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(continued)
Furthermore, in other passages in the VINDICATIO, Lower refers in
detail to the analogies between accension in the heart and air-controlled
combustion.7 He even mentions
an experiment in which the heart of a vivisected animal is revived
by blowing in air, with the mouth, through a tube into the chyle vessels
or vena cava.8 Finally, in a slightly different context, Lower describes active expulsion of blood from the heart during cardiac systole;9 Willis, by contrast, had spoken merely of blood being "wheeled about after a constant manner, as it were in a water Engine."10
These minor unorthodoxies apparently played on Lower's mind for several years. Then, at the Royal Society, Lower began to collaborate with Hooke, who for some time had been interested in respiratory physiology. Already in 1664 Hooke had tried to determine whether the efficacy of the lungs depended on their motive effect on the blood or on the role they played in admitting air to the body. In 1667 he perfected an experimental technique that allowed him to keep the lungs motionless and inflated, even with the chest cavity fully exposed. Hooke pricked holes in the lungs and blew a continuous stream of air through the motionless lungs of a dog by a bellows arrangement.
In October 1667 Hooke and Lower began to collaborate on cardiopulmonary experiments. Upon Hooke's suggestion, they attempted together to determine the exact effect on the blood of its passage through the lungs; and to accomplish this by altering the normal route, bypassing the lungs, and transmitting blood directly from the pulmonary artery to the aorta through an air-free channel.
Preliminary results from these experimental techniques had an enormous impact on Lower's thinking. He was now able for the first time to observe closely the appearance of the blood, both as it left the right ventricle of the heart and before it entered the lungs, and as it returned from the inflated lungs via the pulmonary vein. Lower could now see clearly that only exposure to the air in the lungs altered the blood's appearance; whereas blood still appeared venous as it left the right ventricle, it was already arterial as it moved from the lungs to the left ventricle. Thus the bright, scarlet color of arterial blood depended on contact with air and not on effervescence in the heart (which should have occurred as surely in the right as the left ventricle). Lower could also observe closely the continual, rapid, and vigorous pumping action of the heart, which now seemed clearly to be unrelated to a postulated effervescence in the cardiac chambers.
An intense period of reconceptualization and experimentation followed this work at the Royal Society, and led Lower to the publication of his TRACTATUS DE CORDE (London, 1669), which comprised five chapters. The fourth chapter quickly reviews the history of transfusion and presents Lower's principal results; the fifth surveys Lower's thoughts on chyle and its transformation into blood.
The first three chapters of the DE CORDE are exclusively concerned
with the heart, the blood, respiration, and circulation. Lower begins
with detailed descriptions of the muscular anatomy and nerve supply
of the heart, comparisons of the fibrous structure of the human heart
with that of other animals, and an account of the heart's contractive
and expulsive movements. He now denies that there is any nitrosulfureous
ferment in the heart and explains that the blood is "too inert to
effervesce so violently and suddenly in the Heart or its Vessels."11
Lower stresses the movement of the blood by the active cardiac systole
(an early emphasis of his) and pointedly asks, "If the blood moves
through its own power, why does the Heart need to be so fibrous and
so well supplied with Nerves?"12
Lower also reports experiments he performed to determine the velocity of circulation. In one of these, by taking the average capacity of the left ventricle, counting the number of beats per hour, and estimating the total quantity of blood in the body, he finds that all the blood passes through the heart thirteen times per hour. In another experiment Lower drains almost all the blood from a dog, through the cervical arteries, within three minutes. Both experiments clearly suggest that there can be no profound difference between venous and arterial blood, since overall circulatory velocity is too great to allow drastic transformation.
Finally, Lower comes to a series of experiments on the influence of
the air on blood color. He reports that he once held different views
on this matter, confessing that he had "relied more ... on the authority
and preconceived opinion of the learned Dr. Willis than my own experience."13
Acknowledging his indebtness to Hooke, Lower presents the new experimental
basis for his greatly modified thinking. He reports his observation
that blood withdrawn from the pulmonary artery "is similar in all
respects to venous blood,"14
and claims that this would not be so if a cardiac effervescence were
responsible -- as he once believed -- for the different appearance
of venous and arterial blood. Exposure of the blood to the air is
the crucial occurrence, which, he explains, can be further established
by blocking of the trachea and noting the still-venous appearance
of blood that passes through the air-blocked lungs. This proves definitively
that the bright red color of arterial blood is "due to the penetration
of particles of air into the blood"; it is the "nitrous spirit of
the air" that normally enters the blood in the lungs.
The TRACTATUS DE CORDE was quickly recognized as a major new work on physiology. Warmly reviewed in the PHILOSOPHICAL TRANSACTIONS for 25 March 1669, it won plaudits both in England and abroad and in a short time dramatically changed the thinking of many about the role of the heart and the lungs. Even Willis was deeply impressed. In 1670 Willis published an essay, "De Sanguinius Accensione," in which he abandoned his old views for Lower's new ones and applauded "the most learned Doctor Lower" for making him see the light.
Mayow, whose TRACTATUS QUINQUE of 1674 was to represent the next major breakthrough in respiratory physiology, was also greatly influenced. The favorable reception proved enduring, and for many years Lower's TRACTATUS DE CORDE continued to be cited as an important and authoritative work, clearly in the high Harveian tradition of "anatomical experiment." In the next century, too, Lower continued to receive credit. His accomplishments were enthusiastically acknowledged by Senac in his TRAITÉ DE LA STRUCTURE DE COEUR (Paris, 1749) and by the influential Boerhaave. The DE CORDE itself was published in a Leiden edition as late as 1749.
After the DE CORDE, Lower published only one minor work on anatomical physiology, the DISSERTATIO DE ORIGINE CATARRHI (London, 1672). Here Lower codified the ideas and experiments he and Willis had performed to show that no passage existed for discharging serous fluids from the cerebral ventricles through the palate and nose; Willis had already reported similar results in chapter twelve of his CEREBRI ANATOME (1664), as had Lower himself in the TRACTATUS DE CORDE. Other medical works bearing Lower's name appeared in later years, but none of these can be definitively traced to Lower's pen. It seems clear that after the DE CORDE Lower's active interest in physiology gave way to a vigorous cultivation of his medical practice, and it was as a physician that he concluded his career.
-- Theodore M. Brown
Notes
1. THE WORKS OF THE HONOURABLE ROBERT BOYLE, Thomas
Birch, ed., V (London, 1744), 518.
2. Ibid., 525-526.
3. Lower, TRACTATUS DE CORDE (London, 1669), 173.
4. Thomas Birch, THE HISTORY OF THE ROYAL SOCIETY,
I (London 1756-1757), 303.
5. Thomas Willis, THE REMAINING MEDICAL WORKS OF ...
DR. THOMAS WILLIS (London, 1681), 59.
6. DIATRIBAE THOMAE WILLISII ... DE FEBRIBUS VINDICATIO
ADVERSUS EDMUNDUM DE MEARA (London, 1665), p. 116.
7. Ibid., 117-119.
8. Ibid., 125-126.
9. Ibid., 59.
10. Willis, REMAINING MEDICAL WORKS, 64.
11. Lower, TRACTATUS DE CORDE, 62.
12. Ibid., 64.
13. Ibid., 163.
14. Ibid., 164.
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