320 DIGESTION. 



Bidder and Schmidt, that starchy the principal nutrient matter 

 contained in vegetables, is in part converted in the stomach into 

 sugar, and even into lactic acid ; this metamorphosis of starch 

 within the stomach is, however, so far as we can conclude from 

 our former experiments, solely dependent upon the quantity of the 

 saliva that is excreted; the greatest part of the starch is first 

 metamorphosed in the intestine. We have already sufficiently 

 alluded to the fact that the conversion of this substance in the 

 intestine takes place most rapidly when it is finely comminuted 

 and thoroughly saturated with water (in short, when it is boiled). 

 If we confine ourselves solely to the question of the digestibility 

 of starch, we should regard it as in general easy of digestion, 

 although we very frequently meet with considerable quantities 

 of it passing through the rectum of man and animals. This 

 last-named fact is dependent partly on the circumstance of an 

 excessive quantity of raw (unboiled) starch having been taken (for 

 the saliva, pancreatic fluid, and intestinal juice are not secreted in 

 such quantities, and with such powers, as to metamorphose any 

 amount of starch), and partly upon the fact that the starch is 

 enclosed in vegetable cells, through which the digestive fluid can 

 only enter by endosmosis. Hence the digestibility of vegetables 

 depends chiefly on the nature of the cells in which the starch and 

 the vegetable protein-bodies are inclosed; if the cells are still 

 invested with epidermis, no portion of them is dissolved, since the 

 epidermis of plants is completely proof against the digestive 

 fluids. Boiling is so far useful in regard to vegetable food, that it 

 thoroughly loosens the intercellular substance of the parenchy- 

 matous cells, and hence allows the digestive juices to make their 

 way more readily between the cells ; moreover, the process of 

 boiling causes the outermost layer surrounding the starch-granules 

 to burst, and it is this layer which is the main impediment, in the 

 case of raw starch, to the action of the digestive fluids. Since the 

 protein-bodies occurring in plants exist in a state of the finest 

 comminution, they offer far less opposition to the action of the 

 digestive juices (when the latter once come in contact with them) 

 than the corresponding animal protein-bodies. Hence, moreover, 

 it is easy to see why bread is comparatively so easy of digestion. 

 We must, however, again recur to the fact that in the case of 

 vegetables we are even far less able to draw any conclusion 

 regarding their digestibility, from their longer or shorter retention 

 in the stomach, than in the case of animal food. The most 

 important part of the digestion of vegetables assuredly takes place 



