CHAP, ii.] THE CONTRACTILE TISSUES. 155 



prominent that some have been tempted to regard a nervous impulse 

 as essentially an electrical change. But it must be remembered that 

 the actual energy set free in a nervous impulse is, so to speak, in- 

 significant, so that chemical changes too slight to be recognized by 

 the means at present at our disposal would amply suffice to provide 

 all the energy set free. On the other hand, the rate of transmission 

 of a nervous impulse, putting aside other features, is alone sufficient 

 to prove that it is something quite different from an ordinary 

 electric current. 



The curious disposition of the end-plates, and their remarkable 

 analogy with the electric organs which are found in certain animals, 

 has suggested the view that the passage of a nervous impulse from 

 the nerve fibre into the muscular substance is of the nature of an 

 electric discharge. But these matters are too difficult and too 

 abstruse to be discussed here. 



It may however be worth while to remind the reader that in 

 every contraction of a muscular fibre, the actual change of form is 

 preceded by invisible changes propagated all over the fibre and 

 occupying the latent period, and that these changes resemble in 

 their features the nervous impulse of which they are, so to speak, 

 the continuation rather than the contraction of which they are the 

 forerunners and to which they give rise. So that a muscle, even 

 putting aside the visible terminations of the nerve, is fundamentally^ 

 a muscle and a nerve besides. 



