OF LIVING MATTER 67 



Matter and Motion which constitute Evolution, structural and 

 functional, imply motions in the units that are redistributed ; we 

 shall see a probable meaning in the fact that organic bodies which 

 exhibit the phenomena of Evolution in so high a degree, are 

 mainly composed of ultimate units having extreme mobility." 

 When such mobile units enter into various combinations, this 

 initial property, though masked, is still potentially present, and 

 must have its influence upon the molecular mobility of the com- 

 pounds into which they enter. Hence Herbert Spencer adds, 

 " We may infer some relation between the gaseous form of three 

 out of the four chief organic elements, and that comparative 

 readiness to undergo those changes in the arrangement of parts 

 which we call development, and those transformations of motion 

 which we call function. . . . One more fact that is here of great 

 interest for us must be set down. These four elements of which 

 organisms are almost wholly composed, present us with certain 

 extreme antitheses. While between two of them we have an un- 

 surpassed contrast in chemical activity ; between one of them and 

 the other three we have an unsurpassed contrast in molecular 

 mobility. While carbon by successfully resisting fusion and 

 volatilisation at the highest temperatures that can be produced, 

 shows us a degree of atomic cohesion greater than that of any 

 other known element, hydrogen, oxygen, and nitrogen show the 

 least atomic cohesion of all elements. And while oxygen displays, 

 alike in the range and intensity of its affinities, a chemical energy 

 exceeding that of any other substance (unless fluorine be considered 

 an exception), nitrogen displays the greatest chemical inactivity.' 

 Now on calling to mind one of the general truths arrived at when 

 analysing the process of Evolution in general, the probable signifi- 

 cance of this double difference will be seen. It was shown (' First 

 Principles,' § 123) that, other things equal, unlike units are more 

 easily separated by incident forces than like units are — that an 

 incident force falling on units that are but little dissimilar does not 

 readily segregate them, but that it readily segregates them if they 



' Hence its compounds are generally most unstable. " Here it will be well to 

 note, as having a bearing on what is to follow, how characteristic of most nitro- 

 geneous compounds is this special instability. In all the familiar cases of sudden 

 and violent decomposition, the change is due to the presence of nitrogen. The 

 explosion of gunpowder results from the readiness with which nitrogen con- 

 tained in the nitrate of potash yields up the oxygen combined with it. The 

 explosion of gun-cotton, which also contains nitric acid, is a substantially parallel 

 phenomenon." 



