88 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



movements very soon begin, carrying the food in this direc- 

 tion or that, as described later. At the same time, the gastric 

 mucous membrane changes from a pale pink to a congested 

 red, and soon drops of gastric juice begin to appear. They 

 run to the dependent portions of the cavity and become in- 

 corporated with the alimentary mass. It is believed that if 

 the gastric movements did not occur, this secretion would be 

 limited for fifteen or thirty minutes to a very small area, 

 namely, that with which the food is in contact. But it is 

 comparatively general because the movements bring practic- 

 ally 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 introduction 

 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 gen- 

 eral or not. 



It ought to be added, however, that in recent years secre- 

 tion by mechanical stimulation has been denied, and the de- 

 nial is supported by good evidence. Besides direct proof by 

 experiments, 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 abso- 

 lutely 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 o/ 

 special sense. 



Whether as a reflex or as a result of mechanical stimula- 

 tion, the fact remains undisputed that the flow begins a few 

 minutes after the introduction of food, and lasts until gas- 

 tric digestion is completed. After a time it is supposed that 

 chemical changes in the food itself further stimulate the gas- 

 tric glands, through their influence on the secretory nerves. 



