194 



OF ABSORPTION AND SANGUIFICATION. 



FIG. 81. 



the circulation. This, which may now be considered a well-established fact, 

 was first clearly shown by MM. Tiedcmann and Gmelin, 1 who mingled with the 

 food of animals various substances, which, by their color, odor, or chemical 

 properties, might be easily detected in the fluids of the body : after some 

 time the animal was examined ; and the result was, that unequivocal traces 

 of such substances were not unfrequently detected in the venous blood and 

 in the urine, whilst it was only in a very few instances that any indication 

 of them could be discovered in the chyle. 



138. The process of absorption by the bloodvessels is effected by the opera- 

 tion of forces of a purely physical character, the chief phenomena of which 

 are embraced under the general term of Osmosis, and which may here be 

 briefly noticed. When two fluids, miscible with one another, are placed on 

 the opposite sides of an animal membrane or other porous septum, currents are 

 generally established in opposite directions, the activity of which is essentially 

 dependent upon the nature of the septum and the affinity of the fluids for one 

 another. The instrument by which these effects are best shown, is termed 

 an Endosmometer, and consists (Fig. 81) of a tube B, whose wide extremity is 

 partially filled with the fluid to be experimented on, and is then immersed in 



a vessel of pure water, A, the height of which is accu- 

 rately kept at the same level as that to which the fluid 

 rises or falls within the tube, in order to avoid the 

 effect of unequal hydrostatic pressure. In the ma- 

 jority of experiments of this nature the membrane is 

 capable of being wetted by the fluids on both sides, as 

 when water and a solution of some salt are employed. 

 It is then found that a strong current sets from the 

 water to the saline solution, termed the eudosmotic 

 current, the energy of which is within certain limits 

 proportional to the density of the solution, 2 whilst the 

 amount of water entering will, of course, vary with 

 the extent of surface presented by the membrane. 

 On the other hand, the water without becomes im- 

 pregnated with a portion of the salt from the estab- 

 lishment of a counter current, hitherto termed the 

 exosrnotic current, which will continue until the 

 density of the fluids on the two sides of the membrane 

 is equal. The experiments of Prof. Graham, Briicke, 

 and others, however, render it probable that the 

 passage of two fluid currents in opposite directions 

 through the membrane is only apparent, and that the phenomena may in 

 reality be explained by the admission of only a single current setting in- 

 wards from the pure water to the saline solution, the apparent exosinotic 

 current being due to the particles of salt passing outwards by a process of 

 solution in successive layers of the pure water contained in the pores of the 

 membrane until the outer surface is reached, when they immediately diffuse 



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 Icanal ins Hint gelarigen, Heidelberg, ISL'o. 



1 It is considered by Liebig, that, the purgative etfects of concentrated saline solu- 

 tions are to hi' aeeotmted fop on tins principle, the establishment of an osmotic cur- 

 rent fnnii instead <>t' Ai//w/v/.< the circulating system. It is difficult, however, thus to 

 account for all (he phenomena of saline purgation ; and the Author greatly doubts 

 the validity of the explanation. Some experiments performed by Aubcrt are also 

 strongly opposed to it, for he found that the injection of solutions of many of the 

 iciilral salts into the veins produced active purlin;:; and here, of eour-e, the expla- 

 nation sugge.-ted by Liebig is inadmissible. (See. Zeitschrift fur rat. Mcd., 1832, t. 

 ii, p. 225.) 



Aii Endosmometer. 



