106 Wilson and Cramer 



Gamgee's method by means of warm alcohol (see p. 104) and by extraction 

 with boiling absolute alcohol. In the latter case the boiling solvent is 

 poured on the powder and the mixture kept boiling for one to two minutes 

 in a water bath, moving the mixture all the time. The alcoholic solution is 

 filtered through a hot-water funnel ; the filtrate is allowed to drop into a 

 vessel cooled in ice. The same process of extraction is repeated twice. 

 The crude crystalline product is washed with ether and dried in vacuo. 



Recrystallisation is effected by pouring boiling absolute alcohol on the 

 sample of protagon. The solution is kept boiling for one minute and then 

 filtered as before. 



This method offers many advantages. Water and all the substances 

 soluble in cold alcohol and cold ether are removed before the extraction 

 begins, so that the bulk of the material is greatly reduced and less of the 

 hot solvent is necessary. In this way even a large quantity of material, 

 fifteen to twenty ox brains, can be worked up easily, while with other 

 methods the bulk of the material and the volume of alcohol are so 

 great that the manipulations cannot be carried out neatly and require 

 a longer time. 



Is Protagon a Definite Compound or a Mixture of Phosphatids 



AND CeREBROSIDES '* 



In the preceding pages we have considered protagon simply as a 

 substance prepared from brain, and having constant and definite chemical 

 and physical properties. The question whether it is a definite chemical 

 compound or a mixture we have left open, so that the facts which we have 

 observed and the conclusions which we have drawn remain independent 

 of this controversial subject. 



Conclusive proof of the chemical individuality of protagon can onl}' 

 be brought by synthesis. Evidence to the contrary could be obtained 

 by isolating the substances of which the mixture protagon is con- 

 stituent and to reconstitute protagon from them. Rosenheim and 

 Tebb hope to be able soon "to reconstitute a pure protagon" with a 

 phosphorus percentage varying from 0'9 to 1"26, by making a mechanical 

 mixture in certain proportions of substances nearly phosphorus free and 

 substances containing about 3 per cent, phosphorus. We have no doubt that 

 it is possible to obtain in this way a mixture of the same phosphorus per- 

 centage as protagon. But if that were to prove that protagon is a mixture, 

 one might also prove that fat is a mixture of glycerine and fatty acids, 

 because a mixture of these substances in certain proportions would have 

 the same carbon percentage. If Rosenheim and Tebb wish to prove that 

 this mixture of alcohol-soluble and alcohol-insoluble substances is identical 

 with protagon, they will have to show that this mixture retains its com- 

 position after repeated recrystallisations and that it has the same specific 

 rotatory power as protagon. 



