EXAMINATION OF THE LIVER. 135 



several times, then digest two to three days in an air-bath at 

 40. The digestion with chloroform-water effects two 

 objects: (1) it causes the complete cleavage of the nucleins; 

 and (2) it removes substances, always present in the extracts 

 of organs, which disturb or entirely prevent the precipitation 

 of the xanthine bases by silver nitrate. The first object 

 can only be attained otherwise by boiling with dilute acids 

 (Kossel). Whether the second may also be completely 

 effected by dilute acids alone has not been determined as yet 

 with certainty, though it is probable. At any rate, the- 

 digestion with chloroform- water has the advantage of great 

 convenience. 



After the digestion heat the mixture to boiling in a large 

 enameled iron dish or agate-ware pan and continue the boil- 

 ing, after acidifying faintly with acetic acid, until the albumin 

 has been completely precipitated. Then filter and evaporate 

 further to a volume of 800 to 1000 cc. Make the solution 

 moderately alkaline with ammonia, filter from the slight 

 precipitate formed, and precipitate completely with a 3 per 

 cent, ammoniacal solution of silver nitrate: a gelatinous 

 precipitate of the silver compounds of the xanthine bases is 

 formed. Care must be taken that no silver chloride precipi- 

 tates. If this should happen, more ammonia must be added.. 

 Add the silver nitrate solution until a small portion of 

 the filtrate, after acidifying with nitric acid and adding 

 some hydrochloric acid, gives a milky turbidity. Filter off 

 the precipitate, wash well, place it in a flask and dissolve it- 

 while still moist in hot nitric acid of 1.1 specific gravity 

 (equal volumes of nitric acid, specific gravity 1.2, and water) 

 to which some urea has been added. The solution must be 

 almost clear. Filter hot and let stand twenty-four hours. 

 Guanine-, adenine- and hypoxanthine-silver nitrate crystal- 

 lize out, while xanthine-silver nitrate remains in solution.. 

 Filter and wash the precipitate. 



