Page:Popular Science Monthly Volume 8.djvu/730

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OT all matter is capable of performing vital acts. Those substances alone possess this property which, owing to their peculiar composition, readily undergo molecular changes; that is to say, whose parts are grouped in very unstable equilibrium, and which are always ready to form other combinations. This state of instability is the result of complex combinations of six simple bodies, which at common temperatures have a very weak affinity for one another, but a strong affinity for elements outside of these combinations. Of the six, four, namely oxygen, hydrogen, carbon, and nitrogen, enter into these combinations in large proportions, while of the other two, namely sulphur and phosphorus, only a few atoms enter; and these latter elements are so readily oxidized that their presence increases the instability of the compound. Besides, the atoms of these simple bodies, though occurring in identical proportions, may be grouped according to different modes of aggregation (isomerism and polymerism), and the organic compounds which they make up stand midway between liquids and solids; their molecules are highly inconstant, whence result two well-known properties: the plasticity of organic matter, and its permeability to other substances. These properties are further causes of instability, inasmuch as they expose the organic substances to a number of disturbing influences. Thus, organic matter is not only subject to decomposition by light and heat, but also by the direct or indirect chemical action of bodies entering it, or acting on it from without. In such cases the effect of the disturbance is to cause the organic substance to pass from a state of relative instability to one of relative stability, or even to the state of compounds the most stable in the organic world.

At the same time that it undergoes the action of these external forces—and among external forces we include those developed in organized beings, but applied to other tissues than those producing them—at the same time that under the action of these external forces organic matter suffers decomposition, it becomes the scene of notable reactions. Even very inconsiderable changes in the external forces, which serve as its conditions, produce in it new molecular arrangements which offer a contrast, in their extent and importance, to the comparative insignificance of their cause. These new arrangements, being succeeded by more stable combinations, in turn bring about a disengagement of a great amount of force, in passing from