THE PROTEIDS OF MILK. 137 



the pseudo-nuclein is partly soluble in gastric juice ; l it is by far the 

 most soluble of the nucleins, 2 though the majority are partly soluble 

 after pancreatic digestion. 3 



Casein. This name should be restricted to the proteid formed by 

 the action of renhin, or of ferments that act like rennin. As a general 

 rule, it is more insoluble than caseinogen ; it is, however, readily soluble 

 in dilute alkalis such as lime water. From these solutions it is readily 

 precipitable by traces of calcium chloride ; and also by sodium chloride 

 (Hammarsten.). The precipitate with calcium chloride increases on 

 heating, but, like many calcium compounds, partially redissolves on 

 cooling (Kinger). 



The main distinction between casein and caseinogen is, however, 

 that which was first insisted on by Hammarsten, namely, that caseinogen 

 can be curdled by rennet, casein cannot. Some recent work by D. F. 

 Harris 4 and Peters 5 appeared to cast doubt upon this essential distinction, 

 and to suggest the possibility of recoagulation of casein, analogous to 

 that of myosin. The fallacies into which these observers were drawn 

 have been pointed out independently by Edmunds, 6 Hammarsten, 7 and 

 E. Benjamin. 8 Peters, for instance, used a preparation of rennet, rich in 

 sodium chloride and calcium salts ; the precipitate he obtained by adding 

 this to a solution of casein was due to these salts, not to the ferment. 



Pancreatic casein. An interesting variety of casein is that formed 

 by the action of pancreatic juice on milk, which has been recently 

 investigated by Brodie and myself. 9 



Kiihne 10 was the first to point out that extracts made from the 

 pancreas of the dog cause milk to coagulate ; this action was described 

 in some detail by Sir William Eoberts. 11 Various conditions which 

 influence the clotting were observed by Edkins, 12 and the occurrence of 

 the action in pancreatic extracts from a number of animals determined by 

 Harris and Gow. 13 



Our attention was drawn to the subject by a sentence in Prof. 

 Gamgee's " Physiological Chemistry," u in which he points out that it does 

 not necessarily follow that because extracts of the organ have a clotting- 

 action, the pancreatic juice possesses it also. 



We accordingly performed experiments with the actual pancreatic 

 secretion, obtained from temporary fistulse in dogs, and our conclusions 

 are summarised as follows : 



1. The pancreatic juice obtained from temporary pancreatic fistulse, 

 from dogs, produces a change in the caseinogen of milk. 



1 The nutritive value of casein is given by Marcuse (Arch. f. d. ges. PhysioL, Bonn, Bd. 

 Ixii. S. 223) as equal to that of meat proteids. 



2 E. Salkowski ( Virchow's Archiv, Bd. cxliv.) states that caseinogen, if not coagulated in 

 the process of preparation, is completely digested by gastric juice, if a sufficient volume of 

 the latter is employed, e.g. 500 parts of gastric juice to 1 of caseinogen. 



3 Sebelien, Ztschr. f. physiol. Ohem., Strassburg, Bd. xx. ; Popoff, ibid., Bd. xviii. ; 

 Gumlich, ibid., Bd. xviii. ; Weintrand, Terhandl. d. physiol. Gfesellsch., Arch. f. physiol., 

 Berlin, 1895; Clara Willdenow, Inaug. Diss., Bern, 1893; W. Sandmeyer, Ztschr. /. 

 physiol. Ohem., Strassburg, 1895, Bd. xxi. S. 87. 4 Loc. cit. 



5 Preisschrifc, Rostock, 1894. 6 Loc. cit. 



7 Ztschr. f. physiol. Chem., Strassburg, 1896, Bd. xxii. S. 103. 



8 Virchow's Archiv, 1896, Bd. cxlv. S. 30. 



9 Journ. PhysioL, Cambridge and London, 1896, vol. xx. S. 97. 



10 Verhandl. d. naturh.-med. Ver. zu Heidelberg, N. F., Bd. iii. S. 3. 



11 Proc. Roy. Soc. London, 1879 and 1881. 



12 Journ. Physiol., Cambridge and London, 1891, vol. xii. p. 193. 



13 Ibid., 1892, vol. xiii. p. 469. 14 Vol. ii. p. 446. 



