100 Wilson and Cramer 



The portion remaining insoluble is called "insoluble protagon," and is 

 purified by recrystallisation from alcohol and then called " protagon thrice 

 recrystallised." This protagon is therefore insoluble in boiling acetone. 

 On page 11a method for the preparation of protagon is described, which 

 consists in extracting brain with boiling acetone. The substances crystallis- 

 ing out on cooling from the various extractions are alleged to be " typical 

 protagon." We wish to point out that even if protagon is a mixture, it 

 cannot be at the same time soluble and insoluble in one and the same 

 solvent. We doubt whether the substances obtained by the method of 

 acetone extraction are protagon. The evidence given by Rosenheim and 

 Tebb on this point is neither very clear nor very conclusive. The nitrogen 

 and phosphorus contents of the crude products only are determined. 

 Although they differ from each other and partly from protagon, it is not 

 said which product is considered to be protagon. No attempt is made to 

 show that a substance of a constant chemical composition identical with 

 protagon is obtained after repeated recrystallisation. Besides, in our ex- 

 perience, protagon is not easily soluble in acetone. When the experiments 

 described in a previous paper by Lochead and Cramer were carried out, 

 acetone was tried as a means of extracting protagon from brain and found not 

 to be a suitable solvent. The samples of protagon which we have prepared 

 are also not readily soluble in acetone. We believe that we have found an 

 explanation of the apparent contradiction between these observations on the 

 solubility of protagon in acetone, and shall refer to it later. 



Here it may be sufficient to point out the inconsistency in applying the 

 name protagon both to a substance soluble in acetone and to a substance 

 insoluble in this solvent. 



It is evident that many observations, on the basis of which the existence 

 of protagon as a definite chemical compound has been denied, were made 

 on material called protagon, which, however, was not identical with 

 protagon, but at the best represented a crude product containing protagon, 

 together with other substances. 



This looseness of designation is, as we have seen, due to the fact that, 

 contrary to the ordinary rules of chemical investigations, the chemical 

 composition is not considered to be a criterion of protagon but its method 

 of preparation. In this way the impression has gained ground that 

 protagon is such a variable substance that it is a mere accident if a sample 

 is obtained of the same composition as Gamgee's protagon. We believe 

 that we have found an explanation of these failures to obtain protagon, and 

 shall show later that protagon can be prepared without difficulty, if certain 

 conditions are observed during its preparation and recrystallisation. 



Protagon is a Product of Definite Physical Constants. 

 We have spoken of the chemical composition as the only means of 

 identifying protagon, because its physical characters, even its crystalline 

 form, are neither very conclusive evidence of its identity nor do they allow 



