ADVANCED EXPERIMENTAL PHYSIOLOGY 117 



by injury is, as Gotch pointed out, to be considered as a current 

 of action. These facts can be demonstrated by the following 

 experiments. 



The Rheoscopic Frog. Galvani's Experiment, Contraction without 

 Metals. A long length of the sciatic nerve is dissected in a pithed 

 frog and the muscles of the thigh are ex- 

 posed and cut across. The trunk of the 

 sciatic nerve is laid along the longitudinal 

 surface of the muscles of the thigh, and 

 then by raising the end of the nerve by a 

 small glass rod the transverse section of the 

 nerve is allowed to fall upon the cut sur- 

 face of the muscles (Fig. 116). At this 

 moment a twitch of the muscles of the leg 

 moves the foot or toes. The circuit of the 

 electric current in the muscle has been 

 completed through the nerve. The section 

 of the muscle-fibres has produced a local 

 contraction of the fibres, and this is accom- 

 panied by an electrical change which is 

 sufficient to produce excitation when it is 

 passed through an excitable nerve. 



Secondary Contraction or Secondary Twitch. 



Two muscle- and nerve-preparations are 

 made ; the nerve of A is so placed upon 

 the muscle B that the cut surface of the nerve lies upon the tendon 

 and its longitudinal surf ace upon the muscle-fibres (Fig. 117). The 

 nerve of preparation B is stimulated by a weak induction- shock, 



and thus its muscle is ex- 

 cited and made to contract ; 

 the muscle A will also con- 

 tract. The contraction of 

 the muscle B is accom- 

 panied by an electrical cur- 

 rent, the " current of action," 

 which passes through the 

 nerve A and thus produces 

 a contraction in the muscle 

 A. This is not due to an 

 escape of electrical current 

 from the electrodes, for a 

 secondary twitch can be 

 obtained if mechanical or 

 thermal stimuli be used to 



excite the nerve of preparation B. Further, ligature of the nerve 

 B with a moist thread will show that there is no escape with a 

 weak induction-shock ; the ligature destroys the physiological 

 continuity and prevents the passage of the excitatory state but 

 not that of an electrical current. 



FIG. 116. Diagram of 

 Gal vani ' s experi - 

 ment. Contraction 

 without metals. 



FIG. 117. Diagram of the experiment on 

 secondary twitch. 



