CHEMISTRY OF COWS' MILK II 



of milk is its coagulation by the enzym or chemical 

 ferment contained in rennet, which is an extract of the 

 mucous membrane of a calf's stomach. This property 

 makes possible the manufacture of cheese from milk. 

 The curd formed by the action of rennet is called para- 

 casein or, more properly, calcium paracasein. There 

 appears to be only slight chemical difference between 

 calcium casein and calcium paracasein. The coagula- 

 tion of calcium casein produced by rennet is quite dif- 

 ferent from that produced by acids. Calcium paraca- 

 sein behaves towards acids and alkalis much like cal- 

 cium casein. 



(6) Other changes caused in milk-casein. Under 

 the action of chemical reagents, of enzyms and of va- 

 rious organisms, calcium casein and paracasein may be 

 changed into a large number of other substances. 

 Among the compounds and classes of compounds thus 

 formed are paranuclein, albumoses, peptones, amides 

 (crystallizable bodies) and ammonia. These products 

 are never found in normal milk as it leaves the cow, 

 but may be present in milk that has stood some time. 



Milk-Albumin. Milk-albumin differs from milk- 

 casein in composition and behavior. Thus, milk-albu- 

 min (i) is not acted upon by rennet; (2) is not coag- 

 ulated by acids at ordinary temperatures; (3) is co- 

 agulated by heat alone, though not completely, above 

 160 F. ; and (4) is in solution in milk. 



Milk-Globulin This compound is present only in 

 small quantities in normal milk and is of no special 

 importance, so far as known. 



In connection with the nitrogen compounds of milk, 

 we will refer briefly to a class of compounds which 



