676 THE PRECURSORS OF UREA 



oxidation and hydrolysis, when urea, oxalic acid and C0 2 are 

 finally produced. 



NH - CO NEL CO 9 



CO C-NH\ CO CO. OH NH 9 \ 



| i, CO = I I ^ CO. 



NH-C-NH/ NH 2 CO. OH NH 2 / 



A different decomposition of uric acid is brought about by 

 heating it with strong hydrochloric acid in sealed tubes at 

 170 C., when it is split into glycin, ammonia, and C0 2 . It 

 seems likely that the splitting of uric acid by the tissue ferment 

 resembles this last mode of decomposition, but the information 

 on the subject is as yet meagre. It has been shown that 

 ammonia is produced when uric acid is decomposed with extracts 

 of liver, kidney, spleen, and muscle. It has also been found 

 that when uric acid is digested with kidney a formation of glycin 

 takes place. We may conclude provisionally that, when uric 

 acid is converted into urea in the body, the immediate precursor 

 of the urea is ammonia. 



(d) Kreatin and Kreatinin. They deserve a word in this 

 connection because they bear such an obvious chemical relation 

 to urea and are formed abundantly in the body. Kreatin (methyl- 

 guanidin acetic acid) is split by boiling with alkalies into urea 

 and sarcosin. Muscles contain about 0'4 per cent, of kreatin and 

 kreatinin together, and after severe muscular exercise or prolonged 

 starvation this figure may be more than doubled. It is easy to 

 calculate that the muscles of a man may contain a good deal 

 more than 50 grm. of these substances. The quantity of these 

 substances in the urine is about 2 grm. a day, and it seems likely 

 that, as in the case of uric acid, the urinary kreatinin has two 

 distinct origins, an exogenous and an endogenous. Kreatin given 

 by the mouth to man is excreted as kreatinin in the urine, and it 

 is certain that in meat-eaters some of the urinary kreatinin is 

 derived from the meat of the food. But, in rabbits recent experi- 

 ments have failed to show that more than a minute portion of 

 the kreatin administered was excreted as kreatinin, arid further 

 the balance could not be found in the urine either as ammonia, 

 urea, or uric acid. 



Folin has recently investigated the excretion of kreatinin in the 



