200 QUANTITATIVE AGRICULTURAL ANALYSIS
It is thus seen that the milk of most mammals has been
analyzed and its composition determined but, for practical
purposes, the analyst rarely has to do with any other than cow's
milk and human milk. The analysis of cow's milk may be made
for purely scientific purposes as, for instance, the determination
of the relation between the composition of milk and the breed
of animal, the season of the year or the rations upon which the
animal is fed, or the determination of the changes that occur in
composition during the period of storage, and other similar
questions. The analysis may also be made for purposes of legal
control to detect sophistication. The analysis of woman's
milk is usually made for hygienic purposes, in order to provide
a basis for modification of the mother's diet, in cases where the
infant is not thriving.
The percentage composition of milk varies rather widely
although the same substances are found in practically all milk
from a given species of animal. It is therefore not possible to
fix, by legal enactment, the exact composition of milk that is to
become an article of commerce, but certain minimum figures
are usually established by law and any milk containing a con-
stituent in quantity below the legal minimum is considered to be
adulterated.
Milk is a very complex fluid, secreted through the alveoli cells
of the udder. The fat is present as a suspension (emulsion) of
very small globules. The milk sugar and inorganic salts are
present in true solution while the proteins, casein, albumin,
globulin and fibrin, are in colloidal solution. According to Bab-
cock, the composition of cow's milk is as follows: