NERVOUS TRANSMISSION 101 



light, unlike the glass rod, can so stimulate the surface of 

 an actinian that the subjacent nerve-net will call into 

 action only that group of the longitudinal mesenteric 

 muscles that lies close at hand and hence the nerve-net 

 exhibits under a more normal form of stimulation a type 

 of response much more delicate in character than what is 

 seen when a glass rod is used. Probably these two types 

 of responses are merely extremes of the same thing and 

 differ only quantitatively ; but, however this may be, they 

 show quite clearly that if the mechanical stimulus from 

 such a source as a glass rod could be sufficiently refined 

 there is not the least reason to suppose that it could not 

 be made to call forth as finely graded a response as light 

 does. At all events the nerve-net under these circum- 

 stances does not appear to possess that property which is 

 coming to be so commonly recognized in the nerve and 

 muscle of the higher animals and which is exemplified 

 under the head of the "all or none ' ' principle. 



