The value of milk as a food is obvious from the fact that it constitutes the natural food of all young mammalia during the period of their most rapid growth. There is some danger, however, of overestimating its value in the dietary of adults, as solid food is essential, and liquid taken should act as a stimulant and a solvent rather than as a nutrient. One obtains the greatest benefit from milk when taken alone at regular intervals between meals, or before retiring, and sipped, rather than drunk. Hot milk is often given to produce sleep.
When milk is allowed to stand for a few hours, the globules of fat, which have been held in suspension throughout the liquid, rise to the top in the form of cream; this is due to their lower specific gravity.
The difference in quality of milk depends chiefly on the quantity of fat therein: casein, lactose, and mineral matter being nearly constant, water varying but little unless milk is adulterated.