DIGESTION OF FOOD. 3809 
and we have seen how saliva varies, according as the animal is 
fasting or feeding, etc. 
Bearing in mind, then, that our knowledge is possibly only 
approximately correct, we may state what is known of the se- 
cretions of the stomach. 
The gastric secretion is clear, colorless, of low specific grav- 
ity (1001 to 1010), the solids being in great part made up of pep- 
"E 
Fig. 267.—Gastric fistula in ease of St. Martin (after Beaumont). 4, A, A, B, borders of open- 
ing into stomach ; ©, left nipple; D, chest ; E, cicatrices from wound made for removal 
of a piece of cartilage ; F, F, &, cicatrices of original wound. 
sin with a small quantity of mucus, which may become excess- 
ive in disordered conditions. There has been a good deal of 
dispute as to the acid found in the stomach during digestion, 
It is now generally agreed that during the greater part of the 
digestive process there is free hydrochloric acid to the extent 
of about ‘2 per cent. It is maintained that lactic acid exists 
normally in the early stages of digestion, and it is conceded 
that lactic, butyric, acetic, and other acids may be present in 
certain forms of disordered digestion. 
It is also generally acknowledged that in mammals the 
work of the stomach is limited, so far as actual chemical 
changes go, to the conversion of the proteid constituents of 
food into peptone. Fats may be released from their proteid 
coverings (cells), but neither they nor starches are in the least 
altered chemically. Some have thought that in the dog there 
is a slight digestion of fats in the stomach. The solvent 
