106 Dairy Bacteriology. 



Chemical preservatives. Numerous attempts have been 

 made to find some chemical substance that could be added 

 to milk which would preserve it without interfering with 

 its nutritive properties, but as a general rule a substance 

 that is toxic enough to destro}" or inhibit the growth of 

 bacterial life exerts a prejudicial effect on the tissues of the 

 body. The use of chemicals, such as carbolic acid, mercury 

 salts and mineral acids, that are able to entirely destroy all 

 life, is of course excluded, except when milk is preserved for 

 analytical purposes; but a number of milder substances 

 are more or less extensively employed, although the statutes 

 of practically all states forbid their use. 



The substances so used may be grouped in two classes: 



1. Those that unite chemically with certain b3'-products 

 of bacterial growth to form inert substances. Thus bi- 

 carbonate of soda neutralizes the acid in souring milk r 

 although it does not destroy the lactic acid bacteria. 



2. Those that act directly upon the bacteria in milk, re- 

 straining or inhibiting their development. The substances- 

 most frequently utilized are salicylic acid, formaldehyde 

 and boracic acid. These are nearly always sold to the 

 milk handler, under some proprietary name, at prices 

 greatly in excess of what the crude chemicals could be 

 bought for in the open market. Formaldehyde bas been 

 widely advertised of late, but its use is fraught with the 

 greatest danger, for it practically renders insoluble all al- 

 buminous matter and its toxic effect is greatly increased in 

 larger doses. 



These substances are generally used by milk handlers 

 who know nothing of their poisonous action, and although 

 it ma} 7 be possible for adults to withstand their use in 

 dilute form, without serious results, yet their addition to 



