THE ABSORPTION OF THE REDUCED FOODSTUFFS 1029 



nesium, epsom salt, and others, causes large quantities of water to be 

 poured into the intestinal canal which eventually excite peristalsis. 

 Other cathartics, such as cascara sagrada, act by stimulating the peris- 

 talsis without rendering the- feces especially watery, and still others, 

 such as the inert oils, by lubricating the intestinal surfaces as well as 

 the feces. 



While the experiment just described, lays special emphasis upon 

 osmosis, it may be shown that this factor is by no means the only 

 one concerned in absorption. Thus, it will be remembered that the 

 villi of the small intestine are supplied with capillaries in which the 

 pressure cannot be less than 30 or 40 mm. Hg. Evidently, absorption 

 takes place against this pressure. It has also been shown that if a 

 certain quantity of the animal's own blood-serum is introduced into 

 the intestine, its water and salts will be absorbed, while its proteins 

 are left behind. Some time later, however, all of this serum is taken 

 up and this in spite of the fact that the fluids on the two sides of the 

 intestinal epithelium are practically identical. These and other 

 experiments that might still be mentioned, prove very conclusively 

 that the lining cells of the intestine are able to intervene in this process 

 by virtue of certain forces which originate during their metabolism. 

 This implies that the different substances do not simply pass through 

 the pores in this membrane, but actually interact with the solvent as 

 well as with the cytoplasm of these cells. 



The Absorption of the Carbohydrates. — Since only the mono- 

 saccharides are readily dialyzable, the polysaccharides must first be 

 converted into their simplest form. We have seen that this process 

 involves a constant hydrolysis which is effected by the enzymes 

 mentioned previously. In the intestine, therefore, we have such 

 substances as dextrose, levulose or fructose, and galactose., 



The first is present in largest amounts and is easily diffusible and 

 reduced by the tissue cells. Such disaccharides as cane-sugar, milk- 

 sugar, and maltose, are also soluble and diffusible, but cannot be con- 

 verted directly into glycogen, nor can they be fully utilized by the 

 tissue-cells. The small percentage of them actually made available 

 to the latter, has previously been acted upon by the maltase of which a 

 small amount is present in the body-fluids. The difference in the 

 diffusibility of these sugars is also shown by the fact that as small 

 an amount as 100 grm. of glucose when introduced into the intestine, 

 may give rise to glycosuria, while as much as 300 grm. of cane-sugar 

 may be ingested before the aforesaid symptom is produced. Lactose is 

 absorbed with even greater difficulty and hence, this sugar must pass 

 into the feces whenever lactase is present in insuflicient amounts. 

 The absorption of the simple sugars is effected chiefly in the small 

 intestine, and the chief channel of absorption is the portal vein and 

 not the lymphatic system.^ 



1 Munk, Archiv fiir Physiol., 1890, 376. 



