower 2 
to 3 mm. Hence in the first part of the experiment only muscle 
fibre was being exposed to the glycerine ; and as the muscle did not 
contract, it follows that muscle fibre is not excitable to glycerine. As 
soon, however, as the lower part had been cut away, some of the nerve 
fibres became exposed, and as they are excitable to glycerine the 
muscle was thrown into a series of irregular twitchings. 

'Experiment 4. — Upon the sartorius of the opposite limb perform an exactly 
similar experiment, but use a salt solution (0*65 per cent.) containing a drop 
of ammonia solution. The muscle will be found to be extremely sensitive to 
this, even the vapour of NH 3 from it being quite sufficient to throw it into 
tetanus. Nerve, on the other hand, is not excited by it. Prove this by dip- 
ping the freshly cut end of the sciatic nerve of a gastrocnemius preparation 
into the solution, taking care that the muscle is thoroughly protected from 
the vapour by folds of blotting-paper moistened with normal saline solution. 
It is best, too, to hold the watch-glass of ammonia solution above the level of 
the muscle, and to lift up the nerve by a fine glass rod bent into the form of a 
hook, and thus dip the cut end of the nerve into the solution. No contrac- 
tion of the gastrocnemius residts, but the nerve is not unaffected, for it will be 
found that the part which has been exposed to the fluid, if tested by electrical 
stimuli, has been killed. 

Experiment 5. — Xiihne's Curare Experiment. — Pin down two strips of 
copper foil upon a flat plate of cork with their ends about 4 cm. apart, and join 
them by a strip of blotting-paper moistened with 0*65 per cent. NaCl solution. 
Connect the copper strips to the secondary coil of an inductorium arranged for 
tetanising. Prepare a sartorius and cut it transversely into five pieces of equal 
length, and arrange these in series upon the strip of moist blotting-paper. 
Starting with the secondary coil at some distance from the primary, send teta- 
nising shocks through the preparation, gradually increasing the strength of the 
stimulation until at last one is found which causes the three middle pieces of 
the sartorius to contract while the upper and lower ends remain quiescent. 
Increase the strength of the stimulation still further, when the two terminal 
pieces are also thrown into contraction. If a curarised sartorius be employed 
all five pieces go into tetanus at once, viz. when the stronger stimulus which 
was required to tetanise the two terminal pieces in the first experiment is 
reached. 

The difference in behaviour of the five pieces is due to the fact 
that the two ends contain no nerve terminals, while the three 
centre-pieces do, and as was seen from a previous experiment (ex- 
periment 2) muscle is less excitable than nerve. 

In addition to these experiments other facts are known tending 
to show the inherent excitability of muscle. Nerve, for instance, is 
not excited by stimuli which are arranged at right angles to the 
direction of the fibres, it being necessary that the stimulus or part of 
it should pass in the same direction as that of the fibres. Muscle, on 



INDEPENDENT MUSCULAR EXCITABILITY 79 

the contrary, is quite as excitable to stimuli in a direction transverse 
to the muscle fibres as to one parallel to them. Nerve again is 
especially sensitive to currents of very short duration, whereas muscle 
will not respond unless the duration be sufficiently prolonged. A 
curarised muscle is much less sensitive to shocks of short duration 
than a non-curarised one. 

In a further direction Kuhne showed that chemical stimuli which 
were particularly irritant to muscle (such as NH 3 or very weak HC1) 
were equally effective to both curarised and non-curarised muscles. 
If a strong constant current be sent through a nerve, it is found that 
the excitability of the nerve in the part immediately surrounding the 
anode is very greatly diminished. Kuhne utilised this to lower the 
excitability of the nerve fibres in a sartorius by throwing a constant 
current into its nerve, placing the anode close to the muscle. A muscle 
thus treated was found to be just as excitable to ammonia or weak 
hydrochloric acid, whilst those forms of stimuli, such as glycerine, 
which act on nerve only, are now without effect, or only produce one 
when the excitation becomes excessive. 

If the nerve supplying a muscle be cut and allowed to degenerate 
for some days, the response of the muscle to electrical stimuli becomes 
considerably modified ; while the intra-muscular nerve endings are 
intact the muscle responds more readily to induced shocks than to 
the constant current, whereas when these terminals have degenerated 
the reverse is found to be the case. This change of condition is 
explicable on the fact already tested in experiment 2, which shows 
that muscle is much less excitable to currents of short duration than 
nerve. 



EXCITATION OF MUSCLE BY A CONSTANT CURRENT 

In our experiments up to this point, we have as a rule employed 
an induced shock whenever we wished to stimulate a muscle or its 
nerve, but we have also seen that a muscle is excitable to thermal, 
mechanical, and chemical stimuli as well as to electrical. We have 
now to consider the response of muscle to electrical stimuli other than 
induced currents. We found that muscle was less excitable to induced 
currents than nerve, and this is found to be due to the very short 
duration of these currents. 

If a constant current of sufficient strength be sent through a muscle 
a contraction occurs at the instant of make of the current and again 
at the instant of break, but no effect is as a rule produced during the 
passage of the current. These two contractions are different, not only 



80 



EXPERIMENTAL PHYSIOLOGY 



in amount, but in that they start from different points. Calling the 
electrode at which the current enters the muscle the anode, and that 
at which it leaves, the kathode, it is found that on make of the current 
the contraction starts from the kathode and thence spreads over the 
muscle, but that on break the contraction starts from the anode. 
This very important point in the response of muscle to an electrical 
current can be shown by the following experiments : — 



Experiment 6. — Dissect out a sartorius and fix it to record its move- 
ments as shown in fig. 71. The muscle is lightly clipped between two 
pieces of cork c and d at a point near its tibial end. A fine thread is tied 
round the tendon at that end and attached to a crank lever, l. Two pins are 
passed through the corks c d, and by these the muscle is fixed to the myo- 
graph plate. The remaining longer piece of the muscle is connected to two 
electrodes (unpolarisable, see p. 83) a and b, which are connected to a con- 
stant current through a Pohl's commutator with cross wires, so that the 
direction of the current may be reversed. The muscle is clamped so tightly 
by the corks that it prevents any movement at a or b pulling on the piece of 
sartorius s to the left of the cork clamp, and so moving the lever. It is not, 
however, so tightly clamped as to prevent a wave of contraction passing 
across from the piece s 1 to the piece s. If now a contraction start at one 
instant from a, and passes as a wave along the muscle to s, a longer interval 
will elapse before s begins to contract and raises the lever than if the con- 
traction started at b and had only a short piece of muscle to travel along 

before it reached s. The 
experiment now consists 
in measuring the latent 
periods of four curves : 
two, one at make, the 
other at break of a con- 
stant current when the 
current passes from a to 
b, i.e. when the anode is 
at a, and two when the 
current travels from b to 
a, i.e. when the anode is 
at b. To record the in- 
stants of opening and closing the current a signal included in the primary 
circuit is arranged to record its movements directly beneath the myograph 
lever. This does not give us an absolutely accurate measurement of the 
latent period because there is a latency in the signal ; but as this is the same 
in all four cases this does not matter, for we only require to measure differ- 
ences in the latent period. 




Fig. 71.— Method of studying Polar Excitation of 
a Muscle. 



It will be found that make of the ascending current (anode at b) 
and break of the descending current (anode at a) have practically the 
same latent period, and both are greater than those on break of the 
ascending current or make of the descending current, which in their 
turn are practically equal in value. 

Hence it is argued that the contraction on make of an ascending 



POLARISATION 81 

current starts from a, and of a descending current from b, in both 
cases the kathode ; and, on the other hand, that the contraction on 
break starts from B with an ascending, and from a with a descending, 
current, these two points being the anodes in the two cases. The 
differences are more clearly seen if the muscle be fatigued. 

Experiment 7. — Engelmann's experiment. Curarise a frog, dissect out 
its sartorius, and suspend it by its pelvic end. Arrange two electrodes to 
send a current transversely across this end. On closing the current the free 
end moves towards the kathodic side of the muscle, on opening towards the 
anodic. 

Experiment 8. — Prepare a sartorius from a curarised frog that has been 
previously kept at a low temperature for some hours. Place it on a pair of 
unpolarisable electrodes. On closing the current the rmiscle passes into 
tetanus, and if the muscle be carefully observed, it will be seen that the only 
part in persistent contraction is that around the kathode. On opening, the 
muscle also commonly passes into tetanus, but in this case the contraction 
is limited to the region of the anode. This experiment is all the more 
striking if Biedermann's plan, of striping the sartorius transversely with black 
lines made by a bristle dipped in china ink, be adopted. The region in 
contraction is then clearly marked by the approximation of the black lines. 
The non-contracted part is seen to be stretched out, either by an actual 
stretching due to the contracted part pulling on it, or due to an active 
relaxation in that region. The latter is probably the main cause, as is well 
exemplified by the following experiment. 

Experiment 9. — A frog is pithed and its heart exposed. One electrode 
is now placed on any part of the body, and the point of the other, which 
should be a fine wire, is applied to the heart. If the electrode on the heart 
be the anode it will be seen that at each contraction the part around the point 
touched does not pale like the rest of the heart, i.e. that region does not con- 
tract but is inhibited. Conversely, if it be the kathode, it is seen that that 
spot remains pale during relaxation of the heart, which means that those 
fibres immediately affected do not relax properly. This latter point is not so 
easy to make out as the former. 

Polarisation of Electrodes. — If a pair of clean platinum wires be 
immersed in water, and a current sent through them for a time, it is 
found that both of the platinum terminals become covered with bubbles 
of gas. That one in connection with the negative pole of the battery- 
is covered with hydrogen, and the other with oxygen. If now the 
battery be removed and the two electrodes connected to the two 
terminals of a galvanometer, it is found that a current is shown by 
the galvanometer, which has a direction, in the galvanometer circuit, 
from the electrode covered with oxygen to that covered with hydrogen. 
It is, in other words, in the reverse direction to that of the initially 
employed current. The production of this state at the electrodes is 
spoken of as polarisation of electrodes. The same usually occurs, 
though to different degrees, if solutions of salts be tested instead of 
distilled water, and no matter what metal the electrodes are made of. 
Eegnault discovered, however, that if the electrodes were made of 

a 



82 EXPERIMENTAL PHYSIOLOGY 

pure zinc, and the solution in which they were immersed was a strong 
solution of zinc sulphate, that no polarisation occurred ; and the same 
was found to be the case with less purified zinc if its surfaces were 
thoroughly amalgamated. 

If instead of a solution a piece of fresh animal tissue connects a. 
pair of wire electrodes the same polarisation occurs. Chemical changes 
are set up where the wires touch the tissue which can act in the 
reverse manner, and set up a small current if the battery be removed 
and the electrodes connected by a conductor. This acts as a source 
of fallacy in many experiments, and becomes of great importance 
where we are dealing with a very excitable tissue, such as nerve. 
The existence of this polarisation current may be proved, as in the 
previous example, by sending it through a galvanometer ; but we are- 
also able to show it by its effect in exciting a nerve, as in the following 
arrangement : — 

Experiment 10. — Arrange the apparatus as shown in fig. 72, open the kejr 
K, and close the key k,. The current is thus sent through the nerve by the 
electrodes e, which it will polarise. Note that there is no contraction during 




Fig. 72. — Method of Arranging the Apparatus to Show- 
Polarisation of Electrodes. 

the time the current is passing. In about a minute open k ; and then rapidly 
close and open K 2 , when contractions will occur which are due to the closure 
and opening of the small current set up by the polarised electrodes. The- 
contractions rapidly diminish in amount as the nerve becomes depolarised. 

This experiment illustrates the necessity of avoiding this polarisa- 
tion, if it be possible, when we are experimenting upon nerves or other 
excitable tissues, and Du Bois-Eeymond utilised Eegnault's discovery 
for making electrodes which would not show this defect. In his 
original form (fig. 73, 1) each electrode consisted of a zinc trough on an 
insulating vulcanite base, the outer surface being thoroughly varnished 
and the inner well amalgamated. Into this a thick pad of filter 
paper thoroughly soaked in a saturated solution of zinc sulphate is 
fitted, and the part of the pad lying in the trough is then covered 
with the saturated zinc sulphate solution. If, now, the piece of tissue 
be placed between two such pads the zinc salt rapidly produces 
corrosive effects, and the tissue is rapidly destroyed. To prevent 
this, little masses of china clay worked up into a stiff paste with 
normal saline solution are used, upon which to rest the tissue and 



UNPOLARISABLE ELECTRODES 



83 



connect it with the electrodes. These do not cause any polarisation, 
and at the same time are fairly good conductors. They are spoken 
of as clay -guards. In many cases this form of electrode is too large, 
and it becomes impossible to bring them into contact with any two 




-Several Models of Unpolaeisable Electrodes 

1 and 2, Dn Bois-Reymond's ; 3, Burdon-Sanderson's ; 4, von Pleischl's ; 5, d'Arsonval's. 

In 1, 2, 3, and 4 the component parts are zinc, zinc sulphate, and saline clay ; in 5 a silver rod 
coated with fused silver chloride dipping in normal saline contained in the tube from which a thread 
projects. (Waller.) 

desired points of the tissue to be experimented upon ; and to over- 
come this many forms of electrode have been employed by different 
workers. Some of these are shown in the accompanying figure (73). 

Make a pair of unpolarisable electrodes in the following way. Take a piece 
of glass tubing of fairly thick walls and with an internal diameter of about 
\ inch. Rotate this with its centre in a blowpipe flame without draw- 
ing it out until the central part becomes of a less diameter ; then draw it 
out slightly and allow to cool. Cut it 
through the centre of the constricted 
part and round off these ends in a 
flame. The bore at this end should 
now be about ^ inch. Cut the tubes 
so that they are 2^ inches long and 
round off the upper ends in a flame. 
This glass tube is shown at a, fig. 74. 
Take a cork and bore half through it 
with a cork-borer of such size that the 
upper end of the glass tube is held firmly 
in the hole bored. With a fine bradawl pierce the cork from tbe upper end, and 
this will remove the lower bored piece of cork if that has not already come away 

g2 




Fig. 74. — Simple Form ok Unpolaris- 
able Electrodes. 



84 EXPERIMENTAL PHYSIOLOGY 

inside the borer. Solder an insulated wire to one end of a straight piece of pnre 
zinc wire of about three inches length, and then thoroughly amalgamate the 
zinc wire by dipping it into the amalgamating fluid and rubbing it on a 
clean duster. Now pass the zinc wire through the hole in the cork made by the 
bradawl until it projects well on the lower side. Next take some powdered 
kaolin and make it into a stiff clay with normal saline, and force a little of this 
up the constricted end of the glass tube to act as a plug to close that orifice. 
Then fill the tube with saturated zinc sulphate solution, and fit it into the 
large hole in the cork, so that the zinc wire dips into the solution. All that is 
now required to complete the electrode is to fix to the lower end a plug of 
china clay whose apex may be moulded to any desired shape (see fig. 74). 
In many cases it will be found convenient to fix in the centre of this china- 
clay guard a coarse thread soaked in normal saline, which can then act as 
the terminal part of the electrode. These electrodes can be kept, and all 
that they will require at a future time is a fresh guard of clay, when they will 
at once be ready for use. 

Experiment 11. — Arrange the apparatus exactly as in experiment 10, 
fig. 72, but employ these electrodes in the place of the wire ones of that experi- 
ment. The nerve does not now become polarised. 

Great as is the importance of using unpolarisable electrodes when 
a current is to be sent through a nerve, their use is of still greater 
necessity when we require to examine the currents produced by a 
tissue, and for this purpose are making use of a sensitive galvano- 
meter. 



85 



CHAPTEE VIII 

SOME EXPEBIMENTS TO DETEEMINE THE FUNCTIONS OF NEKVES 

In examining the functions of a nerve we have two main methods 
which we may employ, section and stimulation. 

By section we can observe the loss of function resulting from the 
loss of impulses normally passing along it. 

By stimulation we can observe the converse effect, i.e. the production 
of some functional activity, such as a muscular movement, secretion 
of a gland, &c, when impulses are sent along the nerve. 

The two methods of experimentation illustrate the two great 
physiological attributes of a nerve, viz. conductivity and excitability. 
Section teaches us the function of a nerve by observation of the 
results of interrupting its conductivity at some spot. Stimulation 
makes use of its property of excitability to give us knowledge of the 
results of impulses travelling along the particular nerve. 

We have already made use of a nerve's excitability in our experi- 
ments upon muscle, and in our study of the variations of function of 
a nerve under different experimental conditions motor nerves are 
generally employed, because the muscular response enables us to readily 
determine small changes in the nerve's activity. 

As conductors nerves carry impulses either to or from the central 
nervous system, i.e. they are afferent or efferent in function. At their 
entrance into the cord, the spinal nerves divide into two roots, 
anterior and posterior, the former carrying only efferent, the latter only 
afferent impulses. Show this upon the frog by the following 
experiment : — 

Experiment 1. — Decapitate a frog and cut away the upper third of the 
vertebral column. With a fine pointed pair of scissors cut away the lamina; 
of the remaining vertebrae, taking great care to avoid injuring the spinal cord. 
This brings to view the cord in its lower part with the large roots of the 
nerves which form the sciatic plexus. To see the anterior roots, the posterior, 
which cover them up, must be displaced, (i.) Lift up the largest posterior 
root with a seeker and pass a silk thread under it. Tie this close to the 
cord and cut through the root between the ligature and the cord. Note that 
on tying and on section irregular movements of the limbs are caused which 



86 EXPERIMENTAL PHYSIOLOGY 

vary, however, according to the degree of stimulation. Place the peripheral 
end upon a fine pair of electrodes and stimulate. There is no muscular con- 
traction. 

(ii.) Place a second ligature round another posterior root, this time tying 
as far from the cord as possible, and cut through the nerve peripherally to the 
ligature. Stimulate the central end, i.e. the part still attached to the cord. 
The limbs are thrown into convulsions, more or less marked and extensive 
according to the strength of the stimulation. These two stimulations prove 
that the posterior roots contain no efferent, but do contain afferent 
fibres. 

(iii.) Cut through all the posterior roots of that side. Any mechanical 
stmralation to the skin no longer produces movements of the legs, though 
stimulation of the skin of the opposite leg will produce movements in 
both. 

(iv.) The section of the posterior roots brings the anterior into view. By 
placing ligatures round two of these and tying (a) near the cord and (&) near 
the junction with the posterior root show that stimulation of the peripheral 
end leads to contraction of muscles, but stimulation of the central end produces 
no effect. The anterior root therefore contains efferent but no afferent 
fibres. 

(v.) Cut through all the anterior roots, and then show that no movement 
of that leg can now be produced by stimulation of the skin of the leg of the 
opposite side. 

STIMULI which affect a nerve may be classified as follows : — 

1. Thermal. 

Experiment 2. — Make a nerve muscle preparation and touch the 
end of the nerve with a copper wire which has been heated for a few 
moments in a Bunsen flame. The muscle contracts. That heat should 
act as a stimulus it is necessary that the temperature should be high. 
If heat be gradually applied it will kill without stimulating. 

2. Mechanical. 

Experiment 3. — To produce mechanical stimulation cut through 
the nerve used in the previous experiment just below the point to 
which the hot wire was applied. The muscle contracts, thus showing 
that the mechanical process of cutting has stimulated the nerve. In 
the next place, pinch the upper end of the nerve and show that this 
also acts mechanically as a stimulus. Show also that the nerve can 
be stimulated by giving it a sharp tap with the edge of the handle of 
a scalpel, thus pinching it between the scalpel and the solid support 
upon which it rests. 

3. Chemical. 

Experiment 4. — Take a nerve-muscle preparation and lift up the 
nerve on a glass rod bent as a hook, so that the cut end of the nerve 
hangs down. Touch the cut surface of the nerve with a drop of a 
•8 per cent. KOH solution in normal saline, held in a watch-glass. 
With each contact the muscle contracts, and, if the nerve be immersed 
a little time, passes into an irregular tetanus. Cut away the piece 



STIMULATION BY THE CONSTANT CURRENT 87 

of nerve that has been in contact with the fluid. The muscle 
relaxes. 

Experiment 5. — Next immerse the cut end in a drop of methylated 
spirit. This, too, causes contraction. 

Experiment 6. — Repeat, using a solution of 15 per cent. NaCl. 
The same result is obtained. 

There are very many substances which excite a nerve chemically. 
Of these we may mention glycerine in strong solutions, solution of 
lactic acid, bile salts, or mineral acids if not too dilute. Substances 
which kill but do not excite are basic or neutral lead acetate, 
chromic acid, copper sulphate, ammonia, &c. 

4. Electrical. 

Stimulation by an electrical current has already been frequently 
employed in the experiments upon muscle, when we used indirect 
stimulation. 

THE EFFECTS OF THE CONSTANT CURRENT 
UPON NERVE 

Employing a current of medium strength, e.g. one Daniell, the 
usual result is that a twitch occurs at make and break of the current, 
but that during the passage of the current the muscle remains quies- 
cent, i.e. the nerve is not stimulated. But this is not universally 
true, for if the nerve be very irritable, there may be produced a tetanic 
contraction the whole time the current is passing. This can always 
be produced if the frog from which the nerve muscle preparation is 
taken has been kept for a day or two at a low temperature, between 
0° C. and 10° C. A tetanus at make or break is especially liable to 
occur at the make of a strong descending current, or the break of a 
strong ascending current, where by an ascending current is meant 
one in which the direction of the current in the nerve is from the 
muscle towards the spinal cord, and by a descending the reverse. 
This condition is spoken of as Bitter's tetanus. A Bitter's tetanus at 
break of an ascending current may be stopped by closing the current 
in the same direction, or may be increased by sending in a current 
in the reverse (descending) direction. Therefore, as a general rule, 
the nerve is not stimulated during the whole of the time of passage 
of a constant current, but only when the strength of the current is 
suddenly varied. It follows that when we were using induced shocks 
the excitation was in reality double, but the two stimuli followed 
one another at such a short interval that the effect on the nerve 
was the same as a single stimulation. Though the nerve is not 



88 



EXPERIMENTAL PHYSIOLOGY 



being stimulated the whole of the time the current is passing, still 
we can show that its condition is altered. This altered state, due to a 
constant current, is spoken of as clectrotonus, and its effect is 
expressed as an alteration in the two physiological properties of a 
nerve — its conductivity and its excitability. The alteration is different 
in the parts of the nerve in the neighbourhood of the two points at 
which the current is sent in and taken out of the nerve, i.e. the anode 
and kathode respectively. The condition of the nerve in the neigh- 
bourhood of the anode is termed anelectrotonus, that in the neigh- 
bourhood of the kathode katelectrotonus. 

1. Changes in excitability. 

Experiment 7. — Test the changes in excitability in the following 
manner. Arrange the primary and secondary coils for giving single induced 
shocks (left half of fig. 75), using a pair of fine wire electrodes, E r Fit up a 
'■polarising ' circuit with two batteries, a mercury key, k.-,, and a mercury 
commutator with cross wires, K t . To the commutator attach a pair of un- 
polarisable electrodes, E 2 (right half of fig. 75). Dissect out a nerve muscle pre- 



<&^ 




Fu 



K. 
75.- 



-Plan of Apparatus for Studying the Changes of Excitability 
of Electrotonus. 



paration, taking the whole length of the nerve, and being careful not to injure 
it during the dissection. Fix the gastrocnemius in the crank myograph and 
place the nerve across the unpolarisable electrodes. Place the wire elec- 
trodes under the nerve at a point just below the unpolarisable electrodes 
nearest the muscle. With the key it, still open, move the secondary coil to 
such a position that the muscle gives a small twitch on break of the 
primary circuit. Record the height of this twitch on a stationary drum. 
Move the drum a little by hand and close the polarising circuit. Note that 
the muscle gives a twitch. Again stimulate the nerve with a break shock 
and record the twitch. It will be found that either the twitch is of less 
height or even absent, or that it is of greater height. Now examine the 
direction of the constant current through the nerve. If the twitch has been 
prevented or diminished, it will be found that the current ascends along the 
nerve from muscle towards vertebral end, and therefore the part of the nerve 
stimulated is hi anelectrotonus. If, on the other hand, the twitch has been 
increased in height, it will be found that the electrode nearest the nerve is 
the kathode. After obtaining one of these two results, reverse the direction 
of the polarising current by the commutator K 4 , when the second result will 
be obtained 



ELECTROTONUS 89 

Experiment 8. — Repeat the preceding experiment, but tetanise the 
nerve at the spot to be tested instead of giving it a single stimulus. The 
shocks used should be just above minimal stimuli. Record the results obtained 
on a slowly moving drum. It will be found that if the spot stimulated be in 
anelectrotonus that the contraction on tetanisation is either abolished or 
diminished ; if, on the other hand, it be in katelectrotonus, the contraction is 
increased. 

These experiments show that a piece of nerve in anelectrotonus is 
less excitable than normally, for it does not give so large a con- 
traction, and, on the other hand, the state of katelectrotonus is charac- 
terised by an increase of excitability. These same results have also 
been confirmed by other modes of stimulation, both mechanical and 
chemical. The latter can very easily be shown by the following 
experiment : — 

Experiment 9. — Instead of using the secondary coil for stimulating, 
paint the nerve with a 10 per cent, solution of NaCl at a spot between the 
lower electrode and the muscle. In a short time the muscle is set twitching 
by the stimulus. Arrange the polarising circuit to give an ascending current 
and close the key K r The twitching ceases. Reverse the key, so that the 
kathode is now nearest the muscle. The twitching becomes more marked. 
Record these results on a slowly moving drum. 

By varying the course of experiments of this kind differences have 
been made out in regard to the degree of change of excitability 
and the time it lasts. The katelectrotonic increase of excitability 
reaches its maximum height directly after the closure of the current, 
and then gradually decreases whilst the anelectrotonic decrease 
develops and extends much more slowly, its maximum being reached 
some time after closure. The amount of change of excitability, as 
measured by the amount of contraction, produced by a stimulus of 
fixed strength is found to vary considerably with the strength of the 
polarising current. As the excitability is increased around the kathode 
and decreased around the anode, it follows that there must be one 
spot between anode and kathode at which excitability remains 
unchanged. This is called the indifferent point. The changes of 
excitability are conveniently represented diagrammatically, as in fig. 76. 
In this figure the abscissa line g i is taken to represent the nerve, and 
the polarising current is supposed to enter at A and leave at K. An 
increase of excitability is represented by an ordinate above the 
abscissa, a decrease by one below. With a weak current the changes 
in excitability are represented by the curve anbrc, which means 
that at the point m of the nerve the excitability is decreased to an 
amount represented by the vertical m n. At the point p it is increased 
by an amount represented by j) r. Similarly for all other points 
between a and c. The indifferent point is at b, which is seen to be 
nearer the anode A than the kathode k. The changes in excitability 



90 EXPERIMENTAL PHYSIOLOGY 

are also seen not to extend far beyond the anode and kathode. For 
a stronger polarising current the changes are represented by the 
curve d ef. The indifferent point has moved towards the kathode ; 
the changes are relatively greater and extend over a longer piece of 
nerve, df. With a still stronger current the changes are represented by 
the curve g him which the indifferent point is still nearer the kathode, 




Fig. 76. — Diagram Indicating the Changes of Excitability of a Nerve in 

Electrotonus. 

and there is a further increase in intensity of effect and in extent of 
nerve involved. 

Immediately after opening the current these changes are for a 
short time reversed, the excitability in that part of the nerve which 
was in anelectrotonus is increased, in that part previously in katelec- 
trotonus decreased. These reversed effects gradually disappear. 

2. Changes in conductivity. 

Experiment 10. — Arrange the apparatus as in fig. 75, but place the 
polarising electrodes near the muscle and the exciting electrodes at the upper 
end of the nerve. Tetanise the nerve, and while the contraction still con- 
tinues close the polarising current. The tetanus ceases. Repeat, but 
instead of tetanising apply a crystal of salt or a drop of strong salt solution to 
the cut end of the nerve. The twitchings caused by the salt can be stopped 
by throwing in the polarising current. The same effect is produced whether 
the polarising current be ascending or descending. The polarising current has 
acted as a block, i.e. the nerve at that part has had its conductivity depressed. 

The change of conductivity has also been studied by observation 
of the rate of transmission of a nerve impulse along a piece of nerve 
in anelectrotonus or in katelectrotonus, and further by observations 
of the changes of strength of the negative variation * as it travels along 
the nerve. Such experiments showed that for all currents, except 
the weakest, conductivity was depressed in both the katelectrotonic 
and anelectrotonic states. 

POLAR, EXCITATION OF NERVE 

When stimulating a muscle by the constant current we found 
that the stimulation at make started from the kathode and at 
1 For the explanation of the term negative variation see p. 146. 



POLAR EXCITATION OF NERVE 91 

break from the anode, and the same is found to be the case with 
nerve. As in the analogous experiment upon muscle, the starting 
points of the two excitations have been determined by time measure- 
ments of the two latent periods of the make and break contractions. 
The electrodes are separated as widely as possible ; then if the stimulus 
start from the upper electrode, the latent period should be longer 
than if it started from the lower. Experimenting in this way it is 
found that if the current be ascending, the latent period of the contrac- 
tion on make is longer than that of the contraction on break. From 
this we infer that the contraction on make starts from the upper elec- 
trode, i.e. the kathode, and that on break from the lower, i.e. the anode. 
A converse result is found for a descending current. 

We may also state the fact of polar excitation in the following 
way. The production of katelectrotonus and the disappearance of 
anelectrotonus stimulate a nerve. Or, again, the passage of a nerve 
from a condition of lesser to one of greater excitability stimulates it. 

In examining the effect of opening and closing a constant current 
through a nerve the results obtained are found to vary with the 
strength and direction of the current, and to study these variations we 
must possess some means of conveniently varying the strength of the 
constant current. This is afforded by either of the two following 
pieces of apparatus : — ■ 

The monochord is an application of the principle of the deriving circuit and 
is employed for varying the strength of current to be sent through a nerve or 
other tissue. Fig. 77 illustrates the method of using a monochord. A 
current is sent through a stretched wire, a b, which must not be of too 

low resistance. The two electrodes are E 

connected, one to one terminal, a, of 
the wire, the other to a movable con- 
tact, s. Supposing now the electrodes 
e to be bridged by a nerve, when the key 
k is closed the current on reaching a 
divides, part passing along a s, the other 
through the nerve. The amount of 
current passing through the nerve is 
inversely proportional to the resistance FlG . 77._To Illustrate the Prin- 
of that part of the circuit, and directly ciple of the Monochord. 

proportional to the potential difference 

between a and s. If s be brought nearer to a this potential difference is 
decreased in direct proportion to the distances between A and s in the two 
positions. Where, as in the case we are considering, the resistance in the 
nerve circuit is very high, and therefore the resistance of a s may, in com- 
parison, be neglected, the current through the nerve is directly proportional 
to the potential difference only, i.e. is measured by the length A s. 

If we wished to know exactly the value of this current, it is necessary to 
measure the resistances of the nerve circuit and of a r, and from these the 
total amount of current can be calculated. For most purposes, however, it is 
sufficient to state the current strength as measured by the lengths between a 
and s in different positions. 




92 



EX l'KRIMENTAL PHYSIOLOGY 



A-3a 


T c 


j_B 



Fig. 78 shows a nionochord fitted for convenience on a small base, and 
consisting of a wire wound in a zigzag round pegs, its two ends being 

attached to the binding screws a and 
b. The electrodes are connected 
to a and the movable contact c. 
In the battery circuit a murcury 
commutator, k 1 , with cross wires 
is interposed, so that the direction 
of current can be readily reversed. 
A key, k 2 , is also inserted, so that the 
current can be closed and opened as 
required. 

Another instrument that is fre- 
quently used for varying the strength 
of current is the rheochord. This 
consists, in its simplest form, of two 
wires, s 1 a and s 2 b (fig. 79), stretched 
parallel to one another on a wooden 
base. To the ends, s 1 and s 2 , binding 
screws are fixed, and the wires are 
connected by a metal slider, c, which 
can be pushed along the wires. In 
the figure it is represented connected to send a branch current to a pair of 
unpolarisable electrodes across which a nerve lies. A battery current is sent 
through the rheochord, a commutator, k 1} being interposed, and a key for 
making and breaking the circuit at k,. The current on reaching s 1 divides, 
passing through the rheochord to s 2 or through the nerve. The amount 



Fig. 78. — A Second Form of Monochord. 




Fig. 



79. — The Eheochord as Arranged for Varying the Direction 
and Strength of a Current through a Nerve. 



passing through the nerve varies directly with the resistance of its deriving 
circuit, the rheochord. By increasing this resistance more current is sent 
through the nerve, and on diminishing it less. 

In more complex forms of the instrument the range of the rheochord is 
increased by adding other wires by means of which more resistance can be 
thrown into the rheochord circuit than can be reached by the single pair of 
wires. 

Suppose, for the sake of example, that the resistance of the electrodes and 
nerve is 100,000 ohms, and the resistance of the rheochord 5 ohms ; then 
tctS&SSj of the total current passes through the rheochord, and rdhnr? through 
the nerve. 

Experiment 11. — Fit up the apparatus as in fig. 79. Attach the muscle 
to a myograph lever and arrange it to record twitches on a stationary drum. 



PFLUGER'S LAW 



93 



Start with the slider c close to the screws s,, s 2 , in which position the current 
through the nerve is practically nil. Open and close the circuit by the key 
K 2 . With this very weak current no contraction occurs on make nor on break. 
Arrange the commutator k, to give an ascending current, and slide c a little 
further along the wires, so as to increase the current through the nerve. At 
a certain position of the slider a contraction will be obtained at make but 
none at break. Reverse the current. The same result is obtained. A 
current of this length is spoken of as a weak current. It will vary in strength 
according to the excitability and electrical resistance of the particular nerve 
experimented upon. Increase the current still further, when contractions 
will occur on both make and break of ascending and of descending currents. 
A current of this strength is spoken of as a current of medium strength. 
To complete the series remove the rheochord and attach the electrode wires 
directly to the commutator. It will usually be necessary to further increase 
the strength of the current to four, six, or even eight cells. Increase the 
current till one is found which gives a contraction on make only of a descend- 
ing, and on break only of an ascending current. Such a current is spoken of 
as a strong current. 



