32 PHYSICAL CHEMISTRY IN MEDICINE. 



with a decrease in the temperature, that with a fall in 

 the temperature supersatu ration and finally crystallization 

 of the salt occurs in the solid gelatine, and that when the 

 gelatine is warmed once more the crystals disappear 

 without leaving a trace of their existence behind them; 

 and all this without a change in the state of aggregation 

 of the colloid. 



A study of gels has disclosed yet other interesting 

 analogies with living matter. Variations in the degree 

 of swelling or in the volume of jellies having the approx- 

 imate size of body cells occur with a velocity the mag- 

 nitude of which corresponds very well with that observed 

 in the changes in volume noticed in living matter. Solid 

 colloids also manifest very extensively a group of phe- 

 nomena so-called adsorption phenomena the simplest 

 laws of which still demand much study. In these 

 phenomena a chief role is played by great surfaces which 

 load themselves (depending upon the pressure, tempera- 

 ture, etc.), often very rapidly, with different substances. 

 If one bears in mind the complicated combination exist- 

 ing in a solidified gel between the colloid and its absorbed 

 liquid the water seems to be held in part mechanically, 

 in part in combinations varying from the most firm to the 

 loosest, which renders possible true liquid and solid 

 solutions in addition to pure adsorption one is impressed 

 with the great variety of ways in which substances may 

 be taken up in such colloids. In this way a great selection 

 in the substances offered them is rendered possible, as 

 HOFMEISTER and SPIRO were able to illustrate with biolog- 

 ically instructive examples in gelatine and agar-agar 

 plates. 



Since a part of the imbibition fluid may be mixed 



