ia in the dairy and creamery.

=Effect of drying.= The spore-bearing bacteria withstand
effects of desiccation without serious injury, and many of the
non-spore-producing types retain their vitality for some months. The
bacteria found in the air are practically all derived from the soil,
and exist in the air in a dried condition, in which they are able to
remain alive for considerable periods of time. In a dried condition,
active cell growth is not possible, but when other conditions, such
as moisture and food supply are present, resumption of growth
quickly begins. This property is also of importance in the dairy as
in the preparation of dry starters for creameries and cheese
factories.

=Effect of light.= Bright sunlight exerts a markedly injurious effect
on bacterial life, both in a spore and in a growing condition. Where
the direct sunlight strikes, more or less complete disinfection
results in the course of a few hours, the effect being produced by
the chemical or violet rays, and not by the heat or red rays of the
spectrum. This action, however, does not penetrate opaque objects,
and is therefore confined to the surface. In diffused light, the
effect is much lessened, although it is exerted to some extent.
Sunlight exerts a beneficial effect on the general health and
well-being of animal life, and is a matter of importance to be taken
into consideration in the erection of buildings for animals as well
as for people.

=Effect of chemicals.= A great many chemical substances exert a more
or less powerful toxic action on various kinds of life. Many of
these are of great service in destroying bacteria or holding them in
check. Those that are toxic and result in the death of the cell are
known as _disinfectants_; those that merely inhibit, or retard
growth are known as _antiseptics_. All disinfectants must of
necessity be antiseptic in their action, but not all antiseptics are
disinfectants, even when used in large amounts. Disinfectants have
no place in dairy work, except to destroy disease-producing
bacteria, or to preserve milk for analytical purposes. The so-called
chemical preservatives used to "keep" milk depend for their effect
on the inhibition of bacterial growth. In this country, most states
prohibit the use of these substances in milk. Their only function in
the dairy should be to check fermentative and putrefactive processes
outside of milk and so keep the air free from taints.

=Products of growth.= A