470 ABSORPTION. 



course of this work, we shall only consider fully those facts 

 in the history of endosmosis which are directly applicable to 

 absorption as it takes place in the living organism ; necessa- 

 rily omitting many points which may be interesting, but 

 which have no direct physiological application. It is impor- 

 tant, however, to ascertain precisely how far these physical 

 laws are involved in the passage of liquids through living 

 membranes. 



In entering upon the consideration of this subject, it is 

 necessary to appreciate the fact that the walls of the blood- 

 vessels and lymphatics have no pores which are demonstra- 

 ble ; and the supposition that minute orifices exist in these 

 membranes, that cannot be discovered by the highest powers 

 of the microscope, is entirely gratuitous, and has only been 

 advanced for the purpose of affording a purely physical ex- 

 planation of the passage of liquids. 



It is evident that if liquids be capable of passing through 

 the substance of animal membranes, the membrane itself is 

 capable of taking up a certain portion of the liquid by imbi- 

 bition ; and this must be considered as the starting-point in 

 absorption. 



Imbibition is, indeed, a property common to all animal 

 structures. One of the m^st striking characteristics of or- 

 ganic 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. The researches of Liebig have shown 

 that distilled water is the liquid which is always taken up in 

 greatest quantity, and that saline solutions enter the sub- 

 stance of the tissues in an inverse ratio to their density. 1 

 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 



1 LIEBIU, Recherches sur quelques-unes des Causes du Mouvement des Liquidcs 

 dans l> Organism? Animal Annalcs de CMmieet de Physique, Paris, 1849, 3me 

 s6rie, tome xxv., p. 367. 



