162 UREA. 



the decomposition of casein with concentrated boiling hydrochloric acid and chloride 

 of zinc a base to which he has given the name of 'lysatin.' When boiled with 

 baryta water in excess it yields urea l . 



What knowledge have we of the possible or probable form under 

 which the nitrogen may make its primary exit from the muscles 1 The 

 connection of muscle-kreatin with urea-formation has been already 

 discussed ( 484, 485) and the evidence of the connection may be 

 briefly summed up as follows. A considerable amount of kreatin exists (?) 

 in the muscles at any one time, hence probably a considerable amount 

 is continuously being formed ; there is no evidence that any of this 

 kreatin leaves the body as such, hence it is presumably converted into 

 some other substance before being discharged, and this other substance 

 is probably urea, seeing that kreatin may be readily decomposed into 

 urea and sarkosin. There are further reasons for supposing that the 

 nitrogen leaves the muscles as a compound containing comparatively 

 little carbon, and kreatin answers to this requirement, since it contains 

 only four atoms of carbon to three of nitrogen 2 . If this latter view be 

 correct it implies that the nitrogen is not split off in the form of amido- 

 acids, since there is not sufficient carbon in proteids to convert their 

 nitrogen into the amido-acids with which we have to deal in the body. 

 On the other hand when these amido-acids (glycin, leucin, aspartic acid 

 and asparagine) are introduced into the body they are partly converted 

 into urea, so that if formed they would account for a portion at least of 

 the urea excreted. 



When proteids are decomposed by caustic alkalis, more especially 

 baryta, or during putrefaction, they yield much ammonium carbonate 

 which by simple dehydration would give urea. Now although am- 

 monium carbonate, like many other salts of this base, is readily 

 converted into urea when administered to man or other animals, there 

 is no evidence, although it is a possibility, that the nitrogen leaves the 

 tissues as ammonium carbonate. 



The above statements seem to embrace all that can be suggested as 

 to the tissue-antecedents of urea and it remains now to consider the 

 probable mode and seat of their conversion into urea. As regards 

 kreatin it may be that it is split up into urea and sarkosin, the latter 

 being like other amido-acids, also converted into urea. When the 

 amido-acids are compared with urea it is not conceivable, with our 

 present chemical knowledge, how they can give rise to urea in any way 

 other than by being broken down into an ammonia stage and a 

 subsequent synthesis of urea from this product. The synthesis may 



1 Ber. d. d. chem. GeselL 1890, S. 3096. Cf. Arch. f. Physiol. Jahrg. 1891, S. 

 254 et seq. 



2 Bunge, loc. cit. pp. 320, 328. 



