14 Testing Milk and Its Products. 



stirring ; whole milk of cows or goats is often added and 

 incorporated into such cheese (primosi, gjetost). 



Casein is present in milk partly in solution, in the 

 same way as milk sugar, soluble ash-materials and albu- 

 men, and partly in suspension, in an extremely fine col- 

 loidal condition, mixed or combined with insoluble cal- 

 cium phosphates. The casein and calcium phosphates 

 in suspension in milk may be retained on a filter made 

 of porous clay (so-called Cliamberland filters). 



About 80 per cent, of the nitrogenous compounds of 

 normal cow 's milk are made up of casein ; the rest is 

 largely albumen. If the amount of casein in milk be 

 determined by precipitation with rennet *or dilute acids, 

 and the albumen by boiling the filtrate frcm the casein 

 precipitate, it will be found that the sum of these two 

 compounds do not make up the total quantity of nitro- 

 genous constituents in the milk. The small remaining 

 portion (about five per cent, of the total nitrogenous 

 constituents) has been called by various authors, globu- 

 lin, albumose, hemi-albumose, nuclein, nucleon, proteose, 

 etc. The nitrogenous constituents of milk are very un- 

 stable compounds, and their study presents many and 

 great difficulties ; as a result we find that no two scien- 

 tists who have made a special study of these compounds 

 agree as to their properties, aside from those of casein 

 and albumen, or their relation to the nitrogenous sub- 

 stances found elsewhere in the animal body. For our 

 pose we may, however, consider the nitrogen com- 

 pounds of milk as made up of casein and albumen, and 

 the term casein and albumen, as used in this book, is 

 meant to include the total nitrogenous constituents of 



