100 
Physiology and its Chemistry 
[January, 
knowledge of the chemistry of the brain. Here occur 
groups of phosphorised principles which, for the time being 
at any rate, we may view in a parallel light. For many 
years we knew nothing of the form in which phosphorus 
exists in the brain, and, having passed through that 
stage of its history when its presence was explained by defi- 
nition, Gobley discovered egg-lecithine, and proved that, by 
means of chemolytic agents, it was split up into glycero- 
phosphoric acid, a base, and fatty acids. Next, Thudichum 
discovered other principles in the brain containing phos- 
phorus, namely, kephalin and the forms of myelin ; and on 
continued investigation it has transpired* that all these 
principles are constructed on the same type, and may be 
said to be glycerin either in its simple or condensed forms, 
in which hydroxyls are replaced by fatty acid radicles on the 
one hand and phosphoryl on the other ; the phosphoryl in 
its turn having hydroxyl replaced by a nitrogenised basis 
radicle. 
It is only in the possession of such knowledge that 
we are able to appreciate to the full the enormous difficulty 
experienced by investigators concerning like highly compli- 
cated molecules, for the difficulty in the instance we have 
given is increased through the previously unknown nature of 
some of the fatty acid radicles. Moreover, the faCt that we 
are at length able to classify such groups of bodies is by no 
means the least proof of their chemical individuality, for it 
places in the hands of the worker a law which must be 
obeyed, if the body to which it is applied belongs to that 
class. 
This brings us again to the albuminous bodies of which 
we were treating, and to a study of a line of research which 
— so far as it has yet extended — has led but to insignificant 
results. We refer to the acStion of pepsin upon albuminous 
substances. Of pepsin itself we may be said to know 
nothing, except that from time to time statements crop up in 
current literature purporting to the alleged discovery and 
isolation of the adtual ferments contained in it. But no 
analyses are forthcoming, and these excitements are short- 
lived, and leave us once more in our old position. Yet it 
must be acknowledged that the researches of Erlenmeyer 
(in part published) and of Alex. Schmidt promise to throw 
much light upon these subjects. It is not surprising, then, 
* Thudichum and Kingzett, “ On Glycero-phosphoric Acid and its Salts, 
as obtained from the Phosphorised Constituents of the Brain.” Journ. Chem. 
Soc., Ser. 2, No. 163. 
