IRRITABILITY. 459 



The explanation of these secondary contractions would seem 

 to be that the current passes through the first preparation into the 

 second ; but if the nerve of the second is tied, the secondary con- 

 traction does not take place, so that this explanation is not a true 

 one. Du Bois Reymond's explanation is that each stimulus applied 

 to the first nerve causes a contraction of its muscle and a current 

 of action, which stimulates the nerve of the second preparation, 

 and a contraction of its muscle follows. 



