PHYSIOLOGICAL ABSORPTION. 339 



water are taken up pari passu ; below this strength, the 

 water is absorbed faster than the salt, while above, the salt 

 leaves the gut faster than the water. 



Rohmann, also using- the dogs with Vella fistula, 

 added some points against the pure osmotic theory. 

 Peptone and sugar, in spite of their well-known differences 

 of diffusibility, he found to be absorbed at about the same 

 pace. Again, in a comparison of the diffusibilities of cane 

 sugar and sodic sulphate, as determined by C. E. Hoffmann, 

 for ox pericardium, with their rapidities of absorption in 

 the living gut, he found that while the rapidity of diffusion 

 of sodic sulphate slightly exceeds that of cane sugar 

 ( 1 • 1 5 : 1 ), yet the absorption of cane sugar took place at 

 about ten times the pace of that of the soda salt. 



These experiments of Heidenhain's pupils had all 

 demonstrated cases which were negative as regards absorp- 

 tion by pure osmose, but no cases of absorption under con- 

 ditions excluding the possibility of osmose were brought 

 forward. Such absorptive action was, however, shortly 

 shown to be capable of demonstration by Waymouth Reid, 

 who obtained a transfer of normal saline solution across 

 the exsected gut mucosa of the rabbit under conditions of 

 equality of osmotic pressure on the two sides of the mem- 

 brane, and, moreover, obtained a reversal of the current by 

 adding pilocarpine equally to the two masses of fluid on 

 either side of the intestine. 



Heidenhain himself has again quite recently published 

 more experiments emphasising the necessity of considering 

 the process of intestinal absorption as involving other 

 factors besides those of differences of osmotic pressure 

 between the contents of the gut and the blood of the capil- 

 laries of the villi. The observations deal with the absorp- 

 tion of solutions of salts, and especially of sodic chloride. 

 For determining the total osmotic pressure of such complex 

 fluids as the serum of the blood, Heidenhain has followed 

 Dreser in choosing the method by estimation of the lower- 

 ing of freezing point (Raoult), and used the Beckmann 

 apparatus. The method is, perhaps, not so delicate with 

 watery solutions as the blood corpuscle method of Ham- 



