1906.] 



Special Excitable Substances in Cells. 



183 



stimulated at all by nicotine. Since the contraction caused by a single 

 electrical stimulation of the nerve is a quick contraction, it would naturally 

 follow that it is due solely to the fibrillae. Thus one or other of the two 

 contractile substances would come into action alone. But if the stimulating 

 action of nicotine is solely in the sarcoplasm, we should naturally conclude, 

 in accordance with the argument given above, that its paralysing action is 

 also solely on the sarcoplasm. In this case we should have to conclude 

 that the sarcoplasm normally transmits the stimulus caused by a single 

 electrical stimulation of the nerve without itself contracting, but does not 

 transmit the stimulus caused by nicotine though it does itself contract. 

 This conclusion presents great though perhaps not insuperable difficulties. 



If, in consequence of these difficulties, we take the view that the nicotine 

 causes contraction of the fibrillae and not of the sarcoplasm, there are two 

 possibilities : the receptive substance may be part of the sarcoplasm, or it 

 may be a radicle of the contractile molecule. 



It might be urged in favour of the former view that according to Kuhne 

 the nerve ending is in some cases completely separated from the fibrillae by 

 sarcoplasm. On the other hand, even if a thin layer of sarcoplasm does 

 intervene between nerve and muscle, it does not necessarily follow that it 

 takes any essential part in the passage of the stimulus. 



On the latter view it is clear that the contractile molecule must either 

 have at least one receptive radicle in addition to that affected by nicotine 

 and curari, or it must be capable of direct stimulation. The hypothesis, 

 however, demands that the stimuli passing by the nerve cannot affect the 

 contractile molecule except by the radicle which combines with nicotine and 

 curari. And this seems in its turn to require that the nervous impulse 

 should not pass from nerve to m.uscle by an electric discharge, but by the 

 secretion of a special substance at the end of the nerve, a theory suggested 

 in the first instance by du Bois Beymond. 



Lastly it is to be noted that whether the receptive substance is part of the 

 sarcoplasm or part of the fibrillae, it remains to determine whether the 

 receptive substance is localised in the immediate neighbourhood of the nerve 

 ending or exists throughout the lengtli of the muscle fibre. The observations 

 of Kiihne and Bollitzer (quoted above) on the different irritability of the 

 nerve-containing and nerve-free parts of the muscle afford some evidence for, 

 at any rate, unequal distribution, but the main question can, I think, only 

 be settled by experiments on the effect of local application of nicotine such as 

 I have to mention presently. 



In the preceding statement, the view that curari and a number of other 

 poisons act on muscle has been placed in sharp antagonism with the view 



