SECRETIOX PHYSIOLOGY. 363 



cells, and of special secretory nerves, is unwarranted, unneces- 

 sary, and, in certain particular cases, opposed to the phenomena 

 of the secretion itself. 



SUMMARY OF RESULTS. 



(i) The sympathetic nerve induces salivary secretion by 

 acting on contractile tissue in the glands and thus causing a 

 compression of ducts and alveoli. 



(2) The chorda tympani, or other dilator salivar}', secretory 

 nerve probably causes secretion by its dilator action on the blood 

 vessels, thus increasing osmosis. 



(3) The evidence that the chorda tympani acts on the gland 

 cells is open to serious objections, as follows : 



{a) Atropine probably acts directly on the gland cells and 

 capillary endothelium, diminishing their permeability. 



(U) The post-mortem chorda salivary secretion is possibly 

 due to a back flow of blood from the veins owing to a dilation 

 of the capillaries. 



(<r) The increased content of organic matter in a secretion 

 coincident with an increased rate of secretion is of little value 

 as evidence of secretory nerves, because (i) saliva is generally 

 not a true solution, and (2) a weak stimulus probably arouses 

 but a portion of the gland. 



(<:/) The evidence derived from the action of nicotine and 

 the degenerated chorda tympani that secretion may ensue on 

 stimulation of the chorda without vaso-dilation is of doubtful 

 value, because of an erroneous method of determining that 

 vaso-dilation had not occurred. 



(4) The sweat glands and the amphibian skin glands, like the 

 salivary glands, receive a double nerve supply and prcbably pos- 

 sess a double mechanism of secretion, /. c, a muscular and an 

 osmotic. 



(5) Whether secretory nerves exist or whether secretion is 

 ever a function of the gland cell must be considered at present 

 an open question. 



(6) The thoracic lymph flow in dogs reacts to nerve stimula- 



