460 NUTRITION OF FARM ANIMALS 



body fat, however, by the presence of a considerable proportion 

 of fatty acids of low molecular weight, as already noted in 

 Chapter I (30), where a list of the principal constituents is 

 given. The presence of these so-called " volatile fatty acids " 

 (i.e., acids which can be distilled in a current of steam) affords 

 an important means for the detection of adulterations of 

 butter. 



The percentage of fat in milk varies widely. For the cow a 

 minimum of 1.67 per cent is reported by Konig. Six per cent, 

 on the other hand, is a high figure, although occasionally 7 per 

 cent is reached. Babcock states that 9 per cent is the maxi- 

 mum observed for a cow giving as much as 15 pounds of milk 

 daily. 



The milk fat carries traces of lecithins and cholesterins 

 and also varying amounts of coloring matter, derived, as 

 Palmer and Eckles 1 have shown, chiefly from the carotin of 

 the feed. 



Carbohydrates. Milk contains in solution a disaccharid 

 peculiar to itself, namely, lactose, or milk sugar (13). In 

 distinction from fat, the percentage of lactose in fresh milk 

 shows comparatively small variations, averaging about 5 per 

 cent in cow's milk. The souring of milk is brought about by a 

 fermentation of the milk sugar by which its molecule is split 

 into four molecules of lactic acid. 



Among the organic ingredients of milk should also be men- 

 tioned citric acid, which occurs in appreciable quantities in the 

 form of calcium citrate. 



Ash. The total mineral matter in cow's milk averages 

 about 0.7 per cent according to Van Slyke. 2 



Qualitatively, the ash of milk contains the same ingredients found 

 in all animal substances. Its quantitative composition, however, as 

 compared with the blood serum, on the one hand, and with that of 

 the tissues on the other, shows some interesting relations. Bunge 3 

 gives the following figures for the composition of the ash of the serum 

 of cattle blood and of the ash of cow's milk. To these have been 

 added Lawes and Gilbert's figures for the ash of a calf for the sake 

 of comparison. 



1 Jour. Biol. Chem., 17 (1914), 191-264. 



2 Jordan, The Feeding of Animals, 1908, p. 305. 

 sZtschr. Biol., 10 (1874), 301 ; 12 (1876), 191. 



