136 GENERAL PROPERTIES OF LIVING TISSUES 



most or quite simultaneously throughout the 

 nerve. Eanvier states that it begins first in the 

 end plates. Severed nerves in the brain and 

 spinal cord degenerate in the same way, and this 

 " Wallerian degeneration " (Waller, 1850) is a 

 valuable aid in tracing the path of nerve fibres 

 in the central nervous system. Degeneration is 

 accompanied by changes in the reaction to the 

 electric current which form a valuable aid in the 

 diagnosis of the seat of the lesion in cases of 

 paralysis. The muscle reacts imperfectly, or not 

 at all, to the brief induction current, while its 

 reaction to the long galvanic current may even 

 be greater than usual. 



Expose each gastrocnemius muscle in a frog, 

 the left sciatic nerve of which has been severed 

 ten days before this experiment. Stimulate each 

 muscle with weak induction currents and with 

 the galvanic current. 



The muscle, the nerves of which are degen- 

 erated, reacts more readily to the galvanic current 

 than to the brief induction current. The normal 

 muscle shows the opposite reaction. 



In man, the reaction of degeneration in the 

 case of muscle consists of a lessened or lost 

 excitability to the induced current with increased 

 excitability to the galvanic current. The duration 

 of contraction may be greater than normal. In 



