SECRETION PHYSIOLOGY. 327 



mains only the alternative of an increase in the diameter of the 

 alveoli, probably following an active compression. 



But if the saliva is simply pressed out, why is it that it does 

 not return to its former level on ceasing stimulation ? This was 

 supposed by von Wittich to prove that the nerve increased the 

 amount of saliva in the gland. I fully agree with von Wittich 

 in this contention, but I disagree with him entirely in 

 referring the increase to the action of the nerve on the cell 

 This increase may be readily understood on the muscular theory, 

 without any assumption of nerve activity on the gland cell, as 

 follows : On breaking sympathetic stimulation of considerable 

 duration a temporary vaso-dilation occurs and the ducts and 

 alveoli relax. It takes an appreciable time for the saliva to pass 

 back into the fine tubules, and during this time the cells are ab- 

 sorbing water from the lymph and capillaries. Hence their 

 bulk and the amount of saliv^a is increased and the saliva is 

 never able to return to its former level. The proof of this is 

 sufficiently clear. That vaso-dilation does occur temporarily on 

 ceasing stimulation of constrictor nerves has often been re- 

 marked. I have myself often seen it in the rabbit's ear and in 

 the cat's submaxillary. In the dog's submaxillary I have often 

 seen, also, that coincident with this vaso-dilation a slight secre- 

 tion may actually ensue (See Expt. VII, p. 3 1 1). It is, also, well 

 established that the cells do imbibe fluid and food during or after 

 sympathetic stimulation and thus increase the bulk of undifferen- 

 tiated protoplasm. 



In view of these facts, I believe that von Wittich's and Eck- 

 hard's experiments, instead of proving that sympathetic stimu- 

 tion can not possibly be due to compression of the ducts and 

 alveoli, demonstrates that it must be due to such compression ; 

 that it is impossible to account for the back flow on any other 

 probable hypothesis, and that the fact that the saliva does not 

 reach its former level is readily understood by reference to the 

 nerve's constrictor action and the temporary vaso-dilation ensuing 

 on breaking simulation. I do not believe that von Wittich ever 

 endeavored to analyze in detail his own explanation, or he must 

 have perceived its impossibility. 



