ABSORPTION OF THE VARIOUS FOOD SUBSTANCES 445 



proof. The regeneration, wherever it occurs, must presumably take 

 place in cells, and the only available cells in the digestive mucous 

 membrane are those which line the tube, or the leucocytes which 

 wander between them. Accordingly, both have been credited with 

 the power of absorbing (and perhaps transforming) these substances, 

 but the balance of evidence is in favour of the epithelial cells. We 

 cannot, however, as in the case of the fat, single out any particular 

 tract of epithelium as alone engaged in the absorption (and possibly 

 in the resynthesis) of the products of the digestion of the proteins. 

 In all likelihood the cells covering the villi are actively concerned, 

 but there is no valid reason for denying a share to the general lining 

 of the stomach and small intestine, even perhaps including the 

 Lieberkiihn's crypts or intestinal glands, which morphologically 

 form a kind of inverted villi. It is, indeed, true that the crypts 

 do not take part in the absorption of fat, for no granules blackened 

 by osmic acid occur in them during digestion of a fatty meal. But 

 this is a ground for attributing to them other absorptive functions 

 rather than for altogether denying to them a share in absorption, 

 unless, indeed, we assume that the secretion of the succus entericus 

 engrosses the whole activity of this extensive sheet of cells. Even 

 within physiological limits distension of the gut causes the crypts 

 to become shorter and broader, by a process of partial unfolding 

 which permits a greater part of their epithelium to come into con- 

 tact with the intestinal contents. In extreme distension they may 

 be completely smoothed out. 



The extraordinary efficiency of the small intestine in digestion 

 and absorption is shown by the fact that, after removal of even 

 70 to 83 per cent, of the combined jejunum and ileum in dogs, the 

 metabolism is not necessarily much affected. On a diet poor in 

 fat the animals absorb as much of the fat as a normal dog, although 

 a smaller proportion when the diet is rich in fat. It has been 

 generally stated that it is never permissible to remove more than 

 one-third of the small intestine in man. But in one case 2| metres 

 was resected, or quite one-half, and the patient recovered. Even 

 the large intestine, which possesses Lieberkiihn's crypts, but no villi, 

 is able to absorb not only peptones and sugar, especially mono- 

 saccharides like dextrose, but also fats and native proteins. And 

 although these are powers which can be rarely exercised to any great 

 extent in normal digestion, they form the physiological basis of the 

 important method of treatment by nutrient enemata. The observa- 

 tion already mentioned (p. 325), that considerable quantities of 

 food administered by the rectum can pass through the ileo-colic 

 sphincter and valve into the lower part of the ileum, thanks to the 

 antiperistaltic movements of the large intestine, indicates that an 

 important part of the preliminary digestion and of the absorption 

 of enemata may occur in the small intestine. But remnants of the 



