194 Nerve Endings and Special Excitable Substances in Cells. 



lysing nerve endings. Eeasons, though less complete, have been given for 

 supposing that these poisons have no special action on nerve endings, and 

 that physiologically the nerve ending is not essentially different from the 

 nerve-fibre. In that case not only the function of reacting to numerous 

 chemical bodies, but probably also the special liability of both afferent and 

 efferent nerves to fatigue must be transferred from the nerve endings to the 

 same constituent of the cell. 



This theory adds to the complexity of the cell. It necessitates the 

 presence in it of one or more substances (receptive substances) which are 

 capable of receiving and transmitting stimuli, and capable of isolated 

 paralysis, and also of a substance or substances concerned with the main 

 function of the cell (contraction or secretion, or, in the case of nerve cells, of 

 discharging nerve impulses). So far as this is concerned, it does but 

 accentuate a view which has often been put forward and which indeed in 

 some form or other is inseparable from the idea of protoplasm. 



I have spoken of different " substances " in the cell with the intent to use 

 as vague a term as possible. The " substances," I take it, are radicles of the 

 protoplasmic molecule. At present, however, I do not think it advisable to 

 speculate further either on this question or on certain other questions raised 

 by the conclusions arrived at in the paper. There are a number of obvious 

 experiments still to be made, and these, it may be hoped, will settle some of 

 the problems, the solution of which is now but guess work. 



