FATS AND PLASMA OF MILK. 465 



out all the fatty particles in the solution. Ether cannot extract 

 the fat from cow's milk until acetic acid or caustic potash is added to 

 liberate the fats from their envelopes; but shaking with ether is 

 sufficient to extract the fats from human milk (Radenhausen). Some 

 observers deny that an envelope of casein exists, and according to 

 them milk is a simple emulsion, kept emulsionised owing to the colloid 

 swollen up casein in the milk-plasma. The treatment of milk with 

 potash and ether makes the casein unable any longer to preserve the 

 emulsion (Soxhlet). 



The fats of the milk-globules are the triglycerides of stearic, palmitic, 

 myristic, oleic, arachinic (butinic), capric, caprylic, caproic, and butyric acids, 

 with traces of acetic and formic acids (Heintz), and cholesterin (Schmidt-Miilheim). 

 When milk is beaten or stirred for a long time (i.e., churned), the fat of the 

 milk-globules is ultimately obtained in the form of butter, owing to the rupture 

 of the envelopes of casein. 



Butter is soluble in alcohol and ether, and it is clarified by heat (60C.), or 

 by washing in water at 40C. When allowed to stand exposed to the air it 

 becomes rancid, owing to the glycerine of the neutral fats being decomposed by 

 fungi into acrolein and formic acid, while the volatile fatty acids give it its raucid 

 odour. 



The milk-plasma, obtained by filtration through clay filters or mem- 

 branes, is a clear, slightly opalescent fluid, and contains casein ( 249, 

 III, 3), serum-albumin (p. 49), and to a less extent a body resembling 

 albumin (lactoprotein Millon, Liebermann) ; galactin, albuminose, and 

 globulin; peptone (0'13 per cent.); nuclein, diastatic ferment (in 

 human milk Bechamp). Milk-sugar ( 252), a carbohydrate resemb- 

 ling dextrin (Eitthausen), (? lactic acid), lecithin, urea, extractives; 

 sodic and potassic chlorides, alkaline phosphates, calcium and mag- 

 nesium sulphates, alkaline carbonates, traces of iron, fluorine, and 

 silica ; C0 2 N, 0. 



When milk is boiled the albumin coagulates, while the surface also 

 becomes covered with a thin scum or layer of casein, which has 

 become insoluble. 



When milk is filtered through fresh animal membranes (Hoppe-Seyler), or 

 through a clay filter, the casein does not pass through (Helmholtz, Zahn, Kehrer), 

 while burned pulverised clay and animal charcoal also attract the casein (Dupre 

 and Hermann). 



The coagulation Of milk depends upon the coagulation of its casein. In milk, 

 casein is combined with calcium phosphate, which keeps it in solution; acids 

 which act on the calcium phosphate cause coagulation of the casein (acetic and tar- 

 taric acids in excess redissolve it). All acids do not coagulate human milk (Biedert). 

 It is coagulated by two or more drops of hydrochloric acid (O'l per cent.) or acetic 

 acid (0'2 per cent.). The spontaneous coagulation of milk after it has stood for a 

 time, especially in a warm place, is due to the formation of lactic acid, which is 



30 



