On Protagon 109 



fundamentally different from the view that protagon is a variable and 

 indefinite mixture of cerebrosides and phosphatids. 



COXCLUSIOXS. 



1. Protagon is a substance of a definite chemical composition, retaining 

 this composition after repeated recrystallisation. 



2. Protagon is a substance with definite and constant physical properties. 

 The specific rotatory power and tlie refractive index of several samples of 

 protagon have been determined. 



3. Protagon is identified by its chemical composition and by its physical 

 constants. Many substances to which the name protagon has been given 

 on account of their method of preparation, do not conform to these con- 

 ditions, and therefore have no claim to the name protagon. Couerbe's 

 cerebrote is not identical with protagon, but probably a mixture of 

 substances of which protagon is one. 



4. Protagon is decomposed by a prolonged treatment with warm alcohol. 

 The so-called process of fractional crystallisation is therefore in reality a 

 process of partial decomposition. The conclusions which have been drawn 

 on the assumption that it is a process of recrystallisation are not valid. 

 There is, consequently, no evidence for the view that protagon is a mixture 

 of cerebrosides and phosphatids. 



5. The constancy of the physical and chemical properties of protagon 

 support the view that protagon is a definite compound. The substances 

 isolated from protagon after prolonged treatment with warm alcohol, and 

 formerly held to exist as such in the mixture protagon, must now be con- 

 sidered to be the constituents of the protagon molecule. They are the 

 intermediate decomposition products of protagon. 



6. Details of a method for the preparation of protagon are given, by 

 means of which a prolonged contact with warm or boiling alcohol can 

 be avoided as much as possible. 



Addendum by W. Cramer. 



The paper by Lochhead and Cramer has called forth a polemical 

 paper by Gies (Journal Biolog. Chemistry, iii. 4, p. 339) which is mainly a 

 restatement of the views of Posner and Gies and does not adduce any 

 new facts. Gies believes that our results support his view, and that we 

 obtained " different mixtures by extracting brain with different solvents." 

 He applies to our results a different standai'd from that which led him to 

 state of the protagon samples of Lesem and Gies that the analytical 

 results "accord as well as many analj^tical series for what are undoubtedly 

 individual substances." The phosphorus content of the purified protagon 

 samples of Lesem and Gies varies from 0'89 per cent, to 126 per cent., 

 that of Lochhead and Cramer's purified products from 0-96 per cent, to 

 1"07 per cent. Even if our non-purified products are included, the 



