ABSORPTION OF SPECIAL MATERIALS. 201 



lent the more readily the solution passes into the bloodvessels. 

 In those cases where the equivalent is very high, such as mag- 

 nesium sulphate, there is a tendency of the fluid to pass out from 

 the bloodvessels into the intestinal cavity ; hence the watery stools 

 caused by this and such-like saline purgatives. 



Among the carbohydrates we need only take into account 

 the sugars, for starch unchanged is but little, if at all, absorbed. 

 Only a certain quantity of sugar can be taken up by the intesti- 

 nal absorbents, since some is found in the fseces when the amount 

 taken with the food exceeds a certain quantity. Some of the 

 sugar in the intestine, moreover, undergoes fermentation, by which 

 it is converted into lactic and butyric acid. How much of the 

 sugar is absorbed as lactic and butyric acid has not been deter- 

 mined, but the amount of sugar found in the portal vessels or 

 lacteals does not at all correspond with the amount that disap- 

 pears from the cavity of the intestine. 



Ordinary proteids, being colloids, can only pass slowly through 

 an animal membrane, hence they are said to be changed into pep- 

 tones under ordinary circumstances before they are absorbed. 

 Their absorption takes place chiefly in the stomach, and is com- 

 pleted in the small intestine, as only a small quantity of albu- 

 minous substances is found in the large intestine even after an 

 excessive meat diet. The more concentrated the solutions of pep- 

 tones are the more rapidly are they absorbed, and the rate of 

 absorption is greatest at first and then by degrees diminishes. 

 The presence of alkali is also said to facilitate the absorption of 

 peptones. It is a curious fact that neither in the lacteals nor in 

 the portal blood can any quantity of peptone be found, even dur- 

 ing active proteid digestion ; so that it is impossible to trace out 

 their course as peptones, or to say by which set of channels they 

 reach the blood. If we assume that all proteids must be absorbed 

 as diffusible peptone, we are forced to conclude that during their 

 passage from the intestinal cavity they must be reconverted into 

 ordinary proteids. But we know that soluble forms of albumin 

 are to some extent diffusible (when a solution of salt is used) 

 through a dead animal membrane. But even were this quite im- 



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