100.0
-----

[Illustration: THE CONSTITUENTS OF MILK
In the illustration, a pint of milk is shown in a glass
jar, and the various percentages of water, casein, sugar,
ash, albumen, and fat, which make up its constituent
parts, are shown in separate bottles, the percentage of
each being stated beneath.]

Milk varies a good deal in composition; the different breeds of cows
give varying qualities. The Short-horn gives large quantities of milk of
rather poor analysis, while the Jersey yields smaller proportions of
very rich milk. During the period of lactation (the time which has
elapsed since the cow gave birth to a calf), care in milking, food,
health, etc., all have an effect on the quality of the milk.

The limits of variation may be stated as follows:

Per cent. Per cent.
Water 87.5 to 82.5
Fat 2.5 " 6.0
Casein and albumen 3.0 " 4.5
Milk sugar 3.5 " 6.0
Ash 0.6 " 0.8

These figures are extreme, and it is very seldom indeed that either the
minimum or maximum is reached. Indeed, by the regulation laid down under
Clause 4 of the British Sale of Food and Drugs Act of 1899, when the
percentage of solids not fat falls below 8.5 per cent., and fat under 3
per cent., it is assumed that the milk has been adulterated. This
regulation is a perfectly just one. While genuine milk may, in rare
instances, show figures as low as 7.1 per cent. of solids not fat, or
2.5 per cent. of fat, the right can hardly be claimed of supplying such
an abnormal article to the public as milk of proper quality, and the
dairyman who understands his business, and wishes to deal fairly with
his customers, can, by attention to the conditions enumerated above
which influence the composition of milk, entirely avoid the production
of such a low-grade article.

In the nutrition of both plants and animals large quantities of water
are needed. The solids must be supplied in solution or dissolved in the
assimilative processes, and this cannot take place without water, which
also conveys the dissolved solids to the various parts of the economy,
and in the case of animals removes waste materials. For the most part,
water passes through the body unchanged, but a certain proportion unites
chemically with the food materials and assists in the