830 PHYSIOLOGY 



of which the greater part was useless for the absorption of the common 

 food-stuffs, as would be the case if these could only penetrate the 

 membrane by the narrow chinks between the cells. It seems 

 more probable that the absorption of the different food-stuffs, and 

 probably also of the normal salts of the body, is effected by the cells 

 themselves, in accordance with their nutritional needs, and this view 

 is strengthened when we come to examine into the absorption even 

 of normal saline solutions. If 50 c.c. of normal sodium chloride solution 

 be introduced into a loop of intestine, it is absorbed steadily, so that at 

 the end of an hour not more than about 20 c.c. may be recoverable. 

 The absolute amounts absorbed differ in various experiments, but are 

 fairly uniform for repeated observations on one and the same animal. 

 The absorption of such a solution could be ascribed to the osmotic 

 pressure of the colloids in the blood plasma or lymph within the 

 spaces of the villi. If, instead of using isotonic solutions, hyper- 

 tonic solutions are employed, e.g. a 2 or 3 per cent. NaCl solution, 

 absorption still takes place, but may be preceded by an interval 

 in which there is an actual increase of the fluid contained in the 

 gut. Here, again, we might ascribe the absorption to the physical 

 factors present, were it not that absorption is found to commence 

 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 rapidly 

 as sodium iodide, although its diffusibility is very considerably 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 appar- 

 ently not absorbed at all. 



