44 
CHEMISTRY OF PEPSIN. 
this succinctly under a few heads, I hope to present the 
most important bearings of the subject, and, bv avoiding 
extraneous matter, to claim from chemists and medical men 
a more careful consideration of the mode of action of a pro¬ 
bably very valuable remedy. 
Composition of the Gastric Juice. —The best analyses of the 
fluid which is secreted by the gastric follicles show that it 
does not contain more than 1*72 per cent, of solid matter, 
and that while some small portion of this consists of alkaline 
and earthy chlorides and phosphates, by far the greater 
part is a peculiar organic body to which the name of pepsin 
has been given. Besides these the gastric juice contains a 
free acid. It would seem at first sight no very difficult 
matter to decide what this acid really is; but although the 
question has engaged the attention of many chemists, it can 
scarcely be looked upon as satisfactorily decided. Opinions 
have fluctuated between the hydrochloric and lactic, and the 
nature of the difficulty of forming exact conclusions may be 
thus shortly stated. The secretion contains, as already men¬ 
tioned, alkaline chlorides; and supposing lactic acid to be 
also present, the fluid would, if distilled, give hydrochloric 
acid, for the reason that slight elevations of temperature 
cause the decomposition of the chlorides by lactic acid. 
There are, however, two facts which lead very much to 
belief in the lactic-acid theory. The first of these is, that 
Professor Graham has long since demonstrated by a process 
not involving the necessity for distillation, that this acid is 
present in the normal condition of the fluid. The other is, 
that by a change occurring within the stomach itself, lactic 
acid is known to be produced. This circumstance I shall 
again have occasion to advert to. 
Action of the Gastric Juice. —It was at one time supposed 
that the gastric secretion possessed the power of acting upon 
all the constituents of the food ; that is to say, of acting 
equally on the nitrogenous, the starchy, and the oleaginous 
portions. This idea, however, has, since the researches of 
Frerichs and others with reference to the saliva, been aban¬ 
doned, and it is now a generally accepted truth that the 
proper secretion of the digestive cavity dissolves only the 
azotised matters which are brought into contact with it. 
The amylaceous constituents of the food are by means of the 
saliva, with which the process of mastication impregnates 
them, converted into glucose —a substance which, as far as we 
are aware, requires no further preparation to be assimilated. 
The fatty matters are at the same time merely finely divided, 
and form a kind of emulsion with the chyme, undergoing 
