ORGANIC SIATTEE. 15 



stance, are mechanically weak — are less able than simpler 

 atoms to bear, without alteration, the forces falling on them. 

 That very massiveness which renders them less mobile, enables 

 the physical forces acting on them more readily to change the 

 relative positions of their component atoms ; and so to pro- 

 duce what we know as re-arrangements and decompositions. 

 Further, it seems a not improbable conclusion, that this 

 formation of large aggregates of elementary atoms, and re- 

 sulting diminution of self-sustaining power, must be accom- 

 panied by a decrease of those contrasts of dimension to 

 which polarity is ascribable. A sphere is the iigure of equi- 

 librium which any aggregate of units tends to assume, under 

 the influence of simple mutual attraction. Where the num- 

 ber of units is small and their mutual polarities are decided, 

 this proclivity towards spherical grouping will be overcome 

 by the tendency towards some more special form, determined 

 by their mutual polarities. But it is manifest that in pro- 

 portion as an aggregate atom becomes larger, the effects of 

 simple mutual attraction must become relatively greater ; 

 and so must tend to mask the effects of polar attraction. 

 There will consequently be apt to result in highly com- 

 pound atoms like these organic ones containing nine hun- 

 dred elementary atoms, such approximation to the spherical 

 form as must involve a less distinct polarity than iii simpler 

 atoms. If this inference be correct, it supplies us with an ex- 

 planation both of the chemical inertness of these most com- 

 plex organic substances, and of their inability to crystallize. 



§ 6. Here we are naturally introduced to another aspect of 

 our subject — an aspect of great interest. Professor Graham 

 has recently published a series of important researches, which 

 promise to throw much light on the constitution and changes 

 of organic matter. He shows that solid substances exist un- 

 der two forms of aggregation — the colloid or jelly-like, and the 

 crystalloid or crystal-like. Examples of the last are too fa- 

 miliar to need specifying. Of the first may be named such 



