668 THE PRECURSORS OF UREA 



It has been tacitly assumed that autolysis represents a normal 

 tissue metabolism, and that, if a substance is formed during 

 autolysis, we may believe that it occurs also during nitrogenous 

 katabolism in the living body. This idea, although not universally 

 accepted, is in the present state of our knowledge justifiable. Thus 

 arginin, like the amino acids, is formed during autolysis, and is to 

 be found in the urine during phosphorus poisoning. From this we 

 may infer that arginin is an intermediate product of normal meta- 

 bolism which under these circumstances has failed to be converted 

 into its usual end product, urea. 



The possibility and likelihood of urea being formed in the 

 tissues in accordance with Drechsel's view has been amply de- 

 monstrated. We have to consider now what proportion of the 

 total urea has this origin. The available data are as follows. 

 We have already considered the distribution of arginase in the 

 tissues. Arginin has been demonstrated among the products of 

 the autolysis of almost every tissue. It has been missed in the 

 case of the kidney, thymus, and wall of the alimentary canal, but 

 as these are now known to contain arginase, the absence of 

 arginin may be only apparent. Kossel has shown that the pure 

 proteids of beef, milk, or bread when hydrolysed by acids yield 

 about 5 per cent, by weight of arginin, and would therefore yield 

 less than 2 per cent, by weight of urea from arginin. Levenne 

 has found that liver hydrolysed by acid yields about 0'5 per 

 cent, by weight of arginin, and that pancreas and spleen yield 

 about half that amount. From such data it is impossible to 

 answer the above question ; we do not know how much urea is 

 formed in the body in this way, but it does not seem likely that 

 there is enough arginin in the body to yield a very high propor- 

 tion of the total urea. It has been found that during complete 

 starvation, when the body proteids are being used up, the urea- 

 nitrogen may form only 15 per cent, of the total nitrogen in the 

 urine. It appears, therefore, that the endogenous formation of 

 urea cannot be a very important one. Drechsel calculated that 

 less than 4 out of the 34 grm. of urea theoretically obtainable 

 from 100 grm. of proteid could be" formed from arginin, and he 

 stated a second view to account for the formation of the 

 balance. 



(3) Drechsel 's view ; urea from ammonium carbamate. He 

 pointed out that when free ammonia (NH 3 ) unites with CO 



