PROTAGON. 577 



GIES, POSNER and ROSENHEIM and TEBB l dispute the unit nature 

 of protagon. They have found, on fractional precipitation or on recrys- 

 tallization, that protagons can be obtained from the various solvents, hav- 

 ing variable composition, especially different P and N contents. They 

 are, therefore, as are LESEM, THUDICHUM, WORNER and TniERFELDER, 2 

 and others, of the opinion that protagon does not exist as a chemical indi- 

 vidual, but as a mixture of cerebrosides and phosphatides. It is not easy to 

 come to any decision on this disputed question. The above-mentioned 

 investigations, and especially the recent ones of ROSENHEIM and TEBB, 

 imply the absence of unity of protagon but do not exclude the possibility 

 that protagon is a loose chemical combination between cerebroside 

 and phosphatide, which like other readily dissociable combinations, 

 exist only under certain conditions or in certain solvents. It is difficult 

 to understand how a mixture of amorphous or only difficultly crystal- 

 lizable bodies can be so easily crystallized and yield a product, which 

 with proper care, can be recrystallized repeatedly without changing 

 its composition. According to ROSENHEIM and TEBB if the proper 

 quantity is used in solution a crystalline product can be obtained from 

 the decomposition products of protagon, which has the same specific 

 rotation as protagon and can be repeatedly recrystallized without 

 changing its composition or its optical activity. 3 If this is the case it 

 would be better to investigate the cleavage products than to analyze the 

 various fractions in order to get information on the disputed question. 



As we are not decided whether protagon is only a mixture or is a body 

 contaminated with other substances, it is difficult to decide as to how 

 far the so-called decomposition products exist as preformed constituents 

 of the mixture or whether they are true decomposition products. On 

 boiling with baryta-water protagon yields cerebrosides (see below) and 

 the decomposition products of lecithin, namely, fatty acids, glycerophos- 

 phoric acid, and choline. KOSSEL and FREYTAG indeed found three 

 cerebrosides, namely, CEREBRIN, KERASIN (homocerebrin), and ENCEPH- 

 ALIN. According to KOCH 4 the protagon molecule contains cerebroside, 

 lecithin and sulphuric acid (in ester-like combination with the cerebroside) 

 besides excess of cerebroside. Of interest is the finding of KITAGAWA 

 and THIERFELDER 5 that protagon dissolved in methyl alcohol containing 

 chloroform, deposits crusts of cerebron (not pure) after a time at 



1 Gies and Lesem, Amer. Journ. of Physiol., 8; Posner and Gies, Joura. of biol. 

 Chem., 1; Gies, ibid., 3; Rosenheim and Tebb, Journ. of Physiol., 36 and 37. 



2 Lesem, 1. c.; Thudichum, 1. c.; Worner and Thierfelder, Zeitschr. f. physiol. 

 Chem., 30. 



3 Journ. of Physiol., 37; Proc. physiol. Soc., January, 1908, p. 3. 



4 Zeitschr. f. physiol. Chem., 53. 



5 Kitagawa and Thierfelder, ibid., 49; Rosenheim and Tebb, Journ. of Physiol., 37, 

 341 and 348. 