The result of this experiment may be arranged in tabular form, 
and the statement of results is commonly termed the law of 
contraction. (Pfliiger's Law.) 



Strength of 
Current 


Ascending 


Descending 


M 


B 


M 


B 


Weak . 
Medium 

Strong . 


C 

c 


c 

c 


OOO 


C 



This ' law ' can be explained on the basis of the facts we have 
already studied with regard to changes of excitability and conductivity 
brought about by the constant current and by our knowledge of the 
position at which excitation occurs. Thus, the results with a weak 
current mean that the production of a certain degree of katelectrotonus 
can stimulate, whereas the disappearance of the anelectrotonus pro- 
duced by precisely the same current cannot stimulate. If the kathode 
be nearer the muscle (descending current) there is nothing to prevent 
the impulse reaching the muscle when the stimulus starts from the 
kathode. The muscle therefore contracts on closing the current. 
When the current is reversed the stimulus now has to travel through 
the intrapolar piece of nerve, and through that part in anelectrotonus. 
In both these parts the conductivity is diminished but not sufficiently 
to block the impulse. The muscle therefore contracts. An exactly 
analogous explanation holds for a descending weak current. 

With currents of medium strength the disappearance of anelec- 
trotonus can stimulate. At make of a descending current the stimulus 



94 EXPERIMENTAL PHYSIOLOGY 

starts from the electrode nearest the muscle, and there is nothing 
tending to block its transmission. On break the stimulus starts from 
the upper electrode. There is nothing which prevents it reaching the 
muscle, for the diminished conductivity round the kathode disappears 
as soon as the current is broken. With an ascending current on 
make the stimulus starts from the upper electrode, and as with this 
strength of current the block at the anode is only slight, it reaches 
the muscle which contracts. On break the stimulus starts from the 
lower electrode, and there is nothing to prevent it reaching the 
muscle. 

With a strong descending current on make the stimulus starts 
from the lower electrode, and therefore leads to a contraction. On 
break the stimulus starts from the upper electrode, and has to travel 
through a piece of nerve whose conductivity is strongly depressed, 
sufficiently so to block the impulse, and no contraction results. 
With an ascending current the impulse at make starts from the upper 
electrode, but is blocked by the strong depression of conductivity 
around the anode, and therefore does not reach the muscle. On 
break the stimulus starts from the lower electrode, and therefore 
causes a contraction, as nothing prevents it travelling down to the 
muscle. 



THE VELOCITY OF A NERVOUS IMPULSE 

Just as we found that if a muscle be excited at any point the con- 
traction begins there, and then spreads in a wave-like manner over the 
remainder of the muscle, so too it is found for nerve that an impulse 
started at any point travels along the nerve as a wave of excitation. 
This is brought out most clearly by a study of a motor nerve, in 
which we determine the latent periods of two twitches in one of which 
we stimulate the nerve close to the muscle, in the other at some 
distance from the muscle. Any difference of time in these two 
measurements must be due to the time occupied by the impulse in 
travelling from the one point to the other. The method of carrying 
out the experiment is as follows : — 

Experiment 12. — Arrange the apparatus for recording a simple twitch, 
but with the drum arranged to rotate at as fast a rate as possible. Dissect 
out the gastrocnemius and the whole of the sciatic nerve up to the vertebra;. 
Place two pairs of electrodes under the nerve — one pair near to its 
entrance into the muscle, the other at its further extremity. Connect these 
electrodes e 1 and e' 2 to the terminals of a Pohl's commutator without cross 
wires, as in fig. 80. Interpose a Du Bois key between the secondary coil 
and the remaining terminals of the commutator. The secondary circuit can 
in this way be connected up to either pair of electrodes, e 1 or e' 2 , by 



VELOCITY OF A NERVE IMPULSE 



95 



turning the rocker into the proper position. Take two simple twitches, 
recording them one over the other, stimulating the nerve (a) at e 1 and (b) at 
E 2 . Take a time tracing under the record. 




Fig. 80. 



-Arrangement of Apparatus for Studying the Velocity 
of a Nervous Impulse. 



A tracing obtained in this manner is shown in fig. 81. It is seen 
that the latent periods differ in the two cases, the second one being 
longer than the first. This difference in time can only be accounted 
for by supposing that the molecular changes started in the nerve by 
the stimulation require time for their transmission along it. In the 
figure a is the point of stimulation, b is the instant at which the 
muscle began to contract with the electrodes in the first position, and 
c when they were in the second position. The time tracing is at the 
rate of 100 vibrations per second, and on measuring it is found that the 
length between b and c corresponds to a time of 0"00369 sec. The 
length of nerve between the two positions of the electrodes was 
74 mm. Hence the impulse would in one second travel ™- = 20054 




Fig. 81. — Two Twitches of a Gastrocnemius when the Sciatic was Stimulated 

(a) NEAR THE MUSCLE, (b) NEAR THE VERTEBRA. TlME TRACING, 100 PER SEC. 

mm. per sec. In this experiment, then, the velocity of the nervous 
impulse was 20"05 metres per second. In an experiment of this kind 
it is very important that the recording surface should travel at exactly 
the same rate when the two twitches are taken. Hence it is better 
to take the record upon a pendulum or spring myograph, or two quite 



96 EXPERIMENTAL PHYSIOLOGY 

separate twitches, each with its own time tracing, may he recorded, 
and the difference between the two latent periods can then be 
calculated. 

The velocity of a nervous impulse varies considerably in different 
animals and under different conditions. For the sciatic of the frog it 
is found to vary from 2 to 30 m. per second, the chief variation being 
caused by differences in temperature, the rate being considerably 
diminished by cooling the nerve. When a very rapidly moving re- 
cording surface is not available for the preceding experiment, we may 
make use of this last factor to delay the rapidity of the nervous im- 
pulse, and so obtain curves which have a sufficient difference between 
their latent periods to make the time measure well marked. 



97 



CHAPTER IX 



EXAMINATION OF THE FROG S HEART. 
LIGATURE 



THE FIRST STANNIUS 



To examine the main features of the beat of a frog's heart proceed 
in the following way : — 

1. Expose the heart. Pith the brain, leaving the spinal cord intact, 
and lay the frog on its back. Pick up the skin over the sternum and 
slit it up in the mid line, make transverse incisions on either side and 
reflect the four flaps of skin thus formed. The sternum should now 
be completely exposed. Make a transverse cut through the lower 
cartilaginous piece of the sternum (xiphi sternum), taking care not to 
wound the anterior abdominal vein, and cut through the sternum by 
longitudinal incisions a little on either side of the mid line, and thus 
remove the central piece. Care is to be taken not to injure the peri- 
cardium which lies beneath. The lateral pieces may now be pulled 
apart. This exposes the heart still lying within the pericardium. 
Lift up the pericardium with fine forceps and snip it through from 
the apex of the heart to the base. 

2. Examine the different parts of the heart. Above lie the two 
thin-walled auricles, fig. ^^ ^^\ n 

i % 



82, their line of division 

not being clearly seen, 

as it is mainly hidden by 

thebulbus arteriosus, b a, 

which crosses the auricles 

from below upwards and 

from right to left. 

Below is the single ven 

tricle, bluntly pointed, 

and with a well-marked 

groove, the auriculo-ven 

tricular groove, separat- 

ingitfromthetwoauricles. 

If the heart be now lifted up by the apex, the lower half of the sinus 




Fig. 82. — Anterior and Posterior Surfaces or 
the Frog's Heart, sv, Sims Venosdb. a, Auri- 
cles, v. Ventricles, ha, Bulbus Arteriosus. 



98 EXPERIMENTAL PHYSIOLOGY 

venosus, sv, is brought into view lying in the posterior pericardial wall. 
At its junction with the auricle a transverse crescentic line, white in 
colour, is to be made out, marking the limits of the two cavities. Run- 
ning from a point in the mid line of the posterior ventricular wall, and 
about 2 mm. from the auricular ventricular groove, is a thin cord of 
fibrous tissue which is attached to the posterior pericardial wall. This 
is the frenum, and contains a small blood vessel. Entering the sinus 
from below is the single large inferior vena cava, whose outline can 
be made out below the pericardium. Replace the ventricle and gently 
displace the two auricles by means of a seeker. In this way the upper 
end of the sinus can be exposed with the two smaller superior venae 
cavae running into them. 

3. Note that at each contraction the ventricle becomes pale in 
colour, and with each distension, which occurs very suddenly, the 
ventricle becomes deep red. This change is dependent on the structure 
of the heart wall, which has the form of a sponge-work of muscle bundles 
between which the blood passes during dilatation and causes the dark 
colour. With each contraction the blood is driven out of the sponge- 
work, leaving the muscular tissue only, which has a pale colour. 

4. Determine the rate at which the heart is beating by timing it 
with a watch. Make a note of the number of beats per minute. It 
will be found to vary very greatly in different frogs— from 20 up to 
100 per minute, and in some cases even passing these limits in either 
direction. 

5. Make out the course of the contraction as it travels over the 
heart. This is of some little difficulty even when the heart is beating 
slowly. The contraction starts at the sinus, thence passes to the 
auricle, then to the ventricle, and finally to the bulbus arteriosus. 

6. RECORD THE BEAT OF THE HEART. One of the most 
convenient ways is that known as the SUSPENSION METHOD. Pre- 
pare a lever in the following way (fig. 83). A light straw, s, is selected, 
and near to one end an 8-shaped hook is attached by means of a little 
cement. The hook may be conveniently made from a fine entomological 
pin. 3 cm. from the hook the straw is transfixed by a fine needle, x, 
and is then cut of such a length that when the writing point is fixed 
its length from needle to writing point is about 15 cm. The magni- 
fication will then be fivefold. 

The last 12 cm. of the straw may with great advantage be replaced by a glass 
writing point. This is made of a piece of glass tubing drawn out to a fine 
capillary, which is then bent into the form of an elongated triangle, g l, by 
heating it in the flame of a match. The two ends at the acute angle are then 
fused and the knob of fused glass drawn out by another piece of glass tubing 
into a fine rounded point projecting at right angles to the plane of the 



RECORDING THE BEAT OF A FROG'S HEART 



99 



triangle. It is then fixed to the end of the straw by a little cement. Such a 
writing point possesses the great advantage of a considerable degree of rigidity 




Fig. S3. — Apparatus for Eecording the Heart-Beat by the Suspension Method. 

in the vertical direction with free flexibility in the horizontal direction. It 
is of much less weight than the straw, and owing to its lightness it is not 
readily broken. They are also very easily and quickly made. 

The needle is now fitted into two flat brass pieces, a 1 , a-, which 
slide on a brass rod, b, and have two conical cavities at their lower 
ends to receive the points of the needle. The needle then acts as the 
axis of rotation of the lever, and the hook at the end s hangs down- 
wards. 

Lift up the ventricle, v, of the heart which has already been pre- 
pared and transfix its apex by a sharp-pointed hook, h. Place the frog 
on a cork myograph plate and fix both lever-holder and cork plate on a 
stand, and hook the end of the bent pin fixed to the heart into the 
lower bend of the hook on the straw, s. With the light glass lever it 
will be found necessary to weight the longer arm in order to enable 
it to lift the ventricle up, and so exert a sufficient tension on the 
auricle. The weight w is to be attached by hooking it on to the straw 
at a point about 1 to 2 mm. from the axis. 

Record the movements of the writing point upon a drum which 
should revolve at the rate of 1 cm. per second, and at the same time take a 

H 2 



100 



EXPERIMENTAL PHYSIOLOGY 



chronograph tracing of a spring vibrating two, four, or eight times per 
second (fig. 29). Having recorded several beats, change the rate of 
the drum to h cm. per second, and record again. The rate may still 
further be reduced and so a series of tracings produced. 

Fig. 84 shows some typical tracings taken by this method, but 
from different hearts. In I great care had been taken to avoid any 
loss of blood during the preparation of the heart. We see that there 




Fig. 84 



-Becord of the Movements of the Frog's Heart by the Suspension 
Method. Time Tracing, 4 per sec. 



are four ascents on the curve, viz. (i.) at a ; (ii.) from b to c ; (iii.) from 
d to e ; and (iv.) from e to /. The little notch at a is due to the sinus 
contraction. It is never very marked, and commonly is absent 
altogether. This is due to the position of the sinus, which does not 
allow it to produce much eiFect upon the recording lever ; and secondly, 
because it usually occurs either during the relaxation, or even at the 
end of the ventricular contraction, and is therefore masked by the 
greater movement due to them. Even in this instance we see that 



RECORD OF THE HEART BEAT 101 

the downward stroke due to its relaxation is more marked than the 
upward stroke of the contraction, which was partly masked by the 
ventricular relaxation. The rise from b to c is due to the contraction 
of the auricles. It is at first rapid and then gradually slows. The 
descent from c to d is due to relaxation of the auricles, and from d to 
e is the first part of the ventricular contraction. The processes occur- 
ring just before and at d are in two directions. First there is the 
relaxation of the auricles which would allow the lever to descend, and 
secondly there is the ventricular contraction which causes the lever to 
ascend. The actual movement of the lever is the algebraic sum of 
these two movements, and the upward movement of the ventricle soon 
exceeds in amount the fall due to the auricular relaxation. The part 
of the curve from e to / is especially interesting. It also is due to 
the contraction of the ventricle, so that this contraction occurs in two 
stages. The meaning becomes clear if we cut the two aortse when we 
find that the second stage, e to /, immediately disappears. It is also 
only present in tracings produced from hearts which receive a full 
blood supply. It proves that the ventricle at first is able to empty 
itself comparatively easily, and therefore shortens rapidly. At the 
point c, however, the pressure inside is suddenly raised, and the con- 
traction becomes slower. The last part of the blood is ejected with 
greater difficulty than the first. This receives a further support from 
a study of the arrangement of the blood vessels springing from the 
aortse. The first and main part of the blood is sent into the pul- 
monary and aortic arches, which offer a relatively low resistance. The 
pressure here is thus rapidly raised until it reaches such a height that 
it is able to overcome the resistance of the third arches, and blood then 
passes into the carotids. 

In II and III the characters of the beat are somewhat different. 
In III the heart was beating slower than in II, and it is seen that the 
main increase in rapidity occurs during the systole. The part from a to 
b is the auricular systole ; from c to d the ventricular. The second 
stage of the ventricular systole is only faintly indicated in a few beats, 
and in most it is quite absent. In a quite bloodless heart this second 
stage is entirely absent (see, for instance, fig. 100, p. 123). 

7. EXCISE THE HEART. Remove the frog from the myo- 
graph plate and take away the hook from the ventricle. Count the 
number of beats in a minute. Cut through the two aortee close to the 
bulbus if they have not already been severed. Lift up the ventricle 
by the apex and cut through the pericardium, so as to expose the 
sinus venosus ; cut through the inferior cava and the two superior cavae 
as they come into view, and thus remove the whole heart as in fig. 82. 



102 EXPEEIMENTAL PHYSIOLOGY 

Place it upon a clean glass plate. The process of cutting will be found 
to exert an influence upon the rhythm. Usually it is inhibited for the 
space of a few beats and then recovers and beats very rapidly for a 
short time, but quickly settles down to a regular rate, which, as a rule, 
is slower than that in situ, though the reverse may at times occur. 
When it has settled down count and make a note of this rate per 
minute. Cut away the sinus at its junction with the auricles. The 
effect upon the auricles and ventricle is that they give a series of rapid 
beats and then come to a standstill completely relaxed. The effect 
upon the sinus is usually found to be inhibitory. It stops beating at 
once, though in a few cases, if care be taken to injure it as little as 
possible, it may continue its rhythm unaltered. After a short period 
both parts recommence to beat, but with quite a different rhythm. 
Count the rate per minute. The auricles and ventricle beat at a rather 
less rapid rate than the whole heart. The sinus being more injured 
takes longer to recover and beats at a slower rate. If the course of the 
experiment be modified, in that instead of removing the sinus with the 
rest of the heart the incision be made between sinus and auricles, so 
as to leave the sinus in situ, it is usually found that the sinus beat is 
from the first but little affected, and frequently quite unaltered. Next 
remove the auricles from the ventricle, cutting on the auricular side 
of the auric ulo- ventricular groove so that a small edge of auricle 
is still attached to the ventricle. The process of cutting again inhibits 
both auricle and ventricle. After a time both recommence to beat the 
auricle earlier than the ventricle. If the amount of auricle still 
attached to the ventricle be very small the ventricle may not of itself 
recommence beating. If it do not, it may be taught to beat by 
stimulating it rhythmically with mechanical (e.g. a prick of a needle), 
or with electrical stimuli repeated at regular intervals. In many cases 
it will then be found that the ventricle starts off beating quickly and 
gradually slows down until it ceases altogether. The rhythm may 
then be again started by rhythmic stimuli. If the ventricle recover 
its rhythm cut through it just below the auriculo-ventricular groove : 
the ventricle is brought to a standstill and does not regain an 
automatic beat if left to itself. With each mechanical stimulus a 
contraction follows, and if the stimuli be repeated rhythmically for 
a time, say one per second, the ventricle may regain an automatic 
rhythm, though this does not often occur with a frog's heart. If it 
should, count the rate. 

The results of this experiment should be collected together in a 
tabular form somewhat after the plan adopted in the following experi- 
ment, which is slightly modified from the preceding instructions : — 



RHYTHM AN INHERENT PROPERTY OF HEART MUSCLE 103 



Time 


Observations 


Rhythm 






V. A. a 


11.39 


Heart exposed. Pericardium still unopened 


62 


11.44 


Immediately after opening of pericardium .... 


54 


11.45 


Auricles (a) and ventricle (v) excised, leaving sinus (s) in situ. 
s slowed for a few beats, A and v also inhibited for two to 
three beats ......... 




11.46 


s beat counted ......... 


53 


11.47 


a and v beat counted 


35 


11.50 


s beat counted 


54 


11.51 


a and v beat counted ........ 


38 


11.52 


s excised. Very much slowed but not stopped . 




11.54 


a cut off, leaving a rim attached to the ventricle, v does 
not stop, but the rhythm becomes irregular, and beats occur 






in groups of three, a stops. v. 


36 


11.55 


a has recommenced. a. 


42 


11.56 


s beat counted. s. 
The ventricular beat obviously follows the beat of the piece 
of a still attached to it 


54 


11.58 


v apex cut off. Auricular piece still goes on beating, v 
apex responds to each prick of a blunt needle, but cannot 






be taught to beat rhythmically ...... 





There are several conclusions to be inferred from such experiments. 

A. The excised heart beats rhythmically. Therefore the rhythm is 
not dependent upon external rhythmic stimuli reaching it via its 
nerves, but is due to some intrinsic source possessing a rhythmic 
activity. There are two possibilities, (a) The rhythmic activity 
may be an inherent property of the muscle fibres, (b) The heart 
contains in itself nerve cells and nerve fibres ; and the rhythm may 
be a characteristic of some of these cells. By this experiment taken 
alone we are not able to prove which of these two possibilities is the 
correct one. The last part of the experiment, if it succeed, is the most 
helpful in deciding, but the frog's heart is not a very suitable subject 
to employ for this particular purpose. On a tortoise heart Gaskell has 
shown that the apex, which examination proves to be free from nerve 
cells, can be taught to beat rhythmically. Further facts tending 
to prove that the rhythm is inherent in the muscle cells are : 
(i.) the heart beats rhythmically in embryonic life, while it is still of 
tubular form and before it has gained any nervous connection with the 
central nervous system ; (ii.) nicotine has been proved to paralyse nerve 
cells, but a heart poisoned with nicotine continues to beat rhythmi- 
cally ; (iii.) there is no difficulty in ascribing the rhythm to the heart 
muscle, for cross-striated muscle may be caused to contract rhythmi- 
cally by immersing it, under proper tension, in Biedermann's fluid, ' 
and the bulbus arteriosus, which contains no ganglion cells, beats 

1 Biedermann's fluid is made by dissolving 5.g. NaCl, 2.g. Na H,P0 4 and 0'59.g. 
Na.,CO., in 1 litre of water. 



104 EXPERIMENTAL PHYSIOLOGY 

rhythmically when completely isolated from all other parts of the 
heart ; (iv.) an isolated heart apex can more readily be made to beat 
rhythmically if it be subjected to an internal pressure, as by tying it 
on to a perfusion cannula through which fluid is circulated at sufficient 
pressure. 

B. Taking it as proven that the rhythm is a property of the 
muscle cells, it follows that the cells in different parts do not possess 
the rhythmic capacity to an equal degree. The sinus, if left intact in the 
body, beats with the same rhythm as the intact heart, and this, taken 
in conjunction with the fact that the contraction wave starts normally 
from the sinus, shows that in the sinus rhythmic activity is especially 
developed. That the auricles and ventricle, when severed from the 
sinus, beat at a slower rate is generally taken as indicating that the 
auricles, the part from which the contraction wave starts when the 
auricles and ventricle are removed, possess rhythmic characters to a 
lesser degree than the sinus. Finally in the ventricle rhythmic activity 
is still less developed, and with the ventricle apex can only be demon- 
strated under especial conditions. 

Experiment 2. — The first Stannius ligature. Pith a frog and expose 
its heart, cutting away the pericardium, so as to thoroughly expose the auricles 
and two aortse. With an aneurism needle pass a thread tuider the bulbus 
arteriosus and above the two superior cavae. Lift up the apex of the heart, cut 
through the frenum, and bring the ends of the thread round the heart, so that 
it lies under the auricles. Tie a loop in the thread and tighten it, so that it 
lies over the crescentic junction of sinus and auricles after the ligature is 
tightened. The auricles and ventricle usually give a few beats and then come 
to rest in a fully relaxed condition, whilst the sinus continues to beat at the 
same rate as before. At times the auricles and ventricle still continue 
beating, though at a slower rate. This is usually due to the ligature being 
wrongly applied. It should be relaxed and tied a second time a little nearer 
to the auricle, when the required standstill will usually occur. 

In fig. 85 the effect of the application of the Stannius ligature is 




Fig. 85. — Application of the First Stannius Ligature to the Frog's Heart 
at the Point a. At b a Beat due to a Mechanical Stimulus. 

recorded graphically. At the point a the ligature previously placed 
in position was suddenly tightened. The two peaks immediately 



THE STANNIUS LIGATURE 105 

recorded are mechanical and due to the process of tying. The 
auricle and ventricle beats stopped at once, and the recorded line only 
shows slight undulations, which were caused by the contraction of the 
sinus. The rhythm of the sinus is seen to be at first slowed. At the 
point l> the ventricle was stimulated by a prick of a needle. It gave 
a single contraction. 

Prick the auricle. With each stimulus the quiescent part gives a 
single beat. Repeat on the ventricle. The same result is obtained. 
Next stimulate with an induced shock. A single contraction is also 
obtained in this way. 

The Stannius ligature is of great importance because it enables us 
to study a single contraction after the same method adopted in studying 
a single twitch of a muscle, whereas while the heart is still beating 
rhythmically this is impossible. 

Experiment 3.— Test the response of the heart to electrical stimuli of 
different strengths. Attach the apex of a heart brought to a standstill by the 
Stannius ligature to the recording lever, as in fig. 83. Remove the secondary 
coil to such a distance from the primary that neither make nor break shocks 
excite a contraction. Bring the writing point to the surface of a drum at 
rest, so as to record heights of twitch only. Move the secondary coil gradu- 
ally up to the primary, stimulating the heart with each new position until one 
is found at which a contraction occurs at break. Move the drum 1 or 2 mm. 
by hand. Bring the secondary 1 cm. nearer the primary, and, allowing 
fully 30 seconds to elapse, stimulate once more. The height of the con- 
traction is the same as before. Further increase the strength of the stimulus 
and record the contractions. There is no increase in the height. 

Therefore a minimal stimulus causes a maximal contraction. If a 

heart contracts at all it contracts to its full power. 

The reason for allowing an interval of from 30 to 60 seconds to 
elapse in the preceding experiment before applying a second stimulus 
is because a second stimulus of even the same strength is found to 
produce a greater effect than the first if it follow the first within a 
second or so. This can be shown in the following way : — 

Experiment 4. — Arrange the drum to rotate at a very slow rate, about 
2 cm. per minute. Apply electrical stimuli every five seconds, recording the 
contractions on the moving surface. Record some twenty contractions in this 
way. 

Fig. 86 shows the result obtained. The second contraction is seen 
to be higher than the first, the third than the second, and so on up to 
the fifth, from which time they all reached practically the same height. 
The increment of height of the second over the first is greater than the 
increment of the third over the second, and this increment gradually 
decreases until it vanishes. This increase of effect on repeating the 
stimulation, keeping to the same strength, is spoken of as the staircase 



106 



EXPERIMENTAL PHYSIOLOGY 



effect. We have already found that skeletal muscle gives a similar 
result (pp. 63 and 69). 




Fig. 86. — Electrical Stimulation of the Ventricle of the Frog's Heart 
in Standstill by the Stannius Ligature to Show the ' Staircase ' Effect. 
Interval between the Stimuli 5 secs. 

Experiment 5. — Record a single beat of the heart. Arrange the drum 
to rotate at the rate of 2 cm. per second. Fit up the apparatus as for record- 
ing a single muscle twitch (fig. 37). For electrodes in the secondary circuit 
make a pair with fine silk-covered wire as in fig 87. Cement the two wires 
together by a touch of sealing-wax or marine glue at a point, c, near to their 




Fig. 87. — A Simple Form of Flexible Electrodes. 



free ends. Scrape off the insulation from their projecting ends, e, which 
should be cut of equal length. Take a piece of flat cork of the shape of k 
and pass two pins, f and g, through it. Slit up the cork in two places at 
its apex and pass the wires through these slits by which they are held 
firmly ; then wind each wire round one of the pins and attach the two 
ends to the Du Bois key in the secondary circuit. Apply a Stannius liga- 
ture to a heart and, passing a bent pin through its apex, attach it to the 
recording lever, as in fig. 83. Twist the electrodes, e, until the wires lie 
above one another and pin down the electrodes to the cork base of the 
myograph, so that the wires touch the base of the ventricle. Arrange a chrono- 
graph vibrating thirty times per second to record directly under the heart 
lever. Bring the writing point to the surface and record a contraction in the 
same way as if recording a simple muscle twitch. Mark the point of stimu- 
lation and draw vertical lines with the recording lever to mark on the time 
tracing the point of stimulation and the points (1) when contraction begins, 
(2) when it reaches its maximum, and (3) when relaxation ends. Draw a zero 
abscissa line. Bepeat the experiment, varying the rate of the recording surface. 

The tracing obtained is of the form shown in fig. 88, and presents 



A SINGLE CONTRACTION OF THE HEART 



107 



features closely analogous to those of a simple muscle twitch. The 
great difference lies in the time occupied. The time measurements 
are seen to be — 

(a) The latent period, 0117 sec. 

(b) The period of contraction, 
0-767 sec. 

(c) The period of relaxation, T067 
sec. 

In examining the general form of 
the curve it is seen that the top tends 
to be flattened ; a condition which is 
often more prominent than in this 
particular curve (see curves of fig. 91). 
In different hearts the form of the 
curve varies considerably, differences 
which are largely due to the different 
temperatures at which they are ex- 
amined, and secondly to the time of 
the year. The flattening of the top 
of the curve tends to show that the 
contraction wave possesses so slow 
a rate that the first fibres affected 
return to rest before the wave has 
extended over all the heart fibres. 
This follows from the same considera- 
tions which we have already gone 
into when discussing the features 
of the contraction wave in muscle 
(p. 73). 

In figs. 89 and 90 we have two 
further tracings taken from different 
hearts, and with the recording surface 
moving at different rates. In these 
figures the relaxation of the heart is 
seen to be more rapid than the con- 
traction ; a condition which is com- 
moner than the reverse effect recorded 
in fig. 88. In both these figures the 
first and major part of the relaxation 
is most rapid ; it then becomes much 
slower and gradually ceases. Note 
that the apex of each curve is very blunt, even flattened, indicating 
that the contraction is sustained for some time. 



108 



EXPERIMENTAL PHYSIOLOGY 



Upon a heart brought to a standstill by the Stannius ligature we 
are further able to study the effect of two successive stimuli, which 
enables us to demonstrate one of the great physiological characteristics 
of heart muscle, namely, its long refractory period. 




Fig. 89.- -A Single Contraction of the Frog's Ventricle. Time, 30 per sec. 




Fig. 90. — A Piepetition of the Tracing of Fig. 89 with a Slower 
Movement of the Recording Surface. Time, Tracing, 8 per sec. 

Experiment 6. — Arrange the drurn as for recording the effect of two 
successive stimuli on muscle (fig. 58). The drum should be so geared that it 
rotates at the rate of 2 to 3 cm. per second. Pith a frog, expose its heart, 
and apply the Stannius ligature. Pass a bent hook through the apex of 
the ventricle and attach to the recording lever, fig. 83. First remove one 
of the contacts and record a single beat as in the previous experiment. 
Mark the point of stimulation and draw an abscissa line. Now arrange the 
second contact at such a distance behind the first that the second point ot 
stimulation will fall near the end of the period of relaxation and record the 
result of the double stimulation. Mark the points of stimulation on the 
curve. Move the two contacts nearer and repeat the stimulation. Carry out 
the process until a distance between the points of stimulation is reached, 
when only a single contraction results. 

In this way tracings such as those reproduced in fig. 91 are 
obtained. 

Curve I. gives a record of the single beat. The time from the 
point of stimulation to the highest point of the curve is § £ths sec. 
The total duration is ^hs sec - 

Curve II. This is the result of two successive stimuli, the second 
following the first after an interval of f£ths sec. It therefore fell near 



THE REFRACTORY PERIOD 109 

the end of the period of relaxation. We see that the heart responded 
by giving a second beat, but that there was no real summation of the 
contraction. The apex of the second contraction is at exactly the 
same height as that of the first. 

The one difference observable is that the second contraction is 
carried out a little quicker than the first. There is less flattening of 
the apex. The measurements of the ' apex time ' show this very 
clearly. They are f^-ths sec. and f^ths sec. respectively. 




Fig. 91. — The Effect of Two Successive Stimuli upon the Ventricle of 
the Frog's Heart. Time Tracing, 30 peb sec. 

In curve III. we have practically a repetition of curve II., but the 
second point of stimulation falls a little earlier, f^ths sec. after the 
first, and therefore nearer the commencement of the period of relaxa- 
tion. Again we find no true summation of height. The second 
contraction repeats the first, but starts with many fibres already con- 



110 



EXPERIMENTAL PHYSIOL* H J V 



tracted. As in the previous curve the second is rather more rapid 
than the first contraction. The apex times for the two are f$ ths and 
5-^ths sec. 

Curve IV. The second stimulation in this instance follows the first 




Fig. 92. — Tetanisation of a Feog's Venteicle in Standstill by the Stannius 
Ligatuee. In 1 the Secondaey Coil AT 10 CMS. ; IN II AT 12 CMS. ; IN III 
AT 13 CMS. FEOM THE PEIMAEY. MAGNIFICATION, 10. THE DUEATION OF 

Tetanisation is Indicated by the Shoet Veetical Mabks undee Each Teacing. 

after an interval of ffths sec, i.e. at the end of the period of contrac- 
tion. We note the most striking result that no second contraction is 
produced. It has fallen on the muscle fibre during a time when it is 



REPEATED STIMULATIONS OF THE HEART 111 

unable to respond to a stimulus. That time during which a stimulus 
produces no response in a muscle fibre is termed its refractory 
period. We see, then, that for the heart the refractory period lasts 
through the whole of the period of contraction. In contrast with 
this we have previously found that the refractory period for skeletal 
muscle was practically identical with its latent period. 

Experiment 7. — Upon the same heart study the effect of a rapidly 
repeated series of stimuli. Arrange for the recording surface to move 
very slowly. Set up the coil for giving tetanising shocks, and then stimu- 
late the heart, varying the strength of stimulus employed. 

In fig. 92 are shown three curves obtained in this way with 
different strengths of stimulus. In i the stimulus was strongest, and 
we see that during the whole period of stimulation, lasting during 
the interval between the two vertical marks, the ventricle never com- 
pletely relaxed. The important result, however, is that there is no 
complete fusion. A heart cannot be sent into complete tetanus. At 
first the amount of fusion was marked, but as the stimulus proceeded 
fusion became gradually less, and a rhythmic contraction, which 
was not very regular, was produced. Putting it in another way, 
we may say that as tetanisation proceeded the refractory period 
tended to increase. Note, moreover, that a contraction occurred 
after stimulation had ceased, showing that the effect of the stimuli 
did not stop immediately stimulation ceased. Tracing n was taken 
from the same heart, but the secondary coil was removed 2 cm. 
further from the primary. With this weaker stimulation there is no 
summation of effect, except in the case of the first two beats. A 
rhythmic beating was started which ceased on the stimulation being 
stopped. In the third curve (in) the stimulus was still weaker, and 
only two contractions were produced at the commencement and 
none during the rest of the time of stimulation. 

A single break shock with the secondary coil at 13 cm. produced 
no response, whereas at 12 cm., the position during tracing n, a con- 
traction was produced. 



112 



EXPERIMENTAL PHYSIOLOGY 



CHAPTEE X 

THE ACTION OP HEAT AND COLD UPON THE FBOG's HEART 

THE EFFECT OF HEAT AND COLD UPON THE EXCISED 
BLOODLESS HEART 

Experiment 1. — Pith a frog and expose its heart. Cut through the 
frenuru and pass a bent hook through the apex of the ventricle. Cut away 
the lower jaw and now remove the heart entirely with the pericardium, 
cutting out with it the surrounding tissues pretty freely. Pin this on to a 
cork base fixed to a metal bar made in the foUowing way (fig. 93). Select a 
round flat cork and bore through it from the side, making a hole sufficiently 
large to fit tightly on the short arm of a brass L-piece. Fix the cork to the 
L-piece with a little sealing-wax. The pins should pass through the floor 
of the pericardium, so as to fix the heart firmly to the cork. The heart can 

be fitted to the recording lever as in 
the previous experiments (see fig. 83). 
A small beaker is then filled with defibri- 
nated ox-blood, diluted with four times its 
volume of normal saline, or with Ringer's 
solution, 1 which has previously been 
cooled in a freezing mixture to about 0° C. 
The writing point is brought to the sur- 
face and a chronograph marking seconds 
arranged to write immediately under 
it. The drmn is set in motion, and after 
a short length of tracing has been taken 
the beaker of cooled fluid is raised so 
as to immerse the heart. The character 
of the tracing is at once altered, and after 
about half a minute, when the record no 
longer changes, the fluid is lowered 
and the gradual change in the beat, as 
the temperature returns to its original 
height, is recorded. Take several tracings 
in this way, raising the temperature of the fluid five degrees for each fresh 
tracing. 

