The heart we regard as the grand regulator of the blood’s flow; and it is admirably situated for measuring out a regular portion of blood at every contraction. John Bell, believing in the Harveian theory, said, “It is awful to think of the unfixed position of the heart;” and Dr. Arnott declared that “the heart, the heart alone, is the ragged anomaly in the laws of fitness in mechanics.” The heart was now seen to have a right position; for it should swing loose that its moorings be not endangered; and, as whatever impugns the Creator’s unerring wisdom must be wrong, so the presumption is, that whatever vindicates it must be right.

My hypothesis assumed the principle, that, if an endless hollow tube be filled with a liquid, the liquid can be made to circulate perpetually, if it be heated at one point and cooled before its return. A drawing of the simple apparatus by which this problem was proved, is given in my published work on “the Motive Powers, &c.” The figure which represents this apparatus gives the learner the most simple idea possible of the connection of the respiratory and circulatory systems, and of the combination of the two motive powers; the first, or chemical, coming from the lungs, and the second, or mechanical, from the heart.

Suppose the heart divided into right and left hearts by dissection at the septum: the circulatory system might then be represented by an endless tube. Let such an one, nine or ten feet in length, and of one inch bore (to be filled with water) be placed upon a horizontal table. Let an enlargement of the tube be made by a tin vessel to represent the lungs, which shall contain about one-fifth part of the water. Let the tube connected with the right side of the vessel have, at a little distance from the vessel, a smaller enlargement, composed of india-rubber, which can be grasped by the hand, to represent the heart’s right ventricle, with a valve on each side opening towards the tin vessel, the two to represent the tricuspid and semi-lunar valves. Let the whole be made nearly full of water; then, under the tin vessel (representing the lungs), let a fire be made. As the water heats, it will expand; and as the valve closes to the right, it will go off to the left side of the vessel. But, as no water will come in from the right, on account of the valves, there will be no current. Now let the hand grasp the india-rubber, and the fluid between the valves being displaced by its pressure, all the water will go towards the tin vessel, because, while the valve representing the tricuspid would close, that representing the semi-lunar (between the mimic heart and lungs) would open—and very freely; because the expansion made by the heat under the tin vessel had created a vacuum, and thus made a suction power to draw it forward, while there is a driving power behind to force it onward into the tin vessel. Then relaxing the hand, a vacuum will exist between the two valves; and the valve in the rear of the current now begun (the tricuspid) would open, and the water rush in to fill the vacuum in the india-rubber ventricle, to be again pressed forward by the next grasp of the hand; and thus—the fire (representing respiration) being kept up, and the alternate grasping and relaxing of the hand (representing the heart’s regular impulse)—a perpetual circulation might be made to go on;[1] but not without another condition of the problem.

And it was in performing this experiment that a truth was discovered, which, had it been known, many who have ignorantly lost their lives might have preserved them. When the fluid in the apparatus became equally, or nearly as much, heated at the extreme parts of the circulating tube as at the heating vessel, then the motive power of expansion ceased, and (the hand’s impulse being too weak of itself to carry it on) circulation failed; but it was restored by putting snow or ice around the extreme parts of the tube. How often have we heard of ladies who, having gone into warm baths, have been found dead by their friends, or too nearly so, to be restored.[2] Through ignorance of the cause, no right means would be taken to restore them, such as dashing cold water upon the exterior, with simultaneous efforts to produce, in fresh air and in proper position, such artificial respiration as leads to the natural. Where no internal lesions have occurred, there is every reason to believe that such measures might produce restoration.

My imperfect machines gave me to see how much might be done for this important part of physiology by a more perfect apparatus. Mine was merely horizontal—but one might be made to take as many positions as are natural to the human frame; and how many facts might such an one elicit concerning the effects of position on the circulation, by which lives might every day be saved! But skilful mechanicians, not ordinary mechanics, are needed, who are men of intellectual capacity, and are furnished with carte-blanche for time and expense.[3]

The years 1836-’7-’8 witnessed, on my part, several extraordinary and fruitless efforts to get before the public the theory, of whose truth and importance I was then fully convinced. In 1839, Dr. C. Smith, then of Troy, an able medical lecturer, became a convert to the theory; and showed me, in post mortem dissections, the organs of respiration and circulation. At the close of that year, having carefully corrected and made out copies of my manuscript theory, which I had before written, I sent two to Paris—one to the two brothers, Drs. Edwards, members of the French Institute, and one to my friend, Madame Belloc. I also sent one to Edinburgh, to Dr. Abercrombie. Dr. Milne Edwards soon after wrote a book, in which he made it a point to show that animals could live several minutes without breathing; and Dr. Frederic Edwards wrote me a short letter of objections to my theory, and adherence to that of Harvey. This letter was copied and answered in my work published in 1846.

About this time, Dr. Aikin, of Baltimore, wrote to me on the subject; and showed, by calculations, that the mere gradual expansion of the water of the blood was not sufficient, of itself, to produce a current as rapid as that of the blood was proved to be, even on the lowest estimate of its velocity. This did not shake my faith in the great fact that circulation was created by respiration. It must be so; for in life, such respiration as produces heat is the invariable antecedent of circulation, and nothing else is. There was something, then, which remained to be discovered. Again, I placed before me the conditions of the great problem, and set myself intently to its study; and I soon found what I thus sought, and then discerned for the first time that the blood moves, as does the railroad car, by steam. John Bell, my favorite author, had shown that the lungs work in vacuo. A great proportion of the blood is water, which, in a vacuum, springs into vapor at 67°, and the temperature of the blood in the lungs is 101°. Its expansion, then, was not merely the gradual increase of bulk by transmitted heat, but also that of instantaneous expansion, by the vaporization of so much of it as is needed; and what expanded water could not do, steam certainly could. At once, a throng of proofs came to my