THE VITAL FORCE. 71 



selves. The imprisoned gases pine for their wonted 

 partner, and stretch themselves out towards their 

 destined liberator. Set free from constraint their 

 affinities operate again, and the materials of the 

 living body and the atmosphere re-unite themselves. 

 But no " affinity " need be supposed to hold together 

 the organic substances; their elements are coerced 

 into union by extraneous force, not drawn to it by 

 attraction from within. In this respect these sub- 

 stances are like the inorganic compounds in which 

 force is embodied, such as gunpowder, in which the 

 components are placed side by side in definite pro- 

 portions, but are not united to each other. The 

 organic substance is analogous rather to the mixed 

 gases of oxygen and hydrogen, resulting from the 

 decomposition of water, and ready to explode on the 

 application of an electric spark, than to a compound 

 united by affinity. 



But in considering the source of the force con- 

 tained in organic bodies, we must not forget the 

 frequent presence in them the constant presence in 

 all their most active portions of nitrogen, solidified 

 as it were from that gaseous condition to which it 



