128 THE PROTEIN SUBSTANCES. 



in common were formerly considered as the following: They all give 

 the color reactions of the proteins, but with the biuret test they give a 

 more beautiful red color than the ordinary proteins. They are pre- 

 cipitated by ammoniac al lead acetate, by mercuric chloride, tannic, phos- 

 photungstic, and phosphomolybdic acids, by potassium-mercuric iodide 

 and hydrochloric acid, and also by picric acid. They are precipitated 

 but not coagulated by alcohol, that is, the precipitate obtained is soluble 

 in water even after being in contact with alcohol for a long time. The 

 proteoses and peptones also have a greater diffusive power than native 

 proteins, and the diffusive power is greater the nearer the questionable 

 substance stands to the final product, the now so-called true peptone. 



These old views have gradually undergone an essential change. After 

 HEYNSIUS' l observation that ammonium sulphate was a general pre- 

 cipitant for proteins, and for peptones in the old sense, KUHNE and his 

 pupils 2 proposed this salt as a means of separating proteoses and pep- 

 tones. Those products of digestion which separate on saturating their 

 solution with ammonium sulphate, or can indeed be salted out at all, 

 are considered by KUHNE and also by most of the modern investigators 

 as proteoses, while those which remain in solution are called peptones 

 or true peptones. These true peptones are formed in relatively large 

 amounts in pancreatic digestion, while in pepsin digestion they are formed 

 only in small quantities or after prolonged digestion. 



According to SCHUTZENBERGER and KUHNE 3 the proteins yielded 

 two chief groups of new protein bodies when decomposed by dilute 

 mineral acids or with proteolytic enzymes; of these the anti group shows 

 a greater resistance to further action of the acid and enzyme than the 

 other namely, the hemi group. These two groups are, according to KUHNE, 

 united in the different proteoses, even though in various relative amounts, 

 and each proteose contains the anti as well as the hemi group. The 

 same is true for the peptone obtained in pepsin digestion, hence he calls 

 it amphopeptone. In tryptic digestion a cleavage of the amphopeptone 

 takes place into antipeptone and hemipeptone. Of these two peptones 

 the hemipeptone is further split into amino-acids and other bodies 

 while the antipeptone is not attacked. By the sufficiently energetic 

 action of trypsin only one peptone is at last obtained the so-called 

 antipeptone. 



1 Pfliiger's Archiv, 34. 



2 See Kiihne, Verhandl. d. naturhistor. Vereins zu Heidelberg (N. F.), 3; J. Wenz, 

 Zeitschr. f. Biologic, 22; Kiihne and Chittenden, Zeitschr. f. Biologic, 22; R. Neu- 

 meister, ibid., 23; Kiihne, ibid., 29. 



3 Schiitzenberger, Bull, de la Soc. chimique de Paris, 23; Kiihne, Verhandl. d. 

 naturhist. Vereins zu Heidelberg (N. F.), 1, and Kiihne and Chittenden, Zeitschr. f. 

 Biologic, 19. See also Paal, Ber. d. deutsch. chem. Gesellsch., 27. 



