402 CHEMISTRY OF THE PEOTEIDS CHAP. 



irreversible one. Soldner 1 and Courant 2 have stated that to bring 

 about coagulation a soluble lime salt is essential in addition to the 

 calcium caseinogenate, and although Hammarsten 3 contradicts this 

 view, there cannot be any doubt that an additional soluble lime salt 

 facilitates coagulation greatly. Rennet causes coagulation whatever 

 the reaction of the caseinogen-solution may be. Coagulation is 

 hastened by small amounts of acid and is slowed by alkalies. 4 This 

 is due, as Soldner has shown, to acidification of the milk leading to 

 larger amounts of soluble lime salts being formed at the cost of the 

 calcium phosphate, and vice versa. The precipitation of caseinogen by 

 means of salt is an altogether different process from the coagulation 

 caused by acids, although both processes may be at work simultane- 

 ously, as, for example, when milk reaches the stomach. According to 

 Lindemann 5 no difference exists as regards digestibility between the 

 precipitated calcium caseinogenate and the coagulated calcium casein- 

 ate, or, if there be a difference, it is one due to the size of the flocculi. 6 

 The reunification of milk by the gastric mucous membrane of the 

 calf and also by certain plants was known to the ancients, but 

 gradually it has also become known that the gastric juice of non- 

 mammals, 7 the pancreatic juice, 8 the digesting secretions of many 

 invertebrates, 9 and also many extracts of organs 10 contain a rennet- 

 like ferment, that, in short, the rennet-ferment seems to occur where 

 proteolytic ferments are met with. Pawlow n has therefore expressed 

 the hypothesis that rennet is not a special ferment at all, but that all 

 proteolytic ferments possess the power of coagulating milk. Space 

 forbids to enter more fully into this questi'on. 



So far caseinogen has been represented as an individual substance, 

 and this view of Hammarsten's is the one generally accepted, but 

 the following points against this view must be noted (Cohnheim). 



1 F. Soldner, Dissertation, Eiiangen, 1888. 



2 G. Courant, Pflilger's Archiv, 50. 109 (1891). 



3 0. Hammarsten, Holy's Jahresber. 4. 135 (1874). 



4 A. Weitzel, Arbeiten a. d. Kaiserl. Gesundheitsamt, 19. 126 (1902). 



5 W. Lindemann, Virchow's Archiv, 149. 51 (1897). 



6 E. v. Dungern, Miinchener medizin. Wochenschr. 1900, II. p. 1661. 



7 R. Neumeister, Lehrbuch der physiol. Chem., 2. Aufl., Jena, 1897, p. 242. 



8 W. Kiihne, Heidelberger naturh.-med. Verein, N.F. I. Heft 4, 1876; W. D. 

 Halliburton and F. G. Brodie, Journ. of Physiol. 20. 97 (1896) ; A. Lob, Zentralbl. 



Jilr Bakteriol. 1. Abteil, 32. 471 (1902). 



9 0. Cohnheim, Zeitschr. f. physiol. Chem. 35. 396 (1902) ; R. Robert, Pfiugers 

 Arch. 99. 116 (1903). 



10 A. Edmunds, Journ. of Physiol. 19. 466 (1896). 



11 J. P. Pawlow and S. Parastschouk, Verh. d. Sektionf. Anat., Phys. u. med. Chem. 

 der Vers. nordischer Naturforscher und Arzte in Ifelsingfors, 1902, p. 28. 



