PROTEOSES AND PEPTONES. 127 



Between the peptone, which represents the final cleavage product, 

 and the proteose, which stands closest to the original protein, we have 

 undoubtedly a series of intermediate products. Under such circumstances 

 it is a difficult problem to try to draw a sharp line between the peptone 

 and the proteose group, and it is just as difficult to define our concep- 

 tion of peptones and proteoses in an exact and satisfactory manner. 



In the past we used to consider the peptones as the end products 

 in the hydrolysis, they still being true proteins, but we must call atten- 

 tion to the fact that since that time we have learned of polypeptide- 

 like cleavage products of the proteins, and also that polypeptides have 

 been prepared synthetically. With this in mind it is not possible to say 

 what we understand by the conception true proteid, and also that there 

 possibly exists a large number of intermediary steps between the original 

 modified proteid and the simplest cleavage products. There is no doubt 

 that those bodies which have been called proteoses and peptones are 

 chiefly mixtures ; and the question has been proposed by ABDERHALDEN 1 

 whether it is not best to drop the conception of proteoses and to call 

 all products precipitable by ammonium sulphate, etc., and previously 

 described as proteoses, peptones. 



Although there is much in favor of such a proposition, still on account 

 of the great importance which the conception of the proteoses has gen- 

 erally received, it is probably too early to drop the question of proteoses 

 entirely from a text-book, and we will therefore, as in the past editions, 

 discuss the historical development of the proteoses and peptones in the 

 ordinary sense. 



The proteoses (or albumoses) used to be considered as those protein 

 bodies whose neutral or faintly acid solutions do not coagulate on boil- 

 ing and which, to distinguish them from peptones, were characterized 

 chiefly by the following properties : The watery solutions are precipitated 

 at the ordinary temperature by nitric acid, as well as by acetic acid and 

 potassium ferrocyanide, and this precipitate has the peculiarity of dis- 

 appearing on heating and reappearing on cooling. If a proteose 

 solution is saturated with NaCl in substance, the proteose is partly 

 precipitated in neutral solutions, but on the addition of acid saturated 

 with salt it is more completely precipitated. This precipitate, which 

 dissolves on warming, is a combination of the proteose with the acid. 



We formerly designated as peptones those protein bodies which are 

 readily soluble in water and which are not coagulated by heat, whose 

 solutions are precipitated neither by nitric acid, nor by acetic acid and 

 potassium ferrocyanide, nor by NaCl and acid. 



The reactions and properties which the proteoses and peptones have 



1 Oppenheimer's Handb. der Biochem., Bd. 1, 1908. 



