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 



