128 THE PROTEIN SUBSTANCES. 



or alkalies, and by the putrefaction of the same. They may also be 

 formed in very small quantities, as by-products, in the investigations 

 of animal fluids and tissues, and the question as to the extent to which 

 these exist preformed under physiological conditions requires very 

 careful investigation. 



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 circum- 

 stances 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 

 conception 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 

 possibly there 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 pro- 

 teoses 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 solu- 

 tion is saturated with NaCl in substance, the proteose is partly pre- 

 cipitated 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. 



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



