Composition of Milk and Its Products. 13 



globules in fresh milkers is about 0.004 millimeter, or 

 one-six-thousandth of an inch; that is, it takes about six 

 thousand such globules placed side by side to cover one 

 inch in length. The globules in any sample of milk 

 vary greatly in size; the largest globules are recovered 

 in the cream when the milk is set or run through a cream 

 separator, and the smallest ones remain in the skim milk; 

 thoroughly skimmed separator skim milk will contain 

 only a small number of very minute fat globules. 



Milk fut is composed of so-called glycerides of the fatty 

 acids, i. e., compounds of the latter with glycerin; some 

 of the fatty acids are insoluble in water, viz., palmitic, 

 stearic, and oleic acids, while others are soluble and vol- 

 atile, the chief ones among the latter being butyric, cap- 

 rylic, and caproic acids. The glycerides of the insoluble 

 fatty acids make up about 92 per cent, of the pure milk 

 fat; about 8 per cent, of the glycerides of volatile fatty 

 acids are therefore found in natural milk- (and butter-) 

 fat. The distinction between natural and artificial but- 

 ter lies mainly in this point, since artificial butter (but- 

 terine, oleomargerine) as well as other solid animal fats 

 contain only a very small quantity of volatile fatty acids. 

 The glycerides of the volatile fatty acids are unstable 

 compounds, easily decomposed through the action of 

 bacteria or light; the volatile fatty acids thus set free, 

 principally butyric acid, are the cause of the unpleasant 

 odor met with in rancid butter. 



Cows 7 milk generally contains between three and six 

 per cent, of fat; in American milk we find on the 

 average toward four per cent, of fat. The milk from 

 single cows in perfect health will occasionally go below 



