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860

The Force of the Heart.

blood:-1. When the heart is removed the circulation stops abruptly and completely. 2. When the main artery of a part is tied there is no circulation in the vessels beyond it. 3. When circulation is carried on in a limb only by the main artery and vein, all other parts being secured, the current through the vein is completely arrested by the compression of the artery. (Kirkes.)

The office of the arteries in the circulation is thus described by this physiologist :-1, the conveyance and distribution of blood to the several parts; 2, the equalization of the current and the conversion of the pulsatile jetting movement given to the blood by the left ventricle into the uniform flow; and, 3, the regulation of the supply of blood to each part. This threefold office is accomplished by the combination of the elastic and muscular coats of the arteries.

A knowledge of the facts detailed under the three heads of arteries, capillaries, and veins, prepares us for the discussion of the following subjects.

The force of the Heart.

1096. The arterial tension of four pounds to the square inch, marked by its supporting in a tube connected with the arteries, a column of blood eight feet high (see Art. 1092), is produced by the action of the heart; but as the heart, while injecting the blood, has moreover to overcome the resistance both of the quantity injected and of the mass in the great artery, first moved by the injection, as also the resisting elasticity of the vessel which yields to a momentary increase of pressure, the heart must act with a force exceeding four pounds on the inch. As the left ventricle of the human heart, when distended, has about ten square inches of internal surface, the whole force exerted by it is a matter of simple calculation.

The force with which the left ventricle contracts, is twice as great as that exerted by the contraction of the right. Valentin, a modern physiologist, estimates this force at th the weight of the whole body, while that of the right ventricle is equal to th. This would give in a man weighing 150 pounds a force for the left ventricle of about three pounds and a half. The difference in the amount of force exerted by the two ventricles, arises from the walls or muscular substance of the left being twice as thick as those of the right. The left ventricle has a greater resistance to overcome. While it has to propel the blood through every part of the body, the right ventricle is required only to force it through the lungs.

Cause of the Pulse.

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The capacity of the two ventricles is considered to be nearly equal, and each contains on an average three ounces of blood, the whole of which is thrown into their respective arteries at each contraction. According to Dr. Kirkes, the heart of a healthy adult man in the middle period of life, acts from seventy to seventy-five times in a minute. Assuming seventy contractions as a standard, 210 ounces, or about 13 pounds of blood, would thus pass through the heart in a minute. If the quantity of blood in an adult is taken at 30 pounds, the whole would be circulated and distributed through the body by the contractions of the heart in two minutes and onethird. Valentin has calculated that the whole of the blood may pass through the heart in 62 seconds. This will convey some idea of the astonishing rapidity with which substances are absorbed by the blood and conveyed to all parts of the body.

The pulsations of the heart gradually diminish from the commencement to the end of life. Just after birth they are 140 in a minute; during the third year 100; at the seventh year 90; in the middle period of life 75 to 70; and in old age 65 to 60.

Some physiologists have expressed surprise that the force of the heart should be so great as it is, remarking that much less would have sufficed to propel the blood to the most distant capillaries; but they did not reflect that the heart, besides carrying on the general circulation, has to force blood into those parts of the flesh which, in the various positions of sitting, lying, or standing, are for the time compressed by the weight of the body above; for if it were not strong enough for this purpose, either the compressed parts, deprived of their nourishment, would quickly die, or the person, obliged to be every moment changing his position, could obtain no lengthened repose. A pressure equal to that of one and a half or two inches of mercury is considered to be sufficient to propel the blood through the vessels of the lungs.

The Pulse.

1097. The opinion which the ancients held that the arteries contained vital spirits or air, and not blood, rendered the pulse to them a very mysterious phenomenon; and many curious hypotheses were framed to explain it. We now know that each gush of blood thrown into the aorta from the great left chamber of the heart, causes an undulation, perceptible to the touch, to spread from the heart to the most distant extremities.

By an ingenious application of mechanics, an instrument called

862

Measurement of the Pulse.

the sphygmograph has been invented and applied to the determination of the form, force, and frequency of the pulse as felt at the wrist. The instrument is so secured over the radial artery that at each pulse-beat a lever is raised, and this communicates the impulse to another lever armed with a pen-point, which has a vertical movement, and records the result in an irregular line. A strip of paper is moved by machinery steadily across the pen-point, and thus receives the undulating mark produced by it. The height of the elevations indicates the strength of the pulse, and the number of them over a given space, its frequency. Valvular and other diseases of the heart are thus indicated by the sphygmographic tracings on the paper.

The annexed figures illustrate the state of the pulse as taken under different conditions; I represents the pulse of a healthy man, aged twenty-three, the pulse being 72; 2 represents the pulse of the

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same man after he had taken a small dose of nitrite of amyle, a narcotic; 3. Pulse at the commencement of typhoid fever; 4. The pulse on the thirteenth day of a severe case of typhoid fever. These are taken from observations made by Dr. Galabin.

