274 PHYSIOLOGY CIIAI-. 



by a permeable membrane, but was rather due to the specific 

 activity of the living epithelium that clothes the intestine. This 

 idea was supported by a series of experiments carried out in 

 Heidenhain's laboratory, and published by Leubuscher in 1885. 

 Even after this, however, there remained no little uncertainty as 

 to the point at which the laws of diffusion intervened and 

 favoured the phenomenon of absorption. 



Albertoni in 1891 pointed out that the absorption of sugars 

 took place equally, whether the specific gravity of the solution was 

 greater or less than that of the blood. In 1892 his first results 

 were confirmed by new experiments and brought out an important 

 fact, viz. that absorption of sugars (glucose, lactose, maltose) 

 which had been freely administered was most active in the 

 first hour, and much less in the succeeding hours relatively to the 

 quantity that remained in the alimentary canal. The reason of 

 this phenomenon is unknown. It seems not to depend on satura- 

 tion of the body by glucose, as Albertoni at first assumed, because 

 he afterwards found that the osmotic pressure of the blood alters 

 very little during absorption of sugar. Since his experiments 

 showed that the colloidal content of the blood increases consider- 

 ably after the first hour of absorption, he thought this fact was 

 probably in causal relation with its subsequent diminution. 



In order to solve the problem of absorption, it was necessary to 

 attack it again in the light of more advanced physical methods, 

 particularly in reference to the absorption of those easily diffusible 

 substances which were classed together by Graham under the name 

 of crystalloids. Among the alimentary substances that come 

 under this category we find especially the Salts and the Sugars, 

 sodium chloride and glucose in particular. 



Heidenhain (1894) was the first who undertook an exhaustive 

 criticism of the Theory of Intestinal Absorption. He found that 

 solutions of sodium chloride with an osmotic pressure greater than, 

 or equal to, blood, were, when injected into an isolated loop of 

 intestine in a fasting dog, absorbed indifferently, although in the 

 first case (according to the laws of osmosis) hardly any water should 

 have passed from the intestine to the blood, and in the second no 

 absorption at all should have taken place. He concluded that the 

 absorption could only be explained as the effect of specific forces 

 inherent in the living cells of the wall of the intestine. In his 

 opinion this conclusion was confirmed by the fact that when the 

 intestinal epithelia were functionally injured by a moderate 

 poisoning with sodium fluoride without any perceptible cytological 

 change, the absorption of the foregoing solutions was modified so as 

 to be in complete agreement with the laws of osmosis. 



These results of Heidenhain were confirmed by Hamburger 

 (1895-96). He, too, found that solutions of sodium chloride, sodium 

 nitrate, or sugar, with a greater or less osmotic pressure than the 



