THE BEGINNINGS OF LIFE. 53 



of the molecules of which they are compounded. Prof. 

 Graham 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 

 enquiry suggests itself whether the colloid molecule 

 may not be constituted by the grouping together of a 

 number of smaller crystalloid molecules, and whether 

 the basis of colloidality may not really be this com- 

 posite character of the molecule.^ In all probability, 

 two of the distinguishing characteristics of colloids, 

 namely, their very slow rate of diffusion and their 

 want of any tendency to assume a crystalline form, 

 are referrible to this large size and complexity of the 

 molecules of which they are compounded. No hard 

 and fast line, however, separates the colloids from the 

 crystalloids. Although multitudes of bodies exist 

 which may be easily placed in one or the other class, 

 multitudes of others are to be met with having 

 properties of an altogether intermediate character. 

 Nay, even the most typical colloids may undergo a 

 rearrangement of their elements, whereby they are 

 converted into .crystalloids ^. Nothing could show 

 more plainly than this that the difference between a 

 crystalloid and a colloid is merely^ one of degree, and 

 that the properties of colloids are different merely by 

 reason of the more complex molecular arrangement 



^ See p. 39. 



