New York Agricultural Experiment Station. 281 



of an enzyme which converts some of the lactose of the milk into 

 lactic acid, the acid thus formed precipitating the casein. 



Hammarsten 2 was the first to show that this coagulation of milk 

 is due to the presence of a soluble ferment which acts directly 

 upon the casein, producing, as he thought, two substances, the 

 insoluble curd, Kdse, which we call paracasein and a soluble prod- 

 uct which he called whey-protein (Molkeneiweiss). He also showed 

 that the change of casein to paracasein is independent of coag- 

 ulation, the coagulation being due to the presence of soluble calcium 

 salts. 3 



A great number of papers have been published upon this subject 

 since the early work of Hammarsten. 4 As his explanation of the 

 action of rennin has been generally accepted as correct, most of 

 the recent investigations have been concerned with the influence of 

 soluble salts upon the coagulation. These investigations have shown 

 that the soluble salts of calcium, barium and strontium favor or 

 hasten coagulation while salts of ammonium, sodium and potas- 

 sium retard or inhibit coagulation. 



Recently Van Slyke and Bosworth 5 have shown that casein and 

 paracasein are acids having the same percentage composition; that 

 the molecular weight of casein is probably 8888 ±, while the mole- 

 cular weight of paracasein is one-hall that of casein; that both have 

 a combining equivalent of 1111; that combinations of casein or 

 paracasein with one equivalent of calcium, barium or strontium are 

 insoluble in water while the combinations with one equivalent of 

 ammonium, sodium or potassium are soluble; and that ammonium, 

 sodium or potassium caseinates can be changed by rennin to para- 

 caseinates which are soluble and are precipitated by calcium chloride 

 as calcium paracaseinates. 



These facts would seem to indicate three things: 



First, that rennin action consists of the hydrolytic splitting of 

 the casein molecule into two similar molecules of paracasein; per- 

 haps in somewhat the same manner that maltose is split into two 

 molecules of dextrose. 



Second, that, as a consequence of this cleavage it would seem 

 to be doubtful if Hammarsten's whey-protein could be one of the 

 products of rennin action. 



Third, that rennin is not, strictly speaking, a coagulating fer- 

 ment, the coagulation of paracasein being due to the fact that cal- 

 cium paracaseinates are less soluble than the calcium caseinates, 

 especially in the presence of soluble salts of calcium, barium or 

 strontium. 



2 Hammarsten: Mahfs Jahresbericht, 1872, p. 118; 1874, p. 135; 1877, p. 158. 



3 See also Arthus and Page: Arch, de physiol. (5th series), ii. 



4 An excellent review of the literature with references may be found in Bulletin 

 56 of the Hygienic Laboratory of the Public Health and Marine Hospital Service 

 of the United States. 



6 Van Slyke and Bosworth: Jour. Biol. Chem., 14:203-236. 



