368 
EXPERIMENTS ON DIGESTION. 
gastric juice. We have found this in every experiment on the 
horse, the dog, or the cat ; but the degree of acidity varies according 
to the nature of the food. The tincture has been most decidedly 
reddened in the dog, after the white of egg, fibrine, butter, cheese, 
gluten, milk, meat raw or cooked, bone, cartilage, and barley-bread, 
had been given. It was less decided when starch, rice, or potatoes, 
had been used. It was least of all decisive, or rather it was scarcely 
perceptible, after we had given the white of a raw egg — this sub- 
stance containing a little alkaline carbonate, which had, probably, 
partly saturated the acid of the stomach. The red was more in- 
tense in horses that had been fed on oats, than in those to whom 
starch had been given in any form. 
It is evident from this that the degree of acidity in the gastric 
juice corresponds exactly with the greater or less facility of 
solution, or, in other words, with the greater or less solubility of 
the food. Bones, cartilage, fibrine, cooked albumen, caseous mat- 
ter, flesh, gluten, and bread, are more difficult to digest than starch, 
potatoes, rice, gelatine, and liquid albumen. This maybe expressed 
in another way — the degree of acidity of the gastric juice depends 
on the degree in which the mucous membrane of the stomach is 
stimulated by the food. 
As to the nature of the acids developed in the gastric juice in 
the process of digestion, they are the same as those which we have 
found in animals whose stomachs, in a state of fasting, have been 
stimulated by mechanical agents : they are the hydrochloric, the 
acetic, and the butyric. 
The Solvent Action of the Gastric Juice on the Aliment. 
Being mixed with the aliment, the gastric juice softens and dis- 
solves it. If it is naturally soft, or is comminuted and rendered 
pultaceous by mastication, the gastric juice penetrates it, and 
rapidly converts it into a fluid. If, on the contrary, it has a cer- 
tain consistence, or if it is swallowed in masses too voluminous, 
its softening and solution are slowly effected, layer after layer, 
and from the outside to the centre. It often happens that the sur- 
face is already reduced to a bouillie , while, interiorly, the food pre- 
serves its consistence, and has not undergone any change. The 
dissolved portion is slowly pushed towards the pyloric orifice by 
the pressure which it exerts on the alimentary mass. 
The time which the alimentary substances demand in order to be 
dissolved or digested, varies considerably, according to their chemi- 
cal composition, or their solubility in the gastric juice. 
