48 BUTTER-MAKING. 
growth. As milk is composed largely of water, bacteria find in 
milk a good medium for growth. All the other required food 
elements are also found in abundance in milk. Damp utensils 
and rooms are always more conducive to the growth of germs 
than are utensils and rooms which are thoroughly dried and 
ventilated. This is well illustrated by a refrigerator. A very 
damp dark refrigerator is always more conducive to the growth 
of molds in butter than is a dry refrigerator. 
Unfavorable Conditions for Bacterial Growth.—The reverse 
of the favorable conditions mentioned above would be un- 
favorable to the growth of bacteria. As it is practically im- 
possible to make conditions unfavorable for the growth of 
bacteria by taking away food, other means must be used. 
Extremely high temperatures destroy bacteria. Low tem- 
peratures check their growth, but so far as known do not 
destroy them. Absence of moisture and presence of direct 
sunlight are conditions which are not conducive to bacterial 
growth. Certain chemical substances when added to milk, or 
to the medium in which the bacteria are present, are very un- 
favorable to their growth. Some of these chemicals entirely 
destroy all germ life when added in even very small quantities. 
These are called disinfectants (formaldehyde, corrosive subli- 
mate, etc.). Other chemicals are more mild in their effect upon 
germ growth, and merely inhibit or retard the growth of micro- 
organisms. The chemicals which have this milder effect upon 
germs are called antiseptics. Boracie and salicylic acids are 
examples. Practically all disinfectants are violent poisons, and 
should not be used in any quantity or in any form in milk 
or dairy products which are intended for human food. The 
milder preservatives, or the antiseptics, are, as a rule, not so 
poisonous or injurious to human health. In some countries 
they are allowed to a small extent. For instance, according to 
reports, the laws of England permit the use of boracic acid to 
the extent of 0.5 of one per cent. It is, however, safest not to 
use any of these chemicals, except for preserving samples for 
analytical or similar purposes. As low and high temperatures 
