664 THE PRECURSORS OF UREA 



subject them to elementary analysis. As a method of estima- 

 tion, the preparation of urea crystals could yield only minimal 

 figures. 



THE PRECURSORS OF UREA 



(1) Hofmeister's view ; the formation of urea by an oxidation 

 synthesis. He showed that urea could be obtained directly from 

 egg- albumin or gelatine when they were oxidised with potassium 

 permanganate in the presence of ammonia. He further showed 

 that urea could be obtained by the same method from certain 

 products of proteid hydrolysis, the mono-amino acids glycin, leucin 

 and aspartic acid. It has not yet been shown that diamino acids 

 can by the same means be converted into urea, although it would 

 seem probable that they could. He experimented in the same 

 way with a large number of substances, and found that only 

 certain arrangements of the C atom would yield urea when oxi- 

 dised in the presence of ammonia. He found that the acid radicle 

 - CHOH . COOH, or the amino-acid radicle - CH 2 . NH 2 . COOH, 

 readily yielded urea, and that in certain other groups the same 

 was true of the simpler compounds and not of the more complex 

 members of the same series. Thus with the CO . NH 2 group, 

 formamide (H . CO . NH 2 ) yielded urea but not acetamide ; with 

 the CN group, formo-nitrite (H . CN) but not aceto-nitrite ; and 

 with the CH 2 . OH group, methyl alcohol but not ethyl alcohol. 

 From these various radicles he supposed that a radicle CO . NH 2 

 was produced either as oxamic acid (CO . NH 2 . COOH) or as 

 formamide (H . CO . NH 2 ), and that this radicle combined with 

 NH 2 , derived from the oxidation of ammonia, to produce urea. 



H . CO . NH 2 + NH 3 + O = NH 2 . CO . NH 2 + H 2 O. 



This theory supposes that in the body proteids are broken down 

 into mono-amino acids and ammonia, which together yield urea 

 by undergoing further oxidation and a final synthesis of their 

 nitrogenous products. All the conditions necessary for this view 

 are present in the body. It is obvious that urea, which contains 

 two NH 2 groups, could not arise direct from a mono-amino acid 

 except by some process of condensation of two molecules into 

 one, and it has been found that in the absence of ammonia 

 oxidation of proteid with potassium permanganate does not yield 



