210 



PHYSIOLOGY OF MUSCLES AND NERVLS. 



If the nerve of the muscle B is then irritated, either by 

 closing or by opening a current, by an inductive shock, by 

 scission, by pressure, or in any other way, the muscle A 

 is observed to pulsate also. This is called second- 

 ary pttlsation. The explanation is easy. The muscle- 

 current from B during its pulsation suffered a negative 

 variation. This variation took place also in that por- 

 tion of the current which passed through the applied 

 nerve ; and, as every nerve is irritated by sudden change 



FiQ. 57 & 58. Secondahy PULSATrON. 



in the strength of the current, the result was a secon- 

 dary pulsation. 



A variation of this experiment is very interesting. 

 The heart of a frog continues to beat for some time 

 after it has been extracted from the body. If the nerve 

 of a muscle is placed on this heart so as to touch its 

 base and point, the muscle pulsates at every beat of 

 the heart. In this case, the heart-muscle affords the 

 muscle-current, the negative variation of which irritates 

 the applied nerve and causes secondary pulsation. 



' pulsation without metals ' (^ZucliUfffi oJn/e Mehdlc) which lias 

 gained celebrity from the writings of Volta, Humboldt, and others. 



