SUMMARY OF THE DIGESTIVE CHANGES. 565 



ric acid, with an accompanying separation of carbonic acid and hydro- 

 gen. Thus : 



{1 Butyric acid 

 2 Carbonic acid 

 4 Hydrogen 



f C 4 H A 

 C 6 H 12 O 6 = 2C 3 H 6 O 3 = ^2C0 2 



UH 



The albuminoid bodies begin to be digested in the stomach, by the 

 gastric juice ; whilst their solution is continued, and completed, in the 

 small intestine, by the additional action of the intestinal juice. Fluid 

 albumen, and especially vegetable albumen, and coagulated fibrin, are 

 easily digested ; coagulated albumen, casein, gluten, and legumin, 

 more slowly. Casein is first precipitated in a flocculent form, and then 

 dissolved. All albuminoid substances are converted at once into al- 

 buminose or albumen-peptone. Gelatin and gelatin-yielding tissues 

 are converted into gelatin-peptone. These peptones, and also the 

 saliva, pepsin, and pancreatin, are absorbed from the stomach, as well 

 as from the small intestine, and chiefly by the bloodvessels. 



Fats, whether pure, and merely melted by the heat of the stomach, 

 or whether forming part of an organized tissue, and set free by the 

 digestion of the enveloping areolar tissue and walls of the adipose cells, 

 coalesce into small drops in the stomach and upper part of the duo- 

 denum. In the small intestine, so long as its contents remain acid, 

 the fats are merely emulsified by the pancreatic juice, aided possibly 

 by the bile ; in the lower portion of the small intestine, however, 

 where the intestinal contents become more or less alkaline, certain 

 quantities of the fat are probably decomposed into their fatty acids 

 and glycerin, by the further action of the pancreatic juice, and may 

 even be saponified by the strongly alkaline intestinal juice. Thus 

 emulsified, decomposed, or saponified, all but a small residue of the 

 fatty matters are absorbed by the lacteals of the intestines. 



Alcohol, in all its forms, ethers and other soluble acid and sapid 

 bodies, are absorbed unchanged, along the whole surface of the ali- 

 mentary canal, chiefly, if not entirely, by the bloodvessels. This ab- 

 sorption begins even in the mouth, otherwise these substances would 

 produce no flavor. The organic acids probably decomposed into car- 

 bonates. 



The extractive matters, creatin and creatinin, the cerebric acid, 

 those which are uncrystallizable, and perhaps some of the cruorin and 

 myochrome, are also probably absorbed without change, by the blood- 

 vessels. 



The saline constituents of the food are chiefly absorbed without al- 

 teration ; the soluble ones, from the mouth, stomach, and intestinal 

 canal generally ; whilst the less soluble phosphates of magnesia and 

 lime, appear rather to be dissolved in the large intestine. Any car- 

 bonates contained in the food or drink, must be decomposed by the 

 acids of the gastric juice, by the lactic acid of the food, and by the 

 acids resulting from the decomposition of saccharine matters. The 



