v INTERNAL RESTITUTIVE SECRETIONS 275 



blood-serum of the animal experimented on, became in the course 

 of absorption isotonic with the latter, and were all eventually 

 absorbed. But since he found that the same phenomena of absorp- 

 tion of solutions which were isotonic, and also of such as were 

 hypertonic, with the serum, could be obtained from animals 

 killed some hours previous to experiment, he denied the importance 

 which Heidenhaiu allotted to the living cells, and invoked the 

 imbibition of the colloidal substances of which the epithelia consist 

 as a possible explanation of the facts which Were opposed to the 

 laws of diffusion. 



Heidenhain at once replied that it is not possible to establish 

 a comparison between the phenomena that can be observed on 

 living animals with circulating fluids that are rapidly renewed, 

 and those observed on dead animals in which the fluids con- 

 tained in the depth of the intestinal walls stagnate. It is obvious 

 that even if the phenomena are apparently similar in the two 

 cases, they will not bear the same interpretation. It must also 

 be remembered that in the living animal there is simultaneously 

 with the phenomenon of intestinal absorption a secretion of succus 

 entericus, i.e. a current opposed to that of absorption, which is 

 absent in the dead animal. 



0. Cohnheim (1897), in Klihne's laboratory, repeated Ham- 

 burger's experiments on the absorption phenomena in living and in 

 dead dogs, under proper experimental conditions, and his results 

 confirmed and extended the theory of Heidenhain. On circulating 

 a continuous current of 0'9 4 per cent salt solution heated to 40 C. 

 through the blood-vessels of the dead animal, and introducing a 

 solution of glucose into a loop of intestine tied at the ends, he saw 

 that a double current was set up, so that part of the sodium 

 chloride passed into the intestine, and part of the sugar into the 

 circulating fluid. Each of the dissolved substances diffused inde- 

 pendent of the other, according to their respective degree of diffusi- 

 bility. The salt being three times as diffusible as the sugar, 

 passed much more rapidly from the capillaries into the intestine 

 than the sugar from the intestine to the capillaries. Under these 

 conditions, therefore, the mucous membrane behaves like any inert 

 membrane, and the double current which passes through it 

 conforms perfectly to the laws of diffusion and osmosis. There 

 is never any diminution of fluid in the loop ; with both hypotonic 

 and hypertonic solutions, there is always an undoubted increase of 

 the fluid in the intestine. The possibility of absorption, as it takes 

 place in the small intestine in living animals, is therefore bound 

 up with the integrity and functional capacity of the intestinal 

 epithelium. According to the results obtained by Cohnheim, the 

 epithelium of the gut is capable of absorbing, inasmuch as it is 

 the seat of a specific force which favours the passage of the 

 dissolved substances from the intestine into the depths of the villi, 



