FROM THE SMALL INTESTINE 649 



physical processes which could be held responsible for the results. 

 By using the dog's own blood serum, he considered that he had 

 excluded osmosis and diffusion ; by simultaneously measuring the 

 pressures in the mesenteric vein and the gut he was able to 

 exclude filtration, for he found that the pressure in the vein was 

 about four times greater than that in the gut, and the pressure 

 in the mesenteric capillaries must have been still greater. He 

 also tied the mesenteric lymphatics in order to prevent the 

 pumping action of the villi ; whether this would bring about the 

 desired result is unknown, but the procedure had no effect upon 

 the absorption. It is impossible to exclude imbibition experiment- 

 ally ; Reid attempted to do so by washing the loops with serum 

 before the experiment began, and found that it did not influence 

 the result ; but it is clear that such a procedure could not pre- 

 vent a continuous process such as imbibition is supposed to be by 

 Hamburger. The results obtained by Reid may be gathered from 

 a typical experiment. 50 c.c. of the dog's own serum were placed 

 in a loop of ileum 80 cms. long ; at the end of an hour the 

 pressure in the mesenteric vein was 13*5 mm. Hg, and that in 

 the gut 4'0 mm. Hg ; there had been absorbed 56 per cent, of 

 the water, 5 8' 5 per cent, of the salts, and 30 per cent, of the 

 organic solids. At the end of the experiment the alkalinity and 

 the partial pressure of the Nad in the dog's plasma and in the 

 serum in the gut were the same ; this excludes the possibility 

 that the one-sided permeability of the gut to NaCl could be 

 made responsible for the absorption. In the absorption of the 

 serum work had been done, and, according to Reid, with no 

 apparent force to do it excepting the physiological activity of 

 the living intestinal epithelium. But it seems that Reid has 

 really proved too much, for it would follow from these results 

 that in the absence of this cell activity no absorption could take 

 place. And this he found to be the case in some experiments in 

 which the epithelium was poisoned with NaF. But in an ex- 

 actly similar experiment, in which the dog was in unusually good 

 condition, the NaF reduced absorption scarcely at all. Again, 

 Hamburger had shown that serum was absorbed from the intestine 

 of a dog which had been dead four hours, and at a rate which cor- 

 responded to about a third of that observed by Reid in normal 

 animals with an intact circulation. Reid himself obtained much 

 the same result when the epithelium had been destroyed by 



