a molecular contest of refined organic principles, not visible or audible in its details, but in general scope and outcome as manifest and beneficent in its operation as its more familiar congener.
Though the conservative influence of reversion is quite apparent in variations of a normal kind, it is far more so in those that are morbid or abnormal. Here the struggle between the variation and the tendency to the maintenance of durable types is usually so sudden, violent, and quickly decisive, that it is vividly realized. Upon the tendency of deranged actions to revert into the old channels of health does the therapeutist ground all hopes of his ability to assist in the process. When that is manifestly impotent, no means he can bring to bear will arrest the speedy termination of life. Cullen attributed the tendency in disease to reversion or recovery—for they are identical—to a vis medicatrix naturæ. The conception is little more than a barren ideality, and does not accord with the fundamental truth that of causes we can know nothing only of the relations of phenomena to each other. The vis medicatrix naturæ has not been shown to have any antecedent; it is simply a name for a supposed entity, apparently latent until disease appears. According to the views here adduced, it is resolvable into the general principle manifest in all kinds of organic life: the strong tendency to the maintenance of characters which a great lapse of time has proved are the most fit. If this generalization be truly grounded, it adds another to some more notable in which modes of action once considered as produced by independent forces were really transmutations of one.
The frequency with which the principle of reversion gains the mastery in attacks of acute disease is one of the most striking phases of vital action. Form and function are seen to revert to their old types and channels of action as if they had never nearly perished. The struggle against abnormal variations is violent, continuous, but not prolonged. Either the abnormity or reversion quickly gains the mastery; in the former case the end is dissolution, in the latter health. In some instances the morbid variation is slow, insidious, or mild in nature; the struggle is then less conspicuous, 'more prolonged, but never suspended. When the abnormal variation gains the mastery, it does not survive or establish its fitness by indefinite perpetuation, and so acquire the prepotency of reversion. Untimely death is the signal and sequel of its mastery, and until this or reversion gains supremacy no peace or continued harmony of action is possible. True, blood affected by a morbid variation chronic in its nature often displays sluggish and varying fortunes in its struggle with reversion for mastery; favoring conditions now giving reversion the ascendancy, then unfavorable conditions impart a renewed energy to the unhealthy tendency. Yet a marked lineage struggle for survival is rarely very extended—the compass of a single life's observation not unfrequently witnessing its close.
