Of all animal foods milk is the most important, as it may be regarded as
the type of human food. Case 55 contains an analysis of cow’s milk,
human milk, and asses milk, and is accompanied with explanatory labels.
Milk is preserved in various ways, so that it may be taken on long
voyages or otherwise employed as a diet where living animals cannot be
kept to produce it. It is preserved both in a liquid and solid state.
The latter mode of preparation appears to have the advantage.
Butter is formed from cream by the process of “churning.” The casein is
held in solution in the milk by the aid of certain salts; when these are
removed by acids the casein coagulates, and forms “curds.” When the curd
is removed with the butter and pressed it forms cheese. The best and
highest-priced cheeses are those in which there is most butter. The
casein without the butter is hard and indigestible.