states and properties to the things of the inorganic world, we are ever more assuredly referred to the same great centre as efficient cause of the phenomena we witness in the world of organization. That which is the source of Motion in the Universe, we need not hesitate to acknowledge as the source of motion in each and all of its individual parts; for our modern philosophy recognises none but general, eternal, allpervading Laws.

Heat passing from a hotter to a colder medium, then, is transmuted into mechanical effect or work in the world of brute matter; into vital effect or work in the world of matter organized. With the heat of the sun stored in the fuel consumed by the steam engine turned into motion, we have the hundreds or thousands of foot-pounds of available power set free, with transference in space at an approach to planetary speed. With the heat of the sun the air of the atmosphere and the mineral contents of the soil arrested by plants, we have the wonderful evolution of life in union with organic structure and unconscious sensibility; and, with the same great force stored in the food appropriated by animals, represented by the blood and tissues of their bodies, consumed and turned into motion, we attain at length to Muscular Contractility, Glandular Secretion, Conscious Sensibility, Moral Emotion and Understanding. Life in the aggregate then meets us in its highest manifestation— man-as motion due to the action of oxygenated blood

upon the elementary tissues of which the organism is composed, ceaseless consumption of itself and of these being implied. Hence the necessity of ever fresh supplies of fuel to the engine, of food to the animal ; the fuel appearing as mechanical motion in the one, the food as vital motion in the other.

It may scarcely be necessary to speak of the conditions indispensable to such transmutation of the initiatory heat-force. Suffice it to say that the heat must disappear if motion is to appear. The highpressure engine would stand still in an atmosphere of its own temperature; the condensing engine would not give a stroke without its cold chamber. There could then be no conversion of heat into mechanical motion. In the same way precisely, the animal body, in an atmosphere in which it could lose no heat, would necessarily suffer arrest of all motion, or die.

In speaking thus of heat as the cause of vital motion, I would beg to be understood as meaning to say, that I believe it to be the immediate agent in the phenomena we witness in animal bodies. How it is so, how it came to be so, we do not know. But we can say with Harvey, speaking of generation, that “he who derives it from the same Eternal and Omnipotent Deity, on whose nod the Universe itself depends, takes the right and pious view of the matter. Nor do I think," he continues, "that we are greatly to dispute about the name by which this First Agent is to be called-whether it be God, Nature, or the Soul

of the Universe-all still intend by it that which is the beginning and the end of all things; which exists from Eternity, which is Author or Creator, is Omnipresent, and not less in the single and several operations of natural things than in the infinite Universe." In so far as sensible phenomena help to a conclusion we might perhaps be emboldened to say that the immediate cause of the heart's contraction is the contact of the blood poured into it with the diastole. Thus an animal killed by decapitation and having the chest laid open, the heart is seen pulsing feebly for a few seconds, and then ceasing whilst the animal is held erect. But the body being inclined and the blood contained in the veins of the abdomen and lower extremities made to flow to the heart, its action is immediately restored, and continued until the supply of blood is exhausted.

SECTION VI.

TRANSFUSION OF THE BLOOD FROM ARTERIES TO VEINS, AND THE IMBIBING POWER OF THE VEINS.

IN speaking thus of the cause of the motion of the heart, the doctrine of the circulation would nevertheless not be complete. That there must be ceaseless transfusion of blood from arteries to veins, Harvey demonstrated to be a physical necessity; but, as we

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have seen, he did not know precisely how it was accomplished, and he certainly erred when he affirmed that it was not by continuity of canal between the two orders of vessels, as shown by Malpighi, who had the good fortune first to see the capillary arteries pouring their tide into the capillary veins, and these in turn transferring it to the venous trunks.

But even with the addition of this important fact, all is not yet complete. The arteries are canals bringing supplies of nourishment to the tissues, and the veins conduits carrying back so much of the vitalizing fluid as is not wanted for their growth and maintenance. Still within the vessels, however, the tissues can have no advantage from the nutriment they contain. The matured, most perfect portion of the blood-the plasma-must transude the walls of the arteries and bathe the tissues immediately before they can select from it the elements they require for their growth, nutrition, repair, secreting faculty, or vital endowment. Such transudation, we must presume, is readily effected by the force of the heart putting the coats of the arteries on the stretch. Then does the finer portion of the blood transude the walls of the arteries, and bone, muscle, skin, glandular parenchyma, nerve and brain select that which each requires for the maintenance of its structure and the performance of its function; the heat, engendered by the molecular and chemical changes that now take place in the blood and tissues, being at the same instant dissipated

and turned into motion, with the marvellous results briefly hinted at above.

Nor are all the processes dependent on the access of arterial blood yet accomplished. The plasma, the vitalizing pabulum of the organism, has been presented immediately to the parts, and they have appropriated so much of it as they require for their maintenance and their functions; but so much as was not required for these, and the molecules that have been replaced by the fresher matter appropriated, have to be removed, and either renovated by the action of the air in the breathing apparatus, or thrown out of the system in the shape of carbonic acid by the lungs, of bile by the liver, and of urea by the kidneys.

The question that now presents itself is, therefore, this: How is the plasma shed from the arteries, having done its office and replete with sordes, to get back into the current of the circulation? By the absorbing faculty of the veins, is the answer ready at hand. But in virtue of what do the veins acquire the absorbing power they possess in such perfection? Secretion by cell-formation, as we know the process to go on in glands, would enable them to attract with every requisite degree of rapidity the fluids effused into the tissues amid which they run. But the veins are not secreting vessels; they have not the cell-elements of glands in their structure; they are mere membranous canals for returning to its source the blood that has been sent from the heart by the arteries.

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