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Updated: June 25, 2025
If you turn to the production of the chick in ovo, however, you will find at first no more a vesicle or auricle, or pulsating drop of blood; it is only by and by, when the development has made some progress, that the heart is fashioned; even so in certain animals not destined to attain to the highest perfection in their organization, such as bees, wasps, snails, shrimps, crayfish, etc., we only find a certain pulsating vesicle, like a sort of red or white palpitating point, as the beginning or principle of their life.
Previously all the blood went from the auricle through the aortic arches into the gills, but now only part of it goes to the gills, the other part passing to the lungs through the new-formed pulmonary artery. From this point arterial blood returns to the left auricle of the heart, while the venous blood gathers in the right auricle.
These differences in structure are all accounted for by the work done by the different portions of the heart. The greater the work, the heavier the structures that perform the work. The right ventricle forces the blood through the lungs and into the left auricle. The left ventricle forces blood through all parts of the body and back to the auricle. The auricles force blood into the ventricles.
This pressure diminishes rapidly in the small arteries, becomes comparatively slight in the capillaries, and falls practically to nothing in the veins. Near the heart in the superior and inferior venæ cavæ, the pressure at intervals is said to be negative. This means that the blood from these veins is actually drawn into the right auricle by the expansion of the chest walls in breathing.
Consequently, although a pathologic condition of the node is a frequent, and perhaps the most frequent, cause of auricular fibrillation, other conditions, especially anything which dilates the right auricle, may cause it. If the pulse is intermittent and there is apparently a heart block.
Since all things, both argument and ocular demonstration, show that the blood passes through the lungs, and heart by the force of the ventricles, and is sent for distribution to all parts of the body, where it makes its way into the veins and porosities of the flesh, and then flows by the veins from the circumference on every side to the centre, from the lesser to the greater veins, and is by them finally discharged into the vena cava and right auricle of the heart, and this in such a quantity or in such a flux and reflux thither by the arteries, hither by the veins, as cannot possibly be supplied by the ingesta, and is much greater than can be required for mere purposes of nutrition; it is absolutely necessary to conclude that the blood in the animal body is impelled in a circle, and is in a state of ceaseless motion; that this is the act or function which the heart performs by means of its pulse; and that it is the sole and only end of the motion and contraction of the heart.
We must now inquire the real names of whatever has figured in our story. The two great compartments are called ventricles, the two small pouches auricles, and they are also distinguished as being on the right or left side; right ventricle, left ventricle, right auricle, left auricle. The inner doors on which depends all the action of the machine, are called valvelets.
Injury to the auricle, or pressure for any reason on the auricle, may so disturb the transmission of stimuli and contractions that the contractions of the ventricle are very much fewer than the stimuli proceeding from the auricle. In other words, a form of heart block may occur.
The sense of direction by the ear is known to be due in part to the action of the auricle, or projecting part of the ear. This collects the air-waves, and so adds to the intensity of the sounds, especially those coming from in front, and thus assists in the estimation of direction. Thus, sounds really travelling from a point in front of the head will appear to come from behind it.
The elements of anatomy, physiology, and hygiene, are taught in all our high schools and academies, and it is no uncommon sight to see a class of girls handling the bones of a human skeleton, or, unmindful of stained fingers, searching for the semi-lunar valves in an ox's heart, with as much delight and intelligent interest as that with which they examine the parts of a watch or the machinery of a locomotive; while they can sketch on the black-board, in a few minutes, the form and relative location of all the important organs of the body, and follow the course of the blood from left auricle back to left auricle again, and that of the food, from the teeth to the descending vena cava.
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