CHAPTER II. 



THE FAT OF MILK. 



Constitution. The fat in milk is found in the shape of small 

 globules varying in size, according to Besana, Fleischmann, and 

 other authorities, from 0-01 mm. to 0-0016 mm. in diameter. 

 There is some probability that the total weight of globules 

 of any size is equal to the total weight of globules of any other 

 size. 



The fat consists of a mixture of glycerides i.e., ethereal salts 

 of glycerol. It appears most probable that there are three acid 

 radicles in combination with each glycerol residue, thus 



G 3 H 5 < C ]8 H 33 O a 

 ( C 18 H 35 2 



which represents glyceryl butyro-oleo-stearate. This view has 

 been formed from the following facts : (1) Were the fat a 

 mixture of glyceryl tributyrate with other glycerides, it would 

 be possible to dissolve out the glyceryl tributyrate by 

 means of alcohol, leaving nearly the whole of the other 

 glycerides behind. This is not the case. The portion soluble 

 in alcohol contains a notable quantity of the higher 

 glycerides. 



(2) If glyceryl tributyrate existed as such in milk fat it should 

 be possible to distil it off under reduced pressure, but this cannot 

 be done. 



(3) Several definite mixed glycerides have been separated from 

 butter. 



We know little of the way in which the fatty axnds are 

 combined with glycerol ; it is convenient, however, to state the 

 composition as if each glyceride existed separately. 



Composition. The average composition of the fat of milk 

 appears to be, from the mean results obtained by different 

 observers, as follows : 



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