Tracings obtained in this way are reproduced in fig. 94. In the first 

the heart was suddenly immersed in diluted blood at 4° C. The following 

beat is seen to be of less height and considerably prolonged, the second 

one of greater height, and then the heart settled down to a slow 

rhythm of considerable force in which the contraction was sustained 

at its height for some time, and relaxation was considerably prolonged. 

1 Kinger's solution is made by saturating 0-65 per cent. NaCl solution with 
calcium phosphate and then adding 2 c.c. of a 1 per cent, solution of potassium 
chloride to each 100 c.c. 




ACTION OF HEAT ON THE EXCISED HEART 113 

The rate before cooling was 24 per minute ; during cooling, 7. After 
removing the cold blood the heart very rapidly increased in rate, and 
for the first few beats in force. The rate was increased until the beat 
became faster than the original rate. The force gradually decreased 
until at last both rate and force after about five minutes returned to 
their original state. 

At a rather higher temperature 11° C. the same effects are observed, 
though to a much less marked degree (fig. 94 a). 

At 25° C. it is seen that the rate is greatly increased— from 51 
to 93 per minute. The force of the ventricular and auricular con- 
tractions remains practically unaltered, but the time of each is markedly 
diminished, so that the auricular relaxation is finished before the ven- 
tricular contraction begins. On removing the warmed blood these 
changes gradually disappear. 

If a heart be immersed in blood at about 35° C, fig. 94 b, a very 
interesting result is obtained. The ventricular contraction at once 
ceases, but the auricular persists — at first very weak, but gradually 
becoming stronger. If immersion be prolonged one beat is dropped at 
irregular intervals, at times two successive ones. On cooling, the heart, 
after some few seconds, once more begins to beat, and at first with 
greatly increased frequency. Sometimes, as in the tracing reproduced, 
the ventricular contractions after a time are once more dropped, and 
the auricular become much weaker. After a varying interval, rhythm 
for a second time returns, and the heart apparently recovers com- 
pletely. During both periods, when the ventricular contractions cease, 
the ventricle will respond with a single beat on mechanical or electrical 
stimulation, though the stimulus required is greater than normal. 

Another change which this tracing shows is in the amount of ' tone ' 
of the heart. Directly after immersion the heart begins to elongate, at 
first fairly rapidly, and then more slowly, i.e. there is a diminution of 
tone. As soon, however, as the heart recommences beating this tone is 
recovered, and even becomes greater than before. When the ventricle 
once more ceases beating the tone immediately falls again. 

In some hearts a different result is produced at this temperature. 
The heart may at first beat very rapidly before the ventricle finally stops. 
This is because the heart takes a little time before it reaches the tem- 
perature at which the ventricle stops, and if the fluid be only just above 
this temperature the time required to reach this point is much longer 
than if the temperature be distinctly higher. 

In the last tracing the immersion fluid was at 38° O, and it is seen 
that after one short contraction the ventricle ceased, and then some 
five or six beats later the auricle also stopped. The heart then relaxed 
a little, i.e. there was a diminution of tone. About 30 sees, after im- 

i 



ACTION OF HEAT ON THE EXCISED HEART 



115 



mersion a new change occurred, viz. a gradual and regular contraction. 
This is the production of heat rigor. The heart was kept at this tem- 




perature for four minutes and was then cooled. No relaxation occurred, 
though after three minutes the heart once more regained a rhythm^ 



though of much weaker force than before. 



i2 



116 EXPERIMENTAL PHYSIOLOGY 

If the heart be kept much longer at this temperature, or for a 
shorter time at a higher temperature, heat-contraction is more pro- 
nounced, becomes complete, and then no recovery occurs on cooling. 

The effect of heat and cold upon the heart in situ. — The effect upon 
the beat of raising or lowering the temperature of the whole heart has 
been determined by several methods. We can employ the same 
arrangement as that of the previous experiment, but having pithed 
the brain it is best to curarise the frog. It is then pinned down to 
the cork and the heart attached to the lever. The beaker of fluid is 
then brought up as before, allowing the legs to remain out of the 
beaker. The results obtained by this method are practically the same 
as those already described above. 

Engelmann passes a tube through the oesophagus and out of an opening 
in the stomach wall. Water of different temperatures is then circulated 
through the tube. 

Another simple plan is to arrange the heart for recording by the suspen- 
sion method, and then while the tracing is being taken a fine stream of 
normal saline at the temperature required is directed on to the heart through 
a glass tube drawn out to a fine capillary orifice. By this method it is 
possible to limit the cooling or heating mainly to the auricles and sinus 
without affecting the ventricle. 

A third plan is to record by the suspension method, having previously 
arranged a coil of platinum wire around the heart. The coil is then heated 
by an electrical current, and thus forms a small source of heat, whose action 
may, by altering its position, be limited chiefly to either the sinus and 
auricles or to the ventricle. 

The results given by these methods are similar to those already 
given for the excised heart, but with the difference that where the 
alteration of temperature is limited chiefly to the sinus, the result 
tends towards alteration in rhythm without alteration in the character 
of each beat. On the other hand, where the heating or cooling effect 
is chiefly localised to the ventricle the main effect is an alteration in 
the force and character of the beat with no change in the rhythm. 
As in the first experiment, when the rhythm alone is altered, heat 
tends to accelerate ; when the character is altered, heat up to about 
20° tends to increase the force, above that temperature to decrease the 
force, until at about 30° the rhythm is stopped, though on again cool- 
ing the heart will recover. At about 35° C. the heart begins to pass 
into the state of heat-rigor, and no complete recovery is then possible. 

THE EFFECT OF HEAT AND COLD UPON A SINGLE 
CONTRACTION OF THE VENTRICLE 

In addition to examining the result of varying the temperature 
upon a heart beating rhythmically the alteration in a single beat should 



ACTION OF HEAT UPON SINGLE BEATS 



117 



also be studied a little more closely. 
This can readily be done by the aid of a 
heart brought to a standstill by the Stan- 
nius ligature. 

Experiment 2. — Prepare the apparatus 
for recording single contractions as in ex- 
periment 5, p. 106. The drum should rotate 
2 cm. per second. Pith a frog, expose its 
heart, and apply the Stannius ligature. 
Hook a bent pin through the tip of the 
ventricle apex. The heart may now be 
excised and attached as in fig. 93. Fix 
the electrodes for stimulating the ventricle. 
Take a small beaker full of the diluted 
blood (or Ringer's solution), which has pre- 
viously been cooled in a freezing mixture, 
and bring it up around the cork base, so as 
to immerse the heart. Take the tempera- 
ture of the dilute blood. After about a 
minute's immersion lower the beaker and 
record a contraction. Raise the temperature 
of the dilute blood five degrees by placing 
the beaker for a few seconds in hot water. 
Again immerse the heart for one to two 
minutes. Then lower the beaker, see that 
the writing point is again at the same level, 
and record a second contraction over the first. 
In this way record a series of contractions, 
increasing the temperature each time until 
a range of from 5° C. to 30° C. has been 
reached. Mark the point of stimulation, 
draw an abscissa line, and take a time- 
tracing of 30 per second beneath the zero 
abscissa. 

Pig. 95 represents such a series of 
curves. Measurements of each should 
be taken and arranged in a tabular form, 
as has been done for this experiment in 
the table on next page. 

Prom this figure and its accompany- 
ing table the following points are clear : 

1. As the temperature rises the 
latent period becomes shorter. 

2. As the temperature rises the 
period of contraction becomes shorter, 
at first very rapidly and then more 
slowly. 

3. The period of relaxation shows 
a sudden shortening from 7 to 10° C. It 



118 



EXPERIMENTAL PHYSIOLOGY 





Duration in ^th Sec 


of 






Temperature 








Total 
Time of 


Height of 
Contraction 










Latent 


Period of 


Period of 


Contraction 


in Mm. 




Period 


Contraction 


Relaxation 






7°C. 


4-5 


49 


28-5 


82 


17 


10 


4 


39 


11 


54 


13-5 


15 


4 


27 


12 


43 


16 


20 


3 


14 


12 


29 


16 


25 


3 


9 


11 


23 


3 


30 


3 


4 


4 


11 


1-5 









TTJ-T 










80 


titrli'i 4 


trfW-j 


EEEEgi 


-ft 


-t-t . — 






III 

</> 60 










-K 

z 

~ 40 
ui 


-flff^' 4 


<"tP 


iKj! 






+P 




Z 
20 


wit 


:±t:±:± 
::±:±:± 


: +Hii- + 

#f 
mum 


rtt 


rmt 








;fflp| 






|=B 









/0° /5° 20' 25* 

TEMPERATURES 

Fig. 96. 



30' C 







































































































































































































'10 /0 




-H — |- 


i::::::"::::::::: 


:::H!":::::::::H: 





































































































































































































































/0' /5" 20° 25" 

temperatures 

Fig. 97. 



30* C 



then remained perfectly constant until 30° C. was reached, when there 
was again a sudden diminution. 



INFLUENCE OF HEAT 119 

4. The total time showed at first a rapid diminution, and then a 
more gradual one as the temperature rose. 

5. The height of contraction showed a maximum at 7° C, a relative 
minimum at 10° C, a relative maximum from 15 to 20° C, and an 
absolute minimum at 30° C. 

These different points can be very clearly figured by the use of 
squared paper, and should be carried out as in figs. 96 and 97. 

These conclusions should also be compared with those we have 
already obtained when studying the effect of varying the temperature 
upon striated muscle (p. 46). The results are found to very closely 
resemble each other in most of their important features. 



120 



EXPERIMENTAL PHYSIOLOGY 



CHAPTER XI 

THE NERVES OF THE FROG'S HEART AND THEIR FUNCTIONS 



MAKE A DISSECTION TO SHOW THE NERVES OF THE 
FROG'S HEART. — The nerve supply to the frog's heart is from two 
sources, the vagus and the sympathetic. 

To find the vagus expose the heart in the usual manner, leaving, 
however, the pericardium intact to serve as a protection while the 
dissection is being made. Pull aside the lateral pieces of the sternum 
and separate the muscles running from it to the floor of the mouth. 
When this is done a muscle comes into view which is the guiding 
mark for the vagus. This muscle is the petro-hyoid, which arises from 

the base of the skull and is 
inserted into the posterior 
cornu of the hyoid bone. Its 
direction is from the joint of 
the lower jaw, round the 
pharynx in an almost trans- 
verse direction to the body of 
the hyoid. This muscle should 
be clearly made out (fig. 98, 
ph). It is arranged in three 
separate small bands, in series 
one behind the other. Crossing 
it are two nerves : one late- 
rally placed, the glossopharyn- 
geal, gp, coursing from the 
angle of the jaw over the muscle 
to run forwards into the tissues forming the floor of the mouth ; the 
other, the hypoglossal, h, crosses it much nearer the mid line. The 
latter nerve is the first spinal nerve in the frog. In relation to the 
lower border of the muscle lies the carotid artery, a. If the muscle be 
now laid hold of, a nerve will be seen running along its lower edge and 
partly covered by it. This is the vagus, v. A branch of this, the laryn- 
geal, l, usually runs a separate course parallel to the main trunk, 




Fig. 98. — To Show the Course of the 
Vagus in the Frog. 



THE NERVES OF THE FROG'S HEART 



121 



leaving it as the nerve comes towards the anterior mid line. The main 
trunk of the nerve branches near the heart, the larger half running 
backwards towards the lung ; the other is the cardiac branch. The 
vagus must be isolated completely from the surrounding tissues. It is 
important to remember that the nerve thus isolated is not the vagus 
only, but has already been joined, immediately after its exit from the 
skull, by a large branch from the sympathetic. The cardiac branch 
therefore contains both vagal and sympathetic fibres. 



To expose the sympathetic before it joins the vagus, cut away the 
whole of the lower jaw by a single transverse incision. Pick up the 
mucous membrane covering the roof of the mouth and cut it away, 
removing it well down to the oesophagus. This brings into view a 
triangular-shaped muscle, the levator anguli scapulae, m, fig. 99. 
Very carefully cut this through near to its attachment to the base of 
the skull and turn it down. This 
brings the sympathetic into view. 
It is usually accompanied by a blood- 
vessel which lies over it, and being 
pigmented serves as a guide to the 
nerve. 

The nerve is very readily seen as 
it crosses the large root of the second 
nerve, above which it bifurcates to 
pass round the subclavian artery, 
forming the annulus of Vieussens. 
Carefully isolate the sympathetic 
between the annulus and its junction 
with the vagal trunk. Pass a fine 
ligature round it and tie it as far down 
as possible. 

Cut the nerve below the ligature. 
The cardiac fibres of the sympathetic 
leave the cord mainly in the ramus 
communicans from the third nerve, 
and to a less extent in that of the 
fourth nerve. In the same dissection 

it is easy to expose the petro-hyoid muscles and remove them, and in 
this way the vago-sympathetic in its course from the ganglion of the 
trunk of the vagus to the heart can be readily traced. 

Having exposed the two vagi and passed threads under them their 
action should be studied as follows : — 




Fig. 99. — The Course of the 

SYMPATHETIC IN THE FkOC. 



122 EXPERIMENTAL PHYSIOLOGY 

Experiment 1. — Study the Influence of the vagus upon the heart. Pre- 
pare the coil for giving tetanising shocks. Dissect out both vagi. It is 
best to cut the laryngeal branch of each vagus because if this be left intact 
the muscles contract when the nerve is stimulated and acting upon the 
pericardium, pull down the base of the heart, and so alter the level of 
the tracing. Attach the heart to the recording lever by the suspension 
method, fig. 83. If the heart be beating very slowly apply a little warm 
normal saline solution (at 20° C.) by a pipette until the beat is quickened. 
Remove the secondary coil to some distance from the primary. The 
electrodes, fig. 87, should have their ends bent up into a hook, and the 
outer sides of the wires may be further insulated by a little sealing-wax to 
prevent escape of the current. Hook up one vagus on to the electrodes. 
Now take a piece of tracing, the drum rotating about 1 to 2 mm. per second, 
and with a seconds time tracing recorded directly beneath. After about ten 
contractions open the key in the secondary circuit, so that the nerve may be 
stimulated, and mark on the tracing the instant at which the stimulus was 
applied. If no change occur close the key, marking the instant at which 
the stimulation was stopped. Next move the coil 2 cm. nearer the primary, 
and repeat the stimulation as before. Repeat several times, gradually in- 
creasingthe strength of the stimulus until one or two tracings showing complete 
inhibition have been recorded. Time must be allowed after stimulation is 
stopped to record the full series of changes occurring after stimulation. 
Repeat the series, stimulating the vagus of the opposite side. 

It must be remembered that in this experiment we are stimulating 
both sets of cardiac fibres, sympathetic as well as vagal. 

In fig. 100 the result is shown. The laryngeal branch was not cut, 
and we see that on each stimulation the general level of the record 
was lowered. When the secondary was at 19 cm. (tracing 1) there 
was a very slight slowing effect. One evidence of this is to be seen in 
the auricular tracing. Before stimulation the auricle began to contract 
before relaxation of the ventricle was complete. During the stimula- 
tion, however, the time interval between two successive beats is very 
slightly increased, and this allowed relaxation of the ventricle to be com- 
pleted before the next auricular contraction commenced. In tracing 2 
with an increase in strength of stimulation there is a clear diminution 
of rate. Note that the effect does not occur instantaneously. There is a 
gradual production of the slowing lasting over four beats. The rate 
before stimulation was 38 per minute ; towards the end of the time of 
stimulation it was 30 per minute. A second change, occurring as a 
result of the stimulation, is an increase in the force of each beat as 
judged by the height of the tracing. In the measurement of these trac- 
ings, where we are examining the heights of contraction, it must be re- 
membered to measure from the point where the ventricular contraction 
begins to the highest point reached. It will not do to take the total 
height of the tracing as the measure of force, because at times a con- 
siderable amount of the rise may be due to auricular contraction with 
ventricular superadded ; at other parts of the tracing it may be 
purely ventricular contraction. Examine in this connection fig. 102 



THE ACTION OF THE VAGUS 



123 



In the piece before stimulation this is 9 mm., during stimulation it is 
11 mm., and after stimulation it soon returns to its initial height. A 
third change to be observed is with regard to an altered rate of trans- 
mission of the contraction from the auricle to the ventricle. Before 
stimulation the auricular beat was practically completed before the 
ventricular began. Under the influence of the stimulation the time 




Fig. 100. — Effects of Tetanising the Vagus with Different Strengths of 
Stimuli. In Tracing 1 the Secondary Coil was at 19 cms. ; in 2 at 18 cms. ; 
in 3 at 16 cms. ; in 4 at 15 cms. ; and in 5 at 14 cms. from the Primary 
Coil. Time Tracing Seconds. 

relation gradually changed and showed that the wave of contraction 
passed more readily from auricle to ventricular, i.e. that conduction 
between the two was favoured. 

In tracing 3, with slightly increased strength of stimulus, slowing 
is more pronounced, from 35 to 25 per minute. The height of each is 



124 EXPERIMENTAL PHYSIOLOGY 

again increased — 8 mm. before as compared to 10 during stimulation. 
There is again an increase in the rate of conduction of the contraction 
wave from auricle to ventricle. There is also less delay between the 
commencement of stimulation and the production of its effect than in 
the preceding case. 

In tracing 4 the same points are again to be observed, but it is 
noticeable that the slowing becomes less marked as stimulation proceeds. 
Rate of beating was 36 before and 24 during stimulation ; the height 
before, 8 mm. ; during stimulation, 9 mm. 

In tracing 5 we see that after two beats the heart comes completely 
to rest. There is a delay before the effect of the stimulus is apparent. 
After stimulation ceased a short pause occurred, and then the heart 
recommenced to beat. The rate gradually increased. Thus the time 
interval between the commencement of the second beat and corre- 
sponding point of the first is 3| sees. ; between 3rd and 2nd, 3 sees. ; 
between 4th and 3rd, 2| sees. It then quickly regained its original 
rate of 43 per minute. The height of the beat also shows a gradual 
increase. The measurements are : For the 1st, 4^ mm. ; the 2nd, 
5| mm. ; the 3rd, 6 mm. ; the 4th, 6^ mm. ; the 5th, 7 mm. ; and then 
in a few beats it attained a height of 9 mm. as compared to one of 
8 mm. before stimulation. Thus inhibition has had a beneficial 
effect upon the ventricle, enabling it to beat a little more forcibly for 
a time, but this gradually dies away, and in about 20 beats the height 
is once more 8 mm. The same holds true even to a more marked 
degree for the auricular contraction. The rhythm between auricle 
and ventricle beats also shows a very interesting change. In the 
first beat after the stimulation the ventricular contraction commences 
shortly after the commencement of the auricular relaxation ; in the 
second beat at a rather later time ; and as the beats follow one another 
the ventricular beat gradually falls later in the auricular diastole. 
Associated with the gradual slowing of the ventricular beat with 
respect to the auricular it is seen that the auricular contraction begins 
progressively earlier with respect to the ventricular diastole, and that 
at last it occurs when about one half of the diastole is completed. As 
this happens the auricular systole becomes progressively less and less 
marked, and finally is only represented as a break in the descent repre- 
senting the ventricular systole. These facts tend to show that con- 
duction of the contraction wave from auricle to ventricle is at first 
rapid, but gradually becomes slower than normal as an after-effect of 
the vagus inhibition, once more running to its normal rate as that 
after-effect gradually wears off. 

We must remember that in the results we have just been examining 
we are not dealing with the result of stimulation of pure vagal fibres, 



STIMULATION OF THE CRESCENT 125 

but with that of the mixed vagus and sympathetic. To determine 
which of these results are due to vagal fibres only, our only procedure 
can be to stimulate the vagus inside the skull before it has been joined 
by the sympathetic fibres. We may state as the general result of 
impulses passing down the vagus fibres — 

(i.) That they cause slowing or inhibition of the beat, depending 
upon the strength of stimulus employed. 

(ii.) That they tend to weaken the force of the beat when slowing 
occurs. 

(iii.) That as an after-effect there is for a time an acceleration 
accompanied by an augmentation of the force. 

There is often to be observed a difference in effect between the two 
vagi. Sometimes one vagus is found not to possess any inhibitory 
fibres, in which case the opposite vagus is found especially active. It 
is usually found that the effect is not identical on the two sides, one 
usually being more powerful than the other. 

Experiment 2. — Contrast the effect of stimulation of the crescent with 
stimulation of the vagus. Prepare the apparatus as for the preceding 
experiment. Dissect out both vagi, passing fine threads round them, so that 
they may be readily picked up when required. Having attached the heart 
to the lever place one vagus upon the electrodes, and after recording a short 
piece of normal tracing send in a tetanising current into the vagus and record 
its effect. Next repeat on the vagus of the opposite side. Finally apply the 
electrodes, so that they touch the crescentic junction between sinus and 
auricles, and record the result of stimulation in this position 

Fig. 101 gives the result of such an experiment. The first tracing 
is interesting because no inhibition resulted on stimulating the right 
vagus. The only alteration seen is a slight change in the sequence of 
the beat, the ventricular contraction commencing a little earlier in 
the auricular relaxation. Stimulation with stronger currents also 
had no inhibitory effect. Stimulation of the left vagus produced a 
typical inhibition (n, fig. 101). Finally in in is seen the effect of 
stimulation of the crescent. In this latter there are but slight dif- 
ferences from a typical vagus effect. Complete inhibition follows after 
a short latency, and on cessation of stimulation there is after a short 
latency a return of the beat, which shows the staircase effect, though 
not so clearly as in n. After the stimulation the auricular con- 
traction tends to commence earlier in the ventricular relaxation, a 
change gradually occurring, until finally it is seen to begin at about 
the middle of the relaxation. 

Experiment 3. — Examine the action of the sympathetic upon the heart. 
Arrange the apparatus as in the previous experiment. Dissect out the sym- 
pathetic on one side, placing a ligature around it, as described on p. 121. 



126 



EXPERIMENTAL PHYSIOLOGY 



Arrange the heart to record as before, and place the nerve upon a pair of elec- 
trodes. Carry out the experiment upon a similar plan to that used for the 
vagus, and so obtain a series of tracings showing the effect upon the heart 
with different strengths of stimulation. If the heart be beating rapidly the 




Fig. 101. — Tracing i Shows the Effect of Tetanisation of the E. Vagus ; 
ii of the L. Vagus ; and ni of the Crescent. In all Cases the Same 
Strength of Stimulus. 

influence of the stimulation is not very marked, in which case the heart 
should be cooled by allowing a little normal saline, which has been cooled by 
ice, to drop on to it until its rate is slowed. 

Fig. 102 shows a typical result of such an experiment : the upper 
two tracings are from the same heart with different strengths of cur- 
rent, the third from a different heart. The first shows that during 
stimulation the following changes occur : — 

i. Acceleration of the beat. Before stimulation this was 15 per 
minute, during stimulation 30 per minute. After stimulation ceased 
the heart gradually slowed again until its initial rate was once more 
reached. 



THE ACTION OF THE SYMPATHETIC 



127 



ii. An increase in force. Before stimulation the height of the 
ventricular beat was 9 cm., but during stimulation it reached 12 cm. 
These measurements must be made from the lowest to highest points 




of the ventricular contraction, for the increase in force is to a con- 
siderable extent masked by the change in character of the trace 
brought about by the altered sequence. An increase in force of auri- 
cular beat is also produced, though to a less relative degree than 
with the ventricular. 

iii. An alteration in the sequence. There is produced a delay in 



128 EXPERIMENTAL PHYSIOLOGY 

the conduction of the contraction from auricle to ventricle, so that the 
auricle has quite relaxed before the ventricular systole begins. Fur- 
ther, as the rate of beating is faster, it is seen that a contraction of the 
auricle commences before the ventricular contraction is complete. 

iv. A gradual return to the normal state after stimulation has 
ceased. The acceleration gradually disappears. The force of the 
beat at once begins to decline until it reaches the original amount. 
A change in conduction occurs in the reverse direction to that found 
during stimulation. Eate of conduction is increased, and ventricular 
systole commences soon after the auricular contraction reaches its 
maximum. The result is that there is more summation of auricular 
contraction to ventricular, with the result that the total amplitude of the 
trace is greater than during stimulation, though each individually is 
less. This increased rate of conduction gradually dies away and 
returns to the original value. 

These results should be directly contrasted with those found on 
vagal stimulation (p. 122), where they are seen to be in exactly the 
reverse direction. 

In ii a similar effect is found in all particulars, differences being 
only of degree. Eate is increased from 16 to 32 ; height from 9 mm. 
to 11*5 mm. ; and change of sequence is of the same character. 

Tracing in is from a less exhausted heart, and shows the changes 
very clearly. 

Eate before stimulation was 25, during stimulation 42 per minute. 

Height of ventricular contraction before stimulation was 9"5, during 
stimulation 14 mm. 

Change of sequence is at first as in previous tracings, but this is 
then followed by another alteration in which the auricular contraction 
commences later in the ventricular relaxation, though conduction is 
still delayed as previously. After stimulation ceases the same stages 
are passed through as were previously described, and to a very marked 
degree. 

The Second Stannius Ligature. — In a previous series of experi- 
ments we have seen that a ligature applied between the sinus and 
auricles leads to a standstill of the auricles and ventricle in diastole, 
while the sinus continues beating with unaltered rhythm. 

Experiment 4. — Complete the Stannius experiment by apptying a second 
ligature at the junction of the auricles with the ventricle. 

It will usually be found that the auricle still remains quiescent, 
but that the ventricle begins to beat. Count the rate at which 
sinus and ventricle beat. It will be found that the ventricle is 
beating at a slower rate than the sinus. This is the rule, but 
occasionally it is found that the auricle only begins to beat, or 
again that both start beating. As to the meaning to be given to this 



THE SECOND STANNIUS LIGATURE 129 

experiment, opinions differ. One view is that the first ligature causes 
standstill of auricles and ventricle by stimulating the inhibitory 
mechanism at the junction of sinus and auricles, and that this inhibi- 
tion lasts some time, until the mechanism becoming fatigued, the 
inhibited parts gradually regain a rhythmic contraction. This view 
is borne out by repeating the experiment upon a heart poisoned by 
atropine. The atropine paralyses the inhibitory nerve terminals of 
the heart, and it is found that standstill is impeded or prevented by 
atropine. The second ligature is supposed to act by cutting off the 
inhibitory influences, set in action by the first ligature, from the ven- 
tricle, which then commences to beat at its own rhythm. 

According to Gaskell, the probable explanation of the experiment is 
that the first ligature blocks the contraction wave originating in the 
sinus. Auricles and ventricle, therefore, for a time remain quiescent, 
ultimately originating a rhythm of their own, though this requires 
time. This does not, however, thoroughly explain all the facts, for if 
the auricles and ventricle be excised, they gain a fresh rhythm in 
quite a short time, and it therefore seems to follow that the first 
ligature must be causing some inhibitory influences preventing the 
establishment of that rhythm. On Gaskell's view the action of the 
second ligature is to stimulate the ventricle, and consequently to lead 
to a rhythmic contraction. It is difficult to see why the first ligature 
should not also act as a stimulus, or why the second should not 
stimulate the auricle rather than the ventricle. 



130 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE XII 

ACTION OF DEUGS UPON THE FROG'S HEART 

ACTION OF MUSCARINE AND ATROPINE 

Experiment 1. — Take a piece of fairly wide glass tubing and draw it out 
at one end to form a pipette with very fine orifice. Arrange the apparatus 
for recording the heart beats by the suspension method, having dissected 
out the vagi. Record the effect of stimulating the vagus and the sinus. Take 
some of the muscarine solution ' in the pipette and allow it to fall, drop by 
drop, on to the heart while it is still recording. Almost at once the beat 
becomes slower, and gradually force and rate decrease until the heart comes 
to complete standstill in diastole. Stimulate the heart, either mechanically 
or electrically. It will be found to require a very strong stimulus to make 
it respond. After allowing it to remain at rest for a short time to see that 
there is no tendency to recovery, wash out the pipette and fill it with the 
atropine solution.' 1 Let the solution fall onto the heart. Gradually the heart 
begins to beat again, and shows precisely the same phenomena as after inhibi- 
tion by vagal stimulation. If the heart had been beating weakly before the 
application of the muscarine solution, its beats after the application of the 
atropine often attain a much greater amplitude. 

Next place one of the vagi on the electrodes and tetanise it. No slowing 
nor inhibition occurs. Next apply the electrodes to the crescent ; still no 
inhibition takes place. The atropine has paralysed the inhibitory nerve 
terminals in the heart substance. The fact that atropine abolishes the mus- 
carine effect proves that muscarine also acts on the nerve mechanism, 
and not directly upon the heart muscle. 

In fig. 103 a record taken during such an experiment is given. The 
solution of muscarine was applied after the fifth beat of tracing i, and 
very quickly a change in the rhythm of each beat was produced. The 
auricular beat, which previously commenced during the ventricular dia- 
stole, was delayed and became less forcible. The sinus contraction also 
became marked on the tracing. Gradually the force of the auricular 
beat became less and less, though for a time that of the ventricular beat 
was maintained. Later, the ventricular contraction became less forcible 
and slower, and finally suddenly ceased. The line seen at the end of 
the tracing shows undulations which were due to the sinus beat. 

1 Made by adding a drop of a strong muscarine solution to some normal saline 
solution. 

- A | per cent, solution of the sulphate in normal saline. 



EFFECT OF ATROPINE 



131 



After about a minute had elapsed atropine solution was dropped on to 
the heart, commencing at n, fig. 103. After an interval a small contraction 
of the ventricle occurred, - v - 7 ---■= 

and gradually this in- .»••»/.'.. -at, v 

creased in force and fre- 
quency until the charac- 
ter of the beat was once 
more regained. It is 
also seen that the force 
of the auricular beat 
was regained, though 
more slowly than the 
ventricular. In about 
the middle of this tracing 
the rate of conduction 
of the contraction wave 
from auricle to ventricle 
is seen to be slow, and 
from that time on to in- 
crease, until finally it 
became very rapid. 
Atropine, then, favours 
the conduction of the 
contraction from auricle 
to ventricle. Tracing 
in shows that stimula- 
tion of the left vagus 
with strong tetanising 
shocks thrown in from 
a to b produced no 
inhibition nor change of 
force. In iv the sinus 
was stimulated. This 
also proved ineffectual, 
though, previously, 

stimulation of both 
vagus and sinus pro- 
duced the usual inhibi- 
tion. These inhibitory effects are reproduced 
taken just before muscarine had been applied. 

Experiment 2. — To a fresh heart arranged as in the previous experimenl 
apply a few drops of a h per cent, solution of pilocarpine nitrate. It acts 
similarly to muscarine, and its effect is abolished by atropine. 

k 2 




132 



EXPERIMENTAL PH YSIOLOG Y 




Fig. 104. — Tracing i Shows the Effect of Applying a Weak Solution of 
Nicotine Directly to the Heart. The Short Vertical Mark Indicates 
the Instant at which it was applied ; n Gives the Result of Stimulation 
of the Vagus ; in of Stimulation of the Crescent ; and iv of Stimulation 
of the Crescent after a Further Dose of Nicotine had been Applied. 
Time Tracing Seconds. Magnification, 5. 



EFFECT OF NICOTINE 133 



ACTION" OF NICOTINE 

Experiment 3. — Arrange a heart to record as before, having previously 
isolated one vagus and placed it upon a pair of electrodes. Test the vagus 
to see that it causes inhibition on stimulation. Eecord a few normal beats 
and then apply a few drops of aO'l per cent, solution of nicotine in normal 
saline. The heart is slowed for a few beats and then beats rather quicker 
than before. Now stimulate the vagus. There is no inhibition. Apply the 
electrodes to the crescent. The heart is inhibited. 

The action of the drug in a weak solution is to first stimulate nerve 
cells and then to paralyse them. The stimulation is shown in the 
inhibition, which may be but slight or fairly well marked, according to 
the strength of the solution. After a few beats the heart regains its 
rate, and may even become quicker and the force greater than before 
(i, fig. 104). In ii is shown the effect of stimulation of the vagus. No 
inhibition or slowing follows even with strong stimuli, though previously 
the inhibitory effect had been very readily produced. During the 
stimulation an augmentor effect is produced, the height of the beat 
becoming 235 mm. as compared with 21 mm. There is only slight 
acceleration, and both effects gradually die away. In in is seen the 
effect of stimulation of the sinus. It is perfectly characteristic of 
the result given by a normal heart (fig. 101, in). All these three 
tracings were taken quickly one after the other, and then moi^e nicotine 
solution was applied. It was then found that stimulation at the sinus 
no longer produced inhibition. "With weak currents no effect at all 
was perceived except a slight acceleration. The strength of the 
stimulus was then considerably increased, when marked acceleration 
was produced lasting as long as stimulation continued. On cessation of 
stimulation the heart was inhibited, but after a time recommenced 
beating with a rhythm at first slow, but gradually increasing until the 
original' rate was once more attained. 

This experiment is of great importance because it affords an ex- 
cellent example of the value of nicotine, as it is now employed for 
determining the position of nerve cells on the course of visceral nerve 
fibres. It is found to first stimulate these cells and then paralyse 
them, and if the dose be increased the nerve fibres themselves also 
become paralysed. This is a general rule for all visceral nerve 
fibres and cells, and in the experiment as above carried out proves 
that cells are interposed on the course of the vagus fibres, and are 
situated in the region of the crescent ; but that on the other hand the 
sympathetic fibres run straight to their terminals without havi un- 
nerve cells interposed on their course within the heart. 



134 



EX PEKLM ENTA L H I YSIOLOG Y 



CHAPTEE XIII 

SOME FURTHER METHODS FOE EXAMINING THE ACTIVITY OF THE 
FROG'S HEART 

The student must become familiar with some of the other methods 
which are employed for recording the heart movements other than 
the suspension method. 

