I5 2 THE ELECTRICAL PHENOMENA OF MUSCLE. [CH. xn. 



It is in this sense only that an injured or active part of a muscle is negative. 

 To obviate the difficulty created by this mistake which has crystallised in 

 physiological writings. Waller has suggested new terms, viz., zincactive and 

 zincable, instead of negative and positive respectively. 



The Rheoscopic Frog. 



The electrical changes in muscle can be detected not only by 

 the galvanometer and electrometer, but also by what is known as 

 the physiological rheoscope ; this consists of an ordinary muscle- 



Fig. 176. Galvani's experiment without metals. 



nerve preparation from a fresh and vigorous frog. The nerve is 

 stimulated by the electrical changes occurring in muscles, and 

 the nervous impulse so generated causes a contraction of the 

 muscles of the rheoscopic preparation. The following are the 

 principal experiments that can be shown in this way : 



i. Contraction without metals. If the nerve of a nerve-muscle 



Fig. 177. Secondary contraction. (After Waller.) 



preparation A is dropped upon another muscle B (fig. 176) (or 

 upon its own muscle) it will be stimulated by the injury current 

 of the muscle on which it is dropped, and lead to a contraction of 

 the muscle (A) which it supplies. The experiment succeeds best 

 if the nerve is dropped across a longitudinal surface and a freshly 

 made transverse section. 



2. Secondary contraction. This is caused by the current of action. 

 If, while the nerve of A is resting on the muscle B (fig. 177), the 

 latter is made to contract by the stimulation of its nerve, the 

 nerve of A is stimulated by the electrical variation which accom- 

 panies the contraction of the muscle B, and so a contraction of 



