EXAMINATION OF MUSCULAR TISSUE. 25 



separate, and add an ammoniacal solution of 2.5 g. of silver 

 nitrate in about 100 cc. of water. The precipitate, which 

 consists for the most part of hypoxanthine silver besides a 

 .ittle xanthine silver, is then collected on a filter and washed 

 a few times with water. 



Separation of Hypoxanthine and Xanthine. 



The separation of these two xanthine bases is accomplished 

 by converting them into the silver nitrate compounds. These 

 compounds conduct themselves differently towards nitric 

 acid. The hypoxanthine silver nitrate compound is very 

 difficultly solub'e in nitric acid; the xanthine silver nitrate 

 compound is far more readily soluble. The following is the 

 best method of procedure: 



Put the still moist precipitate into a flask and pour over 

 it a mixture of 100 cc. of nitric acid and 100 cc. of water, 

 add 1 g. of urea, heat just to boiling, and let cool. The 

 hypoxanthine silver contained in the precipitate is converted 

 into hypoxanthine silver nitrate, which remains partly un- 

 disso.ved and partly goes into solution, but separates out of 

 the solution again on cooling The addition of the urea is 

 to prevent the formation of nitrous acid, which might decom- 

 pose the xanthine bases. Filter the hypoxanthine silver 

 nitrate off after a few hours and wash until the wash-water 

 no longer reacts strongly acid. Let the filtrate (without the 

 wash-water) stand till next day and filter (without working 

 up the precipitate, which is a mixture of hypoxanthine silver 

 nitrate and xanthine silver nitrate). The filtrate is used to 

 show the presence of xanthine. The hypoxanthine silver 

 nitrate is examined under the microscope (fine needles fre- 

 quently grouped in the form of stars). 



