204 ACTION OF STRYCHNINE AND NICOTINE 



nine as an excitor of all such elements. Dorsal flexure then occurs 

 because the sum of the muscles causing it is greater and more powerful 

 than that of the musculature acting ventrally. Nicotine, on the other 

 hand, while exciting the elements of the dorsal sheath, as regards 

 the ray floor, acts specifically to excite the nervous elements con- 

 trolKng the ventral musculature. Nicotine can have no excitatory 

 effect on the innervation of the dorsal antagonists in the ray floor, 

 since this would of necessity result in dorsal flexure of the ray. These 

 facts indicate a difference in the chemical constitution of the two sets 

 of nervous elements concerned with the functioning of the antagonistic 

 muscles of the ray floor. 



The preceding analysis is further borne out by the fact that a 

 nicotinized Asterias when strychninized shows the characteristic 

 dorsal flexure, while an animal which has been first strychninized can- 

 not be caused to flex ventrally by nicotine. 



