504 ABSORPTION. 



tion described by Milne-Edwards would be by no means an 

 isolated example of a liquid passing out of the blood-vessels 

 to be again absorbed after it has acted upon matters contained 

 in the alimentary canal. This takes place with all the di- 

 gestive fluids ; and the liquid is effused, not by simple exos- 

 mosis, but by an act of secretion excited by the impression 

 made upon the mucous membrane. We are not justified, 

 therefore, in assuming, with Longet, that the absorption of 

 solutions of greater density than the blood is always in op- 

 position to the laws of end osmosis. 



The imbibition of the coloring matter of the bile by the 

 coats of the gall-bladder after death, while nothing of the 

 kind takes place during life, is not due to the absence of vital 

 action. During life, the circulation in the mucous membrane 

 of this reservoir would readily remove the few particles of 

 coloring matter which might penetrate from the bile, and of 

 course there is no time for any coloration to take place. 



In treating of the variations and modifications of absorp- 

 tion, we noted an apparent elective power in the mucous 

 membrane of some portions of the alimentary canal. This 

 is illustrated in the failure of the mucous membrane to ab- 

 sorb the woorara and various of the animal poisons, which, 

 as a rule, are only effective when introduced into a wound or 

 injected into the areolar tissue. The separation of various 

 soluble substances by the process known as dialysis may 

 throw some light upon this subject, but as yet we have no 

 facts which offer a satisfactory explanation of this phenome- 

 non. 1 Certain of these phenomena which show an apparent 

 elective power in absorbing membranes are probably due to 

 a cell-action resembling secretion ; for all these surfaces are 

 covered with epithelium, which must be penetrated before 

 the fluids can get to the blood-vessels. But even with regard 

 to the selection of materials from the blood to form secre- 

 tions, very little of a definite character is known. 



Those who believe that absorption is often modified by 

 1 See page 477, note. 