Experiment 1. — Take a record of the beat of the ventricle by means of one 
of the recording levers represented in fig. 69. The foot of the vertical rod h 
is to be arranged to lie on the ventricle, and will thus rise and fall with 
increase and decrease of thickness of the ventricle. 

During diastole the ventricle wall becomes flaccid, and thus under the 



I 


UUL 


•ill 




III 

Mm 


w 





Fig. 105. — Tracings Recorded by a Lever Resting upon a Frog's Heart. In 
Tracings i and ii the Lever Rested upon the Ventricle ; in hi and iv 
upon the Junction of Auricles with Ventricle. Time Tracing Seconds. 

influence of gravity acting on its own substance and of the weight of the 
lever it becomes flattened. With each systole the ventricle hardens and 
becomes circular in section, and thus lifts the recording lever. If the ampli- 
tude of the record be small, it generally means that the pressure of the lever 
on the heart is too great, and this may be relieved by fixing a wire to the 



ROY'S FROG HEART TONOMETER 



135 



lever near the axis and bending it over, so as to lie to the other side of the 
axis, and thus act as a counterpoise. To its end a small weight can be hung, 
as, for instance, a piece of folded paper, whose position can be varied until 
the best amplitude is obtained. 

Fig. 105 shows tracings taken by this lever. Tracings i and n are 
taken with the lever resting on the ventricle only, in n the drum 
moving rather more than twice as fast as in i. The up-stroke means 
a contraction of the heart, the down-stroke relaxation. At the end of 
relaxation there is a pause for a time before a fresh contraction occurs, 
and in a few of these a slight rise is indicated, which is due to the 
filling of the ventricle on auricular systole. The contraction is seen 
to be sustained for a time before relaxation occurs. In tracings in 
and iv the lever was placed so as to rest on the junction of auricle 
and ventricle ; we see that the two contractions are now recorded. 

Eecording by this method we may study any of the results to 
be obtained in the experiments in which we used the suspension 
method. 

Another method of recording changes in the excised heart's activity 
is the plethysmographic method. 

Experiment 2. — Take a tracing with Roy's tonometer, fig. 106. This 
consists of a small glass bell-jar whose base fits on a brass support. The 
joint is made tight by smearing the ground surface of the run of the glass 
vessel with lard and rubbing it down tightly on to the brass base. In the 



r~\ 




Fig. 106.— Roy's Tonometer. (Halliburton.) 



base is a central hole into which a short cylinder is screwed, and the lower 
orifice fo this is closed with peritoneal membrane. A second orifice is fitted 



136 EXPERIMENTAL PHYSIOLOGY 

with a tube, on which is a tap, which is used for filling or emptying the 
vessel. The heart is tied on to a perfusion cannula fitted in a glass stopper 
which closes the upper end of the glass vessel. This is then brought into posi- 
tion, and the vessel filled with oil. "With each contraction of the heart the 
volume diminishes and the peritoneal membrane, and with it the recording 
lever, rises ; with each relaxation it falls. 

Experiment 3. — Take a tracing with Schafer's heart plethy sinograph. 
A diagrammatic sketch of this apparatus is given in fig. 107. The heart is tied 
on to a two-way cannula and then fitted tightly into a glass bulb filled with 
oil. On either side of the bulb is a glass tube fitted with a tap. The one to 




5? ■ =g 



Fig. 107. — Schafer's Frog-heart Plethysmograph. 

the left is for adjusting the amount of oil in the apparatus ; that on the right 
carries a piston recorder bearing a writing point. With each contraction of 
the heart its volume decreases, and the oil and piston move towards the 
bulb. The writing point is then caused to record its movements upon a 
blackened surface. 

A simple form may be made and used as in the following experi- 
ment : — 

Experiment 4. — Take a tracing with the piece of apparatus shown in fig. 
108, i. A glass perfusion cannula is made from a glass t -piece, t, one end of 
which is drawn to a slight constriction, and the end then bevelled off bj' rub- 
bing it on emery paper and then rounding it in a flame. Through this 
tube, o, a piece of glass tubing, f, drawn out to a fine orifice is passed 
and is cemented in by sealing-wax, c, so that the capillary orifice lies in the 
orifice of the lower end. This is then fixed in a cork in which a second tube, 
a, is also fixed, and the cork fitted to a short piece of wide glass tubing, d. 
The lower end is closed by a second cork through which a wire, w, passes. 
Expose a frog's heart and ligature the frenum near the ventricle. Cut 
the frenum beyond the ligature, lift up the ventricle, and cut into the sinus 
transversely. Introduce the cannula, which must previously be filled with 
diluted ox-blood through this aperture, passing it through the auricle into 
the ventricle, and tie it in by a ligature passing round the auriculo-ventricular 
groove. Free the heart from the surrounding parts and wind a fine copper 
wire round the cannula, touching the ventricle where it is tied to the cannula, 
so as to form an electrode. Fit the cork into the glass tube, d, which is 
filled with normal saline, so that the fine wire electrode is held tightly 
between the cork and the glass. Attach the rubber tube on f to a burette 
containing diluted blood, taking care that no air is included in the tubing. 
Now record the heart's movements in two ways : (i.) by attaching the tube 
a to a tambour by tubing of narrow bore. It is best to replace most of the 
air in this tubing with normal saline, and to interpose on it a glass y-piece. 



THE HEART PRETHYSMOGRAPH 



137 



the lateral orifice being closed with rubber tubing and a spring clip. This 
gives a record by the plethysmographic method ; (ii.) by attaching the tube 
T to the end, a, of a small mercury manometer, fig. 108, n. On the tube A is a 
three-way tap, t, which can be turned so that the tube a is connected with the 
manometer m only, with the exit tube b only, or with both, or completely closed. 
The movements of the manometer are recorded by a small glass float, F, pro- 
vided with a glass writing point. This latter method is that of Kronecker's 
frog-heart manometer. The first method records changes in volume. The 
second method records the pressure attained by the fiuid with each contraction. 
As soon as the heart is fixed in position it may commence to beat rhyth- 
mically, especially if the internal pressure be raised by altering the position 




Fig. 108.- 



-Fro«-heart Plethysmoukaph by which the Pressure Changes 
can also be recorded by a small manometer. 



of the burette of circulating fluid. If it remain quiescent it may be stimu- 
lated by sending induced shocks through it by connecting the secondary coil 
(1) to the wire touching the heart at its base ; and (2) to the stout wire, w. 
It is not necessary for the upper end of w to touch the heart, it need 
only be brought near to it. Bring the secondary coil nearer to the primary 
until the induced current is sufficient to cause a contraction. Repeat the 
stimuli every three seconds and record the contractions. After a certain 
time the heart ceases to beat altogether, but before doing so it becomes 
irregular. A commonly observed form of irregularity is where it gives series 
of beats arranged in groups. These are termed Luciani's groups 



13 > EXPERIMENTAL PHYSIOLOGY 



CHAPTEK XIV 

DEMON STKATION OF THE MOVEMENTS OF THE MAMMALIAN HEART. 
THE CARDIOGRAPH 

For the experiment a dog, cat, or rabbit is chosen, anaesthetised with 
ether and morphia, and subsequently curarised by injecting a 
solution of curare into the external jugular vein. Both vagi are 
exposed, and ligatures passed round them through an incision in the 
mid-line of the neck. The trachea is then isolated, and a Y-shaped 
glass tube tied into its peripheral end. The heart is next exposed by 
cutting through the sternum with bone forceps, keeping to the mid- 
line as far as possible in order to avoid injuring any large blood vessel. 
The thoracic walls are then drawn well apart, so as to thoroughly 
expose the heart lying in the pericardium. 

As soon as the thorax is opened the lungs collapse and no longer 
follow the movements of the thoracic wall. The animal would therefore 
soon die of asphyxia, to prevent which it is necessary to supply it 
artificially with air. This is done by rhythmically blowing up the 
lungs through the trachea and then allowing them to collapse. 

There are many forms of apparatus which permit of this. A simple but 
very effective arrangement is shown in fig. 109. A continuous blast of air is 
obtained by the modified Bunsen pump, p. o is connected to a water tap, and 
as the water is forced through the orifice at v, which nearly fills the con- 
stricted neck of the outer receiver, air is drawn in through s. The mixture 
of water and entangled air is collected in the large glass bulb, and the water 
allowed to flow out through c. The supply of air is directed by a piece of 
tubing, a, to the two-way tap t, whence it passes according to the position of 
the tap along b to g, or, as represented in the figure, along the tube d to a 
Woulffs bottle, h, containing some ether or other anaesthetic. It then passes 
from f to g and thus to a coil of lead tubing, k, immersed in hot water, so that 
the air is warmed to body temperature. Another piece of tubing connects it 
to a Y-tube, one end of which, n, is tied into the trachea and the other is 
covered with rubber tubing which can be partially compressed by the clip M. 
The blast of air is made intermittent by either fixing a spring clip on L, which 
is then opened and closed by hand, or the same residt is automatically effected 
by the arrangement seen at R. This consists of a lever held down by two 
springs so as to compress the tube against the base-board. The lever is 
raised intermittently by an eccentric driven from the shafting. 

The blast of air is moistened in the pumn p. The force of distension of 



ARTIFICIAL RESPIRATION 



139 




140 



EXPERIMENTAL PII YSIOLOG Y 



the lungs can be modified in two ways. First by varying the compression of 
the tube at m. The increase in resistance at m raises the pressure at n, and the 
lungs are therefore more distended. The second method is to vary the 
pressure of the blast of air. This is attained by compressing c, an increased 
resistance to the outflow of water leading to a higher pressure of the air. The 
screw clips are so arranged that sufficient distension is obtained with the 
lowest pressure of air. Expiration is brought about by the elastic c ontraction 
of the lung which drives out the air through the tube M. 

The pericardium is now slit up and its cut edges stitched to the 
thoracic wall on either side. The heart is thus exposed and is attached 
to the recording apparatus, which consists of two levers, L 1 and l' 2 , 
fig. 110, which are moved by two fine cotton threads passing over two 




Fig. 110. — Arrangement of Levers for Recording the Movements of the 
Mammalian Heart by Attaching Threads to the Auricle and Ventricle 
respectively. 

pulleys, P 1 and p 2 . Each thread terminates in a sharp hook, which 
is passed into a small piece of the ventricular and auricular walls 
respectively. If the thread from the auricle does not pass freely over 
the surface of the ventricle it may be made to glide over a glass rod 
held transversely above the heart, so that the thread is quite free from 
surrounding parts. The magnification of the lever l 1 for the ventricle 
is 3-fold ; of the lever l 2 for the auricle 4-fold. Each lever is loaded 
by weights, w 1 , w 2 , placed near its axis, so as to avoid effects of inertia 
as far as possible. 

The writing levers are brought to the horizontal position by 



NORMAL RECORD OF THE MAMMALIAN HEART 



141 



adjusting the lengths of the threads and the positions of the pulleys. 
They are then brought to the writing surface and two chronographs 
are arranged to write vertically below them — one to give a seconds time 
tracing, and the other to act as a signal. 

Fig. Ill reproduces a piece of tracing obtained in this way, 
the drum moving at a slow rate. The tracing is from a rabbit's heart, 
the upper given by the auricle, the lower by the ventricle. It gives a 
measure of the amount of contraction of the two parts, and indirectly 




Fig. 111. — Tracing Obtained from the Rabbit's Heart, Employing the Levers 

of Fig. 110. 



of the force of the contraction, the latter especially if the tension of 
the thread be fairly high. The variations in level of the apices of the 
ordinates are due to the respiratory movements. Each time the lung 
is inflated the base of the heart is a little raised, which slackens the 
thread and the lever descends. 

One vagus is now cut and its peripheral end laid upon a pair of 
electrodes. It is then stimulated a few times and the results recorded. 
Pig. 112 gives the result of a fairly strong current. The stimulus is 
seen to act both on the strength and on the frequency of the beat, and 
to chiefly affect the auricle. Frequency and force are diminished 
both for auricle and ventricle. After cessation of stimulation the ven- 
tricle rapidly regains its previous condition, but the auricle recovers 



142 EXPERIMENTAL PHYSIOLOGY 

much more slowly ; for a short time the extent of its contraction is 
distinctly less. 

The effect of varying the strength of the stimulus is very marked. 
Weak stimuli primarily affect the auricles, diminishing their rate and 



Fig. 112. — Eesult of the Stimulation of the Left Vagus. 

force, but only secondarily affect the rate of the ventricle. Stronger 
stimuli may inhibit the auricle almost completely, whilst the ventricle 
still beats with its original rate and force. The strongest stimuli also 



EFFECT OF CAFFEINE UPON THE HEART 



143 



affect the ventricles and inhibit them. The ventricles therefore are 
much less under the influence of the vagus than the auricles. 

The method is of considerable value in that it offers a convenient 
method of observing the direct action of drugs upon the heart. As an 
instance of this we may record the effect of an injection of caffeine 
citrate into a vein. The external jugular vein is exposed and the 
injection made in the manner described on p. 181. Fig. 113 shows the 
result of injecting 1 c.c. of a 4 per cent, solution of caffeine citrate in 
1 per cent, sodium chloride solution into the external jugular of a cat. 
The solution was previously warmed to body temperature. It is seen 
that there is an almost instantaneous effect upon both auricle and 




Fig. 113. — Eesult of the Injection of 1 c.c. of a 4 pee cent. Solution 
of Caffeine Citrate. Tracing reduced to Half Size. 

ventricle, but more markedly on the auricle. The rate remains prac- 
tically unaltered, but the force is considerably diminished. Afterwards 
there is a gradual recovery, which is fairly rapid in the case of the 
ventricle, but slower in the case of the auricle. If the heart be 
watched during the action of the drug, it is observed that the right 
auricle becomes greatly distended with blood. If larger doses be 
injected the effect becomes much more pronounced, and soon affects 
the ventricle quite as much as the auricle and in the same direction. 
The right auricle becomes very distended and its movements greatly 
impeded. "With about 5 c.c. of the solution there is very frequently no 
recovery of the beat, and the animal dies. 

The effect of other drugs should also be tested. Digitalin is found 



144 



EXPERIMENTAL PHYSIOLOGY 



to produce a gradual increase of force of the auricle, and a less marked 
change in the ventricular contraction when 5 c.c. of a - l per cent, 
solution are injected. Neurine is found to cause a slight slowing of 
the beat and a rapid decrease in force of the auricle, soon followed by 
a gradual increase to about double its initial contraction, and then the 
effect slowly disappears. Upon the ventricle the changes are in the 
same direction, though very much less in amount. 

To complete the demonstration the animal may be killed by 
asphyxia. For about the first half-minute the auricular beats increase 
in amount, remain at this height for some time, and then slowly begin 
to decrease. The ventricle beats remain practically the same for 
about H minute, and then a very rapid change sets in. Some of the 
ventricle beats are dropped and the auricle beats faster ; both decrease 
greatly in force, and there is at first an increase in general tone, which 
is rapidly replaced by a decrease in tone, and then the beats gradually 
decrease and the animal dies. As soon as the rapid change in the 
heart begins, the right auricle is seen to become more and more filled 
with blood and soon becomes greatly distended ; a condition which 
persists up to death. 

For the purpose of the examination of the heart in man we 
possess an instrument whose working should be studied in the follow- 
ing experiment : — 

Experiment I. — Take a tracing of your own heart's impulse by means of 
the cardiograph (fig. 114). This consists of a tambour, f, the lower end of 




Fig. 114. — The Cardiograph. 



which is closed by a rubber membrane, g, on the centre of which is cemented 
a thin aluminium' disc, h. The cavity of this tambour is placed in communica- 
tion with a second, the recording tambour, fig. 34, by the tube b. The tambour 
is fixed on three arms, and at the ends of these are three legs, a 1 , a 2 , and a\ 
which can be screwed up or down and thus allow a vertical adjustment of 



A CARDIOGRAM 



145 



the tambour. Fixed to the end of a spring d is an ivory button, c, furnished 
above with a pin which comes into contact with the disc on the tambour. 
Expose the chest and mark the spot at which the heart's impulse is best felt. 
Fit the tambour on the chest, so that the tambour rests on the three feet, with 
the ivory button over the marked spot. It is held in position by the bands 
e 1 and e-. Now vary the pressure of the button on the skin by altering the 
position of the three feet until the lever of the recording tambour gives a 
good excursion. Record a few beats on a drum revolving | cm. per second, 
taking a seconds time tracing under the record. 

The form of curve so obtained is shown in fig. 115. It is termed a 
cardiogram. The moment of hardening is indicated by a sudden 




Fig. 115. — A Cardiogram taken upon a Man. The Contraction of the 
Heart is recorded by the Up-stroke of the Record. 



ascent of the lever and the end of the ventricular systole by a sudden 
fall of the lever. The chief value of such a tracing is to give us 
reliable information as to the time at which the heart contracts and 
relaxes when we wish to compare it with other phenomena occurring 
at the same time. 



146 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE XV 

SOME EXPERIMENTS IN ELECTRO-PHYSIOLOGY 

That animal tissues are of themselves capable of producing currents 
of electricity was first positively proved by Galvani's experiment of 
contraction without metals, but our earliest accurate knowledge 
relating to these currents is due to Du Bois-Eeymond, who first gave 
us measurements of these currents, and taught us how best to study 
them under different conditions. 

If a frog's muscle be excised — choosing one in which the fibres 
run parallel to one another and to the surface of the excised muscle, 
such as the sartorius or semimembranosus — and connected to a 
galvanometer of high resistance by means of a pair of unpolarisable 
electrodes, one being placed at about the centre of the longitudinal 
surface and the other opposite a transverse section of the muscle 
made by cutting across the muscle near one end, Du Bois-Eeymond 
showed that a current was produced by the muscle, which passed, in 
an outside circuit, from the longitudinal surface to the transverse 
section, and in the muscle, from transverse section to longitudinal 
surface. It was also shown that if the muscle were tetanised 
the amount of this current underwent a change, and in the direction 
of diminution. Du Bois-Eeymond termed the current obtained from 
the resting muscle the natural current or current of rest, and the 
alteration in it produced by stimulation the negative variation. Of 
other workers who have added to our knowledge, Hermann stands 
foremost, and is the author of the opposing view, which has steadily 
gained ground until it is now almost generally accepted, that normal 
muscle is iso-electric at all parts, and that it will only yield a current, 
either when injured at some part, or on contraction. If one electrode 
be connected to an injured part and the other to an uninjured, the 
galvanometer will show a current passing from the uninjured to the 
injured part. Or, again, if two iso-electric points be connected to the 
galvanometer, and a muscle wave then started along the muscle, 
the galvanometer will show a current passing from the resting part to 
that in contraction. Further, a less injured or less active part is 



MUSCLE CURRENTS 147 

electro-positive to one more injured or more active respectively. 
Perfectly uninjured and resting muscle cannot be experimented upon 
because simple exposure of tbe muscle causes sufficient injury to set 
up differences in electro-motivity. Still tbat a perfectly normal 
resting muscle is iso-electric is practically certain. The greater the 
care taken in the exposure of the muscle the less are the currents 
obtainable, and the heart, which can be exposed without injury, 
shows no current when at rest. Conversely if a muscle be purposely 
injured it yields a current which is in proportion to the injury ; and 
an injured resting heart also gives a current. 

I. EXPERIMENTS TO SHOW THE EXISTENCE OF THE 
VARIOUS CURRENTS BY PHYSIOLOGICAL MEANS 

Experiment 1. — Galvani's experiment of contraction with metals. Solder 
a piece of copper wire to the end of a piece of zinc wire. The wires shoidd 
be fairly'thick and about 6 cm. in length. They may then be bent round into 
the form of a U. Pith a frog, remove the skin from the back of the thigh and 
dissect out the sciatic. Lift up the nerve on the end of one of the wires, and 
with the end of the other touch any part of the frog. At each contact the 
muscles of the leg give a twitch. In the more classical form of the experi- 
ment the vertebral column is cut across just above the sacrum, the whole 
of the abdominal viscera removed and the skin stripped off the legs. The 
urostyle and the muscles attaching it to the ilia are removed so as to 
expose both sciatic plexuses. An s-shaped hook of copper wire is then passed 
round both plexuses, and by this the frog is suspended to a clean iron tripod. 
If the tripod be now tilted so that any part of the legs of the frog touches 
the metal a twitch occurs in both legs. 

This was Galvani's first experiment, which he brought forward to 
prove the existence of animal electricity, and which led to the cele- 
brated controversy between him and Volta. Volta proved — by the 
invention of the voltaic pile — that the contraction was in reality due 
to the current caused by contract between two dissimilar metals. 

Experiment 2. — Galvani's experiment of contraction without metals. Very 
carefully dissect out a sciatic nerve and gastrocnemius and place it upon a 
clean dry glass plate. Lift up the nerve on a glass rod drawn out into the 
form of a hook and lower the cut end on to the lower end of the muscle. 
With each contact the muscle contracts in response to the stimulus started 
in the nerve by the closure of the current of injury of the muscle. If the ex- 
periment does not at once succeed, injure the lower end of the muscle by 
touching it with a hot glass rod or wire and then repeat the experiment. 

This is the crucial experiment which definitely proved that part of 
Galvani's views as to the existence of animal currents. 

Experiment 3. — Kuhne's experiment of contraction without metals. Place 
a clean glass plate so that it projects about one inch over the edge of the 
table. Make two rolls of china clay moistened with normal saline and place 
then parallel to each other, so that they project beyond the edge of the 
glass plate, and turn down the projecting ends till they hang below the 

l2 



148 



EXPERIMENTAL PHYSIOLOGY 



plate (fig. 116). Make a nerve muscle preparation — the sciatic nerve and 
the whole of the leg below the knee — and place the cut end of the nerve on 
one clay pad and the middle of the nerve on the other. Great care must be 
taken of the nerve during its preparation. Place a little normal saline in 
a watch glass and lift this up until both clay pads touch the fluid. At the 
contact the leg muscles give a twitch, due to the closure of the current of 
injury of the nerve. 




Fig. 116. — Kuhne's Expeeiment of Con- 
traction without Metals. 



Fig. 117. — Arrangement of Apparatus 
for showing Secondary Contraction. 



Experiment 4. — Secondary contraction. Dissect out two nerve-muscle 
preparations and place them on a dry glass plate. Lift up the nerve of one, 
b, fig. 117, and place it in a loop over the muscle of the other preparation, A. 
Lay the nerve of a over a pair of electrodes, e, in connection with a Du Bois 
key, k, in a secondary circuit. Close k and connect a battery to the primary 
coil for tetanising currents. Open the key k and the preparation a passes 
into tetanus. It is also found that b is thrown into tetanus. On closing K 
the tetanus of b ceases. 

This experiment is of considerable importance on several accounts. 
In the first place we can show by physiological means the existence 
of a current of injury in the muscle of a, for if the nerve of b be 
sensitive and it is laid across the muscle of a and then its cut end 
dropped on to some other point of a, at the contact the muscle of b 
contracts stimulated by the closure of the current of injury of A. In 
the second place it directly demonstrates the ' negative variation ' or 
current of action of A, for it is due to the production of this current 
that the muscle b is stimulated when a is indirectly tetanised. In the 
third place it teaches us one very important fact with regard to the 
nature of the physical events occurring in A while it is being tetanised. 
This results from observing that b passes into tetanus when a is 
tetanised ; and as a muscle does not contract during the time that a 
constant current is passing through it, but only on make and break, 
it follows that the current of action of a must be intermittent. Hence 
although the change of length of A may remain constant, one at least 
of the physical factors accompanying that contraction is intermittent. 
By other methods it has been shown that the rate of oscillation of the 
current of action of A is the same as that of the excitation. 



THE REFLECTING GALVANOMETER 



149 



By a somewhat similar experiment one muscle may be directly 
stimulated by the current of action of another. Thus if two sartorius 
preparations be made from a curarised frog and the one muscle 
pressed tightly against the other, so that at each end one of the 
muscles projects a little, tetanisation of one muscle at its uncovered 
end leads to a tetanus of the second. 

Experiment 5. — Show the current of action of the heart by excising the 
whole heart, and having nearly emptied it of blood by touching it with dry 
blotting-paper, injure the apex of the ventricle and then place it on a 
thoroughly dried glass plate. Dissect out a sciatic very carefully and with 
the leg still attached place it on the heart, so that it crosses the base of the 
ventricle and its cut end lies on the injured spot at the apex of the heart. 
With each contraction of the heart the muscles of the leg give a single 
twitch, being stimulated by the current of action of the heart. 

Apply a Stannius ligature to the heart, which is thus brought to a stand- 
still. With each mechanical stimulation the ventricle gives a beat and its 
current of action leads to a twitch of the leg muscles. 



II. EXAMINATION OF THE DIFFERENT CURRENTS BY 
MEANS OF THE REFLECTING GALVANOMETER 

The galvanometer employed for this purpose consists of a pair of 
suspended magnets which are made very nearly astatic, each being 
surrounded by a coil consisting of very many turns of fine insulated 
wire. 




Galvanometer. Shunt. Lamp and Scale. 

Fig. 118. — Side View of Galvanometer and Shunt, Lamp and Scale 

The galvanometer and scale are placed east and west, and appear as if viewed by an observer 
standing on the north side and looking south ; the path of light is indicated by dotted lines. The 
essential parts concealed by the galvanometer case are diagrammatically given in fig. 119. (Waller.) 

The two coils are connected up so that the current is sent clock- 
wise through one coil, and anti-clockwise through the other (see 



150 



EXPERIMENTAL PHYSIOLOGY 



fig. 119). The resistance of such a galvanometer is very high, from 
10,000 to 20,000 ohms, and therefore tends to weaken the current. 
This does not matter, however, when we are studying the current 
yielded by a piece of tissue whose resistance is very high, and are 
employing unpolarisable electrodes whose resistance is also very 
great. Attached to the upper magnet is a light mirror by means of 
which a beam of light is reflected, and thus any rotation of the 
magnet and attached mirror is detected by the movement of the 
reflected beam. 

The galvanometer is set up so that the mirror faces to the west, 
and the magnets and coils therefore lie in the magnetic meridian. 

The coil is provided with a shunt by means 
of which we can vary the amount of the 
current allowed to pass through the gal- 
vanometer when we are dealing with rela- 
tively large currents. This consists of three 
resistances of ^th, ^th, and o^th of the 
resistance of the galvanometer, and is con- 
nected up in parallel with the galvanometer, 
i.e. as a deriving circuit. By means of a plug 
we can utilise either of the three resistances, 
or by leaving out the plug send the whole 
current through the galvanometer. If the 
plug be inserted so that the resistance of 
^th is in parallel with the galvanometer 
then the current is divided, 1 part passing 
through the galvanometer and 9 parts 
through the shunt, i.e. ^Vth of the total cur- 
rent is sent through the galvanometer. 
Similarly by means of the other resistances 





Fig. 119. 



we can send 



Tiro^h 



or -nrnTrth of the cur- 



rent through the galvanometer. The shunt 
is further provided with a short-circuiting 
key, so that all the current can be sent 
through the shunt and none allowed to 
pass through the galvanometer. 

To observe the movements of the needle 
a source of light is condensed on to a 
narrow vertical slit, and the light from this is collected by a pro- 
jecting lens and then thrown on to the mirror of the galvano- 
meter, and so from this on to the scale (see fig. 118), where it is 
focussed sharply by adjusting the position of the projecting lens. 
First determine the nature of the deflection by sending a small 



Astatic couple of magnets n s, 
s n, suspended by a silk fibre and 
carrying a mirror (indicated by 
the dotted circle) : the surrounding 
line and arrows indicate the dis- 
position of the coils ; N s is the 
neutralising or controlling magnet. 
All these parts are represented as if 
viewed by an observer standing- 
west, i.e. in the position of the 
lamp hi fig. 118. (Waller.) 



MUSCLE CURRENTS 151 

current of known direction through the galvanometer. For this 
purpose arrange the shunt to send r oV^th of the current through the 
galvanometer and take a small battery made of a zinc and copper 
wire with wires soldered to them, passing through a cork, and dipping 
into some weak sulphuric acid in a small tube. The short-circuiting 
key of the shunt is closed, and then the leads are connected to the 
galvanometer. On opening the short circuit the spot of light is 
immediately deflected to one side, because the two wires form a little 
battery of which the copper is the positive pole and the zinc the 
negative. Note which galvanometer terminal is connected to the 
copper wire ; you will then know that if in the experiment a deflection 
occur in the same direction the current causing it enters at that same 
terminal. Let us suppose that when the spot of light is deflected 
to the north, the north terminal of the galvanometer is connected 
with the copper wire, and is therefore positive. 

A pair of unpolarisable electrodes are now prepared and tested to 
show that they are iso-electric by connecting them to the galvano- 
meter and bringing the two clay guards in contact, when no deflection 
must occur. If there be a slight deflection the electrodes may often 
be rendered iso-electric by connecting their two terminals with a 
stout copper wire and then placing the two clay guards in contact, 
leaving them so for some hours. If much deflection be caused it is 
better to remake the electrodes. 

Now make a semimembranosus and gracilis preparation, taking 
great care to injure it as little as possible. Place this across the 
unpolarisable electrodes, so that the centre rests on one electrode and 
the lower end upon the other. Open the key of the galvanometer 
and observe if any deflection be produced. It will usually be but slight, 
and in such direction to show that the tibial end is electro-negative 
to the equator. Now remove the muscle and injure the tibial end by 
touching it with a hot wire. Replace the muscle on the electrodes 
and again open the short-circuiting key of the galvanometer. A 
deflection is now obtained in such direction as to show that the 
injured end is negative to the non-injured surface. This is the 
current of injury. Next apply a pair of electrodes to the upper end 
of the muscle and tetanise it. The galvanometer swings in the 
reverse direction and may nearly reach the zero of the scale. This is 
the current of action, and its direction shows that the injured end 
has become less electro-negative relatively to the centre of the 
muscle. 

It is further to be observed that the diminution of current persists 
throughout the whole time the muscle is tetanically contracted, though, 
as previously found (p. 148), the current of action is of an alternating 



152 



EXPERIMENTAL PHYSIOLOGY 



character. This is because the galvanometer cannot respond to the 
rapid alternations, the inertia of the magnets being too great, and it 
therefore only gives a constant deflection proportional to the mean 
value of the alternations. 

The production of this current proves that a part of a muscle 
which is contracting is electro-negative to one which is at rest or in 
a less degree of contraction. The injured part contracts less forcibly 
than the non-injured, and it is because the injured part does not 
respond so well to stimuli that its negativity remains practically 
constant, whilst the negativity of the central active part becomes 
greater relatively to its previous state. 



MEASUREMENTS OF POTENTIAL 

The method adopted by Du Bois-Eeymond for measuring the 
E.M.F. of an animal current was that of compensation, in which the 
current through the galvanometer is balanced by a fractional part of a 
constant current of known E.M.F. sent through the galvanometer in 
the reverse direction. The principle of the method is illustrated by 
fig. 120. A Daniell battery is connected to the two ends of a long 
platinum wire, a c, a commutator, k, being interposed so that the direc- 
tion of the current through 
the wire can be reversed. 
The current to be measured 
is sent through the gal- 
vanometer and a part of 
the platinum wire, viz. a b, 
the connection at b being 
movable. The muscle 
current in the arrangement 
of the figure passes from a 
to b, and the Daniell current 
is, by placing the commu- 
tator in the proper position, 
directed from b to a. A posi- 
tion of b is now sought at 
which the galvanometer 
remains undeflected, when it follows that the branch circuit from 
the Daniell through the galvanometer is equal to the muscle current, 
and consequently that the E.M.F. between b and a due to the Daniell 
is equal to the E.M.F. of the muscle current. 

"With the high external resistance the difference of potential 
between a and c is practically that of the Daniell cell ; and as the wire 




Fig. 120. — Plan of DuBois Reymonb's Method 
of measuring the muscle currents. 



THE HEART CURRENTS 153 

A c is uniform the fall of potential is regular, and therefore the E.M.F. 
between a and b is — E, where E is the E.M.F. of the Daniell. 

AC 

In any particular experiment the position of b will be found to lie 

quite close to A, so that the ratio of — is somewhere about "03. 
^ AC 

At times instead of using a simple wire, a c, for this purpose, two 
variable resistances are employed : one a low resistance representing 
A b, the other a higher resistance representing B c : but the principle 
is just the same as for the wire. 

For another method of measuring the E.M.F. see p. 155. 

EXAMINATION" OF THE HEAET CURRENTS 

(1) Pith a frog, expose its heart, and apply the Stannius liga- 
ture. Eoll out the clay pads of the electrodes to sharp points and 
apply one to the base of the heart, the other to the apex. On opening 
the key of the shunt no deflection occurs. The resting heart is there- 
fore iso-electric. Eemove the apex electrode, and injure the apex by 
touching it with a hot wire, then replace the electrode. On opening 
the key there is now a deflection which shows the injured spot nega- 
tive to the base or any other non-injured part. Stimulate the heart 
mechanically near the base. With each contraction thus caused, 
there is a diminution of the deflection of the galvanometer. There- 
fore the base becomes negative to the apex. This is the current of 
action of the heart. 

(2) A freshly excised heart is taken and most of the blood 
removed by soaking it up with filter paper. Tt is then laid across the 
electrodes, one touching the base, the other the apex. With each 
spontaneous beat of the heart there is a deflection of the galvanometer. 
This is found to be in such a direction as to show base becoming 
negative to apex. 

On a beating heart exposed in situ it has been shown by the 
capillary electrometer that the electromotive changes with each beat 
are diphasic in character. It is found that first the base becomes 
negative to the apex and then the apex to the base. If the apex be 
injured it then becomes monophasic, base negative to apex with each 
beat. The injured part does not contact normally, and therefore does 
not become as negative as the non-injured during its contraction. 

If the base be injured then its potential remains unaltered and 
apex becomes negative to base with each beat. It was in order to 
render the change monophasic that the apex was injured in the 
preceding experiment (1). 



