SECRETION PHYSIOLOGY. 297 



Evidence of a more positive kind of the direct action of nerves 

 upon the gland cells was not long lacking. Heidenhain showed 

 that stimulation of secretory nerves caused well-marked changes 

 in the structure of the gland cells. -^ He discovered that the 

 specific constituents of the secretion were accumulated in the cell 

 during glandular rest, and discharged from the cell during secre- 

 tion. That these substances were not simply dissolved from the 

 cells by the water stream passing through them he endeavored 

 to show by the fact that on passing from a weak to a stronger 

 stirnulation of the chorda tympani, or other dilator secretory 

 nerve, not only the rate, but also the concentration of the secre- 

 tion increased. Apparently the more rapidly secreted saliva, 

 although in contact with the cell contents for a briefer time, never- 

 theless dissolved more of them than that more slowly secreted. 

 This obviously would have been impossible if the contents of the 

 cell had not been rendered more soluble by the action of the 

 nerve during the stronger stimulus. He brought forward, also, 

 still more convincing evidence. ^^ In the dog's parotid gland 

 stimulation of the cervical sympathetic causes, generally, no 

 secretion, but if this nerve be irritated coincident with the dila- 

 tor secretory nerve the saliva secreted under the influence of 

 both nerves is more concentrated than that secreted during irri- 

 tation of the dilator nerve alone. Apparently the sympathetic, 

 though causing no secretion, must, nevertheless, act on the cells, 

 so as to render their contents more soluble. That this effect of 

 the sympathetic could not be due to any possible action of the 

 nerve on contractile tissue of the gland, as suggested by Schiff,''"' 

 Eckhard^^ and others, Heidenhain believed von Wittich''^ had 

 conclusively demonstrated. That the well-known high concen- 

 tration of the sympathetic saliva could not be referred to the 

 nerve's vaso-constrictor action Heidenhain^^ showed by the 

 fact that, if the gland artery be almost totally compressed, the 

 following chorda saliva was not rendered more concentrated. 



These facts undoubtedly furnish strong evidence that the 

 sympathetic and other nerves act on the gland cells, not only 

 increasing the flow of water through them, but also rendering 

 their contents more soluble. 



