st important group is that embraced under the second head.
It includes not only the true lactic acid types in which no gas is
formed, but those species capable of producing gases and various kinds
of acids. These organisms are the distinctively milk bacteria, although
they do not predominate when the milk is first drawn. Their adaptation
to this medium is normally shown, however, by this extremely rapid
growth, in which they soon gain the ascendency over all other species
present. It is to this lactic acid class that the favorable
flavor-producing organisms belong which are concerned in butter-making.
They are also indispensable in cheese-making.

The third class represents those capable of producing a liquefied or
digested condition on gelatin or in milk. They are usually the
spore-bearing species which gain access from filth and dirt. Their high
powers of resistance due to spores makes it difficult to eradicate this
type, although they are materially held in subjection by the lactic
bacteria. The number of different kinds that have been found in milk is
quite considerable, something over 200 species having been described
more or less thoroughly. In all probability, however, many of these
forms will be found to be identical when they are subjected to a more
critical study.

~Direct absorption of taints.~ A tainted condition in 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 being able to absorb volatile odors, the fat in particular,
having a great affinity for many of these substances. 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absorption may occur before the milk is withdrawn from the animal, or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 this 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" o