Composition of Milk 305 



tains water and solids, the latter being made up of 

 mineral compounds, proteids, fats and sugar. The 

 average composition of normal cow's milk, excluding 

 samples of unusual character, according to a compila- 

 tion by Van Slyke of 5,552 American analyses is as 

 follows : 



Total solids Ash Proteids Fats Sugar Water 



% % % % % % 



12.9 .7 3.2 3.9 5.1 87.1 



The variations in .the composition of cows' milk are 

 large, the proportion of water ranging under per- 

 fectly normal conditions from 84 to 89 per cent, with 

 occasional analyses entirely outside these limits. 

 The chief known causes of such variations are breed, 

 individuality, period of lactation, and nervous dis- 

 turbances. There are material daily fluctuations as 

 well, for which no reasons can now be assigned. 

 These changes are mostly in the proportions of water 

 and total solids, for the composition of the solids, that 

 is, the relative proportion of proteids, butter fats and 

 sugar, is remarkably constant with the same animal. 

 The effect of breed in cows is illustrated by averages 

 obtained in breed tests at three experiment stations: 



Holstein Ayrshire Jersey 



% % % 



Total solids 12.2 12.9 15. 



Fat 3.4 3.6 5.3 



Solids not fat 8.8 9.3 9.7 



These variations and those due to other causes are 

 important in considering the relation of milk forma- 



