146 THE SIGNS OF LIFE [ LE ct. 



i.e., more capable of that electro-positive change which is the 

 essential factor of a blaze-current, and is aroused to action by 

 the direct stimulus of an induction shock whatever its direction. 



84. Solution-pressure. I will bring these lectures to a 

 conclusion with certain theoretical views to which slight allusion 

 was made in the first lecture (p. 16). 



I there attempted to account in some measure for the use of 

 the term " zincative," and promised, when an opportunity should 

 present itself, to formulate on similar lines a view of the 

 mechanism of excitatory phenomena in general. 



You are familiar with the idea that active tissue gives off 

 electro-positive ions to its lymph bath, that in the tissue itself 

 there is current of action from active to resting spot, that active 

 tissue is zincative. You also know that in the electrical excita- 

 tion of nerve and of muscle, the effective pole is the kathode, 

 when current is made, the anode when current is broken. And 

 you know that while a constant current is passing there is 

 augmented excitability by the kathode, diminished excitability 

 by the anode. 



I take the case of medullated nerve, since the results are 

 typical. Moreover, its coarse structure of central core as the 

 essential part and surrounding sheath as the accessory part, 

 which is a familiar image in everyone's mind, will help us to 

 form a clear picture of what can be imagined as the actual 

 movements of ions between any core of living stuff and any 

 surrounding medium. (A word of warning, however this is only 

 a coarse picture, there is no doubt a peculiar commerce of ions 

 between axis-cylinder and medullary sheath of a nerve-fibre, 

 but there is probably a further and more refined commerce 

 of ions between fibrils and fluid within the axis-cylinder 

 itself.) 



Consider then a core of living stuff, bring it in contact with 

 an electrode, and let the latter be suddenly made kathodic by 

 closure of a contact key in the circuit. The core of living stuff 

 has been aroused to action. What have been the movements of 

 ions when the electrode was made kathodic ? 



Clearly, there must have been movement of kations towards 



