URINE. 295 



food. The total purine base content is made up of the products 

 of two distinct forms of metabolism, i. e., metabolism of ingested 

 nucleins and purines and metabolism of tissue nuclein material. 

 Purine bases resulting from the first form of metabolism are said 

 to be of exogenous origin whereas those resulting from the second 

 form of metabolism are said to be of endogenous origin. The daily 

 output. of purine bases by the urine is extremely small and varies 

 greatly with the individual (16-60 milligrams). The output is in- 

 creased after the ingestion of nuclein material as well as after the 

 increased destruction of leucocytes. A well marked increase ac- 

 companies leukaemia. Edsall has very recently shown that the out- 

 put of purine bases by the urine is increased as a result of X-ray 

 treatment. 



EXPERIMENT. 



i. Formation of the Silver Salts. Add an excess of magnesia 

 mixture 1 to 25 c.c. of urine. Filter off the precipitate and add am- 

 moniacal silver solution 2 to the filtrate. A precipitate composed of 

 the silver salts of the various purine bases is produced. The purine 

 bases may be determined quantitatively by means of Kriiger and 

 Schmidt's method (see p. 405). 



2. Inorganic Physiological Constituents. 

 Ammonia. 



Next to urea, ammonia is the most important of the nitrogenous 

 end-products of protein metabolism. Ordinarily about 4.6-5.6 per 

 cent of the total nitrogen of the urine is eliminated as ammonia 

 and on the average this would be about 0.7 gram per day. Under 

 normal conditions the ammonia is present in the urine in the form of 

 the chloride, phosphate or sulphate. This is due to the fact that 

 combinations of this sort are not oxidized in the organism to form 

 urea, but are excreted as such. This explains the increase in the 

 output of ammonia which follows the administration of the am- 

 monium salts of the mineral acids or of the acids themselves. On 

 the other hand when ammonium acetate and many other ammonium 

 salts of certain organic acids are administered no increase in the 



1 Magnesia mixture may be prepared as follows: Dissolve 175 grams of MgSCX 

 and 350 grams of NEUC1 in 1400 c.c. of distilled water. Add 700 grams of 

 concentrated NH 4 OH, mix very thoroughly and preserve the mixture in a glass- 

 stoppered bottle. 



2 Ammoniacal silver solution may be prepared according to directions given 

 on page 407. 



