SECRETION PHYSIOLOGY. 301 



nore the extreme complexity of the theory. The assumption 

 that each, or any, cell of the sub-maxillary gland has acting 

 upon it four totally different nerve ends is, in itself, highly im- 

 probable. A further difficulty is encountered when we critically 

 examine Heidenhain's assumption that the trophic and secretory 

 fibres are unequally distributed to the chorda tympani and sym- 

 pathetic. It seems simple enough to refer the small secretion 

 ensuing on sympathetic stimulation to the presence of a small 

 number of secretory fibres in this nerve, but if it be asked 

 whether these fibres innervate all the cells, or only a portion of 

 them, we are at once plunged into a maze from which there is 

 no way out. If they innervate all the cells we may ask why, 

 if a few fibres suffice, more should be present in the chorda, 

 and why the secretion should not be as copious as the chorda's. 

 If they innervate a part of the cells only, new assumptions must 

 be made to understand why stimulation of the sympathetic 

 should exhaust the constituents of the whole gland. If we 

 abandon the trophic fibres and postulate one sort of fibre only, 

 the secretory, acting on the cell, Heidenhain's facts become 

 largely inexplicable. Furthermore, when Heidenhain^*" assumed 

 secretory nerves to the capillaries he undermined much of the 

 evidence accumulated by him of secretory nerves to glands. For 

 many of the facts of gland physiology might be understood by 

 reference to these capillary nerves. Atropine, for instance, might 

 conceivably prevent secretion by paralyzing the ends of the se- 

 cretory nerv^es of the capillaries, thus inhibiting the production 

 of lymph and fluid necessary for secretion. 



In the present paper I have considered chiefly the physiology 

 of secretion in the salivary glands. The experimental work has 

 been devoted chiefly to studying the exceptional features of that 

 secretion which have seemed difficult of comprehension on 

 any other than the cellular theory of secretion. I have ven- 

 tured, however, to bring some other secretions into relation 

 with the conclusions concerning the mechanisms of salivary 

 secretion. 



