202 ABSORPTION-LYMPH AND CHYLE. 



Imbibition is, indeed, a property common to all animal tissues. It is a well 

 known fact, however, that the tissues do not imbibe all solutions with the 

 same degree of activity. Distilled water is the liquid which is always taken 

 up in greatest quantity, and saline solutions enter the substance of the tissues 

 in an inverse ratio to their density. This is also the fact with regard to 

 mixtares of alcohol and water, imbibition always being in an inverse propor- 

 tion to the quantity of alcohol present in the liquid. Among the other con- 

 ditions which have a marked influence upon imbibition, is temperature. It 

 is a familiar fact that dried animal membranes may be more rapidly softened 

 in warm than in cold water ; and with regard to the imbibition of liquids by 

 sand, the researches of Matteucci and Cima have shown a considerable in- 

 crease at a moderately elevated temperature. While nearly all the structures 

 of the body, after desiccation, will imbibe liquids, the membranes through 

 which the processes of absorption are most active are, as a rule, most easily 

 permeated ; and the character of the liquid, the temperature etc., have a 

 great influence upon the activity of this process. For example, all liquids 

 which have a tendency to harden the tissues, such as saline solutions, alcohol 

 etc., pass through with much less rapidity than pure water. 



Mechanism of the Passage of Liquids through Membranes. The passage 

 of liquids through membranes is called osmosis. In the case of two liquids 

 passing in opposite directions, the stronger current is called endosmotic and 

 the weaker current is called exosmotic. In the passage of liquids into the 

 vessels, in physiological absorption, the process is generally called endosmosis. 

 The attention of physiologists was first directed to these phenomena by the 

 researches of Dutrochet, published in 1826. 



It is now definitely ascertained that the following conditions are necessary 

 for the operation of endosmosis and exosmosis : 



1. That both liquids be capable of " wetting " the interposed membrane, 

 or in other words, that the membrane be capable of imbibing both liquids. 

 If but one of the liquids can wet the membrane, the current takes place in 

 only one direction. 



2. That the liquids be miscible with each other and be differently consti- 

 tuted. Although it is found that the currents are most active when the 

 liquids are of different densities, this condition is not indispensable ; for cur- 

 rents will take place between solutions of different substances, such as salt, 

 sugar or albumen, when they have precisely the same density. 



The physiological applications of the laws of endosmosis can now be more 

 fully appreciated, as it is evident that the above conditions are fulfilled when- 

 ever absorption takes place, with the single exception of the absorption of 

 fats, which has been specially considered. For example, all substances are 

 dissolved or liquefied before they are absorbed, and in this condition, they 

 are capable of " wetting " the walls of the blood-vessels. All the liquids ab- 

 sorbed are capable, also, of mixing with the plasma of the blood. What 

 makes this application still more complete, is the behavior of albumin in 

 endosmotic experiments. In physiological absorption, there is always a great 

 predominance of the endosmotic current, and there is very little transudation, 



