90 THE BEGINNINGS OF LIFE. 



This tendency we must attribute to the large size and 

 complexity of the colloidal molecules 1 . Professor 

 Graham says on this subject: c Another and eminently 

 characteristic quality of colloids is their mutability. 

 Their existence is a continued metastasis. A colloid 

 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 The solu- 

 tion of hydrated silicic acid, for instance, is easily 

 obtained in a state of purity, but it cannot be pre- 

 served. It may remain fluid for days or weeks in 

 a sealed tube, but it is sure to gelatinize and become 

 insoluble at last. Nor does the change of this colloid 

 appear to stop at that point. For the mineral forms 

 of silicic acid deposited from water, such as flint, are 



1 ' Applying to atoms the mechanical law which holds of masses, that 

 since inertia and gravity increase as the cubes of dimensions, while 

 cohesion increases as their squares, the self-sustaining power of a body 

 becomes relatively smaller as its bulk becomes greater; it might be 

 argued that these large aggregate atoms which constitute organic sub- 

 stance, are mechanically weak are less able than simpler atoms to 

 bear, without alteration, the forces falling on them. That very massive- 

 ness which renders them less mobile, enables the physical forces acting 

 on them more readily to change the relative positions of their com- 

 ponent atoms ; and so to produce what we know as rearrangements and 

 decompositions.' (Spencer, loc. cit. p. 14.) Professor Graham also 

 says : ' It is difficult to avoid associating the inertness of colloids with 

 their high equivalents, particularly where the high number appears to 

 be attained by the repetition of a smaller number. The inquiry suggests 

 itself whether the colloid molecule may not be constituted by the group- 

 ing together of a number of smaller crystalloid molecules, and whether 

 the basis of colloidality may not really be this composite character of 

 the molecule.' (Loc. cit. p. 221.) 



