ADVANCED PHYSIOLOGICAL CHEMISTRY 441 



by the demonstrator, or a similar extract may be prepared by dissolving 

 some commercial meat extract in water. 



To remove the phosphates and the last traces of proteids 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.) 1 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 crystals of creatin will have separated out. These are 

 collected on a filter (and for this 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. 



The Chemistry of Creatin. If the oxygen which is attached to 

 the carbon atom of a urea molecule be displaced by an amido group, 

 the body called guanidin 



is obtained. If the two hydrogen atoms attached to one of 

 the side amido groups be displaced, the one by a methyl radicle 

 ^nd the other by acetic acid, we obtain methyl-guanidin-acetic 

 acid, which is creatin. It is prepared synthetically by the union 

 of cyanamide CN . NH 2 and sarcosin (methyl amido acetic acid 

 CH 2 .NH(CH 3 ).COOH). When cyanamide is hydrolysed by boiling 

 it with baryta water it yields urea, and, consequently, when creatin 

 is similarly treated it yields sarcosin and urea. Thus : 



X NH 2 

 NH = C/ 



\N<CHs C OOH + H 2 - - C<f ^ + CH 2 - NH<H &H 



(Creatin) +( Water) = (Urea) (Sarcosin) 



On account of this close chemical relationship it has been supposed that 



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

 dissolved in 200 c.c. water, and to this is slowly added S 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, 



