88 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



minutes to a very small area, namely, that with which the food is 

 in contact. But it is comparatively general because the move- 

 ments bring practically all parts, at least of the fundic mucous 

 membrane, in contact with the food before this time has elapsed. 

 The idea is that up to fifteen or thirty minutes after the introduc- 

 tion of food, the glands are made to secrete by direct mechanical 

 stimulation of the food, and after this time the secretion becomes 

 general, whether mechanical irritation becomes general or not. 



It ought to be added, however, that in recent years secretion 

 by mechanical stimulation has been denied, and the denial is 

 supported by good evidence. Besides direct proof by experi- 

 ments, it is shown that this early secretion occurs without 

 mechanical irritation, as when food is chewed and made to pass 

 through an esophageal fistula, or even by the sight of food. 

 These observers (Pawlow) state that food introduced into the 

 stomach through a fistula produces absolutely no flow if the 

 animal experimented upon does not know of the introduction. 

 Under this view the secretion is a distinct reflex, the impressions 

 being carried to the center by afferent nerves distributed to the 

 mouth, or by nerves of special sense. 



Whether as a reflex or as a result of mechanical stimulation, 

 the fact remains undisputed that the flow begins a few minutes 

 after the introduction of food, and lasts until gastric digestion is 

 completed. After a time it is supposed that chemical changes 

 in the food itself further stimulate the gastric glands, through 

 their influence on the secretory nerves. These stimulating 

 chemical products are not developed alike from all foods; and 

 the conclusion is warranted that some substances do not undergo 

 gastric digestion so readily as others. Ordinary bread and the 

 whites of eggs, for example, are said not to develop them. It 

 has been further shown that fats, oils, etc., actually develop 

 substances which chemically inhibit gastric secretion. There 

 appears also to be a kind of chemical regulation of the amount 