It is a remark respecting the pulse, worthy of full consideration, that if the purpose of the heart and arteries were merely the propulsion and conveyance of the blood, their structure and action would form signal deviations from the ascertained rules of fitness in mechanics. In machines of human contrivance, it is one of the most important maxims "to avoid shocks, or jerking motions ;" and in former parts of this work, we have described fly-wheels, air

Life dependent on the Heart's Action.

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vessels, and springs, as means of accomplishing this object, and thereby of preventing the wearing and straining of parts which else might happen. In the human body, also, we have had to describe the admirable elasticity of the spine, of the arch of the foot, and of the cartilages of joints, as contrivances answering the same ends. The heart alone is the rugged anomaly which, from before birth unto the dying moment, throbs unceasingly, and sends the bounding pulse of life to every part; and which, moreover, instead of being secured and tied down to its place, is attached at the extremity of the aorta, like a weight at the end of an elastic branch of a tree, and every time that it fills the aorta, is thrown with violence, by the consequent sudden tendency of that vessel to become straighter, against the ribs on the icft side, in the place where the hand applied, feels it so distinctly beating. This impulse is most evident in the space between the fifth and sixth ribs, between one and two inches to the left of the chest bone.

1098. The action of the heart is the first indication of life (punctum saliens), its cessation is the true point of death (ultimum moriens). In death from asphyxia (suffocation) the heart continues to pulsate for three or four minutes after respiration has ceased, and while the animal is quite insensible. This has been called apparent death. The state of hybernation in animals is somewhat similar. There is not an actual stoppage of the action of the heart, for this would be inconsistent with the maintenance of any life in the body, but the heart pulsates more feebly and at much longer intervals. It has been found that in the marmot, or mountain rat, when the animal was in an active state, the pulsations of the heart were 90, while in the torpid or hybernating state, they were reduced to 8 cr 10 in a minute.

It is remarkable that there are some vegetable poisons which act specially on the heart, and reduce its contractions even to the suppression of them altogether. This is the effect of the ordeal bean of the West Coast of Africa (Calabar bean). It is there used as a test for witchcraft. An eminent physiologist took a small quantity in two doses, in order to test its action. In twenty minutes he became faint and utterly powerless, and his pulse was reduced to thirteen in a minute. To the bystanders it appeared as if it would stop altogether, when, fortunately, reaction took place and he recovered.

1099. Although the action of the heart is independent of the will, in some rare cases a person has had the power of voluntarily reducing its pulsations, and of passing spontaneously into a state of

864 The Heart-The Number of Pulsations.

apparent death. Dr. Cheyne, an eminent physician of the last century, describes the case of a Colonel Townshend, who in his presence so suspended the pulsations of his heart, that no pulse could be felt at the wrist, and the Colonel remained in a lifeless state for half an hour, when he slowly recovered. There is no doubt that his heart continued to act during this time, but at long intervals, as in the hybernating animals, although no pulse could be felt. The stethoscope, which, when applied to the chest, allows the feeblest sounds of the heart to be heard, had not then been invented. Although the Colonel perfectly recovered, he died nine hours after the performance of the voluntary experiment above-mentioned, and nothing could be found in his body either to account for his death or for the possession of this singular power.

1100. The heart has been elsewhere described as the pump of the blood (Art. 1088), and its action in the body has been compared to the pump-barrel and piston worked by steam, which distributes water through the mains and pipes of a great city. While the mechanical effects are similar, there are differences which require notice. The action of the heart is unceasing so long as life continues. In an adult whose pulse numbers only 60 in a minute, the heart makes no fewer than 86,400 pulsations in the twenty-four hours. Its action has been maintained at this rate for eighty, ninety, and even one hundred years. The heart of an infant will go into the cavities of the heart of an adult; hence the whole substance of the organ must have been removed and replaced in the adult, but still retaining its form, position, and action. Here we come upon the vast differences which exist between physical and animal mechanics. The steam-pump manifests neither growth nor change, but rapidly wears out from the friction of its parts, and is not renovated except by the hand of man; the blood-pump passes spontaneously, like all living matter, through stages of growth, maturity, and decline, and while doing an amount of work which would soon wear out any ordinary machine or engine, is able when so working to repair its own daily waste for a hundred years, without in any way interfering with its mechanical functions. These differences should be considered when we are called upon to admit the theory of a modern school of philosophers who deny the existence of "living" powers, and who can see nothing in a living body but that which is explicable by physics and chemistry.

1101. One use of the pulsation of the heart probably is seen in the agitation and kind of churning which the blood suffers in passing

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