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DIGESTION IN THE STOMACH. 481
This alternate action, according to Cannon l
is due to the fact that
the acid in the pylorus which acts upon the sphincter and makes pos-
sible the passage of the fluid chyme by the contraction of the muscles
of the stomach. In the intestine the acid has a reverse stimulation
upon the sphincter and causes a contraction of the same. As soon as
the acid is neutralized the contractions of the sphincter cease and the
passage of new portions of the chyme occur. If the flow of bile and pan-
creatic juice is prevented, and the neutralization of the acid contents
of the stomach in the intestine is retarded, then the stomach does not
eject its contents so often. The duration of gastric digestion varies
according to conditions, and in consequence the reports of observers are
widely divergent. Beaumont 2
found in his extensive observations
on the Canadian hunter St. Martin that the stomach, as a rule, is
emptied 1£-5| hours after a meal, depending upon the character of the
food.
The time in which different foods leave the stomach also depends
upon their digestibility. Respecting the unequal digestibility in the
stomach we must differentiate between the rapidity with which the food-
stuffs are chemically transformed and that with which they leave the
stomach and pass into the intestine. This distinction is especially
important, and it is evident that the main factors governing speed of
digestion and the time required before the food leaves the stomach are the
kind of food and the fineness of its subdivision, and its action upon the
gastric secretion, upon the pyloric reflexes, etc.
The observations of Boldyreff and others 3
on the action of fats
and fatty acids and not too dilute hydrochloric acid (stronger than 0.2
per cent) are conclusive concerning the manner in which the properties
of the food act upon the gastric secretion and upon the digestion in the
stomach as a whole. Irrespective of the reducing action of the fats
upon the extent and digestive power of the gastric juice Boldyreff
found after food very rich in fat that the bile, pancreatic juice and intes-
tinal juice migrate from the intestine into the stomach so that the diges-
tion in the stomach in these cases is essentially brought about by the
pancreatic juice.
We have numerous investigations on the rapidity with which the
food is digested in the stomach of dogs, but we must especially mention
1
Amer. Journ. of Physiol., 20.
2
The Physiology of Digestion, 1833.
3
Boldyreff, Pfliiger’s Arch., 121, 140; Migay, Maly’s Jahresb. 39; Best and
Cohnheim, Zeitschr. f. Physiol. Chem. 69; Cathcart, Journ. of Physiol. 42. See
also Abderhalden and Medigreeeanu, Zeitschr. f. physiol. Chem., 57.
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