SECRETION PHYSIOLOGY. 361 



planations of the fact that stimulation of the normal nerve with 

 the cord undivided causes no secretion. Either the nerve carries 

 inhibitory secretory as well as secretory fibres, or stimulation 

 of the nerve is unable to cause a secretion without vaso-dilation. 

 The first alternative Heidenhain has particularly combatted in 

 the case of the submaxillary, and it appears to me lacking all 

 proper experimental basis. The second alternative is probably 

 the true explanation, for the reason that stimulation of the nor- 

 mal nerve below the cardiac branches causes no alteration in 

 blood pressure, and for the reason that the treatment to which 

 the nerve is subjected is calculated to give it a dilator action. 

 If this be true the pancreas would appear fundamentally differ- 

 ent from the salivary glands, unless, as I have endeavored to 

 show, the latter are, also, in reality, unable to secrete on stim- 

 ulation of the chorda or other cerebral nerve, unless vaso-dila- 

 tion ensues. 



Further evidence of the dependence of pancreatic secretion 

 on vaso-dilation is furnished by the action of pilocarpine, chloral 

 hydrate^^ and curare, drugs which cause vaso-dilation and secre- 

 tion, and by strychnine, ^'^ or digitalis, drugs which cause vaso- 

 constriction and inhibit secretion. Heidenhain, ^^ also, has 

 observed a close correspondence between vaso-dilation and 

 secretion, and between vaso-constriction and the cessation of 

 secretion. This parallelism between vaso-dilation and secretion 

 can not be accidental. It indicates, I believe, that the dilation 

 is the cause of the secretion, other things being normal. 



VI. GENERAL CONCLUSION. 



We have now considered the evidences of the existence of 

 secretory nerves, and the reasons for believing that secretion is 

 a function of the gland cells. While readily admitting the pos- 

 sibilities that secretion may in certain instances be a function of 

 the gland cell, controlled by the action on it of secretory nerve 

 fibres, we have seen reason to believe that certainly many so- 

 called secretions are due not to the gland cell, but to the action 

 of contractile tissue either within or about the gland. Among 



