84 



THE SIGNS OF LIFE 



[LECT. 



So that, in sum, while pointing to the conclusion that 

 there is, as regards the external cover of an animal body, 

 an outgoing organ-current of action, the facts forbid us to 

 rest content in an exclusive conclusion of such simplicity, and 

 we are obliged to admit that a cutaneous organ-current, even if 

 it really exists by reason of a general functional and structural 

 organisation of the integument, is twisted and obscured by other 

 accessory and complicating conditions. 



Let us, however, imagine how things might have been. The 

 fancy will, if nothing else, remind us of facts, and make us 

 curious for further facts. The facts let me reiterate them once 

 more are that the skin, when first placed on the electrodes, 

 gives an ingoing current which increases, and that excitation of 

 either direction gives an outgoing response which diminishes. 

 The former is " current of rest," the latter " current of action." 



51. A speculation. A lump 9f protoplasm, at rest and 

 homogeneous throughout, is iso-electric throughout ; let it be 



FlG. 38. Indirect responses of a pad of a cat's paw to single induction shocks 

 exciting the sciatic nerve, before and after : 



D, = direct excitation of the pad by one strong break shock. 

 D = ,, by two strong break shocks. 



D a : ,, by tetanisation for 5 seconds. 



D 4 = ,, by tetanisation for 15 seconds. 



It is somewhat surprising that direct excitation should have produced a 

 greater diminution of the indirect response in the frog than in the cat. But 

 in the former case the indirect response was elicited by tetanisation of the 

 'nerve, while in the case of the cat, the nerve was excited by single strong 

 shocks. The regular effects (on the skin glands) of such stimulation are in 

 themselves sufficiently remarkable ; their true physiological character was 

 proved by the long interval between each excitation and response about 

 3 seconds. 