154 



EXPERIMENTAL PHYSIOLOGY 



THE CAPILLARY ELECTROMETER 

The capillary electrometer consists of a piece of glass tubing with its end 
drawn out to a fine capillary of an internal diameter of about 30 ft. This is 
filled with mercury and then immersed in diluted sulphuric acid (1 part to 
6 of water) contained in a second tube, in the bottom of which is some 
mercury which serves by a platinum wire fused in the glass to make 
contact with the acid. The mercury in the upper tube is connected by a 




Fig. 121 Lippmann's Capillary Electrometer. 

1. Pressure apparatus ami microscope, on the stand of which the capillary tube is fixsd. 

2. Capillary tube dipping into ILSO^ in a surrounding tube, and in connection with pressure 
apparatus (the mercury in the lower part of the surrounding tube serves only to establish connection 
with the platinum wire). 

3. The capillary tube and column of mercury as seen in the field of the microscope. (Scale 
in Tooth mm.) (Waller.) 



second platinum wire which forms the other electrode. The changes of 
position of the mercury surface in the capillary are watched under a micro- 
scope. The upper tube is connected by stout rubber tubing to the lower of 
two reservoirs containing mercury, by altering the relative heights of which 
pressure can be exerted upon the surface of the mercury. With a constant 
pressure the mercury in the capillary is brought to a certain position in 
which the capillarity is exactly balanced by the pressure. If a current be 



THE CAPILLARY ELECTROMETER 



155 



now sent through the capillary it is found that the mercury moves in the 
direction of the current. This movement is due to the altered surface 
tension brought about by the current. Thus supposing the current passes 
along the capillary from mercury to acid, the surface tension falls and the 
mercury moves down the tube. If the current travel from acid to mercury 
the surface tension rises, and the mercury moves up the tube until a new 
position is found in which the external pressure is again balanced by the 
capillarity. By increasing the pressure on the surface of the mercury the 
mercury may be again driven down the tube till the original position is once 
more reached. The difference in level of the mercury in the pressure apparatus 
is a measure of the capillarity, and therefore of the difference of potential. By 
measuring the pressure when the position of the mercury in the capillary is 
brought back to its initial position while a current is still passing through it, 
the instrument may be graduated and can then be directly used as a measurer 
of small currents. Its great advantage lies in that its electrical capacity is 
very small, and it can thus show very rapid changes of potential. There is 
no latency with the instrument and no after-oscillation. 

It is to be noted that this instrument measures electrical pressure, i.e. 
potential, whereas the galvanometer is a current-measurer. 

Experiment 6. — Employ the capillary electrometer for the follow- 
ing experiment. Pith a frog, excise its heart and place it on a pair 
of unpolarisable electrodes with the apex on one electrode and the 
base on the other. 




Fig. 122. — Frog's Heaet. Diphasic Variation. 

Simultaneous photogram of a single beat (black line) and of the accompanying electrical change, 
indicated by the level of the black area, which shows the varying level of mercury in a Capillary 
electrometer. The base of the ventricle is connected with the mercury, i. First, phase, base 
negative to apex. II, Second phase, apex negative to base. (Waller.) 

To prevent the contact between electrodes and heart shifting during 
the beats the connection between each electrode and heart should be 
made by a thread moistened in normal saline. The electrodes are con- 
nected to the electrometer through a Du Bois key, so that the electro- 
meter can be short-circuited at any time. 

If the mercury be watched it will be found to move with each beat 
of the heart. 



156 EXPERIMENTAL PHYSIOLOGY 

Instead of watching the changes with a heart beating sponta- 
neously, the effect of a single beat may be observed by first applying 
the Stannius ligature and then mechanically stimulating the ventricle. 
"With each contraction the mercury will move so as to show that 
the part stimulated becomes first negative and then positive to the 
other part. 

Examine the arrangement of a second electrometer which is fitted 
up to record the movement of the mercury meniscus photographically. 
The capillary is brightly illuminated in a projecting lantern and 
placed in front of a projecting lens by means of which a vertical image 
of the mercury is thrown on to a vertical slit, part of which it covers. 
A photographic plate is moved by clockwork behind the slit, and so 
records the vertical movements of the mercury meniscus. 

The result of such an experiment is given in fig. 122. It shows 
that the electrical variation occurring in a single contraction of the 
uninjured heart is diphasic in character. In the first phase (i, fig. 
122) the base was negative to the apex ; in the second phase, n, apex 
was negative to base. 

Experiment 7. — Paradoxical contraction. Pith a frog and expose the 
sciatic nerve, which at its lower end will be found to split into two branches : 
one, the tibial nerve, supplies the gastrocnemius, and the other, the pero- 
neal nerve, supplies the peroneal 
muscles. Follow the peroneal 
nerve a little way down the leg 
and cut it through. In this way 
is obtained a piece of the sciatic, 
ab (fig. 123), with the upper ends 
of its two main branches, one, b c, 
running to the gastrocnemius, g, the 
other, b d, the isolated piece of the 
peroneal. Place a pair of electrodes 
connected with the secondary coil 
under b d. "With each shock sent 
Fig. 123.— Arrangement of Apparatus to through B d the gastrocnemius con- 
show the Paradoxical Contraction. tracts. 

This result is due to a part of the electrotonic current set up in 
the peroneal nerve passing through the fibres to the gastrocnemius as 
they lie side by side in the sciatic, ab, It is not due to an escape of 
the current because the result is prevented by tying a ligature round 
the peroneal immediately above the electrodes sufficiently tightly to 
injure the fibres without, however, cutting through the nerve, which 
could therefore still act as an electrical conductor and permit escape 
of current. Moreover the contraction is not due to the negative 
variation sent along the peroneal fibres as a result of the stimulation, 
because it is not produced when the peroneal nerve is stimulated 
mechanically. 




157 



CHAPTER XVI 

SCHEMA OF THE CIRCULATION. THE SPHYGMOGRAPH 

The flow of the blood through the arteries, capillaries, and veins 
follows the laws which govern the flow of any fluid through a system 
of tubes, so that we are able to illustrate many of the features of 
the blood flow upon an artificial arrangement of tubes drawn up in 
imitation of the circulation. Such an artificial system is known as a 
Schema of the circulation. On examining the conditions of flow 
in the blood vessels, we find that if we expose an artery it feels hard 
and distended to the touch, and that synchronously with each heart 
beat it swells and becomes harder. If we cut into an artery the 
blood spurts out with considerable force which carries it to some 
distance, and in addition the outflow is of variable rate, for with each 
beat of the heart the flow is markedly accelerated. To stop the flow 
it is necessary either to tie or compress the vessel at some point 
nearer to the heart than the orifice which has been made into it. If, 
on the other hand, we lay bare a vein, it is found to be collapsed and 
very readily compressed, and when its cavity is completely oblite- 
rated by compression it swells up on the side farthest from the heart. 
If we cut into a vein the blood flows from it at a good rate, but with 
slight force and in a constant stream, and to stop this flow it is 
necessary to tie the vein at any point of the vessel further from the 
heart than the incision. There are thus many great differences in 
the characters of the flow from an artery and vein respectively. This 
change in the nature of the flow is brought about either at the com- 
mencement of the capillaries or in the small terminal arteries, for if 
we examine the capillaries in a living animal under a microscope, the 
flow is found to be constant and not alternately fast and slow. As 
arteries subdivide, though each branch may be much smaller than the 
main trunk, yet the total transverse sectional area is invariably found 
to be greater than that of the main artery. Again, when we pass 
from the small arteries to the capillaries, though each capillary is of 
very small sectional area, their number is so immense that their total 
sectional area is many hundred times greater than that of the arteries 



158 



EXPERIMENTAL PHYSIOLOGY 



from which they have sprung. In examining the flow of a fluid 
along a tube, it is found that the resistance offered to the flow 
becomes progressively greater as the diameter of the tube along which 
it is forced is diminished. The resistance of the system of capillaries 
and minute arteries must therefore be very great, and this high peri- 
pheral resistance explains many of the important facts that we know 
of the distribution and flow of the blood in the various parts of the 
body. 

Other important points for us to note at the commencement of 
our study of the physical characters of the circulation are : (a) that 
the arterial walls are highly elastic, and (b) that the source of the 
energy required to propel the blood through the vessels is the 
rhythmic contraction of the heart. 

By imitating these three features of the circulation in an arti- 
ficial schema, we can reproduce and study many of the important 




Fig. 124. — Schema of the Circulation. 



phenomena presented to us by the circulation. Thus in the schema 
shown in fig. 124 the heart is represented by the enema syringe s, 
which is provided with two valves, v 1 and v 2 , which permit the flow 
of the fluid from v 2 to v 1 , but not in the reverse direction. The 
arterial system is represented by the rubber-tubing v 1 t, upon the 
course of which two manometers, m 1 and m 2 , are inserted. The mano- 
meter consists essentially of a U-tube held in a vertical position. 
The bend of the U is filled with mercury, and one limb which remains 
open to the air carries a light float which rests on the upper surface 
of the mercury and accurately follows its movements. The upper 



THE SCHEMA 159 

end of the float is provided with a horizontal arm acting as a writing 
point, and thus the variations in the level of the surface of mercury 
can be recorded upon a moving surface. The other limb of the U is 
placed in communication with the interior of the tube t by means of 
a glass T-piece. One of these manometers is placed on the tubing t 
near to the syringe s, the other at the end of the tubing, which termi- 
nates in two branches, one passing through a short piece of tubing 
which can be blocked by the screw clamp c ; the other passes to a 
piece of glass tubing, g, whose centre is tightly packed with glass 
wool. The two branches then reunite and are connected to a third 
manometer, m 3 , which latter is in its turn connected to the syringe s 
by the rubber-tube d. This last piece of tubing is of wider bore and 
its walls are thin so that it may represent the veins. In using the 
apparatus the three manometers are arranged to write their move- 
ments vertically over each other on a recording surface. By this 
apparatus we are able to study the changes in pressure as we vary 
the conditions of the experiment. 

Experiment 1. — First fill the schema with water by disconnecting at 
v 2 and placing both orifices under water. By pmnping the syringe, water is 
then driven through the tubes until all the air is displaced. The tube d is 
then compressed and a little more water forced in until the level of the 
mercury in the free limbs of the manometers lies about 2 cms. above that 
of the other limb. The tube d is then reconnected to the syringe. The 
experiment may now be carried out in the following way : (a) Leave the 
clip c open, when we shall be studying the flow along a closed system of 
elastic tubes of wide bore and consequently offering but little resistance at 
each point. Now imitate the beating of the heart by rhythmically com- 
pressing the syringe s, at first slowly and then gradually increasing the 
rate of the rhythm. 

On studying the tracings obtained the following points can be 
made out : — 

(1) The manometer m 1 begins to rise a little earlier than the 
manometer m' 2 , but later than the instant at which more fluid is forced 
into the tube from the syringe. 

(2) The amplitude of the movement of the second manometer is 
rather less than that of the first. 

(3) The movements of the third manometer m 3 are practically the 
same as those of the other two. 

(4) There is no marked permanent excess of pressure at any 
point of the system over that at any other point. 

(5) The effect of the filling (the diastole) of the syringe varies 
according to the rate at which it is allowed to fill. If the syringe be 
thick-walled so that it possesses considerable elastic recoil, as soon as 
it is let free it rapidly dilates and sucks in fluid from the tube d, thus 
setting up a lower pressure in that tube, which diminution of pressure 



160 EXPERIMENTAL PHYSIOLOGY 

travels as a negative wave backwards along the system, affecting first 
the manometer m 3 , and later m 2 and m 1 . The effect upon the mano- 
meters is greater the thicker the walls of the tube D, and may be 
made quite small by increasing the length of that tube and diminish- 
in» its thickness. It is also decreased by choosing a syringe which 
does not dilate rapidly. 

In this part of the experiment practically the whole of the fluid 
travels through the piece of wide tubing c. 

(b) In the second half of the experiment, vary the conditions by inter- 
posing a high resistance to the flow at one point. This is attained by closing 
the tube c by the clip, when the whole of the fluid must then pass through 
the glass tube a, which being packed tightly with glass-wool divides up the 
stream into a great number of minute channels, resembling capillaries, and 
thus offers a great resistance to the flow. As before, pump fluid through the 
system, when the following results will be obtained : — 

(1) With each systole of the syringe the manometers m 1 and m 2 
will record a rise of pressure as in the former case, but this sudden 
rise will be absent from the record of manometer m 3 . 

(2) By the diastole the manometer m 3 will alone be affected. 

(3) If only one emptying of the syringe be carried out after the 
oscillations have ceased, the manometers m 1 and m 2 stand at a higher 
level than m 3 , and only slowly fall, while m 3 rises until the pressure 
is once more uniformly distributed. 

(4) If, before the pressure becomes thus equalised, the syringe be 
once more emptied, the manometers M 1 and m 2 record a further rise 
of pressure, i.e. a summation of effect has taken place, which is further 
increased by a third emptying of the syringe, and so on. 

(5) If the emptying of the syringe be continued at a definite rate, 
at last a condition is reached at which the pressures recorded in the 
arterial manometers m 1 and m 2 , instead of continuing to rise, oscillate 
about a mean pressure. The maintenance of pressure at a mean 
height means that this pressure is just sufficient to force out through 
the peripheral resistance during the time of one complete cycle 
exactly the same volume of fluid as is emptied into the arterial tube 
at each contraction of the syringe. If the movements of m 3 during 
this time be next studied, it is found that the only sudden variations 
are the negative waves caused by the active recoil of the syringe as 
it returns to its original shape. These rhythmic diminutions in 
pressure do not travel through the high resistance at G, and there- 
fore do not make themselves felt in the other two manometers. If 
the emptying of the syringe be repeated sufficiently rapidly, it is 
found that the mean pressure recorded by the third manometer falls 
below zero pressure, and takes a negative value. If the movements 
of the third manometer be not too much masked by these negative 



THE SCHEMA 161 

waves, it is found that the pressure in that part of the system shows 
a gradual and uniform rise after the filling of the syringe, or, in other 
words, the outflow through the high peripheral resistance is uniform, 
though the inflow into the arterial tube t is intermittent. 

It is while working in this latter manner that the schema very 
closely reproduces the conditions as found in the circulatory system 
during life. The rhythmic emptying of the syringe into the elastic 
tube t, which is filled with fluid exerting a high pressure upon its 
walls, reproduces the emptying of the left ventricle into the over- 
distended and elastic aorta. The relative distribution of the fluid is 
the same in both cases, the arterial tube of the schema being over- 
filled, and its elastic walls stretched, whereas on the venous side the 
reverse is the case. The most important particular, however, in 
which the schema reproduces the conditions found in the circulatory 
mechanism is the conversion of an intermittent flow at the commence- 
ment of the arterial tube into a continuous flow through the venous 
tube. The two factors which lead to this result are : — 

(1) The existence of a high peripheral resistance ; for when that 
resistance was absent, i.e. when the tube c was open, the flow through 
the venous tube was intermittent ; and 

(2) The elasticity of the walls of the arterial tube t. 

The influence of the latter can be best exemplified by considering 
what would happen if the tube were replaced by one whose walls 
were rigid. In such a case, as the fluid is incompressible and the 
tube, being rigid, cannot be expanded to hold a larger volume, any 
fluid forced into the commencement of the tube necessitates the 
ejection of exactly the same volume of fluid from the opposite end at 
exactly the same instant. Hence, if the inflow to such a tube be 
intermittent the outflow must also be intermittent. 

There is another point of view from which we may advantageously 
consider the flow of fluid in the schema, namely, by studying the 
amount of work and the way in which it is applied in setting up the 
flow, and on the other hand the utilisation of that store of energy. 
The source of energy is the pumping of the syringe : the loss is 
caused by the friction the fluid encounters in its flow both against 
the walls of the tubes and at successive layers within the fluid itself 
where it is moving at different velocities. 

We may, for our present purpose, leave out of account the modifi- 
cations caused by gravity, for as the fluid is ultimately returned to 
the same level, they on the whole counterbalance one another. 
The energy of each emptying of the syringe is at once transferred to 
the fluid, and is there represented by the velocity imparted to it, and 
by the pressure set up in it. As soon as the fluid is forced into the 

M 



162 EXPERIMENTAL PHYSIOLOGY 

elastic tube some of the energy is at once imparted to the tube wall 
and is represented by the stretching of the wall, which, being elastic, 
can recoil and thus re-impart its store of energy to the fluid from 
which it received it. This is the most important factor explaining 
the conversion of the intermittent flow from the syringe into a con- 
stant flow through the high resistance a ; for though the original 
source of energy is intermittent in its action, the recoil of the tube 
wall is constant and lasts as long as the tube is kept over-distended. 
The elastic wall therefore acts as a means of temporarily storing 
the energy produced by each forcible emptying of the syringe and 
subsequently yielding it up again, not as a sudden discharge analogous 
to the manner in which it received that energy, but as a steady 
delivery extending over some time. 

There is a further phenomenon of the circulation which we can 
also study upon the schema, namely, the pulse wave. At each 
emptying of the syringe the fluid ejected at first only produces a 
distension of the first part of the arterial tube, and as a consequence 
that part is at a higher tension than that of the piece of tube 
immediately following. It therefore contracts and forces some of its 
contents into the next piece of tubing, which in its turn becomes 
more stretched than the piece next following, and therefore contracts, 
and so the series of phenomena are repeated along the whole tube. 
Thus a wave of distension and contraction passes along the tube, 
which wave is known as a pulse wave. As the pulse wave is in 
reality a wave of pressure we can study it by recording the changes 
in pressure at two points on the tube by means of manometers, as in 
the previous experiment, or we can examine it by recording the 
changes in the transverse diameter of the tube at two different points, 
which is, of course, but another way of recording changes of pressure, 
for the tube is distended in proportion to the pressure of the fluid 
within it. We will employ this latter method, for it is the one 
ordinarily employed in recording the pulse wave in man. 

Experiment 2. — For this purpose we may modify the apparatus of fig. 
124 by omitting the manometers and in their place pass the tube over two 
grooved metal supports, a and b, fig. 125, firmly fixed to collars held upon a 
vertical bar. Attached to the two collars are recording levers l 1 l'-, which 
are moved by two light vertical rods with grooved pads, e and F, at their 
ends where they rest upon the tube. In this way an increase of the diameter 
of the tube is recorded as a rise of the writing lever. Adjust the two points 
to write vertically over one another, and record the movements of the two 
levers caused by a single compression of the syringe, and secondly by a 
series of regularly repeated compressions. 

In such an experiment it is found that there is an appreciable 
time interval between the instants at which the tube begins to expand 



THE PULSE WAVE 



163 



at the two points, and by a measurement of this time (t sees.) and of 
the distance between the two points (I cms.) the velocity of the wave 

is at once given in cms. per sec. by the quotient - . To determine the 

t 

wave length we must divide its velocity by the total time taken for 

the wave to pass any one point. 

Note that in the two tracings the amplitude of the tracing recorded 
by the lever nearer the syringe is greater than that of the second 
tracing, which means that the pressure at the second point does not 
reach so high a value as at the first, some of the energy remaining 
stored up in the preceding portions of the tube. 

In the later portions of the two recorded waves secondary waves 
are seen, which are due to the reflection of the primary wave from 




Fm. 



125. — Apparatus foe Studying the Passage of a Pulse Wave along 
an Elastic Tube. 



the end of the tube, where it impinges on the peripheral resistance. 
Note that these waves occur at an earlier stage in the second tracing 
than in the first. In addition to these, other waves are sometimes 
seen in the early part of the descending portions of the two tracings, 
which are due to the elastic vibrations of the tube. 

Alterations in the characters of the wave, according to the initial 
pressure of the fluid in the tube, should also be examined. As we 
wish to study only a single wave, our object can be best gained by 
compressing the tube beyond the peripheral resistance, so that no 
fluid can escape. After each compression of the syringe the pressure 
of the fluid in the tube then remains permanently raised, and we may 
thus record a series of waves at gradually increasing pressures. It 
is found that as the pressure is raised the velocity of the pulse wave 

m 2 



164 



EXPERIMENTAL PHYSIOLOGY 



is greatly increased, and so, too, is the wave length. Moreover, as 
the velocity increases, the secondary waves, due to reflection at the 
peripheral resistance, occur at an earlier point upon the descending 
part of the record. 

From a consideration of the pulse wave as studied in a schema, 
we may now pass to an examination of the pulse as occurring in an 
artery during life. The instruments by which this is effected are 
termed sphygmographs, and their aim is to record changes in diameter 
of the artery with each heart beat. These changes in diameter are 
due to changes of the pressure of the blood in the artery, and con- 
sequently in taking a pulse tracing we are in reality recording the 
variations of blood pressure in that artery. 

Experiment 3. — Take a pulse tracing by means of Marey's Sphyg- 
mograph, fig. 126. 

It consists of a recording lever which writes on a blackened surface moved 
by clockwork. Fig. 127 shows the principle of the instrument. It is supported 




"Pr" 



Fig. 126. — Marey's Sphygmograph. 




Fig. 127. — Diagram to Show the Arrangement of the Levers in 
Marey's Sphygmograph. 



upon the arm by two runners, between which lies a button, k, placed at the 
end of a spring, s' 2 . The button is placed over the radial artery at the wrist, 






MAREY'S SPHYGMOGRAPH 



165 



and its pressure on the artery is modified by the screw F or by an eccentric 
as in fig. 126. On the upper surface of the spring rests the end of a screw, 
p, which carries a small lever terminating in an upright with a knife-edge, e. 
The knife-edge comes into contact with the recording lever L at a point very 
close to its axis and on the metal piece a. This metal piece is not connected 
to the screw g p. The lever is kept in contact with the knife-edge by a weak 
spring, s 1 . By turning the screw g the knife-edge is raised or lowered, and 
so the lever l is adjusted to record its movements on the recording surface. 

In fig. 128 is reproduced a tracing obtained by this method. Each 
unit is seen to consist of a rapid ascent followed by a more gradual 




Fig. 128. — Sphygmogkam Taken by Marey's Sphygmograph. a b, the Primary 
Wave ; c, the Dicrotic Notch ; d, the Dicrotic Wave ; and e, Post-Dicrotic 
Wave. 

descent. The ascent in a normal tracing is unbroken. In the 
descent is seen one conspicuous break in the curve at c. This is the 
dicrotic notch. The descent from b to c shows one slight break just 
above c : this is the pre-dicrotic wave. The descent from d to e shows 
one or two further waves : these are the post-dicrotic waves. The 
"main wave from a to & is termed the primary or percussion wave. 

The record is one of the changes of transverse diameter of the 
artery, though it is complicated by the fact that the artery is 
accompanied by veins, and the state of distension of these can exert 
an effect upon the tracing. By comparison of the pulse tracing of 
an animal with a simultaneously taken record of the intra-ventricular 
and aortic pressures the meaning of the different parts has been 
elucidated. The sudden rise of the lever from a to b is due to the 
sudden forcing of a fresh quantity of blood by the heart into the 
elastic aorta. This produces a sudden rise of pressure and distension 
of the aorta, which is then propagated as a wave of distension over 
the whole arterial system. The dicrotic notch is immediately 
preceded by the closure of the semi-lunar valves. The dicrotic wave 
is therefore a secondary wave produced by reflexion from the surface 
of the valves. The pre-dicrotic and post-dicrotic waves are waves 
of oscillation produced in the elastic arterial wall. They are more 
conspicuous in pulse tracings taken from -persons in whom the blood 
pressure is high. 



166 



EXPERIMENTAL PHYSIOLOGY 



Experiment 4. — Take another tracing of the movements of the radial 
artery by means of Dudgeon's Sphygmograph (fig. 129). The form repre- 
sented in this figure is a modification of the original pattern due to Richard- 
son. A strip of paper blackened on its upper surface is carried under the 
writing lever by two revolving rollers, the upper one of which is furnished 
with a series of sharp edges which record lines 2 mm. apart upon the 
blackened paper. These edges are interrupted so that the horizontal lines 




Fig. 129. — Kichardson's Modification of Dudgeon's Sphygmogeaph. 



are broken, and the clockwork is so made that each break follows the preced- 
ing break after a distance of 2 mm. 

The arrangement of the levers in Dudgeon's sphygmograph is diagram- 

matically represented in fig. 130. p is a 
little metal pad which rests upon the artery 
and which follows the changes of its dia- 
meter. It is kept in contact with the skin 
by aid of a small weight, w, which slides 
along a rod, k l, pivoted at k. By varying the 
position of the weight the pressure exerted 
upon the artery can be altered at pleasure. 
A. bent brass lever, c b a, rotates round an 
axis at b. Its short arm b a passes through 
a hole bored in the upright of the pad p. 
Fig. 130.-Plan of the Levees Any movement of p is therefore communi- 
in Dudgeon's Sphygmogeaph. cated to ba, and therefore to c, where it is 

magnified about five times, because the long 
arm b c of the bent lever is about five times that of the short one. A second 
lever, dcf, rotates round an axis at d and has attached to it at f a writing 
style, f G. It passes through a ring terminal at c and is kept in contact with 
c by the counterpoise e. The movement at c is therefore communicated to 
d f and magnified at f about five times because d f is about five times d c. 
The movement of the writing point g is practically that of f. Thus the total 
magnification of the movement of p is twenty-five times, m is the writing 
surface. 




DUDGEON'S SPHYGMOGRAPH 



167 



Fig. 131 gives two sphygmograms obtained by this instrument. 
Tracing i is from a rather low-tension pulse, and tracing n from a 
high-tension pulse. The dicrotic notch is much more conspicuous in 
tracing i than in tracing n. In n the pre- and post-dicrotic waves 
are much better marked than in the low-tension pulse. Note further 




Fig. 131. — Two Sphygmograms Taken by a Dudgeon's Sphygmograph. 
Tracing i from a Low-tension, ii from a High-tension Pulse. 



the difference in excursion between the two and the difference in 
rate of beat. The clock is so set that it carries the paper through in 
exactly ten seconds, so that if the total number of waves recorded on 
the paper be multiplied by 6 the rate of beat per minute is at once 
given. 



168 EXPERIMENTAL PHYSIOLOGY 



CHAPTER XVII 

DEMONSTRATION OF BLOOD PRESSURE AND ITS NERVOUS 
REGULATION 



For this experiment the following apparatus is necessary (fig. 132). The 
writing surface consists of an endless roll of blackened paper stretched between 
two drums, one of which can be rotated at a slow rate by a tangent screw in 
the ordinary manner. The recording levers consist of a tambour, t 2 , to record 
the respiratory movements, a mercury manometer, m, with float, w, and two 
chronographs, cc. All these writing points are arranged of such a length and 
in such position that all lie in the same vertical line on the recording surface. 
Of the two chronographs the lower one is connected to a clock, cl, ticking 
seconds and a battery, b-. Attached to the escapement of the clock is a wire 
which each second dips into a cup of mercury (seen vertically below cl in the 
figure), thus closing a circuit and actuating the chronograph. The upper 
chronograph is arranged to record the zero pressure, and is also utilised to 
mark the instant at which any stimulation is made. For this purpose it is 
connected in series with a battery b 1 , the two pillars of a coil a and a key k. 
On closing k the Neef s hammer vibrates, and with each rise and fall of the 
hammer the chronograph lever rises and falls. To the terminals of the 
secondary coil a pair of shielded electrodes, e, is connected. 

To record the respiratory movements for this experiment a receiving 
tambour, t\ is fitted on a horizontal rod with the rubber membrane facing 
downwards. To the centre of the membrane a cork is cemented and the 
tambour is then held over the rabbit in such a way that the cork rests on the 
abdomen at a part that moves freely with each respiration. This tambour 
is connected by rubber tubing, into which a -piece is inserted, with the 
recording tambour t 2 . With each inspiration the abdomen rises, forces air 
out of the tambour t 1 into the tambour t 2 , the lever of which therefore rises. 

The mercury manometer consists of two vertically placed glass tubes of 
equal bore, about half-filled with mercury. In one of these a float, w, rests 
on the upper surface of the mercury. The other is connected by a piece of 
thick-walled pressure tubing to a pressure bottle, pb, which is filled with a 
half-saturated solution of sodium sulphate. A spring clip, l, controls the 
connection of the pressure bottle with the manometer. This second tube of 
the manometer is connected by a lateral piece with a metal tube on which is 
a tap, s, and this, by rubber tubing of narrow bore and thick walls, can be 
connected to the cannula in the artery. 

The apparatus being prepared, a rabbit is tied down to a holder and put 
under ether. Its head is then fixed by a Czerrnak's rabbit-holder. A 
median incision is made through the skin of the neck for about four inches, 
so as to expose the larynx at the upper end of the incision. The platysma is 
cut through in the mid-line. The sterno-mastoid is separated from the sterno- 



BLOOD PRESSURE 



169 




170 



EXPERIMENTAL PHYSIOLOGY 



hyoid, which brings into view the carotid artery o, fig. 133, accompanied 
by a small vein or veins and in relation to several nerves. Superficially lies 
the descendens noni. Immediately behind the artery lies the vagus, w, 
behind and to the inner side the sympathetic, sy, and depressor nerve, d. 
The vagus is first of all separated high up opposite the larynx, and its trans- 
verse branch, the superior laryngeal, sl, fig. 126, is isolated. A small nerve, 
arising either from the superior larjmgeal or by two roots, one from this and 




Fig. 133. 



-Dissection of the Nerves of 



Rabbit's Neck. 



the other from the vagus, is next sought for. This nerve is the depressor 
nerve, d. It is isolated for about two inches of its course and a fine silk 
thread passed under it. The ends of the thread are knotted, so that a loop is 
formed round the nerve, by which it can be easily lifted from the wound at 
any time. A double silk thread of another colour is then passed round the 
vagus and its ends tied together. The vagus of the opposite side is next 
exposed and ligatures passed round it. The sciatic nerve is then exposed by 
an incision down the middle of the external surface of the thigh, cutting 
through the vastus externus, and a ligature is passed round it. 

A cannula is now inserted into one of the carotids. The most convenient 
cannula is of the form shown in fig. 134, b. It consists of a glass bulb with 
._, three tubes leading from it. One is of fine bore 

for insertion into the artery. It has a constricted 
neck and its lower end is cut off obliquely and 
has rounded margins. The tube opposite this has 
two constrictions on it, so that rubber tubing does 
not easily slip off. A short piece of thick-walled 
pressure tubing is fixed to this and a screw clip 
fitted over it, so that it can be completely closed. 
The lateral tube is for attachment to the mercury 
manometer. To insert the cannula a long piece 
of the carotid is isolated and a double thread 
passed under it. One is then tied at the upper 
end of the isolated piece so as to stop the flow of 
blood. On the lower end a pair of bull-dog forceps 
is placed in such a way as to compress the vessel 
and stop the blood-flow. "With a pair of sharp- 
pointed scissors the artery is now cut into by an 
incision which cuts through about one-third of 
the circumference, and is directed obliquely down- 
wards. By holding up the flap of artery wall thus made the cannula can 
easily be inserted into the vessel and tied in by the second thread already 
placed there, the thread lying in the constriction on the wall of the cannula. 




Fig. 



134. — Two Forms of 
Cannula. 



BLOOD PRESSURE 171 

The animal is placed in a convenient position with respect to the mano- 
meter and the cannula connected to the latter. The pressure bottle is raised 
until it is about five feet above the level of the mercury in the manometer, 
and with the tap s turned on fluid is run from the pressure bottle through 
the manometer along the tubing to the cannula, until all the air is displaced 
from these tubes. The flow from the pressure bottle is then stopped. The 
writing point of the upper chronograph is brought to the level of that of 
the float, and consequently draws an abscissa line of zero pressure. It 
should be noticed that the level of the mercury in the two limbs is not the 
same, that in the open limb being a little higher than that in the other, 
because this mercury has to balance the pressure of a column of salt solution 
equal in height to the difference in level between the mercury and orifice of 
the cannula. The clip on the tubing on the free orifice of the cannula is next 
screwed tight. The clip on the tubing from the pressure bottle is once more 
opened, but now no fluid can escape. The mercury in the open limb of the 
manometer therefore rises, and carries the float with it, until the difference 
in level of the mercury in the two limbs balances the pressure of the fluid in 
the pressure bottle acting on the closed manometer limb. This will be at 
a level of about 70 to 80 mm. above the zero abscissa line. The increase of 
pressure inside the manometer is measured by the increase in distance of the 
two mercury surfaces, but the height recorded by the float is only the move- 
ment of the mercury surface in the open limb. If the bore of the tubing 
forming the two limbs be equal, the rise in the one limb is equal to the fall in 
the other. Consequently the increase of pressure exerted by the fluid is 
measured by a mercury column 140 to 160 mm. in height. Therefore in 
a tracing obtained by the mercury manometer to determine the pressure 
recorded at any instant, we must measure its height above the zero abscissa 
line and multiply this by 2, which gives the equivalent height of a mercury 
column which just balances the pressure. 

The bull-dog forceps are now removed from the artery, when the mercury 
will begin to oscillate up and down, and at about the same level as that it has 
been raised to by the pressure bottle. The object of the pressure bottle is in 
the first place to give a convenient means of filling the apparatus with a fluid 
which when mixed with blood tends to prevent its coagulation. Sodium 
carbonate or magnesium sulphate solutions are also employed for this purpose ; 
but, on the whole, sodium sulphate is perhaps the best salt to employ. The 
pressure bottle further performs another very important service in raising 
the level of the mercury to a height which will approximately represent that 
of the blood pressure. If this be not done, on connection with the artery the 
blood itself would have to raise the mercury thus entering the cannula in 
some volume, not only causing a loss of blood to the animal, but leading 
sooner or later to coagulation and blocking of the cannula. Placing the 
pressure bottle too high is also to be avoided, for then some of the fluid will 
leave the manometer and cannula, and pass into the circulating blood. 

In taking the blood pressure by a cannula placed in the carotid we must 
remember that we are not measuring the blood pressure in the carotid as it 
exists in life, because we have completely stopped its flow along the vessel. 
We are really measuring the pressure on the side wall of the artery from 
which the carotid springs, i.e. either the subclavian or aorta, as the case may 
be, along which the blood is still flowing in a normal manner. 

