IMBIIiiriON 



!I7 



medium (see below, Imbibition). In all cases of adsorption the 

 chemical and physical properties of the adsorbed material are 

 altered by the process. Not only are the adsorbed molecules 

 oriented, but they are held under comj)ression. It is in these 

 condensed layers that many typically ])hysiological reactions take 

 place — reactions which could only occur with great difliculty in 

 dilute solutions (Chap. X.), Further, the adsorbed salts are 

 rendered for the time being osmotically inactive. They are 

 removed from any active part in the solution. 



The process of liberating the adsorbed material has been dealt 

 with in a previous chapter (VI.). The result of the process of 

 de-adsorption is the restoration of the physical properties of the 

 adsorbed material. We shall see later (Blood) when, how and with 

 what effect adsorption and de-adsorption take place. 



Imbibition. The adsorption of water is of such biological 

 importance that it requires special consideration. All the physio- 

 logical colloids have the property of taking in relatively large 

 quantities of water even against enormous pressures, and of 

 holding this water against even strenuous methods of removal. 

 This " bound " water stored in the micropores (p. 55) is under 

 considerable compression, so much so that its density and all its 

 physical properties are altered. A very instructive demonstration 

 of this, due to Du Bois Reymond, is given in a modified form on 

 p. 537. A piece of the seaweed laminaria digitata, which can be 

 bought dried and ready for use under the name of tangle tents, is 

 attached by a thin copper wire to a piece of cork of such a size 

 that it just floats in water {i.e. the system cork-wire-laminaria has 

 a density of 1 approx.). The following table gives the results of its 

 immersion in water. 



TABLE XVII 



Compression of Water imbibed by Laminaria 



Wj = Weight of Laminaria in Air. 

 Wo — Weight of Laminaria in Water. 



B. 



