Composition of Milk and Its Products. 19 



mal niilk contains a number of substances which are 

 present in but small quantities and have only scientific 

 interest, such as the milk gases (carbonic acid, oxygen, 

 nitrogen), citric acid, lecithin, cholesterin, urea, hypo- 

 xanthin, lactochrome, etc. 



22. Average Composition. The average percentage com- 

 position of cows' milk will be seen from table I in the 

 Appendix. The following statement shows the limits 

 within which the components of normal American cows' 

 milk are likely to come: 



Minimum. Maximum. Average. 



Water 82.0 per ct. 90.0 per ct. 87.4 per ct. 



Fat 2.5 7.8 3.5 



Casein and albumen.. 2.5 4.6 3.4 



Milk sugar 3.5 6.0 5.0 



Ash 6 .9 .7 



23. Colostrum Milk. The liquid secreted directly after 

 parturition is known as colostrum milk or biestings. It 

 is a thick, yellowish, viscous liquid; its high content of 

 albumen and ash is characteristic, and also its low con- 

 tent of milk sugar. Owing to the large quantity of 

 albumen which colostrum contains, it will coagulate on 

 being heated toward the boiling point. In the course of 

 four to five days the secretion of the udder gradually 

 changes from colostrum to normal milk; the milk is con- 

 sidered fit for direct consumption or for the manufacture 

 of cheese and butter, when it does not coagulate on boil- 

 ing and is of normal appearance as regards color, taste, 

 and other properties. For composition of colostrum 

 milk, see Appendix. 



24. Composition of milk products. In addition to its 

 use for direct consumption, milk is the raw material from 



