First step in the discovery—Animal Heat the product of Respiration.
Second step—Heat evolved in the lungs by Respiration there produces
Expansion. Third step—Expansion; implied motion, which from the
organism must conduct the blood to the left ventricle of the Heart.
Theory imperfect, until the formation of sufficient vapor or steam
in the lungs is perceived and acknowledged.
To Dr. Marcy.—In complying with your request to write for your journal
an article embodying my theory of the motive powers which produce the
circulation of the blood, together with some account of its rise and
progress, I obey what I regard as a call of duty; and thus requested, do
it with pleasure.
But my theory, with its history, cannot thus be written without egotism.
Logicians say, that the way to convince others is to retrace, in order,
the steps by which you yourself became convinced, which is to be
egotistic. But in this case, there is a further reason: the scientific
discoverer must speak of the apparatus by which he experiments, and mine
was often my own physical frame.
Twenty years ago, while yet my mind, laboring with this great subject,
was condemned
“to drudge
Without a second and without a judge,”
you, sir, comprehended the hypothesis which has now become a theory, and
you waited not for others to speak, but you fully acknowledged its
truth; and although, in Hartford, as now in New-York, you were thronged
with practice, (then allopathic), you yet found time to furnish me with
added experiments, made in your office, confirmatory of its truth, which
by your permission were afterwards added in your name to my published
work.
The first step in the theory occurred to my mind in the winter of 1822,
and while I was engaged in founding the Troy Female Seminary. Being in
attendance on a course of lectures on chemistry, and at the same time
teaching to a class Mrs. Marcett’s excellent work on that subject, one
cold morning, as I was walking briskly up a hill, I said to myself, Why
do I grow warm? Whence comes this accession of caloric? It cannot be
transmitted to me from any object without, because every thing which
comes in contact with me is cold. Snow is under my feet, and frosty air
surrounds me; and, as to clothing, even the softest furs impart no
warmth—they but keep from escaping that which comes from within. What
other method besides transmission is there of gaining heat? There is the
elimination of caloric, when, in substances chemically combining, weight
is gained and bulk is lost. Is there any such combination going on in
me? Yes; this atmospheric air, when I inspire it, has oxygen combined
with nitrogen; but when I expire, the oxygen has disappeared, and
heavier substances—carbonic acid gas and watery vapor—are returned in
its place. Thus, it must be, animal heat is evolved. It is the product
of respiration; and it is because I breathe faster and deeper, that more
carbon is oxidized or burned, and more heat is set free in my lungs; and
therefore I grow warm as I walk up this hill, though all around me is
cold.
The mind, excited by new and great thoughts, works with unwonted energy;
and mine at once collected so many proofs, that I became perfectly
convinced of the truth of the hypothesis. In searching books, I found
that Lavoisier had taught the same; but he dying, his doctrine was
discarded by English chemists, Dr. Black leading the way, and therefore
it did not then appear in English systems of chemistry. But from that
time, I cherished it with a mother’s devotion, watched changes in my own
physical frame relating to it, taught it to my pupils, and held warm
disputes with the medical faculty, who opposed and contemned it.
In the summer of 1832, the Asiatic cholera appeared among us, appalling
every heart. This plague, I said, is a disease of coldness and
obstruction; and these doctors, wrong as they are on the subject of
animal heat, can never understand it—though, if Lavoisier were living,
he might. Let me, then, as best I may, consider anew the problem of heat
as produced by respiration, and see whether I cannot find out something
which has a bearing on the fatal coldness of this fearful disease. It is
into the lungs, and no where else, that breathing introduces atmospheric
air; and it is there that the oxidation of carbon or animal combustion
takes place. Thus must caloric be imparted to the blood in the lungs;
and in them is one-fifth of the blood of the system, of which
seven-eighths is water.
The nature of heat is to expand all fluids. The blood in the lungs must,
therefore, expand; and if it expands, it must move; and if it moves, it
must, from the organism of the parts, move to the left ventricle of the
heart, into which the valvular system opens to give it a free
passage—whereas the valves of the right close against it. “Eureka!” I
mentally exclaimed; “I have found the primum mobile of the circulation
of the blood.” I had for years disbelieved that the heart’s slight
mechanical impulse was that cause. In teaching Paley’s “Natural
Theology,” my mind had come in contact with the passage in which he
describes the heart’s more than Herculean labors; and I said, “This is
altogether too much—the heart alone cannot perform all this—there must
be some other power,” and an abiding desire to know what that power
could be, prepared me for receiving this great idea. But my mind was
agitated by it, as the sea is, when a great rock is thrown into its
waters.
The cholera was then raging around me; and as I prepared to flee from it
to a mountain air, I confided to a scientific friend, Professor Twiss of
West Point, my hypothesis, which I regarded as probably the incipient
germ of an important discovery.
But there was first the former theory to be disproved; and then there
were new points to be investigated and established. In the ensuing
winters of 1833, 4, and 5, I gave much attention to the subject, and
employed professors in my school in the departments of chemistry and
natural philosophy, who assisted me,—particularly by their ingenuity in
the construction of such simple pieces of apparatus as were needed.
Thus we proved that, although the heart’s action gives pulsation, it
does not necessarily give circulation. By an endless india-rubber tube,
filled with water, coiled upon a table and struck repeatedly at one
point, a pulsation was produced throughout, but no circulation. By
affixing the tube to a vessel of water, and laying it on an inclined
plane, the water ran through it in an equable current, making
circulation with pulsation. Clasping the hand upon the tube in
successive contractions, the fluid passed on per saltem, producing
circulation and pulsation united, but no acceleration of the current.
Now, add valves to the tube on each side of the opening hand, and you
will have the current—which is moving by gravitation, accelerated by
the hand’s impulse, as the blood’s current, first moved by respiration,
undoubtedly is by the heart’s beat.
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 mind. The most apparent of
these was the vapor expired breathing. I recollected how, in former
times, the stage horses, driven rapidly into my native village of a
winter morning, had clouds of vapor wreathing upward from their
nostrils, while the icicles of condensation were hanging below. The
nurse, who stands over the dying, holds a mirror before the mouth and
nose, and considers that life is only extinct when vapor ceases to be
formed. Then came to mind the solution of that great mystery of
physiology, why the arteries are empty at death, which so long hindered
the discovery finally made by Harvey.
In the state in which chemistry was, even as late as the time of John
Bell, the chemical power of the heat produced by respiration at the
lungs could not have been understood.