254 DIGESTION. 



portion of the intestinal contents is absorbed. We see that here 

 also the known mechanical laws suffice to explain the absorption 

 by capillaries and veins, and we may readily convince ourselves 

 that the same laws of endosmosis here come in question which 

 guided us in our explanation of the absorbing capacity of the roots 

 of plants. We here refer less to the systems of cells, between 

 whose contents endosmotic currents are established, than to the 

 cylindrically shaped membranes in which a tolerably concentrated 

 fluid is continually moving forward an arrangement which is far 

 more favourable to endosmotic motion than the rows of minute 

 closed sacs which constitute the vegetable cells. We have already 

 mentioned (see p. 243) that the blood, as compared with the fluid 

 contents of the intestine, is so concentrated a solution that the 

 chief current must be directed from the intestine towards the 

 capillaries, and that this direction must moreover be always main- 

 tained in consequence of the intestinal fluid generally containing 

 free acid. While we must admit, from these few experimental 

 propositions on endosmosis, that this mechanism in the intestinal 

 canal exerts a suction or pump-like action, we must moreover 

 take into account that the denser fluid of the capillaries is con- 

 stantly flowing onwards, whilst the liquor sanguinis, which is 

 attenuated by endosmosis, is replaced by a fresh and denser blood- 

 wave. Kiirschner* has demonstrated by an excellent experiment, 

 which easily admits of repetition, the extraordinary manner in 

 which this process favours endosmosis. We must take a cleaned 

 portion of small intestine (that of a rabbit, for instance), and place 

 it in a basin filled with a solution of sulphocyanide of potassium, 

 in such a manner that one end of the intestine hangs over the 

 edge, while, by the aid of a funnel, we gradually pour a moderately 

 dilute solution of perchloride of iron into the other end, so that a 

 current of the solution of the salt of iron continuously runs 

 through the gut lying in the solution of sulphocyanide of 

 potassium. When the two fluids which are separated by the 

 animal membrane are relatively at rest, more of the sulphocyanide 

 of potassium passes into the perchloride of iron than conversely 

 (as may be readily seen by the deeper red colour of the fluid on 

 the side of the perchloride of iron) ; if, however, the solution of 

 the perchloride of iron only run in a slow current, we observe that 

 the solution of sulphocyanide of potassium is far less coloured, 

 while if it run through the membranous tube in a very rapid 



* Handworterbuch der Physiologie. Bd. 1,'S_64. 



