302 MATHEWS. 



It may prevent confusion and reconcile what might appear to 

 be contradictory statements, to give here the chief conclusion 

 drawn in the present paper. This is, that there is no single 

 mechanism of secretion. In some glands the stored metabolic 

 products are driven out of the cells by the action of muscle, as 

 in Amphibian skin glands and sudoriferous glands ; in others 

 they are removed by currents of lymph, which are probably the 

 result of osmosis, as in the pancreas, stomach, salivary glands ; 

 in some cases the cells imbibe water until they burst, and their 

 contents rush into the gland-lumen, as in the intestinal cells of 

 Ptychoptera larvae ; in others the inner end of the cell crumbles 

 to pieces, as in the mammalian milk glands. Two, or more, of 

 these mechanisms may coexist in one gland, and it is this which 

 has rendered the physiology of such glands as the salivary so 

 confusing. In the submaxillary gland, for example, I believe 

 we have a muscular mechanism, innervated by the sympathetic ; 

 and an osmotic mechanism, innervated by the chorda. The 

 sympathetic, in other words, causes secretion as Eckhard,^^ 

 Schiff,* ''^ and others^" have maintained, by its action on contrac- 

 tile tissue in the gland body, thus mechanically compressing the 

 ducts and alveoli and squeezing out the secretion. The chorda 

 probably causes secretion, by its dilator action on the blood ves- 

 sels. The following pages present the evidence for these con- 

 clusions. 



Before proceeding farther it is necessary to define the sense 

 in which the word ''secretion" is here used. At present the 

 word has no very definite significance, as it refers to different 

 processes. For the sake of clearness it would be better to 

 designate these various processes by different names. I suggest 

 that, in the future, the word secretion be used to indicate the 

 process of extruding subtances from cells into the lumen of the 

 gland, the process of expulsion from the ducts, and the substances 

 secreted by the gland. By this use of the word cellular secre- 

 tion will be generally coincident in time with glandular. For the 



* Schiff, loc. cit., p. 304, I. " It is probable that the gi-eat sympathetic which 

 causes constriction of the parotid vessels causes, at the same time, the tissue of the 

 gland to contract, and that by this contraction tlie gland empties itself of its con- 

 tents formed independent of nerve action." 



