370 THE FINAL DECOMPOSITION OF FOODSTUFFS IN THE BODY 



tion, but by cleavage of the arginin with absorption of water into urea and 

 diamino-valerianic acid (Drechsel). 



Drechsel estimated that 100 parts of proteid undergoing cleavage in the 

 body would be able to yield in this way 3.8 parts of urea without suffering any 

 oxidation. Since, further, 100 parts of proteid yield altogether 34.3 parts urea, 

 it follows that about one-ninth of the total urea eliminated may issue from the 

 proteid by a simple process of cleavage. In fact we always find in all animals, 

 even in those in which the greatest part of the nitrogen of the urine appears as 

 uric acid, a certain quantity of urea (cf. pages 70 and 75 for the arginin con- 

 tent of the different proteids). 



But by far the greatest part of the urea eliminated arises from proteid 

 by processes of oxidation. When amino acids (glycocoll, leucin, aspartic acid) 

 are digested with finely ground, fresh organs, ammonia is split off from them 

 (Lang). In the mammals these compounds as well as ammonia are trans- 

 formed into urea and as such are given off through the kidneys (Nencki, 

 Salkowski et al). It is conceivable, therefore, that ammonia represents an 

 intermediate stage in the formation of urea. Since, however, both ammonia 

 and the above-mentioned amino acids contain only one atom of N in the 

 molecule, and urea contains two, the latter can only be formed from the 

 former by a process of synthesis. This might take place by the combination 

 of ammonia with carbon dioxide into carbamic acid or ammonium carbamate, 

 and the formation of urea from these by the loss of water. In fact, Drechsel 

 succeeded in preparing urea by subjecting an aqueous solution of ammonium 

 carbamate to electrolysis with an automatic commutator in the circuit, so that 

 the salt was alternately exposed in rapid succession to oxidation by nascent 

 oxygen and reduction by nascent hydrogen. The processes taking place are 

 illustrated by the following scheme: 



I. NH 2 .CO.O.NH 4 + = NH 2 .CO.O.NH 2 + H 2 



ammonium carbamate I 



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



urea. 



The fact that carbamic acid can be demonstrated in the blood and in the 

 urine constitutes a strong argument for this view. 



The formation of urea might also take place by the union of an amido 

 residue, CONH 2 , at the instant of its formation, with the amidogen, NH 2 , aris- 

 ing by oxidation of ammonia (Hofmeister). 



A definite decision between these two possible explanations is not to be had 

 at present ; besides, it is not at all certain that the formation of urea takes place 

 by one method only. 



Concerning the seat of urea formation, we can think of two possibilities : 

 either it is formed fin all parts of the body wherever proteid is broken down, 

 or certain organs have the function of transforming the intermediary prod- 

 ucts of metabolism into urea. After removal of the kidneys urea collects in 

 the body in considerable quantities; these organs cannot therefore play an 

 all-important part in its production. Meissner found in the liver of the dog 

 larger quantities of urea than in the blood, and so designated this organ as 

 the one in which the major part of the urea of mammals originates. 



