INTRODUCTION.

A CERTAIN sanctity appears to have been connected with the blood at a very early period in the history of humanity. Its loss, in quantity, was seen to be so necessarily followed by death, that it even came to be spoken of as the Life in the sacred writings of the Jews; and, poured out upon the altar, it was long held by them, as by so many of the peoples of antiquity, to be not only the most acceptable offering that could be presented to propitiate the Gods, but even as competent to purge mankind from sin.

No wonder, therefore, that the blood, the lifegiving element, at all events, if not the very life, was an early object of study with physiologists, and that it was held to have powers, properties and motion apart from, and independent of, the organisms whereof it is so important an integral part-motion above all, another word for life, even as stagnation is equivalent to death. At no time, therefore, do we observe that the blood was ever thought of as otherwise than in motion.

When we turn to the writings of our predecessors in the field of anatomy, and find them possessed of such an amount of accurate information on the struc

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ture of the animal body, we are at a loss to account for the imperfect, or more positively erroneous, nature of so many of their physiological conclusions. But the old observers were hampered by metaphysical assumptions, irrespective of cognizable fact and by fancies concerning the way and manner in which the world of matter as of mind is ruled. Neither the Macrocosm nor the Microcosm, as the universe and the body of man were designated, was seen to be possessed of powers adequate to produce the phenomena it manifested, and so to make it self-sufficing. The world without, was believed to be dominated by Entities apart from itself; the world within, by Principles distinct from the organs of which it is composed.

No Spinoza had yet appeared had yet appeared to assimilate the "something not himself "--his dream, his shadow on the ground, his reflection in the pool-originated by none of these, but personified and called by so many names by man, with the universe of things; no Leibnitz to announce a "Pre-established Harmony," and, following Spinoza, though using other words, to declare that the World being, as it is, could have been no other than it is; and no Locke to assert the competence of God to have Consciousness an appanage of nerve, and to say that the reason vouchsafed to man was guide sufficient for conduct and conclusion, both as regards the now and the hereafter. But as the astronomer has of late been

suffered to say that the Sun, with his attendant planets and their satellites, suffices for the cosmical phenomena observed in the system he dominates, so has the physiologist more lately still been allowed to own that the organisms of man and animals in their several estates suffice for the faculties they manifest.

None of the natural sciences had in truth such obstacles to contend with, in the shape of metaphysical assumptions - from which, indeed, it has not yet entirely escaped-as physiology. When the facts of observation did not tally with these, it was long held imperative either to pass them by unnoticed, to explain them away, or to regard them as effects of misleading sense. Certain agents by which the organism was presumed to be supplemented and dominated, characterized as Spirits or Principles, were imagined; and, being associated with the more important organs, the functions of these were believed to be severally evoked by them, much as the hand of the musician elicits music from his instrument. Strangely and illogically too, as it seems, these agents were still thought of as dependent on the organs they actuated -to come into play, they had themselves to be engendered. The right ventricle of the heart, with the blood supplied by the liver, produced the Natural Spirit; the left ventricle, with the aid of the lungs, begat the Vital Spirit; and the brain, with the help of the heart, fashioned the Animal Spirit.

Thus believed to be of different kinds, the Spirits

were further thought of as associated with blood of dissimilar qualities, by the medium of which they were communicated to the body. Hence the assumption of Two Kinds of Blood, which stood so long in the way of true physiological conclusions-one derived from the Liver as its source, another from the Heart. Hence, also, two orders of vessels, accordant in structure and property with the presumed qualities of their contents-the Veins, channels of the sluggish and darkcoloured natural blood, product of the liver; the Arteries, conduits of the elaborated, subtle and florid blood, product of the heart. The dark blood distributed from the liver to every part of the body by the vena cava for purposes of growth and nutrition ; the florid blood delivered from the heart by the aorta to supply the frame with heat and vital endowment.

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The two kinds of blood, it was then supposed, moved to and fro in their respective channels, doing their office to the tissues and returning to their sources for fresh supplies of material and renovation of powers; the motions being assimilated now to the ripple on the surface of a lake or stream, and again, and more commonly, to the ebb and flow of the tide in a narrow sea; the outward motions, mainly due to attractions between the parts of the body and the blood in the vessels ; the return, to a per-contra attraction of the centres, and a suction-power connected with the diastole of the heart, both alike aided by the alternate heaving and subsidence of the chest in respiration.

The liver, then, was the laboratory of the natural blood, having derived the materials for its work from the stomach and intestines. This blood sufficed for ordinary growth; but to acquire vitalizing, and as sometimes said, nutritive properties it had to reach the heart and undergo further elaboration in its chambers. On the right side there was obvious and ready access to the ventricle from the vena cava; and there the blood was believed to be altered and improved to a certain extent―to have something of a natural spirit imparted to it; but it was not yet sufficiently attenuated and subtilized to be fit recipient or associate of the vital spirit. To attain to such a degree of refinement it must reach the left ventricle; and this it was presumed to do by permeating the partition between the two ventricles, whereby it became clarified and improved, as is muddy water by filtration through a sponge.

Blood was at best

This, however, was not yet all. a palpable and gross material; spirit was impalpable and etherial in its nature, nearest akin to air among things cognizable to sense; and breathing being seen to be even as necessary to life as the blood, the Vital Spirit was presumed to be finally obtained from the inbreathed air commingled with the purified blood. the Jewish Scriptures, says the writer, "God breathed into the nostrils of man the breath of life, and he became a living soul."

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Communication between the left ventricle and the