THE RELATION OF MICROORGANISMS TO MILK 393 



supply for our cities reasonably free from pathogenic microorganisms, 

 but, in order to insure this safety, the work must be carefully done, 

 and all later contamination avoided. Preferably, the work should be 

 done under expert, municipal supervision. Undoubtedly the ideal 

 method is pasteurization in the sealed bottle which is to be delivered to ' 

 the consumer, since this method reduces to the minimum the danger 

 of subsequent contamination. 



Pasteurization must not be regarded as a substitute for care and 

 cleanliness or a means of renovating old or dirty milk otherwise unfit 

 for use, but rather as an additional means of protecting the consumer 

 against disease-producing microorganisms in the milk supply. 



The Use of Chemicals. — ^The addition of certain chemicals to milk 

 will retard the growth of bacteria. The chemicals most commonly used 

 for this purpose are calcium hypochlorite, borax and formalin. While 

 the keeping quality of milk may be materially increased by the use of 

 such chemicals, their use has been opposed by health authorities and is 

 contrary to the Pure Food Laws. If milk is handled with any degree 

 of care, there should be no need for the use of chemical preservatives. 

 They are simply a means of counteracting the unsanitary conditions of 

 the production and handling. The same results can be obtained by 

 cleanliness in the production of the milk and the use of low temperatures 

 for preventing the contamination and subsequent growth of the 

 bacteria in the milk. The developments in the production of clean 

 milk of the past few years have illustrated very clearly that the use of 

 chemical preservatives is not necessary. 



Normal Development of Microorganisms in Milk 



The flora of any particular sample of fresh milk is determined by the 

 conditions under which it is produced. In stables where extreme 

 cleanliness is practised the flora may be practically limited to those 

 species which occur in the udder of the cows, but under ordinary condi- 

 tions there will be in addition to the normal udder types such others as 

 may occur on the cow's body and in the dust and atmosphere of the 

 stables. Market milk, therefore, when first obtained from the cow 

 ordinarily contains a mixed flora, the different tj^es present depending 

 upon the sanitary conditions under which the milk is produced. 



The future development of this initial flora is largely dependent 



