272 DIGESTION. 



be gathered that there is a kind of circulation constantly pro- 

 ceeding from the intestines into the blood, and from the blood 

 into the intestines again ; for, as all the fluid, probably a very 

 large amount, secreted by the intestinal glands, must come 

 from the blood, the latter would be too much drained, were it 

 not that the same fluid after secretion is again reabsorbed into 

 the current of blood going into the blood charged with nutrient 

 products of digestion, coming out again by secretion through 

 the glands in a comparatively uncharged condition. 



It has been said before that the contents of the stomach dur- 

 ing gastric digestion have a strongly acid reaction. On the 

 entrance of the chyme into the small intestine, this is gradu- 

 ally neutralized to a greater or less degree by admixture with 

 the bile and other secretions with which it is mixed, and the 

 acid reaction becomes less and less strongly marked as the 

 chyme passes along the canal towards the ileo-csecal valve. 



Thus, all the materials of the food are acted on in the small 

 intestine, and a great portion of the nutrient matter is absorbed, 

 the fat chiefly by the lacteals, the other principles, when in 

 a state of solution, chiefly by the bloodvessels, but neither, prob- 

 ably, exclusively by one set of vessels. At the lower end of 

 the small intestine, the chyme, still thin and pultaceous, is of 

 a light yellow color, and has a distinctly fecal odor. In this 

 state it passes through the ileo-csecal opening into the large 

 intestine. 



Summary of the Process of Digestion in the Large Intestine. 



The changes which take place in the chyme after its passage 

 from the small into the large intestine are probably only the 

 continuation of the same changes that occur in the course of 

 the food's passage through the upper part of the intestinal 

 canal. From the absence of villi, however, we may conclude 

 that absorption, especially of fatty matter, is in great part com- 

 pleted in the small intestine, while, from the still half-liquid, 

 pultaceous consistence of the chyme when it first enters the 

 caecum, there can be no doubt that the absorption of liquid is 

 not by any means concluded. The peculiar odor, moreover, 

 which is acquired after a short time by the contents of the 

 large bowel, would seem to indicate the addition to them, in 

 this region, of some special matter, probably excretory. The 

 acid reaction, which had become less and less distinct in the 

 small bowel, again becomes very manifest in the caecum prob- 

 ably from acid fermentation processes in some of the materials 

 of the food. 



