710 
EXPERIMENTS ON DIGESTION. 
In ruminants this free acid is found only in calves while they 
are fed on milk. 
In sheep that have been fed on grass, the contents of the sto- 
mach effervesce on the application of an acid, and the fluid in the 
caeca of sheep fed on oats turn again to blue the reddened colour 
of turnsol. Carbonate of ammonia is produced by the distilla- 
tion of the contents of the stomach in these animals. But, as the 
alkaline principle is less developed in the caecum than at the extre- 
mity of the small intestine, and as the contents of the caecum of 
sheep fed on grass shew themselves to be feebly acid, while those 
of the lower part of the small intestine are alkaline, it would ap- 
pear that the caecum of sheep secretes an acid which partly neu- 
tralizes the alkali. 
We can say nothing positive of the nature of the free acid found 
in the caecum. It appears to be acetic acid with a small portion of 
the hydrochloric. 
2. Albumen . — This substance, of which we found but the slight- 
est trace in the stomach, of which there was a certain quantity in 
the duodenum, and which evidently diminished as we passed along 
the small intestine,, frequently re-appears abundantly in the caecum 
and the colon. It may be obtained in a considerable quantity from 
the filtered fluid of the caecum, in dogs that had been fed on the 
white of eggs ; less was found when they had been fed on cheese 
or gluten, and none at all when milk, or bones, or flesh, had been 
given to them. In the caecum of the horse that had been fed on 
oats, but not in the caecum of him who had been fed on starch. It 
was found in the calf that had not been weaned — in sheep that had 
been fed on straw and oats — but not at all in those that had lived 
on grass. 
3. A Matter reddened by Chlorine, hydrochloric acid, nitric acid, 
&c. — probably a peculiar secretion of the caecum. It was found in 
dogs that had been fed on liquid albumen and bones ; in a horse 
to whom starch had been given ; and in calves and sheep. 
4. Fatty Matter , and the Colouring Principle, and Resin of the 
Bile. — The fatty matter was found in a dog that had been fed on 
animal food and bread — a greenish-brown resin in a horse that had 
been fed on oats, and which resin, on being fused, emitted a smell 
similar to that compounded from excrement and bile — a green-brown 
unctuous resin in sheep that had been fed on straw — and in a calf, 
a portion of cholesterine, and the resin and colouring principle of 
the bile. 
5. The following salts — carbonate of soda and of lime — the 
phosphate of soda and of lime — the chloruret of sodium, and the 
sulphate of soda. 
Theory of the Function of the Caecum. — The caecum is, doubt- 
