milk may result from
the development of bacteria, acting upon various constituents of the
milk, and transforming these in such a way, as to produce
by-products that impair the flavor or appearance of the liquid; or
it may be produced by the milk being brought in contact with any
odoriferous or aromatic substance, under conditions that permit of
the direct absorption of such odors.

This latter class of taints is entirely independent of bacterial
action, and is largely attributable to the physical property which
milk possesses of absorbing volatile odors. This direct absorption
may occur before the milk is withdrawn from the animal, or
afterwards if exposed to strong odors.

It is not uncommon for the milk of animals advanced in lactation to
have a more or less strongly marked odor and taste; sometimes it is
apt to be bitter, at other times salty to the taste. It is a defect
that is peculiar to individual animals, and is liable to recur at
approximately the same period in lactation. The peculiar "cowy" or
"animal odor" of fresh milk is an inherent peculiarity that is due
to the direct absorption of volatile elements from the animal
herself.

Many kinds of feed consumed by the animal produce a more or less
pronounced taint or flavor in the milk. With some plants, such as
garlic, leeks, turnips, and cabbage, the odor is so pronounced as to
render the milk quite unfit for use. In some states along the
Atlantic seaboard, wild plants of this character in woodland
pastures may be so abundant as to make it impossible to pasture
milch animals. The difficulty in such cases is due to absorption of
the volatile principles into the circulation of the animal, and if
such feed is consumed shortly before milking, the characteristic
odors appear in the milk. If consumed immediately after the milk is
withdrawn from the animal, sufficient time may elapse so that the
peculiar odors are dissipated before the milk is again secreted. The
same principle applies in a lesser degree to the use of certain
green fodders that are more suitable for feed, such as rape, green
rye, or even silage. Silage produces a distinct, but not unpleasant
odor in milk, but newly pastured rye often confers so strong an odor
as to render the milk unusable.

Where certain drugs are employed in the treatment of animals, such
as belladonna, castor oil, sulfur, or turpentine, the peculiar odors
may reappear in the milk. Such mineral poisons as arsenic have been
k