338 PHYSIOLOGICAL CHEMISTRY. 



often the cause of the increase found in these cases. The amount 

 of nitrogen contained in the urea does not correspond with the 

 total amount of nitrogen in the urine, since, as PFLUGER has shown, 

 the amount of nitrogen which under physiological conditions occurs 

 combined with other combinations than urea is, on an average, 

 13.4$, sometimes indeed 16$, of the total nitrogen. In disease this 

 relationship may be essentially changed and, as an example, in 

 a case of phosphorus poisoning FRAENKEL observed that the 

 amount of nitrogen contained in the urea was less than one half 

 of the total amount of nitrogen in the urine. 



A diminished elimination of urea occurs in a reduced consump- 

 tion of proteids, and also a fact which is of interest in regard to 

 the importance of the liver in the formation of urea in certain 

 diseases of the liver, as in acute yellow atrophy and sometimes in 

 interstitial cirrhosis. Under these conditions the amount of ammo- 

 nia in the urine as compared to the urea may be increased (HAL- 

 LERVORDEN, STADELMA^N). In diseases of the kidneys which 

 disturb or destroy the integrity of the epithelium of the tortuous 

 urinary passage the elimination of urea is considerably diminished. 



Formation of urea in the organism. The experiments to produce 

 urea directly from the proteids by oxidation have not led to any 

 positive results. We often obtain amido-acids as decomposition 

 products of albumin (see page 17), and we therefore conclude that 

 the amido-acids are intermediate steps in the formation of urea 

 from albumin. It has also been shown that leucin and glycocoll 

 (SCHULTZEK and NENCKI, SALKOWSKI), and asparaginic acid (v. 

 KNIERIEM) may be transformed into urea within the organism. 

 The nature of the chemical processes by which these transforma- 

 tions are effected is unknown. Many other ways for the formation 

 of urea have been suggested, but the only one which has been 

 demonstrated is the formation from ammonium carbonate in the 

 liver. After the researches of v. KNIERIEM, SALKOWSKI, FEDER, 

 MUKCK, SCHMIEDEBERG and WALTER, and HALLERVORDE^ had 

 shown that ammonium carbonate, or such ammonium-salts as are 

 burnt up in the system into carbonate, is converted into urea in the 

 body of carnivora and herbivora, v. SCHRODER furnished a decisive 

 proof of the formation of urea from ammonium carbonate in the 

 liver of mammalia. By passing blood which had been treated with 



