PHYSIOLOGICAL CHEMISTRY 357 



The protein in the extract is then coagulated by boiling, and, after cooling, the 

 coagulum removed by filtration. 



A similar extract may be prepared by dissolving some commercial meat extract 

 in water. 1 



To remove the phosphates and the last traces of proteins from this extract a 

 saturated solution of subacetate of lead is added to it until no more precipitate is 

 produced. (Care should be taken that an excess of the subacetate solution is not 

 added. This may be ascertained by filtering samples of the extract and seeing if 

 these yield further precipitates with the subacetate solution. ) The precipitate 

 thus obtained is removed by filtration. 



The excess of lead is precipitated from the filtrate by passing a current of 

 sulphuretted hydrogen through it. The precipitate of lead sulphide is removed 

 by filtration. The filtrate is then evaporated to small bulk (any sulphur which 

 may separate out being removed by filtration) and allowed to stand on ice for two 

 or three days, when a large number of oblique rhombic crystals of creatin will 

 have separated out. (See Fig. 233. ) These are collected on a filter (for which 

 purpose a suction pump will be found necessary) and are thoroughly washed with 

 alcohol until no more pigment is removed. The filtrate* is preserved for the 

 isolation of the other extractives. 



Xanthin and Hypoxanthin. The creatin-free filtrate is made strongly 

 alkaline with ammonia, and is then mixed with ammoniacal solution of silver 

 nitrate. The purin bodies are thus precipitated. The precipitate is collected on 

 a filter paper and thoroughly washed with dilute ammonia, and the hypoxanthin 

 and xanthin are separated from it by the following method : the precipitate is 

 removed from the filter paper and dissolved in boiling nitric acid (spec. grav. I'l), 

 a few crystals of urea being added to the solution so as to destroy any nitrous 

 acid which may be present, and which would decompose the purin bodies. When 

 all the precipitate has dissolved the solution is quickly filtered hot, and the 

 filtrate is allowed to stand over night, when it will be found that a precipitate 

 consisting of fine needle-shaped crystals (Fig. 234) has separated out. This 

 consists of hypoxanthin silver nitrate combined with nitric acid ; to remove the 

 nitric acid wash it with distilled water, transfer it from the filter to a small 

 beaker and boil it with ammonia until the crystals break up and become 

 amorphous, and then, to remove the silver, pass in H 2 S, filter off the silver 

 sulphide, and evaporate the filtrate slowly to dryness, when a white chalk-like 

 mass of hypoxanthin will be obtained. In order to obtain the xanthin silver salt 

 the filtrate from hypoxanthin should be treated with ammonia, when a few 

 yellow flakes of the salt will be obtained. To separate the xanthin this pre- 

 cipitate is treated in exactly the same way as for hypoxanthin. 



Test for Hypoxanthin. Place a piece of hypoxanthin in a small evaporating 

 dish with a few drops of concentrated pure nitric acid and evaporate slowly to 

 dryness : a brilliant yellow residue is obtained. Cool, and then add a drop of 

 sodium hydrate solution, when the residue will change to orange. If the residue 

 be dissolved in water and the solution again evaporated to dryness the orange 



1 The following amounts are suitable for this preparation : Ten grm. bovril are 

 dissolved in 200 c.c. water, and to this is slowly added 60 c.c. of a saturated 

 solution of subacetate of lead. After the precipitate has settled down a sample 

 of the supernatant fluid is removed by a pipette to a test tube and tested with 

 the subacetate solution to be certain that no more precipitate is produced. 



