A.SYMMI-JTinv A^ALYSI^S 121 



tive "receptive substance" wliicli is tlie tirst to be af- 

 fected by nicotme. 



On tile other hand, since the cUissical works of Loewi, 

 it is known that, in the transmission of impulses from 

 nerves to effectors the various steps are as follows (1) 

 nerve impulse — ^ (2) chemical mediator — ^ (3) receptive 

 substance — v (-t) specific response (for literature see 

 Cannon and Eosenblueth, 1937). There are some indi- 

 cations that the chemical mediator in the voluntary mus- 

 cles of higher animals is acetylcholine. Its action on the 

 receptive substance in this case reminds one of that of 

 nicotine: in small doses it excites, and in larger doses it 

 paralyses, and according to the current views, nicotine, 

 in case of an acute poisoning, atfects in some irreversible 

 way the receptive substance, upon which acetylcholine 

 mediation is no more effective. In other words, nicotine 

 (at least in experiments of our type) acts upon neuro- 

 effector synapses of voluntary muscles. In its action it 

 reminds one of acetylcholine, the substance which trans- 

 mits the excitation in these synapses. Consequently the 

 receptive substance in nicotine poisoning has some close 

 relation to the receptive substance for chemical media- 

 tion. 



The experiments just described permit one to divide 

 the animals into two groups according to the nature of 

 the receptive substance atfected by nicotine. It might 

 be that animals possessing a receptive substance differ- 

 entially atfected and those possessing a receptive sub- 

 stance identically affected by optically isomeric nicotines 

 ditfer also in their receptivity to the normal chemical me- 

 diator, and consequently in peculiarities of the transmis- 

 sion of nerve impulses. 



An examination of the data on the distribution of 

 acetylcholine in different groups of invertebrates will 

 throw a new light on this problem. Despite the often 

 questionable findings concerning the presence of this 

 substance which is ascertained bv the action of extracts 



