FROM THE SMALL INTESTINE 633 



produced by the blood flow in the capillaries, and the pumping 

 action of the villi, which is supposed to be like that of both a 

 suction and a force pump. It is necessary to say a word 

 about the relative importance of these various factors according 

 to Hamburger's view, and to mention the experimental evidence 

 on which the view as a whole is based. 



All observers admit that diffusion and osmosis may play a 

 part in absorption, but they differ in the importance which they 

 ascribe to them. Even on Hamburger's view diffusion and 

 osmosis, like imbibition, play a relatively secondary role. Two 

 varieties of imbibition are recognised, molecular and capillary. 

 By molecular imbibition is meant the taking up of fluid by 

 homogeneous non-porous masses, such as gelatine and agar plates, 

 and by capillary imbibition the taking up of fluid in the pre- 

 formed spaces or pores of a material. The tissues of the body 

 have the power of taking up much more fluid than they normally 

 possess, and Hamburger assumes that this may take place by 

 imbibition. He supposes that during absorption solutions are 

 taken up into the epithelium by molecular imbibition and are 

 then passed by capillary imbibition through the connective tissue 

 spaces of the subepithelial tissue, where they are taken up by the 

 capillary wall again by molecular imbibition and finally passed 

 by capillary imbibition into the interior of the capillary. The 

 fluid reaching the blood-stream is constantly carried away, and 

 this makes a continuous absorption by imbibition possible. There 

 is some evidence to show that imbibition may be a selective 

 process and that gelatine and pieces of dried tissue are by no 

 means indifferent to the solutions in which they are soaked. It 

 has been shown, for instance, that they will take up much more 

 of a solution of Nad than of a solution of Na 2 S0 4 . Sulphates 

 are known to be but slowly absorbed from the alimentary canal, 

 and it has been suggested that the different rates at which salts 

 are absorbed may be due in part to the varying degree to which 

 they can be imbibed. It has been found that dead tissues may 

 show considerable imbibition, but how far living tissues show the 

 same phenomenon it is impossible to say. 



It is impossible to take very seriously the aspiration produced 

 by the blood-stream as a force which is to be capable of absorb- 

 ing fluid from the gut ; for the suction produced by a fluid of 

 the specific gravity of blood travelling at the rate of about 



