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. Boracic 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 



