618 MILK. 



amounts of lime-salts the paracasein-lime precipitates out while the 

 proteose-like substance (whey protein) remains in solution. t 



The paracasein is very similar to casein, but cannot be recoagulated 

 by rennin. As solution of alkali -paracaseinate is much more readily 

 precipitated by CaCl2 than an alkali-caseinate solution of the same con- 

 centration, and the precipitation limits for saturated ammonium-sul- 

 phate solution, the upper as well as the lower limit, lie, according to 

 LAQUEUR, lower with paracasein than with casein. The internal friction 

 of paracasein solutions is also, in his opinion, less than that of casein 

 solutions and indeed even to 20 per cent. 



By continued action of rennin upon paracasein a further transfor- 

 mation has been found in many cases (PETRY, SLOWTZOFF, v. HERWER- 

 DEN l ) . This is explained by the presence of another proteolytic enzyme 

 in the (impure) rennin preparation. This assumption seems to be plaus- 

 ible, and we are here probably dealing only with a secondary process 

 which has nothing whatever to do with the true formation of para- 

 casein. Whey protein is also formed after the very short action of rennin, 

 and the continued cleavage occurs with varying speed. Thus SCHMIDT- 

 NEILSEN found that the quantity of whey protein was even 3 per cent 

 of the casein nitrogen after the action of rennet for 15 minutes and only 

 4.25 per cent after 6 hours action. These and other recent investiga- 

 tions all favor the assumption that the casein coagulation by rennet 

 is a hydrolytic cleavage, but the conditions are not so clear that this 

 can be considered as proven. 2 



Fresh, unchanged milk does not, as is known, coagulate on boiling; but in 

 not too rapid action of rennin a state may be observed in which the milk coagu- 

 lates on heating (metacasein reaction). A solution of paracasein lactate, accord- 

 ing to LAXA, coagulates with rennin the same as a solution of casein lactate, 

 which indicates, he believes, 2 that the paracasein is transformed into casein again 

 by the lactic acid. But as a precipitation of the paracasein from the acid solu- 

 tion is perhaps a pepsin action, the transformation of the paracasein into 

 casein by the lactic acid must not be considered as proven. 



In the digestion of casein with, pepsin-hydrochloric acid primarily a 

 phosphorized proteose is formed, from which then the pseudonuclein is 

 split off (SALKOWSKI). The quantity thus split off is variable, as 

 shown by the researches of SALKOWSKI, HAHN, MORACZEWSKI, SEBELIEN, 

 and ZAITSCHEK. 4 The amount of phosphorus in the pseud onucleins 



the casein coagulation may be found in E. Fuld, Ergebnisse der Physiol., 1; Raudnitz, 

 ibid., 2; and Laqueur, Biochem. Centralbl., 4, 344. 



1 Petry, Hofmeister's Beitrage, 8; Slowtzoff, ibid., 9; v. Herwerden, Zeitschr. f. 

 physiol. Chem., 52. 



2 See also Werncken, Zeitschr. f. Biol., 52. 



3 Laxa, 1. c. 



4 Salkowski, Zeitschr. f. physiol. Chem., 27; Salkowski and Hahn, Pftiiger's Arch., 



