88 Dairy Bacteriology. 



those that are applicable to milk intended for food. Sam- 

 ples destined for analytical use, such as for fat tests, etc., 

 would be treated in a different manner. The various 

 methods that have been suggested may be classified un- 

 der two heads, those attained by the use of chemical, or 

 by physical agents. In some methods the preservation 

 is accomplished by the operation of both physical and 

 chemical factors. 



86. Chemical agents. Under the head of antiseptics 

 and disinfectants, the action of different chemicals on 

 bacterial life has been discussed 1 . Those substances that 

 are inimical to the development of bacteria are usually 

 too strong for use in a food product as preservatives, 

 because the protoplasm of bacteria as a rule is more re- 

 sistant than other forms of living matter. 



For this reason, the application of strong disinfectants 

 like carbolic acid, mercury salts, strong acids, or alka- 

 lies is excluded. The chemical agents that are used in 

 the preservation of milk fall into two classes. 



1. Those that unite chemically with certain products 

 of bacterial growth to form more or less inert substances 

 in the milk. 



2. Those that restrain or inhibit the development of 

 fermentative organisms in the milk. 



To this first class belong those alkaline salts such as 

 bicarbonate of soda, etc., that combine with the acids 

 that are formed in the milk. While salts of this sort 

 neutralize the acidity produced by the sour milk bacteria, 

 they do not kill these organisms, their growth again 

 being renewed after the milk is neutralized. 



As representatives of the second class, salicylic acid, 

 boracic acid, and their derivatives may be mentioned. 



T Lazarus, Zeit. f. Hyg., 8: 207. 



