PROTEOSES AND PEPTONES. 137 



cleavage of genuine proteins like gelatin has given valuable support to 

 KOSSEL'S theory as to a basic nucleus in the protein bodies. 



On account of the cleavage taking place in digestion, the digestive 

 products should have a lower molecular weight than the original protein . 

 This is really the case. As these determinations have been made upor 

 impure substances or mixtures, the results l obtained are only of little 

 value. The same is true for the elementary analysis of the proteoses 

 and peptones. 2 



Besides the behavior in the salting-out process, attempts have been made to 

 find other points of difference between the peptones and proteoses. SCHROTTER 

 and FRANKEL 3 consider the sulphur content as a pronounced point of difference. 

 The peptones, according to them, are free from sulphur, while the proteoses, 

 on the contrary, contain sulphur. FRANKEL has been able to find only one pro- 

 teose (in KUHNE 's sense) which did not contain sulphur. 



In the preparation and separation of various proteoses and peptones 

 all precipitable protein is always removed first by neutralization and then 

 by boiling. The proteoses may then be separated from the peptones 

 by means of ammonium sulphate according to KUHNE'S method, and 

 divided into different fractions according to the method of PICK and the 

 HOFMEISTER school. The separation and preparation of pure hetero- 

 and protoproteoses can be best performed by the method suggested 

 by PICK, but this method, as well as- that with ammonium sulphate, 

 gives good results only when the precautions suggested by HASLAM* 

 are carefully followed. We can here only refer to the cited works of 

 Kuhne and co-workers, of E. ZUNZ and especially those of the HOFMEISTER 

 and the SIEGFRIED schools. In regard to the literature on the detection 

 of proteoses and peptones in animal fluids we refer to Chapters VI and XV. 



If we wish to detect the presence of so-called true peptone, by means 

 of. the biuret reaction in a solution saturated with ammonium sulphate, 

 we add a slight excess of a concentrated solution of caustic soda and cool, 

 and then add a two per cent solution of copper sulphate drop by drop, 

 after the sodium sulphate has separated out. 



In the quantitative estimation of proteoses and peptones we make 

 use of the nitrogen estimation, the biuret test (colorimetric), and the 

 polarization method. These methods do not give exact results. 



The polypeptides have had their most important properties discussed 

 on pages 85-89, and of the cleavage products of the proteins only the 

 amino-acids remain to be discussed. 



^abanejew, Ber. d. d. chem. Gesellsch., 26, 385; Paal, ibid., 27, 1827; Sjoqvist, 

 Skand. Arch. f. Physiol., 5. 



2 Elementary analyses of proteoses and peptones will be found in the works of 

 Kuhne and Chittenden and their pupils, cited in footnote 3, p. 129; also by Herth, 

 Zeitschr. f. physiol. Chem., 1, and Moiiatshefte f. Chem., 5; Maly, Pfliiger's Arch. 

 9, 20; Henninger, Compt. rend., 86; Schrotter, 1. c., Paal, 1. c. 



3 Schrotter, Monatshefte f. Chem., 14 and 16; Frankel, Zur Kenntnis der Zerfalls- 

 produkte des Eiweiss bei peptischer und tryptischer Verdauung, Wien, 1896. ' 



4 Journ. of Physiol., 32 and 36. 