We may now carry out the experiment in the following manner : 
1. Record of the normal tracing. — Two or three short pieces of 
tracing are taken with varying speeds of recording surface. Fig. 135 
gives a typical piece of tracing from the rabbit, but the student should 



172 



EXPERIMENTAL PHYSIOLOGY 



also examine the tracings obtained from other animals, such as those, 
for instance, in figs. 139 and 156. In fig. 135 it is seen that there are 
two distinct series of undulations on the blood-pressure curve — one a 
small undulation, due to the heart beat, and the second a larger and 
slower undulation, which is synchronous with respiration. In an 
animal, such as the rabbit, in which the heart beats very quickly the 



RESPN 




UUUUIAAAJUUUUUUV 


AA 


• 

"'"• .Aft. i ; * 




^a/^vNaaAAAaaA^ 


A / 


w "Hw * ^^ « 


v V 


















. 








.... 












-n_Ji_n_ruiJUi-JiJiJT-JUi_njuiAJuui-JLJULJU^ 



Fig. 135. — Tracing of the Blood Pressure from a Babbit taken by the Mer- 
cury Manometer. resp n , Eecord of the Respiration ; b.p., of the Blood 
Pressure. The Horizontal Line at the Base shows the Position of the 
Zero of Pressure. Time Tracing in Seconds. 

oscillations due to the heart beat are small, not, as we shall see, 
because the variation in total pressure with each beat is small, but 
because the mercury manometer possesses so much inertia that it is 
unable to respond to variations which are carried out so rapidly. 



THE BLOOD-PRESSURE CURVE 



173 



If a record of the heart beat be taken simultaneously with a blood- 
pressure tracing, it is found that the record of rise of pressure 
with each beat follows with a considerable latency after the record 
of the heart itself. The respiratory waves are generally regarded as 
caused by alterations in the volume of blood admitted to the auricle. 
During inspiration the greater negative pressure in the thorax draws 
more blood from the great veins into the thorax, leading to an 
increased flow through the heart and a consequent rise in blood 
pressure. This increased flow does not commence at the instant 




hhh,hhhhhhhhhhhhhkJL-hh-Ji_ 



Fig. 136. — Blood Pressure and Respiratory Tracing of a Curarised Cat 
under Morphia. Artificial Respiration. Time Tracing Seconds. 

inspiration commences, but at a short interval after. The rise in 
blood pressure, therefore, is not instantaneous with the com- 
mencement of inspiration, but follows it after an interval of about 
two to three heart beats. In expiration there is a diminished blood 
flow to the ventricle, and therefore a fall in blood pressure, and there 
is an analogous latency, blood pressure only beginning to fall at an 
appreciable interval after expiration has commenced. The effect of 
the respiratory movements in varying the blood pressure is well 
illustrated by studying the changes during artificial respiration. 



174 



EXPERIMENTAL PHYSIOLOGY 



Here we find the exact converse to the results with normal respiration, 
t.e. a fall in pressure during inspiration and a rise during expiration. 
In inspiration the thorax is now expanded by pressure from within ; 
and, as the pressure is greater from within than without, the flow into 
the auricle is impeded. The result is well seen in fig. 136, which is 




Fig. 137. — Stimulation of the Depressor Nerve in a Babbit. 
Time Tracing Seconds. 

from a curarised cat anaesthetised with morphia. Artificial respiration 
was for a time stopped with the thorax in an expiratory state. The 
pressure showed a gradual constant rise. Then when a fresh inflation 
was caused the pressure rose for two heart beats and then rapidly 
fell to rise again during expiration. The initial rise was due to 



THE DEPRESSOR EFFECT 175 

the extra filling of the left auricle by the increased pressure of 
the air emptying the blood from the lung capillaries. The in- 
creased pressure in the thorax retards the flow of venous blood into 
the right auricle ; less, therefore, is sent into the pulmonary artery by 
the ventricle and the pressure in this artery falls. From this fall in 
pressure, and because of the obstruction to the flow through the pul- 
monary capillaries due to the pressure of the air upon them, less blood 
is delivered into the left auricle, hence less into the left ventricle, and, 
therefore, a fall in aortic blood pressure. 

By measuring the mean height of the tracing in fig. 135, above the 
zero abscissa line it is seen that the mean blood pressure is 140 mm. of 
mercury. 

2. Stimulation of the depressor nerve. — The nerve is laid on a 
pair of shielded electrodes, and is stimulated while a record is being 
taken. The experiment is repeated two or three times, varying the 
strength of stimulation. Fig. 137 gives a typical result. It is seen 
that after a short latent period of about two seconds the blood pres- 
sure gradually fell from a mean pressure of 140 mm. Hg to one of 
124 mm. Hg, but that the character of the tracing was not in any 
way altered. The heart waves and respiratory waves are still present, 
and remain as before. When stimulation ceased the pressure once 
more began to rise after a latent period of about two seconds, and 
quickly regained its original mean value. 

The depressor nerve is an afferent nerve which transmits im- 
pulses from the heart, mainly from the endocardium to the vaso- 
motor centre in the medulla. If the nerve be divided and its peripheral 
end stimulated no result is obtained. Stimulation of its central end 
produces the result already described. It does not act upon the 
cardiac centre, but only upon the vaso-motor centre, whose action it 
so modifies as to cause dilatation of the peripheral blood vessels and 
therefore a fall in blood pressure. Normally it must act as a kind of 
safety-valve to the heart under conditions when it becomes difficult 
for the heart to empty itself against a too high pressure, due either 
to a higher pressure in the aorta or an overfilling of the ventricle. 
The increased resistance thus caused stimulates the depressor, the 
blood pressure falls by dilatation of vessels, ehiefly of the splanchnic 
area, and the heart is now able to empty itself without any special stz-ess. 

3. Stimulation of the sciatic nerve. — While recording the blood 
pressure the central end of the divided sciatic is stimulated, varying 
the stimulus until a typical effect is produced. The sciatic is chosen 
simply as a convenient nerve containing afferent fibres, for precisely 
the same effect is produced with any similar nerve. The result shows 
a rise of pressure, starting soon after the stimulation commenced, and 



176 



EXPERIMENTAL PHYSIOLOGY 



lasting some time after stimulation ceased. This is called a Pressor 
effect. The only variations in the character of the tracing are due 
to differences in respiration, which produce secondary effects upon the 
blood pressure, fig. 138. Often, too, struggling movements are pro- 
duced, especially if the animal be only lightly under the anaesthetic, 




Fig. 138. — Stimulation of the Central End of the divided Sciatic. The 
Latter Portion of the Eespiratory Tracing is imperfectly recorded. 

when with each convulsion the blood pressure rises considerably. The 
only completely satisfactory method of obtaining a pure pressor effect 
is to previously curarise the animal. The reflex muscular movements 
are then absent, and the pressor effect is produced unmasked by the 
rise of pressure caused by each convulsion. The tracing of fig. 139 



STIMULATION OF THE VAGUS 



177 



was obtained in this way : it is from a cat under morphia and 
curarised. It shows that the blood pressure rose from a mean height 
of 94 mm. Hg to one of 144 mm., but that the characters of the 
tracing were otherwise retained in a perfectly characteristic manner. 
This rise in pressure is due to a reflex constriction of the small 
arterioles, and persists for some time. It is almost completely 
abolished by section of the splanchnics. 

4. Stimulation of the peripheral end of the vagus.— While the 
record is being taken one vagus is ligatured in two places and cut 
between the two ligatures. There is, as a rule, no effect upon the 
blood pressure or respiration. The peripheral end is laid on electrodes 



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Fig. ]39. — Pressor Effect Produced by Stimulating the Central End of the 
Sciatic of a Curarised Cat under Morphia. Time Tracing Seconds. 
Tracing Reduced to One-half Size. 

and stimulated, the stimulation being repeated once or twice with 
different strengths of stimulus. Figs. 140 and 141 show the effect of 
such stimulations. Pig. 140 is with weak stimulation, which produced 
slowing of the heart beat but no stoppage. It is seen that there is 
a marked fall in blood pressure, which, however, did not commence 
the instant the stimulus was applied. The variations of pressure now 
recorded as caused by each heart beat are seen to be very much 
larger. This is not due to an increase in force of the ventricular 
contraction, for, as we have previously seen, the force of the beat is 
decreased on vagal stimulation (p. 141 ). Nor, again, is it entirely due 
to the diminished blood pressure, enabling the heart to produce a 

N 



178 



EXPERIMENTAL PHYSIOLOGY 



larger variation with the same force. It is mainly due to the inertia 
of the recording instrument. With the rapidly beating heart the 
manometer could only respond to a limited extent to the change of 
pressure produced ; but now that the beat is slower more 
time is allowed to the manometer, and its movements therefore 



l\ l\ l\ 



miMMm 



B.P. 



JUJUU'LJlJlJuJlJUlJLJLJLjUUUU 



Fig. 140. 



-Stimulation of the Peripheral End of the Left Vagus 
in a Rabbit. 



increase in amplitude. After stimulation ceased the rate of beat 
very quickly increased, and this, aided by an increase in ventricular 
force and a partial constriction of the arterioles, led to a rise of blood 
pressure to a greater height than before ; but this was soon followed 
by a fall, the mean pressure once more attaining its initial value. 
Fig. 141 is a similar result, but the stimulation was stronger and 



ACTION OF THE VAGUS 



179 



inhibition more complete. The fall at the first stimulation is seen to 
be greater, and only a single beat occurred during stimulation. After 
the stimulus ceased the heart soon regained its rhythm, and the 
characters of the trace were practically the same as those studied in 
the previous instance. 

The result of a second stimulation s reproduced because it 
illustrates another effect which is obtained if the vagus be frequently 




Fig. 141. — Two Successive Stimulations of the Peripheral End of the Right 
Vagus with the Same Strength of Stimulus. Rabbit. Reduced to One- 
half Size. 

stimulated. It was obtained by stimulating the vagus with the same 
strength of current as that used for the preceding instance and after 
an interval of fifteen seconds. It is seen that while the stimulation 
still continued the heart recommenced to beat and the blood pressure 
gradually rose. This result is known as the escape of the heart from 
vagus inhibition. It becomes more and more marked the longer tin- 
stimulus is continued, and if stimulation be repeated a few times, at 
last a stage is reached in which no effect upon the heart nor upon the 
blood pressure is produced. 

5. Stimulation of the central end of the vagus.— The result of such 

n2 



180 



EXPERIMENTAL PHYSIOLOGY 



stimulation varies with the strength of stimulus employed. As it 
is an afferent nerve, stimulation of its central end tends to produce 
a pressor effect. This is the result if the stimulus be weak, and it 
is accompanied by an increased rate of breathing, which also pro- 




Fig. 142. — Stimulation of the Central End of the Left Vagus in a Babbit. 

duces an effect upon the curve. Fig. 142 shows such a result, where 
the effect is seen to persist for some time after stimulation ceased. 
If the strength of stimulation be increased convulsive movements are 
produced which send up the blood pressure; but at the same time 



EFFECT OF NICOTINE 



181 



reflex inhibition of the heart is also caused, and this leads to a fall in 
blood pressure. 

If the animal be under curare this reflex inhibition is very clearly 
seen; for it is then uncomplicated by the results of the convulsive 
movements. It is abolished by section of the opposite vagus. 

6. Effect of the intravenous injection of a small dose of nicotine. — 
There are many drugs which when injected directly into the circula- 
tion produce marked results upon the blood pressure. As a typical 
instance 05 c.c. of a 01 per cent, solution of nicotine in 1 per cent. 
NaCl solution is injected into the external jugular vein. To effect 
this the vein is exposed and a ligature passed round it. About one 




Fig. 143, — Effect of an Injection of Nicotine upon the Blood Pressure. 
Rabbit. Reduced to One-half Size. 

inch of it is isolated and the lower end is closed by a pair of bull-dog 
forceps. The vein now distends with blood and the ligature is then 
tied at the upper end. A single turn only is given to the ligature, so 
that it can easily be loosened if at a subsequent time we wish to refill 
the vein with blood. A hypodermic syringe with a fine needle is now 
filled with the solution to be injected, and the needle inserted into the 
vein; a procedure which is rendered easy by the distension of the 
vein. The bull-dog forceps are removed, and at a given signal the 
injection made. The vein is then emptied of blood and solution by 
passing the finger along it and the clip forceps replaced in position. 

The result of such an injection is shown in fig. 143. It is seen 
that a great rise in blood pressure is produced which may be so 



lsj EXPERIMENTAL PHYSIOLOGY 

marked if the dose be at all large that the mercury may be driven out 
of the manometer. In the figure reproduced it is seen that the 
pressure rose gradually from a mean pressure of 84 mm. Hg to one 
of 136 mm., and from that point it gradually sank, though some 
minutes later it was still distinctly higher than at the start. At the 
commencement of the tracing there are some irregularities which were 
due to alterations in the respiratory rhythm. This rise is due to a 
marked constriction of the arterioles. A similar result, though not 
to so marked an extent, is produced by an injection of a watery extract 
of the medullary portion of the supra-renal gland. On the other hand 
an extract of the cortex produces practically no effect upon the blood 
pressure. 

7. The effect of asphyxia. — The experiment may be conveniently 
concluded by killing the animal by asphyxia. This is effected by com- 
pressing the trachea by clip forceps or a ligature. If the animal be 
under the influence of curare, stopping the artificial respiration is 
sufficient. 

Death by asphyxia is described as occurring in three stages, pro- 
ducing typical results in the blood-pressure tracing. The first stage, 
lasting from a to b (pi. 2), is the stage of dyspnoea. The blood pressure 
gradually rises and the animal makes deep inspiratory efforts, each 
being sustained for a time, and expiration is rapidly followed by a fresh 
forcible inspiration. The blood pressure shows variations correspond- 
ing to these respirations. This stage is followed after a varying time 
by the second — the stage of convulsions. (From b to c.) 

In this stage the animal passes into a rapid series of convulsive 
struggles, as seen upon the respiratory tracing ; and with each struggle 
the blood pressure rises considerably. The mean blood pressure reaches 
its greatest height during this stage. The third and last stage is 
characterised by a gradual weakening and slowing of the heart and 
a fall in blood pressure. The animal becomes quiet, and only a few 
respirations are attempted. No other muscular efforts are made. 
The heart gradually ceases to beat and the animal dies. 

Note that at death the blood pressure has not reached the zero 
abscissa, but lies 8 mm. above it. If the aorta be cut into, and the 
blood allowed to escape, the manometer falls to zero pressure. The 
pressure at death is not zero pressure, because the blood is contained 
in a closed system of tubes, which it overdistends, with a uniform 
pressure throughout, and this pressure is spoken of as the mean general 
pressure. During life the blood is very differently distributed, the 
arteries being overfilled, and therefore the arterial pressure is 
much above the mean general pressure. The large veins, on the 
other hand, are not distended to the full amount, and the pressure 
is below that of the mean general pressure. 



ir*ket le convulsive 



FICK'S MANOMETER 



183 




Fig. 144. 



OTHER METHODS OF RECORDING BLOOD PRESSURE 

We have had occasion to note that the mercury manometer is in certain 
respects deficient, owing to the great inertia of its moving parts. A small 
force, therefore, which lasts a short time can only produce a very minute 
effect, and this will be masked by 

any larger effects occurring simul- B D F 

taneously. Even variations in 
pressure of as great amount as 
those produced by a heart beat are 
only recorded after a considerable 
delay, so that before the mercury 
has had time to reach the level 
which represents the highest pres- 
sure attained that pressure has 
ceased to act, and is again falling. 
Fig. 144 illustrates this point. 

Suppose the line a b c r> to represent the actual changes in pressure 
in a liquid where vertical ordinates represent pressures, and horizontal 
ordinates time. If the changes take place very slowly then the mercury 
manometer is able to register them as the line abcd with absolute accu- 
racy. If, on the other hand, the changes are carried out rapidly, the record 
obtained is very different, and something like the line abed. The mean 
value is the same in both cases, but the amplitude of the record is much less ; 
the highest and lowest pressures are not recorded, and, moreover, there is a 
delay : the highest points of the curve b and d lie more to the right, and there- 
fore later than the in- 
stants of time at which 
the highest pressures 
actually occurred. The 
apices also are rounded 
instead of sharp. 

To obtain, therefore, a 
true record of the changes 
of fluid pressure in an 
artery, we see that one of 
the first necessities is to 
choose apparatus in which 
the moving parts possess 
the least possible inertia. 
One of the first means 
that suggests itself is that 
we should record changes 
in diameter of the artery 
whose pressure we wish 
to record. This will give 
us a measure of the varia- 
tions of blood pressure in 
the artery, because the 
artery wall being elastic, 
the lateral pressure upon 
the wall causes a stretch- 
ing of the wall in propor- 
tion to that pressure. Having recorded the variations we can subsequently 
■calibrate them by recording the diameters of the same piece of artery under 




145.— Pick's C-Spbikg Manojd n B. 



184 



EXPER I M KNTA L PI I YS [( >L( )< i V 



constant pressures. This method gives far more accurate results than the- 

mercury manometer, hut possesses certain disadvantages. 

There are two instruments which are employed for the purpose. The 
first of these is Fick's spring kymograph, fig. 145. 
It consists of a C-spring, a, made of thin strips of 
metal united at their edges. If the pressure in the 
space thus caused be increased the spring opens 
out. It possesses little inertia, and therefore re- 
sponds quickly to changes of pressure. Fig. 146 gives 
a small piece of tracing taken with this manometer. 
Recently a modification of this kymograph by v. 
Basch has been introduced in which the C-spring. 

is reduced to the smallest size. It gives very excellent results. 
The other instrument is Hiirthle's rubber manometer. 




Fig. 146. 




Fig. 147. — Hurthle's Manometer. 



HURTIILE'S MANOMETER 



185 



In this instrument (fig. 147) the mass of all moving parts is reduced 
to a minimum. Among these is also included the column of fluid 
connecting the manometer to the blood vessel. This is reduced in 
quantity as far as possible, and, further, by choosing a tambour of very small 
size the movement of fluid in and out of the tambour is rendered extremely 
minute. The instrument consists of a tambour, B, of very small capacity 
whose upper surface is covered with thick rubber. An inlet tube, F, with a 
tap on it, D, communicates with the tambour, and is for connection to the 
artery. A second tube, g, allows of a flow of fluid from a pressure bottle. A 
small vertical metal piece is attached to the centre of the rubber membrane 
and moves a recording lever, o, pivoted about an axis which can be raised or 
lowered by the lever c, so that a horizontal position can be given to the 
writing lever. The lever c can be clamped by the screw h. The manometer 
is also provided with a second writing point, N, for recording the zero pressure. 
This can be adjusted to the writing surface by a screw, a, and can be raised or 
depressed by a second screw, l. Both writing points can be adjusted to the 
blackened surface by a screw, k. 

A record of the pressure changes is taken by this instrument by first filling 
it with half-saturated sodium sulphate from a pressure bottle, and connecting 
it to the cannula, which is also filled, and then closed by the spring clip. The 
manometer is again connected to the pressure bottle, and this time- the tambour 
membrane rises. By the handle c the writing lever is brought to the horizontal 
position, and clamped there by the screw h. The clip on the cannula is again 
opened and the lever o falls. Its level now records zero pressure, and the 
writing point N is brought to that level. The cannula is again closed, the 
pressure in the manometer raised, the tap on G shut, and now the forceps on 
the artery can be removed, and the manometer lever allowed to record its 
movements. 

Fig. 148 is such a tracing taken with the recording surface moving 
at the same rate as that in fig. 135. The tracing i was recorded 



a «.: A A ' A 71 



/v_^v /v_j 



,Mw/r0mn Iwwv f0WMy >»»ww\ y^\ J ^^\/i''^>, i /* 




Fig. 148. — Tracings of Blood Pressure of the Babbit b? Ilnnmi's .M urota rBB : 
i, during Normal Respiration ; n, during Aktiiuiw, Respiration. I'm 
Upper Horizontal Line gives Zero Pressi re, 

immediately before that reproduced in fig. L35 from the mercury 
manometer. A height of 16 mm. in this figure therefore represents 
a pressure of 150 mm. of mercury. The variations due to respiration 



186 



EXPERIMENTAL PHYSIOLOGY 



are not so conspicuous as in fig. 135. This is due to the smaller 
magnification obtained in this instance. The heart beats are, however, 
more conspicuous and show greater oscillations than those caused by 
respiration. If measured they are seen to be lh mm. high in a total 
blood pressure measured by 16^ mm., i.e. the variation caused by 
each beat is T xth of the mean pressure. If we make similar measure- 
ments in the trace yielded by the mercury manometer we find each 
beat is about 1 mm. high in 75 mm. mean pressure, i.e. the variation 
in pressure recorded as due to each beat is T l -,th of the mean pressure. 
Hence in this particular experiment the Hiirthle manometer was seven 
times more sensitive in recording rapid variations of pressure than the 
mercury manometer. Tracing n of fig. 148 is a further illustration 
of the different effects of normal and artificial respiration upon the 
blood pressure. This piece of tracing also demonstrates the fact that 
in artificial respiration a fall of pressure is produced by inflation of 
the lungs. The production of this result we have already explained 
on p. 174. 

In fig. 149 is reproduced a tracing of the effect of stimulation of 
the peripheral end of the vagus of sufficient strength to cause slowing 




Fig. 149. — Stimulation of the Periphebal End of the Vagus. Rabbit. 
Hurthle Manometer. The Uppeb Horizontal Line marks Zeeo Pbessure. 

of the beat but not stoppage. This should be contrasted with those 
given in figs. 140 and 141. 

The most interesting results to be gained by the use of this instru- 
ment are, however, to be seen when the record is more extended by 
making the movement of the blackened surface more rapid. Such a 
record is given in fig. 150. It shows on the blood-pressure tracing 
practically the same variations as those obtained in a sphygmogram 
(see fig. 131, p. 167). Thus from a to b is the rise in pressure due to 



THE RATE OF BLOOD FLOW 



187 



the sudden propulsion of blood into the aorta ; at c is the predicrotic 
wave, and at d the dicrotic wave. 

This piece of tracing must also be compared with that given in 
fig. 146, which was obtained from a dog, using Fick's kymograph. 




mwrnmrnm 






Fig. 150. — Normal Blood Pressure and Respira- 
tion. Rabbit. Hurthle Manometer. 

Both tracings show precisely the same points, 
and further show that by employing these 
instruments we are able to record even the 
smallest and most transient variations in pres- 
sure. 

In connection with the consideration of the 
blood flow the student should examine the con- 
struction of the following piece of apparatus whose 
aim is to enable us to determine the rate of flow of 
the blood along a vessel. Ludwig's stromuhr 
(fig. 151) consists of two glass bulbs, a and b, which 
communicate with each other above, and below 
are fitted into a circular brass base, P, revolving 
on a lower frame, e. Through this frame are two 
channels, opening respectively at c and d. By 
means of two stops the revolving disc p is checked 
in the two positions, so that either a or B can be 
brought into communication with the tube at c. The opposite bulb then 
opens out at o. The method of employing the apparatus is to fill the bulb a 
with oil and the bulb b with defibrinated blood. The tube c is then connected 
to the central end of the artery the rate of flow of the blood along which we 
wish to determine, and d is tied into its peripheral end. At an instant which 
is recorded the blood from the artery is allowed to flow into a. The oil rises 
on the surface of the blood, and the upper orifice of the bulbs being closed it 
forces the defibrinated blood from B into the peripheral end of the vessel. 
As soon as a is filled with blood the bulbs are rapidly rotated, so that the bulb 
B comes to occupy that position previously held by a. The bulb n now con- 
tains the oil, and more blood entering it from the artery, the oil is once more 




C ■""■■ l "™" 

I'm. 151. — Lui>wih> 

Stbomtjhe. 



188 EXPERIMENTAL PHYSIOLOGY 

displaced and the blood previously entering a is sent into the peripheral end 
of the vessel. When b becomes full the apparatus is again rapidly rotated, 
and the operation repeated several times, when the experiment is stopped 
and the total time occupied observed. 

If now we know, by previous measurement, the capacity of the 
bulbs and the number of times they have been rotated, we know the 
total volume of blood that has left the artery during the experiment. 
Suppose this to be V c.c, and the whole time of the experiment to be 
t seconds. Then in 1 sec. a volume of Y/t c.c. left the artery. The 
lumen of the artery is next measured. Suppose this to be a sq. cm., 
and that the velocity of the blood is v cm. per sec. Then the volume 
of blood leaving the vessel in 1 sec. would be a . v c.c. 

Hence a.v = Y/t, 

and v= — . 

a . t 

Thus from a measurement of the area a of the lumen of the vessel, 
and the volume V issuing in a time t, we can, by the above formula, 
determine v, the velocity of the blood flow, along the artery. 



189 



CHAPTER XVIII 

THE KIDNEY. DEMONSTRATION OF AN ONCOMETER EXPERIMENT 

In investigating the mode of action of any organ or part of the body 
one of the first things we require to know is how its blood flow is 
modified under different conditions, in order that we may be able to 
correlate these changes with other functional activities simultaneously 
observed. There are several methods open to us by means of which 
we may observe changes in vascularity of an organ. In many cases 
simple inspection by revealing differences in colour is able to show us 
that there is more or less blood in the organ, but this method can 
only show us gross changes. A second plan is to measure the quan- 
tity of blood issuing from the organ, variations in the rate of outflow 
giving a measure of the amount of blood passing through the organ. 
This is one of the most satisfactory methods if we are working upon 
an excised organ and circulating defibrinated blood through it by tying 
a cannula into its main artery. The third and the most valuable 
is that known as the plethysmography method. Here the changes 
in volume are directly measured by confining the organ in sonic 
enclosed space and then recording the amount of air or of llui 
displaced from this space as the organ expands or contracts. 

The general plan adopted in such an experiment may be bi I 
illustrated by one upon the kidney. 

The original form of apparatus, as invented by Roy for experiments upon 
the kidney, consists of a metal box, in which the kidney is placed, called an 
oncometer (bulk measurer), and a piece of recording apparatus termed an 
oncograph (bulk recorder). The form of the oncometer is shown in tig. 152, 
and a diagram of its general principle in fig. 158. It consists of an ellipsoidal 
metal box made to open by a hinge. Each half consists of a double metal 
box (oc and ic, fig. 153), the one fitting tightly within the other. To prepare \\ 
for use each inner half is removed and a sheet of sheep's peritoneal membrane, 
5i, is fitted over it, and its edges gummed down to the outer surface of the 
capsule, to make an air-tight joint. The membrane is fitted, on verj loosely, 
and thus allows free movement inwards and outwards. The inner bos is 
then replaced in the outer, to which it is tightly clamped by the screw -,. 
Both sides are now filled with oil, so as to fill up the spaces a and B between 
the peritoneal membrane and the inner cases, the membrane being raised 
meanwhile so that when the instrument is closed there is sufficient space 1< fl 



190 



EXPERIMENTAL PHYSIOLOGY 



inside to receive the kidney. The one orifice is then tightly closed by the 
cork B, and a special two-way cannula fitted into the other. The instrument 




Inst. Co. Ltd. CAMb. 
Fig. 152. — Two Sizes of Roy's Kidney Oncometer. 

is then placed in an air-bath to raise its temperature to body ternperature. 
When the kidney is inserted between the two halves, the peritoneal membrane, 




Inst. Co. Ltd. Cams. 
Fig. 153. — To Illustrate the Principle of Roy's Oncometer. 



THE KIDNEY ONCOMETER 



191 



being very flexible, adapts itself to the kidney surface, so that practically the 
kidney is inserted into an oil-tight box filled with oil. The oncograph, fig. 154, 
consists of a metal box whose npper surface is closed by a sheet of peritoneal 
membrane fitted on very loosely, so that it can move fairly freely. On this 
rests a small cylinder of ebonite with its lower end closed, and to this is 
attached a light vertical rod which moves a horizontal recording lever. The 
interior of the oncograph is connected by a piece of rubber tubing with the 




Fig. 154. — The Oncograph. 

interior of one side of the oncometer by the tube t, fig. 153. The whole 
oncograph and tube connection is filled with oil. Thus arranged any expan- 
sion of the kidney drives out oil from the oncometer into the oncograph, the 
peritoneal membrane of which is bulged upwards, and lifts the vulcanite cup, 
and thus the lever of the oncograph. In this way the variations in volume 
are recorded 

A very simple but effective method is to employ an air oncometer made 
after the principle of that used by Schafer and Moore in their experiments 
upon the spleen. A convenient form is shown in fig. 155. It may be made 




Fig. 155.— An Ant Oncojieteb fob the Kidney. 



either of plaster of Paris, which is thoroughly soaked in melted hard 
paraffin, or of wood, which is then thoroughly varnished. The figure 
shows its general shape. It has a lid made either of thick plate glass or of 
wood. A depression is cut away in one wall through which the kidney vessels 
and ureter may pass when the kidney is placed within the box. The whole 
is made air-tight by filling the hole in the side with pieces of wool soaked in 
a stiff mixture of vaseline and hard paraffin, so that the kidne\ vessels are 



lyii EXPERIMENTAL PHYSIOLOGY 

not constricted. The junction with the lid is also made air-tight by vase- 
line. Piercing one side is a hole into which a tube fits tightly, and this 
is connected by rubber tubing of small bore to a tambour (fig. 35). As the 
kidney expands air is driven out of the plethysmograph into the tambour, the 
lever of which therefore rises. 

DEMONSTRATION OF THE CHANGES IN VOLUME OF 
THE KIDNEY" 

The apparatus is first set up as for taking a blood-pressure tracing, and a 
tambour is also fitted up to record vertically above the blood-pressure tracing. 
Care is taken that all the writing points record vertically above each other. 

A dog which has not been fed for the previous twelve hours is put under 
ether and then a dose of morphia is injected, 1 c.c. of a 1 per cent, solution of 
the hydrochlorate per kilo of body-weight. A median incision in the neck 
is made, the external jugular isolated for about 1^ inches, and a simple cannula 
inserted and tied in. The carotid artery is next exposed, and a cannula tied 
in it as described on p. 170. The kidney is next exposed. This may be 
done by a lateral incision in the lumbar region and the kidney isolated from 
the peritoneum without opening the abdominal cavity if possible, though this 
will be found of some difficulty in the dog. There are usually several small 
vessels which enter directly into the cortex of the kidney. These have to be 
divided ; but each must be ligatured before doing so in order to avoid hemor- 
rhage into the oncometer. When the kidney is thoroughly freed it may be 
placed in the oncometer. 

The other method, which has the great advantage that the kidney is more 
fully exposed, is to reach it by opening the abdominal cavity from the front. 
If care be taken to protect the exposed viscera from cooling, this method may 
be safely adopted. A longitudinal median incision is made through the skin, 
starting just below the xiphisternum for about three or four inches. A trans- 
verse incision through the skin at the level of the last rib is now made, from 
the mid-line down to the rib on the left side. The muscles are next cut 
through, one at a time, along this line — first the external oblique, then the 
internal oblique, then the transversalis, and finally the rectus. Care is taken 
that the peritoneum is not opened until all bleeding has been stopped. As 
each vessel is cut through it is caught up on Spencer Wells' forceps and 
ligatured. When all bleeding has been arrested the abdominal cavity is 
opened by cutting through the peritoneum along the incisions made through 
the muscles and in the mid-line. The intestines are pulled well over to the 
right side and protected by covering with a thick layer of cotton wool which 
has been warmed in front of a fire. The kidney is then exposed and the 
peritoneum over it is torn through, any bleeding point being ligatured. Care 
is taken to handle the kidney as little as possible, and it must not be allowed to 
become cooled. Having thoroughly isolated the kidney, especially where the 
vessels leave it, it is placed in the oncometer. This has previously been pre- 
pared by warming it and then placing a few layers of cotton wool containing 
a plentiful amount of the vaseline and paraffin mixture at the bottom of the 
notch in the side wall. The kidney is placed in the oncometer, so that the 
vessels and ureter lie on the vaseline wool in the notch for that purpose. 
Strips of wool soaked in the vaseline mixture are now packed, so as to lie 
between the kidney and the notch, and others to fill up the notch. The whole 
success of the experiment depends upon the careful packing at this stage. 
The notch is to be exactly filled and not overfilled, so that when the lid is 
adjusted there is no pressure on the kidney vessels. Before putting on the 
lid the upper edge of the oncometer is thoroughly covered with vaseline 



THE KIDNEY TRACING 193 

mixture and then the lid is rubbed down into close contact with the edge. 
The lateral tube is now connected by thick-walled rubber tubing to the 
recording tambour. In the rubber tubing is inserted a T-piece, the lateral 
orifice being closed by a rubber tube clamped by a spring clip. The tambour 
now shows the oscillations due to the heart beats. The oncometer must now 
be tested to see if it be air-tight by blowing in a little air through the T-piece 
into oncometer and tambour. The tambour lever is raised and the pressure 
of air inside is greater than atmospheric pressure. If the tambour lever fall 
there is a leak, and the oncometer must be reopened and the packing more 
thoroughly carried out. If the tambour lever remain at the same mean 
level the experiment may be proceeded with. The whole abdomen is thoroughly 
covered up with warmed layers of dry cotton wool, the abdominal wall 
having been previously drawn together by sutures. 

The cannula in the carotid is now connected to the mercury manometer 
and the writing points brought to the recording surface. The procedure of 
the remainder of the experiment can be varied in different ways according to 
circumstances. 

The following five paragraphs give the course of an experiment 
which will show the main facts to be gained by the method. The 
results obtained are examined in the succeeding pages : — 

1. Having brought the air pressure inside the oncometer to 
atmospheric pressure, by opening for an instant the clip on the lateral 
pass of the T-piece, take a piece of normal tracing. 

2. Inject 1 c.c. of a 4 per cent, solution of caffeine citrate in 1 per 
cent NaCl. To do this fill the cannula and rubber tubing in the 
external jugular vein with the solution by means of a pipette drawn 
out to a fine point. Fill a 1 c.c. pipette with the solution and attach 
to the cannula by rubber tubing. Take a short piece of normal 
tracing and removing the bull-dog forceps from the central end of the; 
vein, at a given signal blow in 1 c.c. of the solution. Eeplace the 
clamp on the vein. The instant of injection is marked on the tracing 
by means of a signal. If this dose be not sufficient repeat with an 
increased dose until a typical effect is produced. 

3. After complete recovery from the caffeine citrate inject 5 c.c. of 
a 0*1 per cent, solution of digitalin in 1 per cent. NaCl. Previously 
remove the caffeine solution still in the cannula by sucking it up in a 
pipette drawn out to a fine tube, which can pass down the cannula ; 
then wash out with normal saline, remove the saline, and fill with the 
digitalin solution. Attach a pipette containing 5 c.c. of the new 
solution and inject at a given instant. 

