560 ANNUAL UEI-OKT OF THE Off. Doc. 



Caseiii, 

 Albuiiiiii, 

 Globulin, 

 Galaetase. 



Globulin aud galaetase are pieseiiL iu so small quanliiies liiat we 

 can regard casein and albumin as being essentially the nitrogen 

 compounds ol milk. These bodies are called nitrogen compounds, 

 because they contain, in addition to other elements, the very im- 

 portant element called nitrogen. These nitrogen compounds of milk 

 or milk proteids can be formed only from proteids received by the 

 co»v in the food. 



{2.) Milk-Casein.^ — This is the most important proteid in milk, 

 because it is the one present in largest quantity and also because its 

 presence makes it possible to convert milk into cheese. Milk-casein 

 is most familiar to us in (he form of the white, solid substance, 

 or curd formed in milk when it sours, though, strictly speaking, this 

 while substance is not milk-casein but a compound formed by it 

 with acid, 



(a.j Casein in Milk Xot in Solution, — For a long time it was 

 thought that casein was in true solution in milk; but evidence, pro- 

 duced by different lines of investigation, show beyond question that 

 casein exists in milk iu the form of minute, solid, gelatinous partlcies* 

 in suspension. Casein forms a considerable part of separator slime. 



(b.j Composition of Casein. — Casein is a very complex chemical 

 compound, containing the elements of carbon, hydrogen, oxygen, ni- 

 trogen, sulphur and phosjjhorus. Ii is believed that calcium (or 

 limej compounds are in some way combined with casein. 



(c.j Action of Acids on Casein. — Very dilute acids completely co- 

 agulate or solidify the casein of milk. In this action the acid forms 

 a compound with casein. If a large amount of acid is added to milk, 

 the casein is first coagulated and then dissolved, as in the case of 

 adding sulphuric acid to milk in the Babcock test bottles. The ac- 

 tion of acids in coagulating milk-casein is hastened by increase of 

 temperature, 



(d.) Action of Alkalies on Casein. — Such forapounds as caustic 

 soda and x^otash, ammonia, sodium and i>otassium carbonate, unite 

 with casein and form compounds that are easilj' soluble in water. 

 Thev also dissolve the casein that has been coagulated. Some of 

 these compounds are found in commerce as food preijarations. Nu- 

 trose is a food pifjjaration that consists mostly of sodium casein. 



Ii'.) Action (jf Other Compounds on Milk Casein. — Certain chemi- 

 cal conjpounds, when added to milk in large quantities, coagulate 

 casein, such as common salt, magnesium sulphate (Epsom salt), 

 ammonium sulphate, etc. Other compounds, added in smaller quan- 

 tities, coagulate casein, such as alum, zioc sulphate, corrosive sub 

 limate, formalin, etc. 



