Movements of the heart.—The heart is a muscle of involuntary motion, being, for the wisest of purposes, placed beyond the direct control of volition. The case of Colonel Townsbend * is of too obscure a nature to entitle us to found upon it an opposite doc trine, more particularly as it is at direct variance with every other fact or observation.
The movements of the heart, when the body is at rest or in a state of health, proceed with out our consciousness. In certain cases of disease they are attended by uneasy feelings, but they are never at any time or under any circumstances dependent upon sensation for their continuance.
It is not so easy a matter as may at first be imagined to ascertain the order of succession in which the different cavities of the heart con tract and dilate, and the different circum stances which attend these movements, even by experiments on living animals, more par ticularly the warm-blooded animals; for if the heart when exposed is acting vigorously and rapidly, every one who has examined for him self must have felt the exceeding difficulty of following and analysing these movements by the eye. If, on the other hand, the animal has become debilitated and the movements of the heart languid, these are apt to deviate front their natural order, and to be performed in an irregular and unnatural manner.* It is in this way that we can account not only for the dis crepant statements of the older observers, but also for the very frequent announcement of new views on this subject which appear in the medical periodicals of our own day. As we will find that many of these theories connected with the physiological actions of the heart even in the present day, have been founded upon false notions of the normal anatomy and na tural movements of the organ, and only require a reference to these for their full and satis factory refutation, it will be necessary that we attend particularly to the manner in which these different contractions and relaxations suc ceed each other, and the visible phenomena by which they are accompanied, as observed by the most accurate experimenters.
When the heart of a living animal is ex posed and the organ is acting in a natural manner, the auricles are observed to become distended with blood, then to contract rapidly and simultaneously, and propel part of it into the ventricles; this is accompanied with a corresponding enlargement of the ventricles, which is immediately followed by their simul taneous contraction and the propulsion of their blood along the large arteries: then follows a pause, during which the auricles become gra dually distended by the blood flowing along the veins. When the auricles are filled, they
again contract, and the same train of pheno mena just described occur in uniform succes sion.
Systole and diastole of the aurieles.—The contraction or systole of the auricles is pre ceded by their relaxation or diastole. During the diastole the auricles become distended with the blood flowing along the veins. The com mencement of the diastole occurs during the contraction of the ventricles; the latter part corresponds to the pause in the heart's action, and to the interval between the recurrence of the sounds of the heart, and is more or less long in proportion as the blood flows more or less rapidly along the veins.
The systole of the auricles is performed with great rapidity when the action of the heart is still vigorous, and appears to he effected by the simultaneous contraction of all its fibres. The terminations of the cavx and pulmonary veins are seen to contract simultaneously with the fibres of the auricles, but sometimes they are seen to contract previous to the auricles, into which they expel their blood. In the cold blooded animals this contraction of the ter minations of the large veins extends over a greater surface, and is visible in the ven he paticw.* Judging from the number of mus cular fibres which surround the termination of the pulmonary veins in the human species, we would expect these contractions to occur to a greater extent in these veins than in the caves. These contractions in the veins must assist the vis it tergo, or the force with which the column of blood flows along the veins towards the heart, in limiting the regurgitation along these during the contraction of the auricles. This regurgitation along the veins appears to be to a small extent only when the circulation is pro ceeding in a natural manner, but becomes con siderable where there is any impediment to the free passage of the blood into the ventricles, and when the blood becomes stagnated in the veins. When the actions of the heart are en feebled, the contractions of the auricles are slower, and may become more or less vermi cular, as I have myself occasionally observed. Two or more contractions of the auricle may also now be necessary before the languid ven tricle can be excited to contraction. When the action of the heart is still more enfeebled, particular portions only of the auricles con tinue to contract. According to the obser vations of Harvey, Lower, Senac, Haller, and others, the contractions of the auricles are per formed with considerable force.