the surface somewhere, comes
up so high as to affect the disposal of sewage. Usually no underdrains
will be needed unless the ground water gets up to within three feet of
the surface, and, in a number of cases, underdrains have been laid under
a sewage filter at considerable expense, only to find when the filter
was in operation that they were never in use. In clay soils the
underdrain is not necessary. In fact, it may be noticed that the
underdrain is not for the purpose of taking care of the sewage, but
rather of draining off the soil-water and preventing its interference
with the action of soil on sewage. This principle will indicate where
underdrains are necessary and where not.

When used, underdrains should be laid from three to four feet below the
surface in parallel lines about fifteen feet apart and on grades of not
less than one foot in one hundred. It is always better to have the
underdrains too large than too small, and drains less than three inches
in diameter should not be used, and they should increase in size to four
inches and then to six inches as the separate drains are brought
together. The writer has seen a six-inch underdrain running full of
ground water collected within a distance of a hundred feet, but this was
in gravel soil through which the water passed very freely. No exact
rules can be given for the size of the underdrains, but it will be
noticed that, since water passes through clay soil slowly and through
gravel soil rapidly, larger pipes must be used where the soil is
coarse.

CHAPTER XI

_PREPARATION AND CARE OF MILK AND MEAT_

Milk has long been considered to be one of the most important human
foods, particularly for the young, combining within itself all the
essential elements necessary for the production of cell tissue and for
animal vitality. In composition, it is about 87 per cent water, the
remaining 13 per cent being divided between fat, casein, and sugar in
equal parts, with a small addition of salt.

As is well known, milk is the sole food upon which it is possible to
sustain life for long periods, and while this applies directly to
infants, it is by no means confined to them. Many examples can be given
of men and women of mature life who, either on account of some digestive
disorder or some mental bias, have confined themselves absolutely to a
diet of about two quarts of milk a day and have lived thereon for months
and years without suffering from lack of nutriti