1906.] 



Special Excitable Substances in Cells. 



193 



of adrenalin and of chrysotoxin on tissues which have a double nerve supply, 

 but the evidence cannot be regarded as conclusive. 



In order to account for the special relation of adrenalin to the sympathetic 

 system, Elliott supposes that the excitable substance of the myo-neural 

 junction is formed in consequence of the union of the nerve with the muscle 

 and not in virtue of any inherent property of the muscle. The central point 

 of this theory is clearly applicable whether there is union or only contact of 

 nerve and muscle, and there is much that is attractive in the view that 

 the receptive substance owes its formation to the nerve, but it does not, 

 I think, satisfactorily account for the different degree of action of adrenalin 

 and chrysotoxin on the receptive substance in different cases,* nor for the 

 persistence of the substance after nerve degeneration. If the receptive 

 substance were formed in the muscle solely in consequence of its connection 

 with a nerve, it seems most unlikely that the muscle would be able to take 

 on the formation when the nerves have disappeared. 



The view I take is that the relation of poisons in general to special 

 systems of nerves depends upon the developmental history of the connection 

 of the different systems with the particular tissues. It seems to me certain 

 that the various cells of the body have a constant tendency to vary in 

 chemical composition, and it is probable that these variations in any one 

 tissue are approximately the same at the same time.f It is fairly certain 

 that different systems of nerves establish nervous connections with the cells 

 at different periods of phylogenetic development, and it is probable that 

 when nervous connection is made it tends to make permanent certain of the 

 chemical conditions existing at the time. 



Thus the different systems of efferent nerves would chiefly, at any rate, 

 owe their differences to the different characters of the " receptive " substances 

 of the cells with which they have become connected.* 



General Conclusions. 



In the foregoing account we have seen reason to believe that in each of 

 the three great types of connection of the peripheral end of an efferent 

 nerve with a cell it is some constituent of the cell substance which is 

 stimulated or paralysed by poisons ordinarily taken as stimulating or para- 



* Cf. Langley, ' Journ. of Physiol.,' vol. 33, p. 408, 1905. In this paper I have also 

 considered the action of some other alkaloids which bear on the question, such as those of 

 Anderson on the action of atropine, pilocarpine, and eserine on the denervated pupil. 



t A difference in the time of development of the sympathetic nerves to the skin and of 

 those to the viscera might account for the different degree of action of poisons on the 

 tissues innervated by the two sets of nerves. 



% Some inferences from this theory I have given in the paper quoted above. 



