302 ABSORPTION 



same strength, transports fluid only from the mucous membrane outward and 

 not in the reverse direction (Reid) ; that if the cells of the intestinal epithelium 

 be injured functionally, but not, so far as can be seen, anatomically by poison- 

 ing with sodium fluoride, absorption is actually altered so that osmosis now 

 brings about only an exportation of fluid from the intestine. 



Finally, attention should be called to the discoveries mentioned at page 34 

 with regard to the permeability of animal cells for different substances. Accord- 

 ing to those results, the entrance of a substance into a cell would depend upon 

 its solubility in the lipoid limiting layer of the cell, carbohydrates not being 

 soluble therein. To surmount the difficulty which carbohydrates present, Hoeber 

 supposes that the absorption of these and other compounds which do not pene- 

 trate such a membrane occurs only between the cells. Something of the kind 

 might be true of substances which are taken up in very small quantities; but 

 carbohydrates are absorbed by the mucosa so abundantly that this explanation 

 appears to have little probability in its favor. 



The power of absorption is very different in different divisions of the 

 alimentary canal. In the stomach pure water is not absorbed at all. Sugar 

 or peptone or salts (if concentrated) are absorbed from their water solutions 

 in the stomach the more plentifully, the stronger is the solution. The water 

 is absorbed also under these circumstances, and, as it seems, most actively 

 from solutions of peptone. Absorption of water from peptone solutions in- 

 creases with the concentration, while from solutions of sugar it decreases 

 with the concentration (v. Mering). 



In the upper part of the small intestine (jejunum), sugar and fat are 

 absorbed more rapidly than in the lower part (ileum). On the other hand 

 the water of sugar solutions is said to be taken up by the mucous membrane 

 more slowly in the jejunum than in the ileum (Rohmann and Negano). 



Correspondingly, under a pressure of 10 cm. of water for 1 cm. of length, 

 about 0.7 c.c. of a six-per-cent salt solution was absorbed in one hour by the 

 upper part of the small intestine of the dog, and 1.3 c.c. by the lower part, while 

 in the large intestine under the same circumstances the amount was 2.1 c.c. 



The large intestine appears therefore to be especially well adapted for the 

 absorption of water. Organic foodstuffs also in easily absorbable form are 

 taken up from the large intestine, as has been shown by experiments with 

 nutrient enemas, in which a supply of as much as 1,200 Cal. per day has 

 been maintained. It is to be observed, though, that the ileocaBcal valve is not 

 an absolute barrier to the passage of the contents back into the small intestine, 

 and that a part of the nourishment might be absorbed there instead of in 

 the large intestine. According to observations on men and dogs with fistulaa 

 into the large intestine, carbohydrates are absorbed there best of all the food- 

 stuffs; fats and proteids only to a slight extent. The salt content of the 

 enema also appears to have a certain importance in promoting absorption. 



All kinds of locally stimulating substances (e. g., spices) exert a remark- 

 able influence on the absorption in the stomach and intestine. In the former 

 alcohol is absorbed even to the last trace in two hours, and besides, it accel- 

 erates the absorption of other substances. Common salt, oil of mustard, pep- 

 permint, pepper, etc., have the same effect. The condiments therefore not 



