562 



CHEMISTRY OF THE PROTEIDS 



CHAP. 



The nitrogen - determinations by Kjeldahl's method give lower 

 values than those by Dumas' method, according to Sadikoff. 1 If, 

 however, gelatine is treated with hydrochloric acid, its nitrogen-content 

 becomes lowered, and the difference in the results of the two methods 

 disappears. Whether the phenomenon is to be explained as depending 

 on a dissociation caused by HC1 or on the removal of an impurity is an 

 open question. 



The action of the proteolytic ferments of the liver on gelatine has 

 been studied by Arnheim. 2 The amount of the non-coagulable, by 

 zinc sulphate not-precipitable nitrogen, was in all gelatine experiments 

 much greater than in the control experiments, owing to the gelatine 

 having been converted partly into mono-amino acids, 3 and partly 

 into peptone and di-amino acids, which could be precipitated by 

 phosphotungstic acid. 



The formation of a reducing substance on dissociating-gelatine has 

 only been observed by Sadikoff 1 in the case of gelatine prepared from 

 cartilage, and is probably due to contamination by remnants of 

 chondro-mucoid or chondro - sulphuric acid. The only sulphur - con- 

 taining dissociation - product obtained so far by Horbaczewski 4 is 

 sulphuretted hydrogen. 



Gelatine gives a well-marked, violet biuret reaction, while the 

 reaction of Millon and the xantho-proteic reactions, judging by the 

 dissociation -products, ought to be absent. As a matter of fact, one 

 may always observe, according to van Name 5 and Morner, 6 a very 

 slight pink coloration on boiling gelatine with Millon's reagent, and 



1 W. S. Sadikoff, Zeitschr. /. physiol. Cliem. 39. 411 (1903). 



2 J. Arnheim, Zeitschr. f. physiol. Chem. 40. 234 (1903). 



3 Gum arabic, dextrose, dextrin, and lactose increased the autolysis of the liver 

 substance, while the chlorides of sodium, potassium, and ammonium were without any 

 influence. 



4 J. Horbaczewski, Sitzungsber. d. Wiener Akad. 80. math.-uaturw. Kl. II. June 

 (1879). 



6 W. Gr. van Name, Journ. of Experiment. Med. 2. 117 (according to Malys Jahresber. 

 f. Tierchem. 27- 34) (1897). 



6 C. T. Morner, Zeitschr. f. physiol. Chem. 28. 471 (1899). 



