IMBIBITION AND ENDOSMOSIS. 327 



tion of fatty particles, although they do not offer an explanation of the mechanism by 

 which these particles pass through membranes. It has been demonstrated that the epi- 

 thelium which covers these membranes becomes filled with fatty granules during the 

 absorption of emulsions, and some physiologists invoke the aid of " cell-action," con- 

 cerning which it must be confessed that there exists very little definite information in 

 explanation of this phenomenon. The penetration of fatty particles through membranes 

 must be regarded as one of the points which cannot be explained by the laws of endos- 



mosis. 



There are certain experiments on absorption in the living body, to which a great deal 

 of importance was attached by Longet, which are seemingly in opposition to physical 

 laws. This author states that, when solutions of sugar of different densities are secured 

 in isolated portions of the intestine of a living animal, the denser solutions are absorbed 

 with as much rapidity as those which are less concentrated. He also shows that saline 

 solutions of greater density than the blood are absorbed in the living animal, when, 

 according to physical laws, the current should take place in the opposite direction. The 

 view that these facts are in opposition to physical laws is very successfully controverted 

 by Milne-Edwards. This author, referring to some experiments by Von Becker in sup- 

 port of his position, asserts that there is first an exosmosis of the watery portions of the 

 blood to these dense solutions, with a feeble penetration of the solutions into the blood- 

 vessels, until, by the laws of diffusion, the solutions become so diluted as to be readily taken 

 into the circulation. Such an action as this could not take place between two saline 

 solutions in an endosmorneter, for both the currents would be equal when the liquids 

 became of equal density ; but it has been shown that, after endosmosis in an endosmome- 

 ter has ceased, it may be again induced by simply agitating the liquids. In physiological 

 absorption, the motion is constant and very rapid, and solutions in their passage along the 

 alimentary canal are continually exposed to fresh absorbing surfaces. Farthermore, the 

 albuminoid matters of the blood, which are very slightly exosmotic, will attract an en- 

 dosmotic current from liquids even when they are of the same density. The kind of 

 action 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 mat- 

 ters contained in the alimentary canal. This takes place with all the digestive fluids ; 

 and the liquid is effused, not by simple exosmosis, 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 opposition to the laws of endosmosis. 



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 so-called vital action. During life, the circulation in the mucous membrane of this 

 reservoir would readily remove the few particles of coloring matter which might pene- 

 trate from the bile, and of course there is no time for any coloration to take place. 



In treating of the variations and modifications of absorption, 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 absorb woorara and various of 

 the animal poisons, which, as a rule, produce their effects only 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 phenomenon. Certain of these phe- 

 nomena 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 epithe- 

 lium, 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 secretions, very little of 

 a definite character is known. 



Those who believe that absorption is often modified by so-called vital action offer this 



