UNFA\'ORABLE COXDITIOXS FOR BACTERIAL GROWTH 59 



chemicals entirely destroy all germ life even when added in very 

 small Cjuaniities. These are called disinfectants (formaldehyde, 

 corrosiw sublimate, etc.). Other chemicals are more mild in 

 their effect upon germ growth, and mereK' inhibit or retard the 

 growth of micro-organisms. The chemicals which ha^'e this 

 milder effect upon germs are called antiseptics. Boracic and 

 salicylic acids are examples. Practically all disinfectants are 



Fig. S. — Shows a plate exposed in pasture where air must ha\x- been ver\- pure 

 and free from germs. (Bui. 87, Nebraska.) 



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 preservati^-es or the antiseptics, are, as a rule, 

 not so poisonous or injurious to human health. In some coun- 

 tries they are aUowed to a small extent. P'or instance, according 

 to reports, the laws of England permit the use of boracic acid 

 in butter to the extent of 0.5 of i per cent. It is, howe\'er, safest 

 not to use any of these chemicals, except for preserA'ing samples 



