SECRETIOX PHYSIOLOGY. 349 



c. The Nature of the Action of Atropine and 



Pilocarpine. 



Atropine permits vaso-dilation, on stimulation of the chorda, 

 but prevents secretion. The drug has been supposed to act, 

 not on the gland cell, but on the ends of the secretor}' nerve 

 fibers. The reasoning for this is as follows : In the dog's sub- 

 maxillary, atropine paralyzes the chorda secretion, but not the 

 sympathetic. If the sympathetic innervate the gland cell and 

 cause its secretion by action on the latter, the gland cells con- 

 nected with this nerve have evidently not been paralyzed. As 

 there is no reason to suppose these cells different from those 

 connected with the chorda, it is probable that the cells con- 

 nected with the chorda have not been paralyzed. But if the 

 gland cells have not been paralyzed, and the dilator action of 

 the nerve remains unaffected, we must assume that there is some 

 third element connected with the nerve which has been para- 

 lyzed. This must be the element causing secretion, /'. c, the 

 secretory nerve fiber. The latter must be paralyzed at the nerve 

 termination, since, as far as known, atropine does not act on the 

 nerve fibre. This argument is true only for the dog and not 

 for the cat^' since, in the cat, atropine paralyzes the sympathetic 

 as well as the chorda. The argument, as will be seen, depends 

 on the assumption that the sympathetic causes secretion by 

 action on the gland cells. This, as pointed out, is probably in- 

 correct. The sympathetic produces its secretion by action on 

 contractile tissue. There is, hence, no longer any reason to 

 suppose that the gland cells have not been paralyzed by the 

 drug. How it acts upon the cell is unknown, but the effect of 

 that action is to prevent or diminish the passage ot fluid through 

 the cells. The variation in the susceptibility to its action of dif- 

 ferent glands in the same animal (compare the pancreas, salivary 

 glands and kidneys of dog), or of the same gland in different 

 animals (compare the pancreas of the dog and rabbit) points, I 

 believe, toward an action on the gland cell itself, the variations 

 in its action being due to variation in the chemical composition 

 oi the cells. 



