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Updated: May 15, 2025
Now comes a pause, or rest, after which the auricles and ventricles contract again in the same order as before, and their contractions are followed by the same pause as before. These contractions and relaxations of the various parts of the heart follow one another so regularly that the result is called the rhythmic action of the heart.
And, indeed, a circumstance of the same kind is extremely manifest in the course of the generation of animals, as may be seen in the course of the first seven days of the incubation of the chick: A drop of blood makes its appearance which palpitates, as Aristotle had already observed; from this, when the growth is further advanced and the chick is fashioned, the auricles of the heart are formed, which pulsating henceforth give constant signs of life.
When these intermittences are regular, perhaps two beats to one intermittence, or three beats to one intermittence are the most frequent types. When the auricles also beat slowly, perhaps the vagiare for some reason overstimulated and thus inhibit the heart's activity. The attacks of syncope are doubtless due to anemia of the medulla, because of the infrequent ventricular contractions.
Anatomy shows that the heart is joined to the lungs through the auricles, which are continued into the interiors of the lungs; also that all the viscera of the entire body are joined through ligaments to the chamber of the breast; and so joined that when the lungs respire, each and all things, in general and in particular, partake of the respiratory motion.
In like manner, wherever the heart has a single ventricle, there is an auricle appended, flaccid, membranous, hollow, filled with blood; and where there are two ventricles, there are likewise two auricles.
Heart of a rabbit-embryo, from behind, a vitelline veins, b auricles of the heart, c atrium, d ventricle, e arterial bulb, f base of the three pairs of arterial arches. The appearance of the lungs and the atmospheric respiration connected therewith, which we first meet in the Dipneusts, is the next important step in vascular evolution.
They may be compared to swinging curtains which, by opening only one way, allow the blood to flow from the auricles to the ventricles, but by instantly folding back prevent its return.
They did not count the rest of the heart what we now speak of as the 'auricles' as any part of the heart at all; but when they spoke of the heart they meant the left and the right ventricles; and they described those great vessels, which we now call the 'pulmonary veins' and the 'vena cava', as opening directly into the heart itself. Now that was a very remarkable and striking discovery.
And here I would observe, that whenever I speak of pulsations as occurring in the auricles or ventricles, I mean contractions: first the auricles contract, and then and subsequently the heart itself contracts.
With a blindfolded person test his sense of the direction of sound, e.g., by clicking two coins together. It is very imperfect. Let a person press both auricles against the side of the head, and hold both hands vertically in front of each meatus. On a person making a sound in front, the observed person will refer it to a position behind him. Practical Hints on the Care of the Ear.
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