TO FERMENTATION. 105 



with those constituents of the food which, by themselves, 

 are insoluble in water, the latter acquire, in virtue of a 

 new grouping of their atoms, the property of dissolving 

 in that fluid. During digestion, the gastric juice, when 

 separated, is found to contain a free mineral acid, the 

 presence of which checks all further change. That the 

 food is rendered soluble quite independently of the vi- 

 tality of the digestive organs has been proved by a num- 

 ber of the most beautiful experiments. Food, enclosed 

 in perforated metallic tubes, so that it could not come 

 into contact with the stomach, was found to disappear as 

 rapidly, and td be as perfectly digested, as if the cover- 

 ing had been absent ; and fresh gastric juice, out of the 

 body, when boiled white of egg, or muscular fibre, were 

 kept in contact with it for a time at the temperature of 

 the body, caused these substances to lose the solid form 

 and to dissolve in the liquid. 



9. It can hardly be doubted, that the substance which 

 is present in the gastric juice in a state of change is a 

 product of the transformation of the stomach itself. 

 No substances possess, in so high a degree as those 

 arising from the progressive decomposition of the tis- 

 sues containing gelatine or chondrine, the property of 

 exciting a change in the arrangement of the elements of 

 other compounds. When the lining membrane of the 

 stomach of any animal, as, for example, that of the 

 calf, is cleaned by continued washing with water,. it pro- 

 duces no effect whatever, if brought into contact with 

 a solution of sugar, with milk, or other substances. 

 But if the same membrane be exposed for some time to 



