FORMATION OF UREA. 617 



observed in certain diseases of the liver. This will be considered in 

 detail in connection with the formation of urea in the liver. It is natural 

 that there should be a diminished formation of urea after a decrease 

 in the ingestion of proteins or in a lowered catabolism. In diseases of 

 the kidneys which disturb or destroy the integrity of the epithelium of 

 the convoluted urinary tubules, the elimination of urea is considerably 

 diminished. 



Recently by means of PFAUNDLER'S 1 method, by precipitating the 

 urine with phosphotungstic acid and closely studying the precipitate 

 as well as the filtrate, it has been possible to learn further about the divi- 

 sion of the nitrogen of the urine. We determine a, the total nitrogen; 

 b, the nitrogen of the phosphotungstate precipitate; and c, the nitrogen 

 in the nitrate from the phosphotungstate precipitate. This last con- 

 tains the urea, hippuric acid, oxyproteic acids, and other bodies whose 

 nitrogen is ordinarily designated as monamino-acid nitrogen. The 

 urea nitrogen is especially determined. The bodies precipitated by 

 phosphotungstic acid are not all known; but uric acid and purine 

 bases, ammonia, creatinine, pigments, diamino-acids, diarnines and 

 ptomaines (if they occur), sulphocyanides, carbamic acid, urine mucoid, 

 and proteid belong to this group. Special methods have been suggested 

 for the determination of several of these substances (see below). 



The urea nitrogen is always the greatest part of the total nitrogen, 

 but otherwise the division of the nitrogen undergoes considerable varia- 

 tion. According to v. JACKSCH 2 normal human urine contains from 1.5 

 to 3 per cent of the total nitrogen as amino-acid nitrogen and 5.16 to 8.5 

 per cent as ammonia and purine bodies. Other experimenters have 

 obtained different results, and our knowledge on this subject is not suffi- 

 cient. Very great variations seem to occur not only in the healthy 

 individual, but also and to a greater degree in diseased conditions. 3 



Formation of Urea in the Organism. The experiments to produce 

 urea directly from proteins by oxidation have led to the formation of 

 some guanidine, bat urea has not been obtained positively. On the 

 hydrolysis of proteins arginine has been found among other products, 

 and as it is also produced in tryptic digestion, it is possible that a small 

 portion of the urea is produced in this manner, varying according to the 

 kind of protein (DRECHSEL, KOSSEL, see Chapter III). DRECHSEL 

 claims that about 10 per cent of the urea can be accounted for in this 

 way. 



The possibility of a formation of urea from arginine has gained in 



1 Zeitschr. f. physiol. Chem., 30. 



2 Zeitschr. f. klin. Med., 50. 



3 See Satta, Hofmeister's Beitrage, 6, which also gives the literature, and Erben, 

 Zeitschr. f. Heilkunde, 25. 



