268 LECTURES ON IMMUNITY 



the digestion-product is precipitated by Ca ions. Some 

 very strong arguments are advanced in favour of this view. 

 The reaction goes on at low temperatures without coagula- 

 tion, which then occurs almost instantaneously upon eleva- 

 tion of the temperature to over 25 C., 1 and small quantities 

 of pepton have a strong retarding influence (cf. p. 77). One 

 of the products of decomposition, called para-casein, is sup- 

 posed to yield the coagulum at higher temperature, whereas 

 other products, for instance serum-albumen, remain in solu- 

 tion. In reality Hammarsten has proved that serum-albumen 

 is an albumos-like substance with characteristic reactions : it 

 is not precipitated by acids (acetic and nitric) nor by 

 diluted solutions of CuSO 4 , HgCl 2 , FeCl 3 , K 4 (CN) 6 Fe, nor 

 Pb (CH 3 CO 2 ) 2 J it does not give the reaction of Heller ; but 

 responds to the biuret-reaction and the reaction of Millon ; 

 it is precipitated by tannin in acetic acid and by alcohol. 

 Rennet and casein produce serum-albumen even in absence 

 of calcium or barium salts. Duclaux combats this view, 

 which he says leads to the conclusion that these soluble 

 products ought to pass through a Chamberland filter. 

 Now a Chamberland filter restrains casein, but some of the 

 proteins of milk pass through it. Therefore, according to 

 Duclaux, milk filtered through a Chamberland filter should 

 give a filtrate containing more of the filterable proteids 

 after it had been coagulated by rennet, than before this 

 treatment. This, he showed, was not the case. But the 

 conclusion drawn does not seem to be quite convincing. 

 For, just as the casein does not pass through the filter, so 

 the serum-albumen may be held back by it. That the 



lr This was first observed by Morgenroth (Archives Internationales dt 

 pharmacodynamie^ 7. 265, 1900). 





