IMBIBITION AND ENDOSMOSIS. 321 



both pneumogastric nerves had been divided was retarded about five minutes but that 

 the convulsions, when they occurred, were fully as severe as in an animal which had 

 received an equal dose, without section of the nerves. 



Imbibition and Endosmosis. 



The ideas of physiologists concerning the mechanism of the absorption of soluble sub- 

 stances have become radically changed since the beginning of the present century; and 

 it is now generally admitted that this process takes place chiefly by blood-vessels, and 

 that the absorbents have no such wonderful elective power as was attributed to them by 

 the older writers. This involves the passage of liquids through the coats of the blood- 

 vessels and lymphatics; a process which has been the subject of numerous experiments, 

 resulting in the development of many important physical laws capable of application to 

 physiological absorption. At the present day, therefore, the history of absorption is not 

 complete without a consideration of the laws of imbibition and endosmosis. 



If liquids can pass through the substance of an animal membrane, it is evident that 

 the membrane itself must be capable of taking up a certain portion of the liquid by 

 imbibition; and this must be considered as the starting-point in absorption. Imbibi- 

 tion is, indeed, a property common to all animal structures. One of the most strik- 

 ing characteristics of organic principles is that they may lose water by desiccation and 

 regain it by imbibition. It is also a well-known fact that the tissues do not imbibe all 

 solutions with the same degree of activity. Distilled water is the liquid which is al- 

 ways taken up in greatest quantity, and saline solutions enter the substance of the tis- 

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

 of alcohol and water, imbibition always being in an inverse proportion to the quantity 

 of alcohol present in the liquid. Among the other circumstances which have a marked 

 influence upon imbibition, is temperature. It is a familiar fact that dried animal mem- 

 branes 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 an 

 immense increase at a moderately-elevated temperature. While nearly all the structures 

 of the body, after desiccation, will imbibe liquids, the membranes through which the pro- 

 cesses of absorption are most active are, as a rule, most easily permeated ; and we shall 

 see, when we come to study the mechanism of the passage of liquids through these mem- 

 branes, that 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. These facts will be found particularly interesting in connec- 

 tion with observations on the passage of liquids through membranes, in experiments on 

 endosmosis with artificial apparatus. 



Mechanism of the Passage of Liquids through Membranes. The attention of physi- 

 ologists was first directed to this subject by the researches of Dutrochet, in 1826. Al- 

 though not by any means the first to observe the phenomena which he described under 

 the name of endosmosis, to Dutrochet is generally ascribed the honor of having first 

 indicated the applications of the laws of endosmosis to the nutrition of plants and ani- 

 mals. Undoubtedly, Dutrochet was the first to make experiments upon endosmosis which 

 attracted the attention of scientific men in different parts of the world and which were 

 immediately repeated and extended ; but the experiments made upon living animals by 

 Lebkuchner, in 1819, and by Magendie, in 1820, had already demonstrated most conclu- 

 sively the passage of liquids through the walls of the blood-vessels ; and the explanation 

 offered by these physiologists was fully as definite as that proposed by Dutrochet. 



Dutrochet constructed an instrument called the endosmometer, which consists sim- 

 ply of a small bell-glass, the lower opening of which is closed by a membrane, the open- 

 ing above being connected with a long glass tube by which the force with which liquids 

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