322 BACTERIAL POISONS. 



normal urine, although present in exceedingly minute 

 quantity. Thus from 1200 litres of urine, only 1.2 grammes 

 (0.0001 per cent.) of this substance were obtained. It has 

 not been found in the urine of dogs or in that of leuco- 

 cythsemic patients. Thudichum was the first to isolate 

 paraxanthine from the urine, and he named it urotheo- 

 bromine (1879). ' 



The methiod employed for the isolation of this base is, 

 with a slight modification, that of E. Salkowski, as 

 originally proposed for the preparation of xanthine bases 

 froin urine. The urine in portions of 25 to 50 litres is 

 made alkaline with ammonium hydrate and allowed to 

 stand twenty-fi)ur hours. The clear supernatant fluid is 

 decanted from the precipitate of phosphates and treated 

 with silver nitrate (0.5 to 0.6 gramme per litre). The gray- 

 ish precipitate of xanthine compounds which forms is trans- 

 ferred to a filter and washed with water till free from 

 chloride ; it is then suspended in Water ' and decomposed 

 with a current of hydrogen sulphide. The liquid is filtered 

 by decaiitatiou aud the filtrate iS evaporated to dryness; 

 the residue is fextracted with 3 per cent, sulphuric acid to 

 remove uric acid ; the solution thus obtained, after it has 

 been rendered alkaline with ammonia, is pi'ecipitated by 

 silver nitrate. 



A better procedure is to concentrate the filtrate directly 

 over the flame or on the water-bath, till the uric acid begins 

 to crystallize out. It is then filtered, and the filtrate, after 

 diluting somewhat with water, is rendered alkaline with 

 ammonium hydrate ill order to precipitate any remaining 

 uric acid and phosphates. The whole is allowed to stand 

 one or two days, then filtered, and the filtrate again pre- 

 cipitated with silver nitrate. The thoroughly washed pre- 

 cipitate of the xanthine compounds, now free from uric 

 acid, is dissolved in as little as possible of hot nitric acid 

 of specific gravity 1.1, to which a little urea has been 

 added, and the clear solution is set aside for twenty-four 

 hours. Tiie silver salt of hypoxanthine crystallizes from 

 the solution and is filtered off. It can be purified by re- 

 peated recrystallization from hot nitric acid, containing a 



