THE ABSORPTION OF THE FOOD-STUFFS 737 



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 dex- 

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

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

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

 between the rate at 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 gut 

 would be entirely abolished. Thus 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 absorp- 

 tion. 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 even a strong solution of trypsin. 



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

 as well as of 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 

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

 by the intermediation of forces having their origin in the metabolism of the 

 cells themselves. This work of absorption of the cells may be aided or 



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