

THE ABSORPTION OF THE FOODSTUFFS 783 



before the fluid in the gut has attained isotonicity with the blood. In fact, 

 employing a 1-5 per cent, salt solution, absorption may occur from the 

 very beginning of the experiment. If such a solution is passed through 

 the epithelial membrane into the blood plasma with a smaller tonicity, 

 it is evident that work must be done in the process, work which can only 

 be furnished by the cells of the epithelium. When sugar solutions are 

 employed they behave in somewhat similar fashion to sodium chloride 

 solutions, provided that the sugar is one of the absorbable hexoses, both 

 sugar and water being rapidly absorbed. It is important to note that 

 dextrose is absorbed from the gut almost as rapidly as sodium chloride, and 

 quite as lapidly as sodium iodide, although its diffusibility is very consider- 

 ably less than either of these salts. Moreover, great differences are found 

 between the rate afc which different sugars are absorbed, differences which 

 are not referable to the diffusibility of the sugars in question. Thus the 

 monosaccharides glucose, fructose, galactose are absorbed with double 

 the rapidity of solutions of cane sugar and maltose, and it seems that, in 

 the absence of hydrolytic splitting of the disaccharides, absorption from the 

 gab would be entirely abolished. Lactose disappears from the intestine 

 much more slowly than either of the other two disaccharides, so that large 

 doses may give rise to a laxative effect. In animals devoid of lactase, the 

 lactose-splitting ferment, in their intestinal epithelium milk sugar is apparently 

 not absorbed at all. 



The most cogent argument, perhaps, in favour of an active intervention 

 of the cells of the gut in the process of absorption is furnished by the study 

 of the absorption of blood serum. It has been shown that if an animal's 

 'own serum be introduced into a loop of its intestine the serum undergoes 

 absorption. This absorption affects the water and salts more than the 

 protein, so that the percentage of the proteins in the* fluid remaining in the 

 intestine is increased. Finally however the whole of the serum is absorbed. 

 In this case the fluid within the gut is identical with the fluid within the 

 blood vessels. There are no differences in concentration, quality of salts, 

 or osmotic pressure of proteins. Nevertheless water passes through the 

 cells of the gut from their inner to their outer sides, entraining with it the 

 salts of the serum and a certain proportion of the indiffusible proteins. It 

 is impossible to explain this result as due to the digestion of the proteins 

 and their conversion into diffusible products, since the intestinal loops 

 were washed free of any trypsin that they contained, and serum has itself 

 a strong antitryptic action which would prevent its being attacked by a 

 solution of trypsin. 



The active intervention of the cells in the absorption of salt solutions 

 and serum can be abolished by any means which diminishes or destroys 

 their vitality, such as the addition of sodium fluoride to the fluid to be 

 absorbed, or destruction of the epithelium by previous temporary occlusion 

 of the blood vessels supplying the loop of intestine. 



We must conclude that, when a fluid is introduced into the intestine, an 

 tive transference of water from the lumen into the blood stream is effected 



