MILK 331 



the formation of the film, but are not essential (Rettger 1 ). As Jamison 

 and Hertz 2 have shown, a similar film will form on heating any protein 

 solution containing fat or paraffin. If the milk is of a pronounced 

 acid reaction, through the inception of lactic acid fermentation, or from 

 any other cause, no film will form when heat is applied, but instead a 

 true coagulation will occur. When milk is boiled certain changes occur 

 in its odor and taste. These changes, according to Rettger, 3 are due 

 to a partial decomposition of the milk proteins and are accompanied 

 by the liberation of a volatile sulphide, probably hydrogen sulphide. 



FIG. 104. NORMAL MILK AND COLOSTRUM. 

 a, Normal milk; b, Colostrum. 



The milk-curdling enyzmes of the gastric and the pancreatic juice 

 have the power of splitting the casein of the milk, through a process of 

 hydrolytic cleavage, into soluble paracasein and a peptone-like body. 

 This soluble paracasein then forms a combination with the soluble 

 calcium salts of the milk and an insoluble curd of paracasein results. 

 The clear fluid surrounding the curd is known as whey. This action 

 of rennin may be represented by the following scheme: 



Casein (+ rennin) 



I 



Peptone-like Soluble paracasein 



body | 



+ Ca salts 



I 

 Paracasein 



(insoluble curd) 



1 Rettger: American Journal of Physiology, 7, 325, 1902. 



2 Jamison and Hertz: Journal of Physiology, 27, 26, 1902. 



3 Rettger: American Journal of Physiology, 6, 450, 1902. 



