On ao-called " Protagon " 303 



Micro-chemical Proof of the Composite Nature of "Protagon." 



We have examined the physical properties of the substances isolated 

 from " protagon " somewhat more closely, and found characteristic differ- 

 ences in their optical activity, melting point, solubility, etc. They possess 

 further the remarkable property of crystallising from pyridine under certain 

 conditions in ^uid spherocrystals,^ and we had indications that they also 

 exist in a liquid-crystalline state between the solid and completely fused 

 condition. During the latter observations we noticed a striking difference 

 between them by the help of the polarising micrascope, which furnishes a 

 further proof of the heterogeneous composition of " protagon." 



If a small quantity of the phosphorus-rich material mentioned above 

 (Fraction I.) is carefully fused on a slide under a cover-glass, the clear fused 

 liquid is seen to be isotropic between the crossed nicols of a polarising 

 microscope. On allowing the slide to cool a shower of separate bright 

 spherocrystals, showing dark crosses, appears on the black background. 

 The spherocrystals grow rapidly on cooling until they touch each other, 

 forming finally a complete mosaic on solidifying. The same property is 

 shown still better by the specimen of sphingomyelin described above 

 (see fig. 1). 



Quite different is the behaviour of the phosphorus-poor fraction (Fraction 

 II.) and of pure phrenosin. An isotropic fluid is also produced on complete 

 fusion, but instead of spherocrystals it will be observed that on cooling 

 bright anisotropic needles shoot out on the dark background (see fig. 2). 

 In ordinary white light both the needles of phrenosin and the sphero- 

 crystals of sphingomyelin can only be faintly distinguished by their outlines. 



It seemed to be of interest to examine in the same way samples of 

 " protagon," and this method also proved it to be a mixture. As will be 

 seen from the illustration (see fig. 3), " protagon " when fused and allowed 

 to cool slowly gives rise to an indefinite crystalline mosaic, in which the 

 needles of phrenosin seem to predominate. The identical result is obtained 

 from " artificial protagon," i.e. a mixture of the phosphorus-rich and 

 phosphorus-free constituents which we described previously (loc. cit.) and 

 found to be identical in chemical and physical properties with " protagon." 



Summary. — It will be remembered that the "protagon" idea was 

 originally conceived by Liebreich (1865). In his opinion all the con- 

 stituents of nervous tissue (known at this time as phosphorised fats, 

 lecithin, cerebrin, etc.) do not exist preformed, but are derived from the 

 decomposition of the one and only mother-substance, which was therefore 

 called " protagon." This simple idea had no doubt a certain attraction for 

 the earlier physiological chemists, especially as it was for a time at lea«t 

 adopted by Hoppe-Seyler. Several additional theories, none of which 

 were supported by facts or stood the test of experimental criticism, had to 



1 Joum. of Physiol., vol. xxxvii., 1908, p. 348. 



