This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
29. Dr. Barry states, that the quicker the blood circulates the sooner will the machine wear out. Now, suppose that the pulse of a temperate man be seventy in a minute, and by the use of ardent spirits he forces it up to eighty five, then instead of living seventy years, his number of pulsations will be finished at the age of fifty six ; thus cutting short his life fourteen years.
30. The heart beats more than one hundred thousand times in twenty four hours, and sometimes continues to beat thus for one hundred years. What other machine so complicated, could last as long ? And still it is made of nothing but flesh. How strange that it should act so long, without growing weary ! Truly is it said, that " man is fearfully and wonderfully made!"
31. Some physiologists consider the heart the only moving power of the circulation : Others think that the arteries aid by their contractile power. Others still believe that the capillary vessels have a kind of absorbing and propelling force, independent of the heart and arteries, while a hast class ascribe the circulation to a self moving power in the blood itself. All these theories may have some truth in them, but they err in being too exclusive.
32. That the heart is the chief moving power of the blood is generally admitted. If the heart of a frog be taken from the body and placed in warm water, it will con continue to contract and dilate with great force for a considerable time. This would seem to prove that its action does not depend on the contact of air and blood. In serpents the heart retains this power a long time after death; and it has been known to contract at least four days after life appeared extinct. The heart of a sturgeon was cut out and laid on the ground, and after it ceased to beat it was blown up and ordered to be dried. It was then hung up, when it began to move again and continued to beat, though more slowly, for ten hours ; and it continued to contract till it became so dry as to rustle with the motion. If the heart of any animal be taken from the body immediately after death and carefully washed, it will continue to act for some time ; showing that this alternation of action is natural to its irritable fibre, and results directly from its structure.
33. The arteries have not an equal power of contraction, with the heart, though they are generally found more or less contracted after death. The pulse, which may be felt by placing the fingers on the side of the wrist, takes place at the very instant the heart contracts, and is not probably owing to the contraction or dilitation of the artery, but chiefly to the jet of blood, which is sent along the tube. When arteries are changed into bone, the pulse is still felt. No pulse exists in animals destitute of a heart.
34. That the arteries are not only elastic but contract so as to assist the heart in. circulating the blood, is evident from the following facts. If an artery be laid bare, and two ligatures applied so as to cut off all communication, and then a small opening made between the ligatures, the blood will spirt out with considerable force, and the artery become much contracted. When a person or animal is bleeding to death, the arteries always contract in proportion to the loss of blood ; after death they relax again. Arteries too will contract by the application of stimulants or irritating substances.
35. Besides these facts to prove that arteries contract, We may mention the following. We read of cases of palsy, where in the paralytic limb no pulse could be felt, although the heart beat as strongly as ever. We read of other cases where the arteries continued to beat after the pulsations of the heart ceased. In diseases of the heart, we sometimes have a weak pulse, although the heart beats very strongly. And in apoplexy the pulse is often strong, when the heart acts feebly. Burns relates cases where the pulse at the wrist did not correspond with the contractions of the heart: and it cannot be denied that in some animals a circulation exists, although they have no heart. Although fishes have a heart, their blood is moved through the body by vessels. After the heart is taken out of the body, the blood is still seen to flow in the small vessels.
36. I have stated that arteries contract by an irritating substance being applied to them. Hartshorn, or ammonia, will make an artery shrink so as to lose one eighth of its circumference. A partial enlargement of an artery takes place in a living animal by exposing it, and rubbing it between the finger and thumb, but in general no pulsation will be seen in an artery thus exposed.
37. The capillary vessels have an action independent of the heart. When the blood has reached the ends of the arteries, or the capillary vessels, the force of the heart and arteries is probably nearly, if not quite exhausted. Dr. Ar nott says that the blood is driven into them, by a force equal to four pounds to the square inch. There is no doubt that the action of the heart is sufficient to force the blood through the arteries into the veins ; for when the heart acts feebly the surface of the body is pale and cold. But the blood is known to move in a backward or retrograde direction. When a leech is applied to the skin, the blood flows to the spot from all quarters. In blushing, the capillaries of the cheek dilate instantly and admit more blood; under the influence of fear they contract, and the face becomes pale ; tears will gush from the eye in a moment and suddenly disappear ; now all these things could not happen if these vessels did not act independent of the heart.
38. It is probably capillary action which moves the fluids in all animals that have no heart. Persons have lain in a swoon apparently dead for days together and then revived, In these cases life was preserved in the capillary circulation.
I have seen a case of this kind, where a young lady of this city, was kept a fortnight after she was supposed to have died; her looks being so natural that her parents were unwilling to bury her, for fear she would come to life. Although she lay in a room without a fire in the winter season, yet her body retained its natural warmth for several days, her cheeks their florid colour, and her limbs their usual flex ibility. These singular phenomena were perhaps owing to a continuance of the capillary circulation,