CHAPTER IX 



METHODS OF EXAMINING MILK 



Milk may be subjected to various methods of exami- 

 nation for the purpose of detecting adulteration or dilu- 

 tion, the addition of preservatives, or the presence of 

 pathological products, and for the determination of the 

 reaction, the bacterial content, the relative number of 

 leucocytes, the quantity of sediment or dirt, etc. 



Collecting Samples. When milk is permitted to 

 stand undisturbed, the fat rises to the top and the heavier 

 substances settle to the bottom. Some of the cells and 

 bacteria gravitate to the bottom, but many of them are 

 carried up with the fat. The upper part of the milk 

 contains more fat than the lower even before a cream 

 layer is visible. For these reasons, the milk in the con- 

 tainer should be thoroughly mixed before a sample is 

 taken for examination. When the milk is cold, consid- 

 erable shaking or stirring is required to mix the fat 

 equally. In collecting samples of which the specific grav- 

 ity, the per cent, of fat and total solids or the acidity 

 are to be determined, or which are to be tested for pre- 

 servatives, alkalies, nitrates and nitrites, etc., the same 

 dipper may be used in taking the different samples with- 

 out affecting the accuracy of the tests. There appears 

 to be some danger, however, of carrying typhoid fever 

 and diphtheria infection over from one sample to an- 

 other, although we have no proof of this having actually 

 occurred. The same dipper may be used for stirring 

 and mixing the milk. But when the bacterial content 

 or the ferment reactions are to be determined, each sam- 



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