4. Inject 1 c.c. of a solution of neurine made by adding one drop 
of a 25 per cent, solution of neurine to 5 c.c. of 1 per cent. XaCl. 
The cannula is to be washed out and filled with the solution as in S. 

5. To complete the experiment, record the kidney changes during 

asphyxia. Dissect out the trachea, open it widely, and while a tracing 

is being recorded suddenly plug it tightly with cotton wool soaked 

in water. 

o 



194 



EXPERIMENTAL PHYSIOLOGY 



Typical tracings obtained in such a demonstration are given in 
the following figures. It is seen that as a rule the trace follows 




Fig. 156. —Simultaneous Tracing of the Volume Changes of the Kidney and 
of the Carotid Blood Pressure in a Dog. Time Tracing Seconds. The 
Horizontal Line marks Zero Blood Pressure. 



exactly the curve of blood pressure simultaneously recorded. The 
variations in volume with each heart beat are well marked, and the 



NORMA], KIDNEY TRACING 196 

rise and fall of blood pressure during respiration are represented by 
an increase and decrease of volume of the kidney. This is exactly 
the result we should expect to obtain if the vessels follow passively 
any variations of blood pressure, and this is the result during ordinary 
conditions when the kidney is at rest. Comparing fig. 156 with fig. 
157, both of which were yielded by the same animal, we see how 
closely volume changes follow blood pressure changes. Fig. 156 was 
obtained at the commencement of the experiment, and is therefore to 
be taken as especially typical of the volume changes. Fig. 157 was 
obtained later, and with a less magnification. The respiratory move- 
ments altered in character as this tracing was being recorded. There 
occurred an increase in kidney volume and a fall in blood pressure, 
so that the fall in blood pressure is chiefly to be explained as due to 
dilatation of blood vessels in which the kidney took part. The altera- 
tion in volume closely follows that of the blood pressure. In watch- 
ing the two being recorded it is very obvious how the rise of the 
oncometer lever precedes by a quite appreciable interval the rise of 
the manometer float. This difference is purely instrumental in origin, 
the kidney rise being recorded by apparatus having very little inertia, 
whereas the inertia of the mercury manometer is great. 

Changes in volume of the kidney may be brought about in either 
of two ways : — 

(i.) Passively, in which case the increase and decrease of volume 
follow proportionately a rise and fall of blood pressure. This is the case, 
as we have seen, with the ordinary kidney trace, where the rapid undu- 
lations in the blood pressure, due to heart beats, and the slower, due 
to respiratory effects, are exactly reproduced in the kidney oncogram. 

(ii.) Actively, in which case changes in volume of the kidney are 
brought about independently of changes of blood pressure or force of 
heart beat, and may even work against these. Thus an active con- 
striction of the kidney vessels leads to a diminution of kidney volume 
and a rise in blood pressure. These changes in kidney volume are \ 
best studied by experiments which locally influence the kidney i 
vessels. Of these changes some of the best known are those pro- 
duced by drugs which are known to influence the secretion of urine. 
They are also of greatest interest because they teach us at the same 
time something of the way in which the kidney works when it is called 
upon to secrete more actively. 

Action of Caffeine. — In fig. 158 is reproduced the effect of an 
injection of 2 c.c. of a 4 per cent, solution of caffeine citrate in 
normal saline directly into the external jugular vein. After a period 
of delay it is seen that the blood pressure falls, the variations in prefl 
sure with each heart beat become less, then increase, and the blood 



196 



EXPERIMENTAL PHYSIOLOGY 



pressure soon rises again and returns to its initial value. In the case 
of the kidney trace there is the same delay before any effect is 
produced, and then a little later, after the blood pressure begins to 




Fig. 157. — Kidney Volume and Blood Pressure in a Dog. 

alter, the kidney volume falls and remains less for some time, finally 
expanding, often to a much higher volume than before the injection. 
Finally, after a variable time it once more returns to its initial state. 
The explanation of these changes in volume of the kidney may be 



ACTION OF CAFFEINE UPON THE KIDNEY 



19; 



twofold, i.e. either passive or active. The fall in blood pressure must 
produce a diminution of the kidney volume unless it be over-compen- 
sated by another volume change in the reverse direction. The fall of 
volume that actually occurs is partly to be explained by the fall in 
blood pressure, but not entirely, for the fall in blood pressure usually 
precedes by a definite interval the fall in the kidney trace, and 
secondly the blood pressure attains its original height long before the 
kidney begins to expand. The main cause producing the diminution 
of the kidney volume is therefore active, and due to constriction of its 




Fig. 158. — Effect of Caffeine upon the Kidney Volume ani> Blood Pressure. 
Tracing reduced to Half Size. 



blood vessels. This constriction ultimately yields, and is followed by 
a dilatation lasting a still longer time, and then the kidney returns to 
its initial state. When the rate of secretion of the urine is recorded 
at the same time as the kidney changes it is found that this rate 
varies and accurately follows the changes in volume of the kidne\ 
When the kidney vessels contract the rate of secretion drops, and in 
the second stage, the period of relaxation, the secretion is accelerated, 
and finally, as the kidney regains its original state, the rate of secre- 
tion returns to that observed at the commencement of the experiment. 
The fall in blood pressure produced in this experiment is due to the 



198 EXPERIMENTAL PHYSIOLOGY 

direct action of the drug upon the heart. This follows from the 
experiment already demonstrated, in which the force of the heart 
beats was directly studied (fig. 113, p. 143). 

The changes of rate of flow studied in association with the changes 
in volume are of interest when connected with the observations which 
show that rate of secretion of urine depends rather upon rate of flow 
of blood through the kidney than upon changes in blood pi'essure — 
though these must of course act secondarily. Increase in urine flow 
being associated with a dilatation of the kidney vessels directly con- 
firms this view. 

Action of Digitalin. — The effect on the blood pressure is a fall of 
short duration followed by a rise of much longer duration. During the 
rise the rate of heart beat is slower, but each beat is more forcible. The 
changes in the kidney tracing are not synchronous with those of the 
blood pressure. There is produced a slow constriction of the vessels 
which reaches a considerable amount and is very persistent. Gradually 
relaxation occurs and results in a greater volume than before the injec- 
tion ; but finally there is a return after several minutes to the initial 
volume. We must note that during the kidney constriction the passive 
variations in volume due to heart beats are very well marked. These 
only become masked or obliterated if the constriction be very great ; 
as, for instance, after a very large dose of the drug. The alterations in 
rate of urine secretion are interesting. During the period of constric- 
tion the rate slows considerably, but is accelerated to a certain degree 
during the subsequent relaxation. Neither the relaxation nor the rate 
of flow ever attains to the same degree as that observed after an 
injection of caffeine. 

Action of Neurine. — The tracing (fig. 159) is introduced here 
because it forms a very good demonstration experiment. In the experi- 
ment reproduced 05 c.c. of a solution, made by adding one drop of a 25 
per cent, solution of neurine to 6 c.c. of 1 per cent. NaCl, was injected 
into the external jugular of a dog. The effect upon the respiration is 
very striking. After a brief period of delay the animal passes for a 
short time into a series of short respiratory spasms, next the respira- 
tion rapidly slows and ceases, to ultimately recommence, first with 
some irregularity, then expiration becomes rapid and short and in- 
spiration prolonged, the rhythm remaining regular. Changes in blood 
pressure closely follow these changes in respiratory rhythm (see fig. 
159). At first there is a slight fall, partly due to diminished force and 
rate of the heart beat. This is followed by a marked rise in pressure 
as the inspiratory gasps occur, and is accompanied by an acceleration 
of the heart beat. Then follows a period of fall of pressure in which 
the heart beat is slow r ed, and finally as respiration is once more 




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200 EXPERIMENTAL PHYSIOLOGY 

established the rate of heart beat is increased and the mean pressure 
becomes higher. 

The changes of kidney volume do not exactly follow those of the 
blood pressure, but are to a certain degree independent of them. 
After a period of delay, which is longer than that necessary to produce 
changes in the blood pressure, there is a sudden constriction of the 
kidney vessels, at first very rapid, then more gradual, and finally 
so marked that the variations due to heart beat are almost obliterated. 
In this part of the trace a dilatation is to be observed synchronous 
with the rise of pressure due to the inspiratory spasms. Next follows 
a very sudden dilatation, and the volume then follows the blood- 
pressure changes very closely until respiration recommences, when a 
further very marked dilatation takes place, the volume becomes greater 
than initially, and then as respiration and blood pressure gradually 
return to the normal, so the kidney volume recovers, thougn at a 
slower rate than the blood-pressure changes. During the marked 
second dilatation the rate of urinary flow is increased. 

THE COURSE OF THE VASO-MOTOR NERVES TO 
THE KIDNEY 

By means of oncometer experiments the vaso-motor nerves to the 
kidney have been mapped out. Vaso-constrictor nerves are proved to be 
present among the particular fibres stimulated if a diminution of the 
kidney volume result, accompanied by either no change or by a rise 
of blood pressure. Simultaneous records of the blood pressure 
changes exclude the possibility of the observed kidney changes 
being due to variations brought about passively on changes in the 
blood pressure. These nerves have thus been proved for the dog to 
leave the cord mainly in the anterior roots of the 11th, 12th, and 
13th thoracic nerves, and to a less extent in the 7th, 8th, and 9th. 
Nerve cells, shown by the nicotine method (see p. 133), are found on 
the course of these fibres, situated in the cceliac, mesenteric, or renal 
ganglia. Vaso-dilators have been found in the 11th, 12th, and 13th 
anterior roots with ganglion cells in the solar or. renal ganglia. 



201 



CHAPTEE XIX 

DEMONSTRATION OF THE NERVOUS REGULATION OF RESPIRATION. 
THE STETHOMETER AND PNEUMOGRAPH 

In a previous experiment, p. 168, we saw how we could record the 
respiratory rhythm in an animal by the aid of a tambour resting on 
the thorax or abdomen. This method gives us all that is required so 
far as the main details of time of inspiration and expiration and rate 
of breathing are concerned, but we also require some method that will 
give us a means of recording these same points, and in addition the 
depth of breathing with some greater accuracy. One method that 
has been adopted is to make the animal inspire from a large glass 
vessel which is placed in communication with a tambour, so that 
changes of pressure inside the vessel cause movements of the tambour 
lever. Each inspiration causes a fall in pressure in the glass chamber, 
and therefore a fall of the tambour lever. For this method it is not 
necessary to have the vessel completely closed. The air must also 
be frequently renewed. 

Another method that has been largely employed is to introduce 
one end of a stiff lever so as to lie between the liver and the under 
surface of the diaphragm. The lever moves about an axis near to 
this end, so that all that is necessary is to record the movements of 
the free end of the lever. This is usually carried out by attaching it 
to a writing lever by a fine thread. 

In the case of the rabbit we possess a further very convenient 
and accurate method, for there exists in this animal a slip of the 
diaphragm in the anterior mid-line which can be isolated without 
opening the pleural cavities. A record of the movements of this 
slip is the method employed in the following demonstration :— 

DEMONSTRATION. THE NERVOUS REGULATION OF 
RESPIRATION 

A rabbit is anaesthetised with ether. By a median incision in the neck, 
extending for about 1§ inches above and below the larynx, the two Tag] 
are first isolated and threads passed under them. The superior laryngeal on 



202 EXPERIMENTAL PHYSIOLOGY 

one side is next isolated and a thread passed under it, so that it may readily 
be lifted up when required. The nerve is easily found as a branch of the 
vagus running off at right angles to the trunk towards the rnid-line at the 
level of the larynx. It usually passes beneath the carotid artery. The glosso- 
pharyngeal of one side is separated in a similar manner. It is found by 
tracing the vagus up to the base of the skull. It is found running from the 
vagus deep down opposite the angle of the jaw, and there lies to the outer 
side of the carotid. It runs forwards to disappear under the posterior edge 
of the mylo-hyoid. 

A median longitudinal incision about 2 inches in length is next made 
with the xiphoid cartilage as its central point. All the tissues are then cut 
through down to the sterniun and cartilage, and any bleeding is stopped. 
The abdominal cavity is opened at the tip of the ensiform cartilage, and the 
two muscular strips of the diaphragm isolated on either side. The cartilage 
is then cut across, care being taken not to injure the attachment of slips to 
its under surface nor the blood vessels to the slips, which leave the lower 
surface of the sternum at about its junction with the cartilage. A sharp hook 
made of a bent pin is then passed through the edge of the cartilage, and 
attached by a thread to one of the levers of fig. 110. The magnification of 
the movement need not be greater than two-fold, and the loading should be 
effected isotonically and varied until the best excursion of the lever is 
obtained. 

The first few records of figs. 160 and 161 show the form of the trac- 
ing. A rise of the lever is caused by a contraction of the diaphragm 
slip and therefore represents an inspiration, a fall, expiration. It is seen 
that relaxation of the diaphragm is carried out very rapidly, much 
more so than the corresponding contraction. The rate of breathing is 
rapid, at times as fast as two per second, at other times much slower. 
If the animal be deeply under the anaesthetic the rate is usually 
somewhat slowed. To show the influence of nervous stimuli upon 
the rate and depth of breathing, the following nerves should be 
stimulated : — 

1. The superior laryngeal. — We may stimulate this nerve in two 
ways. We may imitate the normal method by introducing into the 
larynx a curved probe whose end has been wrapped in cotton wool. 
In this instance, and indeed for all these nerve stimulations, the rabbit 
must not be too deeply under the anaesthetic. The result of this 
stimulation is shown in i, fig. 160. In n, fig. 160, is seen the effect of 
weak tetanising shocks applied directly to the nerve. In both cases 
we see that there is slowing of the respirations, pauses occurring in 
expiration. By contrasting these with the well-known result of the 
presence of a foreign body in the larynx we see quite clearly that the 
results are very different. The effect of the anaesthetic has been to 
very greatly diminish the effect upon the respiratory centre, and in the 
case of the electrical excitation of the nerve there seems to be no 
doubt that the impulses thus originated are of very different character 
from those normally passing along the nerve after it is stimulated. 



ACTION OF GLOSSOPHARYNGEAL 203 

The same remarks apply with equal force to the other stimulations we 
are about to examine. 




Fig. 160. — Alteration in Eespieation on Stimulation of the Superior Laryn- 
geal Nerve: i, by Mechanical Irritation of the Larynx; ii, by Tetanisa- 
tion of the nerve. rabbit. 

2. The glosso-pharyngeal. — We can show the effect of this nerve 
on respiration, as in the previous case, by two modes of stimulation : 
(i.) By making the animal swallow a little water, and (ii.) by electrical 
excitation of the nerve. Fig. 161 gives the usual result of these 
stimulations. In i the animal was made to swallow about 2 c.c. of 
water placed in its pharynx. We see that inspiration is immediately 
inhibited, and that a very gradual relaxation occurred. During this 
time the animal was making rapid swallowing movements. Inn with 
electrical stimulation we have a corresponding result. Breathing 
was at once inhibited for the time of about three respirations, ami 
then recommenced, at first with shallow, then with deepening 
spirations. After stimulation ceased there are seen to be two altera- 
tions in the curve, namely at a and b. These were synchronous with 
two swallowings. It is seen that in each case swallowing commenced 
in the middle of inspiration, which was then immediately inhibited, a 
slight expiration followed, and then as the swallowing ended the in- 
spiration was completed. 

3. Effect of section of the two vagi.— While the respiration is 
being recorded, the one vagus is lifted up by the loop previously placed 
round it and cut. After a short time the second is cut in a similar 



204 



EXPERIMENTAL PHYSIOLOGY 



manner. The effect of section of the first vagus may be nil, no change 
either in rate or depth occurring ; or there may be slight slowing 




Fig. 161 Effect upon Eespiration of Stimulation of the Glossopharyngeal- 

Nerve : i, by Making the Animal Swallow Water ; n, by Tetanisation of 
the Nerve. 




Fig. 162. 



-Result of Section of the Vagus, the other Nerve having 
been Previously Divided. 



accompanied by an increase in depth. The effect of section of 
the second vagus (fig. 162) is always to diminish the rate and increase 




Fig. 163. 




Fig. 164. 
Figs. 163 and 164.— Stimulation of the Central End of the Vagus, BOTH 
Vagi having been Divided. In Fig. 163 the Strength of Stimulus was 
Weaker than in Fig. 164. 



206 



EXPERIMENTAL PHYSIOLOGY 



the depth of respiration, the increase in depth to a certain extent 
compensating for the diminution in rate. 

4. Stimulation of the central end of the vagus. — What we may 
regard as the most typical result of stimulation of the central end, 
both vagi being cut, is that recorded in fig. 163. In this case the 
tetanisation was very weak and caused an acceleration in rate from 32 
respirations per min. to 36 per min., and the amplitude of the record 
diminished from 5 cm. to 4 cm. The diminution in extent is seen to 
be brought about by a less complete relaxation, as well as by a less 
extensive contraction. This result is much better obtained if the 
anaesthesia be not too deep. If the strength of stimulation be increased 
the effects are found to vary considerably. A common result is 
that reproduced in fig. 164, where it is seen that there is a gradually 
increasing tendency to standstill with the diaphragm neither relaxed 
nor contracted, but in a state of mid-contraction. In some cases 
standstill is produced in an inspiratory phase, inspiratory tetanus ; in 
others, again, in an expiratory phase, expiratory tetanus. 



RECORD OF THE RESPIRATORY MOVEMENTS IN MAN 

Various instruments have been devised for recording the move- 
ments of the thorax in man. Of these the two following should be 
examined : — 

Experiment 1.— Take a tracing with Marey's pneumograph (fig. 165). The 
instrument consists of a thin flat iron plate, /, with two stout bars of brass at 
either end. Attached to one bar is a tambour, h, which moves a lever, b. To 




Fig. 165. — Marey's Pneumograph. (McKendrick.) 

the other is fixed a vertical bar with a horizontal screw, g, which fits into the 
upper part of the lever b. By the band e e d the apparatus is tied firmly on 
to the chest. Then with each inspiration the plate / is bent, the vertical bar 



THE STETHOMETER 



207 



pulled from the tambour, which is therefore expanded. The variations in 
volume of the tambour are then recorded by a second tambour. 

Experiment 2.— Take a tracing by Burdon-Sanderson's stethometer. 




Inst. Co. Ltd. Caui>. 

Fig. 166. — Sanderson's Stethometeu. 



Fig. 166 shows the general form of the instrument, and fig. 167 the way in 

which it is fitted to the chest for recording the changes in transverse diameter. 

It consists of a large tambour a with a central disc of metal fixed to its 




Fig. 167. 



■ Mode of Applying the Stethometeb to Record Ciiam.i - i\ 
Transverse Diameter of the Chest. 



rubber membrane. An ivory knob, b ; , attached to one end of a BOTOX carried 
at the end of a spring e serves for adjustment to one side of the cheat. At 



208 



EXPEPUMENTAL PHYSIOLOGY 



the other side is another knob on the end of a bar, b', for adjustment to the 
corresponding point on the opposite side. An increase in diameter leads to 
a separation of the two knobs, only one of which can move relatively to the 
framework. This drives air out of the tambour and causes a rise of the lever 
of the recording tambour. The most important diameters to employ are (1) 
that which connects the 8th rib in the axillary line with the same rib of the 
opposite side, and (2) that from the lower end of the sternum to the 8th 
dorsal spine. 

Eecord the changes in these two positions (1) during quiet breathing, 
(2) while sipping a glass of water, and (3) while swallowing a mouthful of 
biscuit. 

The results obtained will be similar to those reproduced in fig. 168, 
which were taken with the instrument recording changes in the trans- 
verse diameter of the thorax. It is seen that inspiration and expiration 
each occupied about the same time ; that at first the movement is rapid 




Fig. 168. — Eecord of Changes in the Transverse Diameter of the Thorax 
during Eespiration (Man). The Upper Curve taken during Quiet Breath- 
ing : the Lower Curve shows the Effect of Swallowing. Time Tracing 
Seconds. 

in either direction, and then gradually slows. In the lower of the two 
tracings the inhibition of respiration during swallowing is recorded. 
A glass of water was slowly swallowed, and respiration was at once 
inhibited at the commencement of expiration, remaining in that state 
until swallowing ceased, when a fresh and rather deeper inspiration 
followed. From this time respiration resumed its usual characters. 



209 



CHAPTER XX 

DEMONSTRATION OF THE SECRETION OF SALIVA FROM THE SUB- 
MAXILLARY GLAND OF THE DOO 

A dog is secured to the animal holder and placed under ether ; the 
hair is then clipped from the jaws and neck and the skin cleaned with 
a wet sponge. The necessary operation ' is then carried out in the 
following stages : — 

1. Make an incision along the inner border of the lower jaw, 
beginning about its anterior third, a little in front of the insertion of 
the digastric muscle, and extend it backwards to the transverse pro- 
cess of the atlas, dividing the skin and platysma. 2. Expose the 




Fig. 169. 



The Relation of the Veins to the Submaxillary Gl\m> in tiik 
Dog. (After Bernard.) 



jugular vein (fig. 169) at or near the point where it divides into two 
branches, A and P, and lay bare those branches also. One of them, 
p, passes upwards behind the gland ; the other, a, passes forwards 
below it and then divides into two branches. The gland itself has 
two veins : one of them, v 1 , comes from its lower side and enters 

1 The description of the operation is taken from the Handbook for the Phi/sin- 
logical Laboratory, by Brunton, Foster, Klein, and Sanderson. 



L>10 



EXPERIMENTAL PH YSIOLOG Y 



the vein a. The other, V 2 , comes from its posterior aspect and 
enters the vein p. Sometimes one vein is the larger, sometimes the 
other. 3. Tie both branches of the lower division of the jugular a 
little beyond v 1 . Tie the upper of the two branches where it crosses 
the ramus of the jaw and remove the part between the ligatures. 
4. Tie the other division (p) on the distal side of the place where it 
receives the gland vein, v 2 . 5. Eemove the cellular tissue from the 
surface of the digastric, and from the groove between it and the 
masseter. Be careful not to injure the facial artery, and the duct of 
the gland which runs forwards and inwards between it and the 
masseter. 6. Separate the digastric muscle by means of a director or 




Fig. 170. 



-Relations of the Duct and Nerves of the Submaxillary 
Gland in the Dog. (After Bernard.) 



aneurism needle from the facial artery. Tie the arterial twig which 
supplies the muscle. Separate the muscle from its attachment to 
the jaw, or divide it about its anterior third, cutting it through very 
carefully so as not to injure the duct and nerves which lie below it. 
7. Lay hold of the lower end of the digastric with a pair of artery 
forceps and draw it backwards. This brings into view a triangular 
space whose apex is directed forwards, and whose base is formed by 
the reflected digastric. Its lower margin (the dog being supposed to 
be in the upright position as in the figures) is formed by the genio- 
hyoid muscle, and its upper one by the ramus of the jaw and the 
lower edge of the masseter. The anterior half of its floor is formed 
by the mylo-hyoid muscle, on which some nerves ramify. The 
carotid artery enters the triangle at its lower angle and runs along 



OPERATION ON SUBMAXILLARY GLAND 211 

its base, giving off first the lingual artery, secondly the facial. Just 
as the carotid begins to pass in front of the digastric, it is crossed by 
the hypoglossal nerve, h, and is accompanied by filaments of the 
sympathetic. At the upper angle of the triangle several structures pass 
from it to the hilum of the gland, close to the margin of the digastric. 
These are : 1, the duct ; 2, the nerves ; 3, the principal artery of the 
gland. The artery is given off by the facial. It lies beneath the 
nerves, but is easily reached by drawing them aside. 8. Carefully 
isolate the digastric by a director or aneurism needle from all the 
structures just mentioned. Divide it close to its insertion into the 
temporal bone. 9. Divide the mylo-hyoid muscle, m, cutting its fibres 
across about their middle, and reflect the upper half, taking care not 
to injure the mylo-hyoid nerve which lies upon it, and tying all the 
veins which come into view on its surface with a double ligature. 
This brings into view the lingual nerve, l, which issues from under 
the ramus of the jaw just opposite the groove between the digastric 
and masseter muscles, and, after passing across the floor of the triangle 
towards the middle line, enters the mucous membrane of the mouth. 
10. Draw the parts a little towards the middle line with the fingers, 
and follow the lingual nerve to the ramus of the jaw. A small twig, c, 
will then be seen, which passes off from its posterior aspect, bends 
down, making a sort of loop, and then runs backwards to the gland in 
close relation to the duct. This nerve is the chorda tympani. In the 
angle between the chorda and the lingual lies the submaxillary gan- 
glion. 11. Isolate the chorda and pass a thread under it, so that 
the nerve may be raised from its place at will. 12. To reach the 
sympathetic divide the hypoglossal nerve, h, just where it crosses the 
carotid, and lift up its central end. Close to the inside of the carotid 
lies the vagus, and when this is raised the sympathetic is seen lying 
underneath and to the inner side of it. The sympathetic separates 
from the vagus at this point, and passes to the superior cervical gan- 
glion. From the ganglion, fibres accompany the carotid and enter 
the gland along with its arteries. The ganglion can easily be found 
by following the carotid filaments backwards. 13. Place a cannula 
in the submaxillary duct. The ducts of the submaxillary and sub- 
lingual pass along the middle of the triangle close to one another. 
The submaxillary duct lies closer to the ramus of the jaw, and is 
larger than the sublingual duct. Isolate it slightly with an aneurism 
needle. Pass under it a thread for the purpose of tying in the 
cannula. Pass under the duct a smooth splinter of wood or a piece of 
card, half an inch long by one-eighth of an inch wide, on which it may 
rest. Close the duct as near the mouth as possible with a clip, or tie 
a thread round it, so as to obstruct it. Raise the chorda 1>\ the thread 



212 EXPERIMENTAL PHYSIOLOGY 

which has been passed round it, and stimulate it by a weak interrupted 
current — the purpose of this is to distend the duct with secretion, and 
thus render the introduction of the cannula much easier. Open the 
duct with a pair of sharp scissors, insert the cannula, and tie it in. 

To show variations in rate of secretion the secretion may he collected in 
small glass tubes or capsules, having attached a short piece of rubber tailing 
to the end of the cannula. The following plan is a very good one for class 
demonstration. A long piece of glass tubing with thick walls and of about 
1 mm. bore is taken. To one end of this a piece of rubber tubing is fixed, in 
the course of which is inserted a glass T-piece, the lateral orifice being closed 
by a piece of tubing and spring clip. The rubber tubing and a few inches of 
the glass tubing are filled with a solution of methylene blue. The cannula is 
then filled with fluid and connected to the long glass tube by the rubber 
tubing. The glass tubing is then held in a horizontal position against a 
white surface, so that the coloured column of fluid stands out clearly. It is 
also convenient to have the tube marked with transverse lines at short 
intervals. When the demonstration is being made to large classes, it is often 
convenient to project an image of the coloured column on to a screen by 
means of a lantern. As saliva is secreted the coloured fluid is moved along 
the horizontal tube, and its rate can be very accurately watched. The 
meniscus of the fluid can at once be brought to any position of the tube by 
aid of the T-piece on the rubber tubing. By opening this some fluid inay be 
'forced out or sucked in, if the end of the rubber tubing be immersed in fluid. 

We may now show the chief facts in the rate of secretion of saliva 
by the following experiments : — 

1. Observe the rate of floiv of saliva from the unstimulated gland. 
In animals anaesthetised with ether this rate is, as a rule, greater than 
when other anaesthetics are employed. 

2. Stimulate the chorda. — Lift up the nerve, place it upon a pair 
of shielded electrodes, and tetanise it with weak induced currents. The 
rate of flow of saliva is very greatly accelerated. 

3. Stimulate the sympathetic. — The rate of flow, in the case of the 
dog, is no greater than before stimulation. 

4. Observe the vascular changes in the gland on stimulation of the 
two nerves. When the chorda is stimulated the gland will be dis- 
tinctly observed to become redder, due to dilatation of its blood vessels. 
On the other hand, sympathetic stimulation is followed by a paling of 
the gland, due to constriction of its vessels. 

5. Take a camel's-hair pencil moistened with a - l per cent, solu- 
tion of nicotine in 1 per cent. NaCl solution and paint the submaxillary 
ganglion with the solution of nicotine, taking care to limit the action 
of the nicotine to the submaxillary ganglion. Now stimulate the 
chorda once more and a rapid flow of secretion is again obtained. In 
the next place paint the chorda with the solution of nicotine at a spot 
about 1^ inch from the hilum. Then once more stimulate the 
chorda near its origin from the lingual. A free flow of saliva is 



SECKETION OF SALIVA 213 

still obtained. Lastly, paint the chorda with the nicotine solution, 
just at its entrance into the hilum, and again stimulate. No secretion 
is obtained. 

Finally apply the electrodes to the hilum of the gland, when on 
stimulation a free secretion will again be obtained. This experiment 
with nicotine demonstrates the existence of nerve cells on the course 
of the chorda fibres. Nicotine in minute doses is known to paralyse 
nerve cells without injuring the nerve fibres, though in large doses it 
paralyses nerve fibres as well. The experiment therefore proves that the 
nerve cells in the submaxillary ganglion are not placed on the course 
of chorda fibres running to the submaxillary gland. They are, in 
fact, known to lie on the course of secretory fibres running to the 
sublingual gland. The result of painting the chorda with nicotine 
proves that the nicotine solution is not strong enough to paralyse the 
nerve fibres. The absence of secretion on stimulation after the hilum 
has been painted with nicotine proves that there are gland cells on 
the course of the secretory fibres which are placed on the nerve at or 
near its entrance into the hilum. This is further confirmed by 
obtaining a secretion on subsequent stimulation at the hilum, for then 
the post-ganglionic fibres are excited. 



214 EXPERIMENTAL PHYSIOLOGY 



CHAPTEE XXI 

REFLEX ACTION AS STUDIED UPON THE SPINAL CORD OF THE FROG 

Experiment 1. — Destroy the brain of a frog, leaving the spinal cord intact. 
This should be done with a blunt instrument, so that the animal loses as 
little blood as possible. If the animal be tested immediately by pinching one 
of the toes it may or may not respond by a movement of the leg. If it be 
kept for half an hour or a little longer it will very readily respond. The 
absence of response just after the destruction of the brain is due to the shock 
of the operation, but this rapidly passes off hi the case of the frog. 

After this period of rest note the condition of the frog. It lies on 
the table without any attempt at spontaneous movement. Its head 
and body lie in contact with the table, whilst in an intact frog they 
are always inclined to the surface on which it rests. The legs are 
usually drawn up and the fore limbs may be extended at right angles 
to the axis of the body or may lie folded over the sternum. The eyes 
are closed and no respiratory movements are attempted. The general 
attitude of the animal should be contrasted by comparison with that 
of an intact frog. 

Having determined these points its behaviour when its position is 
altered should be investigated. If a leg be stretched out it is usually 
drawn up again to its original position as soon as the fingers are 
withdrawn. Place it on its back ; it will lie at rest practically in the 
position in which it is placed. It makes no attempt to turn over into 
its previous position, whereas an intact frog immediately turns over 
as soon as it is allowed to. Suspend the frog by passing a bent pin 
through the lower jaw. The pin does not act as a stimulus, and so 
cause reflex movements, because the centres of the sensory nerves of 
this part have been destroyed in pithing the brain. The frog may thus 
be supported in any convenient manner and the reflex movements in 
response to various forms of stimuli studied. 

1. Mechanical. 

(a) Pinch any one of the toes of the right foot ; the right leg is drawn 
up. If the toe be held you will feel a puil on the fingers, tending to 
lift the leg. This pull is not continuous, but varies in strength. Pinch 
a toe of the left foot ; the left leg is drawn up. Pinch the skin of the 



EEFLEX ACTION 215 

flank ; the leg of the same side is rapidly drawn up, as if to push away 
the object stimulating the skin. These are all instances of unilateral 
reflex movements, and may be extended in many directions. 

(b) Pinch the skin over the anterior surface of the pubes or round 
the anus ; both legs are now drawn up to rub the spot stimulated. 

(c) Pinch one of the toes gently. With a mild stimulus there 
may only be a slight flexion at ankle and knee. Increase the strength 
of the pinch, and the movements of the leg become more marked. If 
the strength be still further increased, movements of the opposite leg 
will also be produced. 

2. Electrical. 

(a) Single induction shocks.— Apply a pair of wire electrodes from 
the secondary coil to the skin of the leg. Stimulate with single induced 
shocks, gradually increasing the strength of the shock. No reflexes 
are produced, though a twitch produced by the direct excitation of 
the muscles may be produced if the stimulus be sufficiently strong. 

(b) Bepeated induced shocks. — At first employ very weak stimuli. 
A reflex is quite readily obtained. This forms an instance of summa- 
tion of effect. A single stimulus produces no result ; but if repeated, 
even though weak, the effects are gradually summed up until they are 
able to produce a series of reflex impulses. 

3. Chemical. 

(a) Take some 0-2 per cent, sulphuric acid in a small beaker, 
and with the frog suspended move one leg to one side with a 
loop of thread or a glass rod, and then immerse the other foot 
in the dilute acid. In a short time the leg is withdrawn from the 
acid, but will again relax, dip into the acid and be withdrawn for a 
second time. Remove the acid and wash the skin thoroughly with 
water to remove all traces of acid. Allow the frog to rest for a few 
minutes. 

In all cases where a chemical irritant has been employed it is of 
the greatest importance that this resting period should be sufficiently 
long — five to ten minutes — before a fresh excitation is attempted, other- 
wise the results obtained are not characteristic. 

(b) Repeat the experiment, using 10 per cent, acetic acid instead 
of the sulphuric. 

4. Thermal. 

Touch one of the toes with a heated wire ; the foot is withdrawn. 

Having shown by these experiments that a reflex act is produced 
in response to mechanical, electrical, chemical, or thermal stimuli, 
proceed next to study the characters of the reflex. 



