Then came the great "humoral" or "vital fluid" theory of disease which ruled during the Middle Ages. According to this, all disease was due to the undue predominance in the body of one of the four great vital fluids,--the bile, the blood, the nervous "fluid," and the lymph,--and must be treated by administering the remedy which will get rid of or counteract the excess of the particular vital fluid in the system. The principal traces of this belief are the superstition of the four "temperaments," the _bilious_, the _sanguine_, the _nervous_, and the _lymphatic_, and our pet term "biliousness," so useful in explaining any obscure condition.
Last of all, in the fullness of time,--and an incredibly late fullness it was,--under the great pioneer Virchow, who died less than a decade ago, was developed the great cellular theory, a theory which has done more to put disease upon a rational basis, to substitute logic for fancy, and accurate reasoning for wild speculation, than almost any discovery since the dawn of history. Its keynote simply is, that every disturbance to which the body is liable can be ultimately traced to some disturbance or disease of the vital activities of the individual cells of which it is made up. The body is conceived of as a cell-state or cell-republic, composed of innumerable plastid citizens, and its government, both in health and disease, is emphatically a government "of the cells, by the cells, for the cells." At first these cell-units were regarded simply as geographic sections, as it were, sub-divisions of the tissues, bearing much the same relation to the whole body as the bricks of the wall do to the building, or, from a little broader view, as the Hessians of a given regiment to the entire army. They were merely the creatures of the organism as a whole, its servants who lived but to obey its commands and carry out its purposes, directed in purely arbitrary and despotic fashion by the lordly brain and nerve-ganglia, which again are directed by the mind, and that again by a still higher power. In fact, they were regarded as, so to speak, individuals without personality, mere slaves and helots under the ganglion-oligarchy which was controlled by the tyrant mind, and he but the mouthpiece of one of the Olympians. But time has changed all that, and already the triumphs of democracy have been as signal in biology as they have been in politics, and far more rapid. The sturdy little citizen-cells have steadily but surely fought their way to recognition as the controlling power of the entire body-politic, have forced the ganglion-oligarchy to admit that they are but delegates, and even the tyrant mind to concede that he rules by their sufferance alone. His power is mainly a veto, and even that may be overruled by the usual two-thirds vote.
