284 PRACTICAL PHYSIOLOGY 



directly into the drain pipes of the sinks to avoid all risk of generation 

 of HCN. 



Standard uric acid solution. Dissolve in a 500 c.c. flask exactly 1 gm. 

 of uric acid in 150 c.c. of water by the aid of 0-5 gm. lithium carbonate. 

 Dilute to 500 c.c. and mix. Transfer 50 c.c. to a litre flask : add 500 c.c. 

 of 20 per cent, sodium sulphite solution ; dilute to 1,000 c.c. and mix. 

 Transfer to small bottles (200 c.c.) and stopper tightly. In unopened 

 bottles this solution keeps almost indefinitely, in opened bottles it 

 remains good for two to three months. 



Estimation of the Total Purine Bodies. Modified Garnered 's Method. 

 Principle. Ammoniacal silver nitrate, in the presence of neutral salts, 

 or, better, of magnesium mixture, combines with all the purine bodies 

 to form an insoluble salt of definite composition. The nitrogen in 

 this can be estimated by Kjeldahl's method, and the result expressed 

 as total purine nitrogen. This method is exceedingly useful in studying 

 the metabolism of purine bodies. 



Solutions Necessary. 1. Magnesia mixture. This consists of crystal- 

 lised magnesium chloride 110 gms., ammonium chloride 110 gms., 

 and -880 ammonia 284 c.c., made up with water to 1,000 c.c. 



2. Ammoniacal silver nitrate. Dissolve 26 grs. silver nitrate in 

 about 300 c.c. water, add ammonia to this until the precipitate of silver 

 oxide, which first forms, redissolves. Dilute the solution to 1,000 c.c. 



3. Kjeldahl's apparatus and solutions (see p. 279). 

 Determination. 240 c.c. protein-free urine are mixed with 30 c.c. 



magnesia mixture, and 30 c.c. of a 20 per cent, ammonia solution. This 

 process is best done in a measuring cylinder. After the precipitate has 

 settled, which it does in a few minutes, it is filtered through a dry folded 

 filter and two portions of the filtrate are taken amounting to 125 c.c. each. 

 Each of these corresponds to 100 c.c. of the original urine. They are 

 both treated in exactly the same way, and should yield similar results. 

 Each is mixed with 10 c.c. ammoniacal silver nitrate, and the mixture, 

 after the precipitate has settled somewhat, filtered through an ash-free 

 filter paper (of 10 cm. diameter). The last traces of the precipitate are 

 removed from the beaker by means of weak ammonia water. The next 

 stage consists in washing the precipitate with distilled water at 60 until 

 it is free from ammonia, as the presence of this would vitiate the 

 determination of the nitrogen. In order to do this, the precipitate 

 should be allowed to stand exposed to the air overnight so that it may 

 become partially dried, in which state the washing with water is much 

 easier than when the precipitate is moist, for then it forms a gummy 

 mass. The washing must be continued until the washings no longer 

 react alkaline to litmus. In order to remove the last traces of ammonia, 

 the filter paper, with the precipitate on it, is carefully removed to a 

 Kjeldahl's combustion flask ; about 50 c.c. of water and a little (0-5 gm.) 

 magnesium oxide are added. The mixture is then boiled, whereon 

 the magnesia expels the ammonia. The boiling is continued until 

 only about 10 c.c. of fluid remain, and then 20 c.c. sulphuric acid, etc., 

 are added, and the nitrogen determined in the usual way. 



Estimation of Creatinine. Folin's Method. The urine must be free 

 from aceto-acetic acid and hydrogen sulphide, and must contain not 

 more than traces of acetone. Measure 10 c.c. urine with a pipette 

 into a 500 c.c. graduated flask. Add 15 c.c. saturated aqueous 

 picric acid solution (about 1-2 per cent.) and 5 c.c. 10 per cent, caustic 

 soda solution. Mix and allow to stand for five minutes. Fill up the 



