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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