54 THE BEGINNINGS OF LIFE. 



which prevails — an arrangement, however, which, by 

 the mere influence of physical conditions, the molecules 

 of certain crystalloids are known ^spontaneously' to 

 assume. A further consequence directly flowing from 

 this superior complexity of the colloid molecule, is, 

 as we have previously endeavoured to show, the greater 

 instability which characterizes them as a class. Very 

 slight changes in the conditions or influences to which 

 the colloid is exposed lead to changes in its constitu- 

 tion — owing to the ease with which a re-arrangement 

 is brought about amongst its constituent atoms or 

 elementary molecules. Its very existence, as Prof. 

 Graham pointed out, is one of ^continual metastasis,' 

 and ^ may be compared in this respect to water while 

 existing liquid at a temperature under its usual freezing 

 point, or to a supersaturated saline solution.' 



Colloids, like crystalloids, are soluble — sometimes 

 largely so — though generally ^they are held in solution 

 by a most feeble force.' The feeble force with which, 

 when in the state of solution, their molecules are com- 

 bined with those of water, is another peculiarity emi- 

 nently favourable to the occurrence of rearrangements 

 or recompositions amongst their molecules. Thus 

 when in a state of solution colloids are most favour- 

 ably situated, in all respects, for undergoing whatever 

 changes the incidence of physical forces is capable of 

 eflFecting. 



It will be well now to enquire a little more fully 