216 



EXPERIMENTAL PH YSIOLOG Y 



1. The latent period or reflex time. 

Arrange a time marker recording \ seconds and a signal to write 
vertically over one another on a blackened surface set to rotate at about 
1 cm. per 2^ seconds. Take some of each of the four strengths of sulphuric 
acid, 0*1 per cent., 0*2 per cent., 0*3 per cent., and 0"4 per cent., in small 
beakers, labelling each. Dip the foot up to the ankle in the weakest solution, 
recording the instant of immersion by closing the key of the signal. Wait 
until the foot is withdrawn and then open the key of the signal. Count the 
number of oscillations of the time marker which have occurred dming the 
closure of the current through the signal. This is the reflex time for that 
strength of acid. Wash the skin thoroughly, allow the frog to rest for a 
time, and then repeat the experiment, using the 0*2 per cent, solution. In the 
same way repeat for the other strengths of solution. 

Arrange the results thus obtained in tabular form as in the follow- 
ing instance : — 



Strength of Acid 


Reflex Time in Seconds. 


IVr criit. 

o-i 

0-2 
0-3 
0-4 


3-25 

3-0 
2-25 

2-0 





2. Purposive character of the reflex. — In all the reflex actions 
studied it will be noticed that the muscular response is a very complex 
one. It is in no way an irregular series of twitches of the limb 
muscles, but is a movement similar in nature to those carried out by 
the frog during its life. It involves several muscles, each of which 
contracts at the right instant, to the proper extent, and at the proper 
rate, and another set of muscles which relax to the right degree, and 
at the right time ; i.e. it is a co-ordinated movement. In addition to 
this the response obtained is different according to the part stimulated, 
and when examined is seen to tend either to remove the irritating 
body, to move that part of the body from the irritant, or to remove the 
whole body. This purposive character of the response is well seen in 
the following experiment : — 

Take some squares of filter paper, about 4 mm. each side, and dip them 
into some 20 or 40 per cent, acetic acid. Remove the excess of acid from one 
of these and place it upon the flank of the frog. After a latent period the 
limb on the same side is drawn up, and the flank rubbed with it as if to wipe 
away the irritating body. In this the movement frequently succeeds. Wash 
the skin, and after a period of rest apply another square and hold the leg of 
the same side. The leg of the opposite side will probably be moved so as to 
remove the irritant. Wash the skin again and study the effects of altering 
the position of the irritant. In all cases characteristic but different movements 
are produced. 

3. Irradiation of reflex movements. — In many of the experiments 
we have so far tried it has been noted that with a given stimulus 



INHIBITION OF REFLEXES 217 

applied, say, to one part of a limb, a fixed response is obtained ; but if 
the strength of the stimulus be increased, the movement may involve 
parts on the other side. This is termed irradiation. In studying the 
question of response with regard to strength of stimulus employed it is 
found that as the strength increases the stimulus tends to spread first 
to the same level on the opposite side, e.g. from one leg to the other ; 
and that only when the stimulus is still further increased does it tend to 
spread upwards and downwards to fresh levels. There are conditions 
in which the extension of a stimulus to other parts is greatly facilitated ; 
as, for instance, in strychnine poisoning. 

Take a frog with its brain destroyed and inject 2 drops of a 0*5 per cent, 
solution of strychnine sulphate. In a few minutes stimulation of the skin in 
any part of the body excites a general convulsion of the whole body. All 
the muscles are thrown into violent tetanic spasms and the limbs become 
extended and rigid. The tetanic spasm passes off to be at once repeated on 
even the slightest stimulation, such as a tap on the table. Note that these 
contractions are not co-ordinated muscular movements, but are general 
tetanic contractions. 

Destroy the cord by pithing. At once the contractions cease, showing 
that the effect of strychnine is one acting directly upon the cord, not upon the 
nerves and muscles. 

4. Inhibition of reflexes. — Employing the frog at first taken, expose 
the upper end of the cord and place a crystal of sodium chloride upon 
it. After a minute try to obtain any of the reflexes previously 
obtained easily. They will now be found not to occur, and may not 
be produced even though the strength of the stimulus be considerably 
increased. 



218 EXPERIMENTAL PHYSIOLOGY 



CHAPTER XXII 

SOME EXPERIMENTS IN THE PHYSIOLOGY OF THE EYE. 
ACCOMMODATION, OPHTHALMOSCOPY, COLOUE SENSE, PERIMETRY 

Accommodation. — An object can be seen distinctly if it be placed 
close in front of the eye, or if it be removed to some distance from 
the eye. But as an object can only be seen distinctly if its image be 
accurately focussed on the retina, it follows that the eye possesses 
some mechanism by means of which any image can at will be focussed 
upon the retina. This means consists in a power of alteration of 
the curvature of the lens. That this is the optical change pro- 
duced may be proved by studying the images reflected from the curved 
refracting surfaces of the eye, while the eye is fixed first upon a 
near and secondly on a distant object. The power of throwing a 
distinct image, now of a near object and now of a distant one, upon 
the retina is termed accommodation. 

Before examining these images reflected from the eye make out the fol- 
lowing points upon a series of watch glasses of different curvatures : — 

1. When light falls upon the surface of a medium of different refrangi- 
bility from that in which it is travelling some of the light is reflected, even 
though the medium be transparent. 

2. Hold a lighted match in front of a sheet of polished glass. An erect 
image of the flame is observed of the same size as the match. 

3. Repeat, but use the convex surfaces of watch glasses of different degrees 
of curvature, starting with nearly flat ones and choosing a series in which the 
amount of curvature gradually increases. In all these cases images are pro- 
duced which lie behind the glass, i.e. they are virtual, and which decrease in 
size as the curvature increases. Note further that the images are erect, and 
that, as they become smaller with the increased curvature of the surface, the 
virtual image comes to lie nearer to the reflecting surface. 

4. Next examine the images produced from the concave surfaces of the 
series of watch glasses. These are all inverted and lie in front of the sur- 
face, i.e. they are real. They are all smaller than the object, and diminish 
in size and move towards the surface as the latter becomes more curved. 

Now examine the images of a candle formed from reflection from 
the eye. Hold the candle a little to one side and in front of the ob- 
served eye and then look obliquely at the eye. One image is very 
clearly seen : it is erect, small and virtual, and therefore comes from 
a convex surface. The positions at which reflected images can be 



SANS0N-PUI1K1NJE IMAGES 219 

formed, i.e. the surfaces separating media of different refrangibility, 
are (1) the anterior surface of the cornea, (2) the anterior surface of 
the lens, and (3) the posterior surface of the lens. We shall find 
that reflected images are formed by these three surfaces and that 
the first produces the brightest image because it separates two media 
possessing a greater difference of refrangibility than is the case with 
the other surfaces. The clear image already described comes, then, 
from the anterior surface of the cornea. On examining carefully in a 
darkened room, a second image will be observed lying apparently be- 
hind the first, much less bright than that image, but erect and somewhat 
larger than the first image. This image is therefore produced by a 
convex surface lying behind, and less curved than the anterior sur- 
face of the cornea. It is from the anterior surface of the lens. On 
further examination a third image can be made out less bright than 
either of the preceding ; it is, moreover, inverted, real, and smaller 
than either. It comes, therefore, from a concave surface more curved 
than either of the preceding. This surface is the posterior surface 
of the lens. These three images are called the Sanson-Purkinje 
images. The changes in size and position of these images may be 
utilised to prove that the curvature of the lens alters during accom- 
modation. For this purpose the observed eye shovfld first be accom- 
modated for a distant object and then for a near one, the reflected 
images being observed as the change occurs. It will be found that 
the first image remains unchanged, but that the second image becomes 
smaller and moves nearer to the first. This proves that the surface 
forming it, the anterior surface of the lens, becomes more convex. 
The movement towards the first image is due to two causes : firstly, 
that the anterior surface of the lens becomes more convex ; and 
secondly, that the anterior surface of the lens approaches a little 
nearer to the cornea. 

The third image is also found to change, but to a much less degree. 
It becomes a little larger, and appears to move further from the 
second. The apparent size and position of this image are, however, 
modified by the fact that it is viewed through the two surfaces of the 
cornea and lens ; and careful measurements of this image have shown 
that the changes observed are due, not to a change of curvature of the 
posterior surface of the lens, but to the change in the anterior surface 
through which it is viewed. 

The observation and measurement of these images are much facilitated 
by the phakoscope, an instrument devised by von Hehnholtz for that pur- 
pose. It consists (rig. 171) of a triangular box whose angles are cut off. At one 
angle two prisms, b and b' ', are fixed which, when illuminated, concentrate two 
beams of light upon the observed eye. At the opposite angle, ". is an aperture 



220 



EXPERIMENTAL PIIYSinUx; V 



for the observer's eye, and at the third another aperture through which the ob- 
served eye looks straight forward through an aperture above c. The observed 
first looks at a far object and the images are then noted, especially with re- 
^ = ^____ gard to their size and position. The images 

^a^l obtained are given in fig. 172 a. The two 

bright ones to the left are from the ante- 
rior surface of the cornea, the lower one 
being formed from b, the upper from V. 
The middle pair are much larger than the 
first, and the third pair are smaller than 
any, and inverted. Prove this by blocking 
b' with a card. The lower image of the 
right-hand pair and the upper images of 
the other two pairs disappear 

The observed eye is now accommo- 
dated for a near object by looking at a 
pin in the shutter c, when the images 




el I m 



Fig. 171.— The Phakoscope. 
(McKendrick.) 



Fig. 172. — The Reflected Images as seen in 
the Phakoscope : a, while the Eye is at Rest ; 
b, during Accommodation. (McKendrick.) 

change to those seen in b, fig. 1 72. The middle pair become smaller, lie 
closer to one another, and approach the first pair. The third pair separate a 
little from one another and become a little larger. 

The changes in the media of the eye, brought about during ac- 
commodation, are further illustrated by the following experiment, 
known as 

Scheiner's Experiment. — Take a long strip of wood, and to one end 
fix a card vertically, and pierce this with two fine pin-holes lying close 
together and on a horizontal line. They must be so near each other that 
they both lie within the diameter of the pupil. Fix two needles vertically 
on the wood, one about eight inches in front of the card, the other about 
twenty-four inches away. Close one eye and look through the pin-holes in 
the card at the two needles. 

1. Fix the eye upon the distant needle. A clear single image is obtained 
of this, but two blurred images of the nearer needle are at the same time ob- 
served. Now close the right-hand pin-hole, when the left-hand image of the 
near needle disappears. On closing the left-hand pin-hole the right-hand 
image disappears. 

2. In the second place look at the nearer needle, when a double image of 
the far needle will be observed. Now close the right-hand pin-hole, when 
the right-hand image disappears. On closing the left-hand pin-hole, the 
left-hand image disappears. 

The meaning of this experiment will become clear from a study of 



SCHEINER'S EXPERIMENT 



221 



fig. 173. i illustrates the condition of things in the first part of the 
experiment, c c 1 is the card, a and b the two pin-holes ; P is the far 
needle in transverse section, and r the near needle. The eye is 
accommodated for the far needle r, and the rays of light from it (e.g. 
the continuous lines of the figure) which pass through A and B meet 
on the retina at y. Hence there is a clear single image of P. The 
light from r (i.e. the interrupted lines of the figure) are not, with the 
position of the refracting surfaces, sufficiently refracted to meet on the 
retina, and consequently fall upon it in two patches at r 1 and r-. 
These are able, however, to give a moderately good image, because 
they are only formed from the rays passing through two minute 




Fig. 173. — To Illustrate Schkinek's Experiment. 



orifices, a andB. On now closing the left-hand pin-hole, a, the image 
at r 1 disappears. This lies on the retina to the left of the second 
image at r 2 . But the left half of the retina is normally concerned 
with objects lying to the right, and vice versa. Consequently the 
mind projects the image at r\ as if it were coming from an object to 
the right, and the image at r 2 as from an object to the left. Blocking 
a therefore causes the right-hand image to disappear, and blocking B 
the left-hand image. 

ii gives the condition of things for the second half of the experi- 
ment. The eye is accommodated for B, and the rays are more 



222 EXPERIMENTAL PHYSIOLOGY 

refracted than in the previous case. The rays from k meet accurately 
upon the retina at r, and produce a clear image there. The rays from 
p are more refracted, and meet at a point in front of the retina, cross, 
and impinge at two positions, p x and p 2 , upon the retina, where they 
give rise to the sensation of two images of the needle P indistinct and 
blurred. The image j? will be referred as coming from an object 
lying to the right of that caused by p l . On now blocking the left- 
hand pin-hole a the image formed by p l disappears. This is the 
left-hand image. Similarly on blocking the right-hand hole b the 
right-hand image due to p 2 disappears. 

The ophthalmoscope. — On looking at an eye the pupil always 
appears black. This is because most of the rays entering the eye 
are absorbed by the retinal and choroidal pigment, and those few 
which are reflected travel back along nearly the same path as that 
they took on entering the eye. To see any part of the interior of the 
eye, these reflected rays must enter the observing eye ; but as soon as 
the eye is placed to intercept them, it also blocks the course of the 
entering light. The first condition, then, is to be able to receive the 
reflected rays without at the same time intercepting the rays from the 
source of light. 

This is attained by the instrument invented by von Hehnholtz, 
the ophthalmoscope. The principle of this is to reflect light into the 
eye by a mirror in the centre of which is a small aperture through 
which the observer looks, and is thus able to receive some of the rays 
reflected from the interior of the observed eye. 

There are two methods of employing the ophthalmoscope, which are 
known as the indirect and direct methods respectively. 

I. The indirect method. — The person whose eye is to be examined is 
seated in a darkened room with a large steady flame placed a few inches 
from his head on his left side on a level with his eyes. For examining his 
right eye take the ophthalmoscope mirror in your right hand, and with the 
mirrortowards the observed eye look through the central aperture, with the 
right eye so that (with the left eye closed) you can see the observed eye 
clearly. Now open the left eye, and watching the position of the reflected 
light rotate the mirror until the reflected light is thrown on to the eye. Now 
tell him to look steadily at some object behind you at the other end of the 
room. The pupil will now become a bright red. Get him to move his eye 
in various directions and in one position, when it is turned a little inwards ; 
the red will change to a yellowish colour. This indicates the position of the 
optic disc. Now take the large biconvex lens in the left hand, holding it 
vertically about 2 to 3 inches from the eye, steadying your hand by resting 
your little finger on the temple. Your eye shoidd be about 15 inches from his. 
In this position an image of the fundus of the eye will be formed by the lens 
about 2 or 3 inches in front of it, i.e. about 10 inches from your eye, and you 
will be able to see this image, which if the observed eye have not been moved 
will be one of the optic disc. Most beginners find some difficulty in avoiding 
the reflection from the cornea and in adjusting the accommodation, and the 
distance of the head, so as to see the image clearly. The head must be 



THE OPHTHALMOSCOPE 



223 



slowly moved a little nearer to or further from the observed eye, and at the 
same time an attempt made to accommodate the eyes for a point between 
the observer and the lens. 

Fig. 174 gives diagrammatically the course of the light in this instance. 
E is the observed eye and m m the concave mirror with its central aperture, 




Fig. 174.— The Course of the Light in the Indirect Method of Employing 
the Ophthalmoscope. 



s a source of light the rays from which falling upon the mirror are reflected 
to form an image at 0. They then diverge, but are again condensed by the 
lens, and entering the eye, E, form a second image just behind the lens ; they 
then again diverge and diffusely illuminate the fundus oculi. The rays of 
light reflected from two points, i and m, on the fundus, diverging from the eye, 
are refracted by the lens to form an inverted real image, i l m l , larger than 
the object, i m. These latter rays then diverging are collected and focussed 
by the observing eye e 1 to form an image i 1 >ir on the retina. 

The indirect method of examination is most generally useful because it 
gives a large field of view under a low magnifying power (about five 
diameters). In the view obtained it must be remembered that all the parts 
are inverted, that seen to the right being from the left part of the fundus, 
and vice versa. 




Fig. 175.— The Course of the Light in Examining the Eve r.v the 
Direct Method. 

II. The direct method.— In this method the examination is made 'with 
the mirror alone, without the intervention of the biconvex lens. In tins 
method a small concave mirror is used, and is broujjhl as close as possible 
to the observed eye, which should be accommodated For distant vision. The 



224 EXPERIMENTAL PHYSIOLOGY 

reflected rays from any point of the fundus in a normal eye then emerge 
parallel, and the observer's eye should also be accommodated for distant 
vision in order that a clear image may be thrown upon his retina. As this 
latter is at first difficult and requires some practice, it will be found easier to 
insert a biconcave lens behind the aperture of the mirror to render the rays 
divergent, and then the observer accommodates until distinct vision is 
obtained. 

Fig. 175 shows the course of the rays of light when employing this 
method, s is the source of light and m m the mirror which reflects the rays 
of light, these are focussed by the eye being examined (e) to a point in 
the vitreous, and from this cause a diffuse lighting of the fundus. Rays of 
light issuing from a pointy emerge from the eye parallel to one another, and 
entering the observing eye e 1 are brought to a focus, p 1 , which lies on the retina, 
as the eye is accommodated for distant vision. Similarly a point m will give 
rise to an image at m 1 , and a point n at «'. 



HOLMGREN'S METHOD OF TESTING COLOUR VISION 

In this method a large number of sample skeins of worsteds of 
different colours and shades of colour are employed. The colours 
include reds, oranges, yellows, yellowish greens, pure greens, blue 
greens, blues, violets, purples, pinks, browns, and greys. The method 
of testing consists in picking out one of the skeins and requesting the 
subject to be tested to select skeins from the pile which resemble it in 
colour. No two skeins are alike, so that the examinee is to pick out 
skeins which appear of the same colour, though they may be lighter, 
or darker, or of nearly the same shade. 

When testing for colour blindness the following plan is recom- 
mended. A pale green, a purple, and a red skein are chosen and 
are termed test skeins. 

I. The green skein is first picked out. This skein should be the 
palest shade of pure green, which is neither a yellow green nor a 
blue green. The examination is continued until the examinee has 
picked out all the other skeins of the same colour, or else placed 
with them one or more skeins of what are termed the confusion 
colours. These confusion colours which a colour-blind person will 
thus pick out are of various tints, according to the amount of his 
defect. Thus there may be greys, light reds, or light purples. The 
fact that any confusion colour is picked out is sufficient to show that 
he is colour blind. To determine the kind and degree of colour 
blindness the next test skein is given. 

II. This is a purple skein, and should be midway in colour 
between the lightest and darkest purple in the heap. The test is 
continued until the examinee has picked out all the purples, or until 
certain confusion colours have been selected. 



THE PERIMETER 



225 



A person who has been proved colour blind by the first test, but 
who only selects purples in the second, is incompletely colour blind. 

If he select with the purples blue and violet, he is completely red 
blind. 

If he select with purple only green and grey, he is completely 
green blind. 

As a final and confirmatory test, the third test skein is presented. 

III. This is a bright red skein of medium shade tending rather 
to a yellowish red. 

The red-blind person chooses with the reds, greens and browns 
of darker shade than the skein presented. 

The green blind chooses with the reds, greens and browns of 
lighter shade than that of the test skein. 



PERIMETRY 

When we wish to carefully examine any object we turn our eyes 
to such a position that the image of the object falls upon the fovea 
centralis. This is termed direct vision. The vision produced by 
images formed on the peripheral parts of the retina is in contradis- 
tinction termed indirect vision. Indirect vision is much less acute 
than direct, but still the periphery of the retina is capable of appre- 
ciating movements or changes in intensity of light falling upon it. 

In order to test the limits 
of indirect vision the peri- 
meter (fig. 176) is employed. 
This consists of a vertical 
pillar carrying a horizontal 
axis which bears on one side 
a circular arc and on the 
other a vertical disc to which 
a chart can be fixed. A little 
holder can be moved along 
the arc into any position. A 
second support terminating in 
a knob is provided, against 
which the cheek is held about 
an inch below the centre of 
the eye to be tested. The 
opposite eye is then closed, 
and the other one fixed in 
position by looking steadily 
at a white knob in the centre 
of the axis of the instrument. 
A chart is next fixed in posi 




Fig. 170. 



-Priestley-Smith's Perimeter. 
(Halliburton.) 



tion in the vertical disc, and first a white square held in the carrier on the 
rotating arc. This is moved from the periphery towards the centre until it 
is clearly observed, and its position then marked upon the chart. The arc 

Q 



226 



EXPERIMENTAL PHYSIOLOGY 



is then moved into a fresh meridian and a fresh observation taken, and so 
on until a series of points have been mapped out upon the chart which lie 
on the limit of distinct vision. These are united by a curved line, such as the 
dotted line in fig. 177, which represents the normal average field of vision for 
white light for the right eye. 

Having determined this for a white object, next determine similar lines 
for coloured objects. 

For the white object it is seen that the field of vision extends more 




100 



100 



180 
Fig. 177. — A Perimetric Chart for the Right Eye. (Hallirurton.) 



to the outer than to the inner side, and further above than below the 
horizontal meridian. 

In the case of colours it will be found that the capacity for distin- 
guishing them diminishes more rapidly at the periphery than is the 
case for white light. 

The field of vision is more extensive for blue than for other 
colours ; it is least extensive for green and intermediate for red. 



INDEX 



Absolute force of muscle, 52 
Acceleration of heart by sympathetic, 

126 
Accomodation, 218 
After-load, 42 

Ammonia, excitation of muscle by, 78 
Anelectrotonus, 88 
Anodic contraction, 80 
Anterior root of spinal nerve, function 

of, 86 
Apex-time in isometric curves, 42 
Artificial respiration apparatus, 138 
Asphyxia, action of heart during, 144 

— changes in blood-pressure during, 
182 

Atropine on frog's heart, 131 

Batteries, 1, 2, 3 
Beat of heart, record of, 98 
Bernard's curare experiment, 76 
Biedermann's fluid, 103 
Blood-flow, velocity of, 188 
Blood-pressure, arrangement of appa- 
ratus for, 168 

— effect of asphyxia, 182 
nicotine, 181 

stimulation of depressor nerve, 

175 
of vagus, 177, 186 

— mean general, 182 

— normal tracing, 172 

Brain, behaviour of frog when its brain 

is destroyed, 214 
Break, extra-current, 14, 19 
Break-key, 30 
Break-shock greater than make-shock, 

14,18 
Bunsen battery, 2 

Caffeine citrate, action upon the heart, 
143 

— upon the kidney, 195 

Cannula, arterial, 170 

— perfusion, 136 



Capillary electrometer, 154 
Cardiogram, 145 
Cardiograph, Marey's, 144 
Chemical stimulation of nerve, 86 
Chorda tympani, dissection of, 211 

stimulation of, 212 

Chronogram, 22 
Chronograph, 23 
Circulation, schema of the, 157 
Coil, induction, 4 
Colour-blindness, 225 

— vision 224 
Commutator, Pohl's, 12 
Conductivity of nerve, changes during 

electrotonus, 90 
Constant current, action on nerve, 87 

excitation of muscle by, 79 

Contact key, 10 
Contraction, Law of, 93 

— paradoxical, 158 

— period, 33 

— secondary, 148 

— wave in muscle, 73 

— with metals, 147 

— without metals, 147 
Contractur, 67 

Convulsions, effect upon blood-pressure, 

182 
Crank lever, 26 
Crescent in frog's heart, 98 

— stimulation of, 125 
C-spring manometer, 183 
Curare, effect on muscle, 76 
Current, constant, action on nerve, 87 

— of action of muscle, 151 

— of injury, 151 

— of rest, 146 
Cut-out key, 13 
Cylinder, recording, 24 



Daxiell battery, 1 

Depressor nerve, action of, 175 

anatomy of, 170 

Dicrotic notch and wave, 165 



228 



EXPERIMENTAL PHYSIOLOGY 



Digitalin, action on mammalian heart, 
143 

on kidney, 198 

Direct excitation, 18 

— vision, 225 

Du Bois-Beymond's key, 11 

Dudgeon's sphygmograph, 166 

Dyspnoea, effect upon blood-pressure, 182 



Electrical stimulation of nerve, 87 
Electrodes, polarisation of, 81 

— simple flexible, 106 
wire, 26 

— unpolarisable, 83 
Electrometer, capillary, 154 
Electro-physiology, 146 
Electrotonus, 88 
Engelmann's experiment, 81 
Excitability, changes of, in electro- 
tonus, 88 

— independent muscular, 76 
Excitation, direct and indirect, 18 

— maximal and minimal, 26 

— polar, of muscle, 80 

— — of nerve, 90 

— unipolar, 28 
Extra-current, causation of, 6 

— break, 14, 19 

— make, 19 



Fatigue of muscle, changes in height 

of twitch, 69 

study of, 66 

Fick's manometer, 183 

Field of vision for colour, 227 

Force, absolute, of muscle, 52 

— of heart-beat, decrease of, by vagus, 

122 
increase of, by sympathetic, 

127 
Forceps, muscle, 25 
Friction-key, 11 



Galvani's experiment, contraction with 
metals, 147 

without metals, 147 

Galvanometer, 149 

Gastrocnemius preparation, 16 

Genesis of tetanus, 59 

Glosso-pharyngeal, action on respira- 
tion, 203 

Gracilis and semimembranosus pre- 
paration, 19 

Graphic method, 21 

Green blindness, 225 

Grenet battery, 2 

Grove batterv, 3 



Heart (frog's), anatomy of, 97 
— action of atropine on, 131 

■ muscarine on, 130 

— nicotine on, 133 

pilocarpine on, 131 

— — temperature, 112 

currents of, 153 

current of action of, 149 

excision of, 101 

■ Luciani's groups, 137 

— ■ minimal stimulus causes maximal 
contraction, 105 

— nerves of, 120 

— plethysmography record of, 135 

— rate of beat, 98 

— record of beat, 98 

— rhythm of, 102, 103 

— stimulation of crescent, 125 

Heart (mammalian), action during 
asphyxia, 144 

of caffeine on, 143 

— ■ — of digitalin on, 143 

of neurine on, 144 

of vagus on, 141 

— recording movements of, 140 
Helmholtz modification, 9 
Helmholtz's phakoscope, 219 
Holmgren's worsteds, 224 
Hiirthle's manometer, 184 
Hyoglossus preparation, 20 



Images formed by reflection from curved 

surfaces, 218 
Independent muscular excitability, 76 
Inertia, effect of, on single twitch, 37 
Impulse, nervous, velocity of, 94 
Indirect excitation, 18 

— vision, 225 
Induction coil, 4 

Inhibition of frog's heart by vagus, 
123 

— of heart by muscarine, 130 

— of reflexes, 217 
Injection, intravenous, 181 
Injury, current of, 151 
Irradiation of reflex movements, 216 
Irritability, independent muscular, 77 
Isometric contraction, 39 

— lever, 40 

— muscle-curves, 41 
Isotonic contraction, 39 



Katelectrotonus, 88 
Kathodic contraction, 80 
Key, break, 30 

— cut-out, 13 

— du Bois, 11 

— friction, 11 



INDEX 



229 



Key, mercury, 10 
— ■ spring, 10 

— trigger, 54 

Kidney, course of vaso-motor nerves to, 

200 
Kidney-volume, action of caffeine on, 

195 

of digitalin on, 198 

of neurine on, 198 

— normal tracing, 194 
Kronecker's frog-heart manometer, 137 
Kuhne's curare experiment, 78 
Kiihne's experiment of contraction with- 
out metals, 147 

— sartorius experiment, 77 



Laryngeal, superior, action on respira- 
tion, 202 
Latent period of muscle contraction, 33 

of reflex action, 216 

Law of contraction, 93 

Leclanche battery, 3 

Leg-muscles of frog, 17 

Lever, crank, 26 

— simple, 25 

Load, influence of, on single twitch, 48 

Luciani's groups, 137 

Ludwig's stromuhr, 187 



Make, extra-current, 6, 19 

— - shock less than break-shock, 14, 18 

Manometer, 158 

— Fick's, 183 

— Hurthle's, 184 

— Kronecker's frog-heart, 137 

— mercury, 171 
Marey's pneumograph, 206 

— sphygmograph, 164 

— tambour, 28 
Maximal excitation, 26 
Mechanical stimulation of nerve, 86 
Mercury key, 10 

Minimal excitation, 26 
Moist chamber, 18 
Monochord, 91, 92 

Muscarine, action on frog's heart, 130 
Muscle, excitation by constant current, 
79 

— fatigue of, 66 

— forceps, 25 

— iso-electric when normal, 147 

— less excitable than nerve, 77 

— of frog's leg, 17 

— simple curve, 34 

— ■ thickening of, during a twitch, 71 

— wave of contraction, 73 
rate of, 75 

Muscular excitability, independent, 76 



Neee's hammer, 8 
Negative variation, 146 

nature of, 148 

Nerve, action of constant current on, 87 

— changes of conductivity during elec- 
trotonus, 89 

of excitability during electrotonus, 

88 

— forms of stimuli for, 86 

— functions of, 85 

— more excitable than muscle, 77 
Nerve-muscle preparation, 16 
Nerve-cells, submaxillary, paralysed by 

nicotine, 212 
Nerves of rabbit's neck, 170 

— to frog's heart, 120 
Nervous impulse, velocity of, 94 
Neurine, action on kidney, 198 

on mammalian heart, 144 

Nicotine, action on frog's heart, 133 
on submaxillary gland, 212 

— effect on blood-pressure, 181 
Non-polarisable electrodes, 83 

Oncograph, 191 
Oncometer, Roy's, 189 

— air, 191 
Ophthalmoscope, 222 

Paradoxical contraction, 156 

Pendulum myograph, 53 

Perfusion cannula for frog's heart, 136 

Perimeter, 225 

Period, latent, 33 

— of contraction, 33 

— of relaxation, 33 
Pfliiger's law, 93 
Phakoscope, 219 
Pilocarpine on frog's heart, 131 
Pithing a frog, 16 
Plethysmography Schiifer's frog-heart 

136 
Plethysmography method for frog's 

heart, 135 
Pneumograph, Marey's, 206 
Pohl's commutator, 12 
Polar excitation of muscle, 80 

— — of nerve, 90 

— — Biedermann's method, Hi 

— — Engelmann's method, 81 
Polarisation of electrodes, 81 
Posterior root of spinal nerve, function 

of, 85 
Potential, measurement of, 152 
Pressor effect, 176 
Pressure bottle for manometer, 171 
Primary coil, 4 
Pulse-wave as studied on the schema, 

162 



230 



EXPERIMENTAL PHYSIOLOGY 



Pulse-wave in man, 165 
Purkinje-Sanson images, 210 

Rate of heart-beat, 98 

— of muscle-wave, 75 

— of work in simple twitch, 35 
Recording cylinder, 24 

— tambour, 28 

— time, 22 
Red-blindness, 225 
Reed, vibrating, 60 
Reflex action, 214 
Reflexes, inhibition of, 217 

— irradiation of, 216 

— purposive character of, 216 
Reflex time, 216 
Refractory period of heart, 108 
Relaxation period, 33 

Respiration, action of central end of 
vagus, 206 

— action of the glossopharyngeal, 203 

— effect of swallowing upon, 203, 208 

— methods of recording, 201 

— result of section of the two vagi, 203 
Respiratory movements, effect on blood- 
pressure, 173 

Rheochord, 92 

Rhythm of heart, 102, 103 

effect of heat upon, 113 

Ritter's tetanus, 87 

Roots of nerve, functions of, 85 

Salivary gland, secretory nerves to, 212 

— secretion, 209 
Sanderson's stethometer, 207 
Sanson-Purkinje images, 219 
Schemer's experiment, 220 
Schema of the circulation, 157 

action of elastic tube, 161 

Sciatic nerve, effect of stimulation of, 

upon blood-pressure, 175 
Secondary coil, 4 

— contraction, 148 
Secretion of saliva, 209 
Semimembranosus and gracilis prepara- 
tion, 19 

Shunt of galvanometer, 150 
Slowing of frog's heart by vagus, 123 
Sphygmogram, 165 167 
Sphygmograph, Dudgeon's, 166 

— Marey's, 164 

Spinal cord, study of reflex action in 

214 
Spring chronograph, 24 

— key, 10 
Staircase-effect, in heart, 105 

— — in muscle, 63, 69 
Stannius ligature, the first, 104 
the second, 128 



Stethogram, 208 

Stethometer, Sanderson's, 207 

Stimulation, unipolar, 28 

Stimuli for nerve, 86 

Stromuhr, 187 

Strychnine, action on spinal cord, 217 

Submaxillary gland, secretion by the, 
209 

Submaximal excitation, 27 

Summation of muscular contraction, 56 

Superior laryngeal, action of, upon the 
respiration, 202 

Supra -renal extract, effect upon blood- 
pressure, 182 

Suspension method of recording heart- 
beat, 98 

Swallowing, effect of, upon respiration, 
203, 208 

Sympathetic, action on heart, 125, 126 

on submaxillary gland, 212 

— course of fibres to frog's heart, 121 



Tambour, 28, 29 

Temperature, influence of, upon a single 
muscle-twitch, 44 

a single beat of the heart, 116 

upon the frog's heart, 112 

Tetanisation of frog's ventricle, 110 
Tetanus, complete, 64 

— fatigue during, 70 

— genesis of, 59 

— Ritter's, 87 

Thermal stimulation of nerve, 86 
Thickening of muscle during a twitch, 

71 
Time, measurement of, 22 
Tonometer, Roy's, 135 
Trigger-key, 54 
Twitch, simple, 30 

— thickening of muscle during a, 71 

— modified by fatigue, 67 



Unipolar excitation, 28 
Unpolarisable electrodes, 83 

Vagus, action of central end upon re- 
spiration, 206 

on heart, frog's, 122 

mammalian, 141 

— course of, to frog's heart, 120 

— effect of section upon respiration, 
203 

— — of stimulation upon blood-pres- 
sure, 177 

— inhibition, escape of heart from, 
179 

Varnish for tracings, 32 



INDEX 



231 



Vaso-motor nerves to kidney, 200 
Velocity of nervous impulse, 94 

— of the blood-flow, 188 
Ventricle contraction, 107 

effect of heat, 116 

of tetanisation, 110 

— — — of two stimuli, 109 
Veratrine, influence of, on muscle, 

49 



Vibrating reed, GO 

Vision, direct and indirect, 225 

Wave of contraction in muscle, 73 

— pulse, studied on schema, 162 
Work performed during a twitch, 34, 50 

— in simple twitch, rate of, 35 

— variation in amount with different 
loads, 51 



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