ADULTERATIONS OF MILK 223 



ADDITION OF PRESERVATIVES TO MILK 



In adding preservatives to milk, one of three objects is sought, 

 namely: 1, Prolongation of the period of sweetness; 2, the de- 

 struction of pathogenic bacteria together with saprophytes; 3, 

 the neutralization of acid formed by bacteria. 



Since decomposition of milk depends upon the presence of 

 micro-organisms, the chief purpose of adding a preservative is to 

 destroy micro-organisms, in whole or in part. If preservatives 

 are added in relatively small quantities, multiplication of bac- 

 teria is restrained and decomposition is deferred. The question 

 comes up whether substances which destroy bacterial cells do not 

 also injure the cells of the digestive tract, a question of special 

 importance when milk is intended for consumption by infants and 

 invalids. In relatively small quantities the action of preserva- 

 tives on bacteria is selective. It is necessary, in order to ac- 

 complish the desired end, to use preservatives in sufficient amount 

 to really destroy at least all pathogenic bacteria. To destroy 

 spore-bearing organisms larger amounts of preservatives are 

 required than for vegetative forms. On the other hand, there is 

 danger of too much preservative being used. This may result 

 from ignorance or from repeated addition of preservatives at dif- 

 ferent stages of the milk's journey from producer to consumer. 

 A preservative may be added by the producer, again by someone 

 at the collecting station, and finally by the dealer. Further- 

 more, in the warm season a larger amount of preservative is re- 

 quired than during the cold months. 



The preservatives that have been used in milk are chiefly the 

 following: formaldehyd, either as formalin, or under some trade 

 name, as Preservaline, Iceline, or Freezine; and borax and boric 

 acid, sold under the trade name Aseptine. Less commonly used 

 are salicylic acid, benzoic acid, hydrogen peroxid, fluorids, potas- 

 sium bichromate, sodium carbonate or bicarbonate. 



Formaldehyd is used to a greater extent than any other pre- 

 servative, and while the other substances mentioned are not 

 used as frequently as formaldehyd, they are found frequently 

 enough, and methods for determining their- presence must be 

 applied. Salicylic acid is dissolved with difficulty unless the 

 milk is first heated, and the quantity necessary to produce the 

 desired effect is so great that its presence can be recognized by 

 the taste. 



Chester and Brown have shown that formaldehyd in milk in 

 the proportion of 1 : 2000 to 1 : 800 causes a rapid decrease of 

 bacteria during the first twenty-four hours, and that only a few 

 resistant spores remain at the end of five days. In the proportion 



