ACTION OF GASTRIC JUICE. 
191 
This fluid possesses the power of dissolving albuminous sub¬ 
stances of various kinds, when these are submitted to its 
action at the constant temperature of 100° (which is about 
that of the stomach), and are frequently shaken-up with it. 
The solution appears to be in all respects as perfect as that 
which naturally takes place in the stomach, but requires a 
longer time. It does not seem, however, that the gastric juice 
has a special solvent power for any other than albuminous 
substances. Gelatinous and saccharine matters are taken-up 
by it, as by other watery fluids ; but neither starchy nor 
oleaginous substances undergo any other change by its action, 
than consists in the separation of their particles by the solu¬ 
tion of the membranes and fibres which held them together. 
There is every reason to believe that what is true of artificial 
is true of natural digestion; and that so far from the whole 
operation being performed in the stomach, as was formerly 
supposed, gastric digestion is limited to the solution of the 
albuminous, gelatinous, and saccharine constituents of the 
food. 
209. With regard to the precise mode in which the gastric 
fluid acts in dissolving albuminous substances, there is yet 
some uncertainty ; although there can be no longer any rea¬ 
sonable doubt, that the operation is of a purely chemical 
nature. An artificial gastric fluid, capable of effecting all 
that can be done by that which is secreted in the living 
stomach, may be made, by macerating (or soaking) a portion 
of the membrane lining the stomach of a pig, or of the fourth 
stomach of a calf (even after it has been washed and dried) 
in water, which dissolves a portion of the pepsin; and by 
then acidulating this solution with muriatic or acetic acid. 
It has been proved that both the acid and the pepsin are 
essential to the process of solution ; for the acidulated fluid 
without the animal matter acts extremely slowly upon pieces 
of meat, hard-boiled egg, &c., submitted to it ; and water in 
which the stomach has been macerated, but which contains 
no acid, will not act at all. But the acidulated water alone 
will readily dissolve the substances just mentioned, at a higher 
temperature; and thus it appears that the acid is the real sol¬ 
vent ; and that the pepsin has for its office to produce some 
change in the albuminous substances, by which they are more 
readily dissolved The recent inquiries of Liebig and other 
