Cyanosis has so long constituted a special subject, of anatomical inquiry, that our work would be incomplete were we to omit stating our views in reference to this affection, and the relation it bears to heart-diseases. We must however observe, that our opinions are not derived from a careful consideration of all the known cases of cyanosis of the heart, but are, properly speaking, the mere expression of the views we have adopted from personal observation, and from the study of a limited number of the cases reported by others (Morgagni, Ferrus, Louis, etc).

A distinction is commonly made between cyanosis, arising from organic heart-disease, acquired in advanced periods of life, or from diseases of the lungs, and cyanosis depending upon congenital malformations of the heart. The latter form is specially designated cardiac cyanosis; but we shall see in the sequel that both forms are identical in origin and character.

The cause of cyanosis, when depending upon original malformation of the heart, has usually been sought in the admixture of the venous with the arterial blood, either in the ventricles, the auricles, or the trunks of the vessels; and this admixture, together with the cyanosis, has been supposed to arise from a deficiency in the septa between the cavities of the heart.

According to our view, cyanosis does not arise from an admixture of the venous and arterial blood, which is in many cases very problematical, and not unfrequently altogether impossible, but depends rather upon an obstruction in the passage of the venous blood into the heart, and upon an overcharging of the venous system, which is either transient or habitual, according to the circumstances of the case, and induces a corresponding repletion of the capillaries. We moreover consider that all cyanoses generally admit of being classed under one head, however the causes from which they immediately arise may differ in depending on original and congenital, or acquired anomalies of the heart and lungs.

We are led to conjecture from our own experience, confirmed by the observations of others, that cyanosis never arises from malformations of the heart, consisting in deficiency of the septa, unless there exists at the same time some special anomaly of the arterial trunks, as narrowness or insufficiency of calibre, or contraction of the ostia of the heart. We will limit ourselves in the following notice to the most remarkable forms of this affection, and to cases which admit of being observed during a prolonged period after birth.

Patency of the Foramen ovale, although not uncommonly observed after death, is very generally not manifested by any symptoms during life, unless it occur in connection with some anomaly of the arterial trunks. This circumstance is the less remarkable when we remember that, under similar conditions, there may be an entire absence of the auricular septum, unaccompanied by the presence of cyanosis.

This patency cannot, in ordinary cases, be referred to any definite cause, and is, as far as we know, purely accidental; but in some comparatively rare instances, it certainly depends upon an anomaly of the arterial trunks, the patency of the ductus arteriosus, the presence of apertures in the ventricular septum, endocarditic metamorphosis of the valves, giving rise to contraction of the ostia in the foetus, or upon pulmonary diseases, as catarrh, atelectasis, etc.

It must be observed, in reference to the question of a mixture of the venous and arterial blood, in patency of the foramen ovale, that in ordinary cases it is most probable that no such admixture actually occurs, inasmuch as the masses of the blood accumulated in the auricles equipoise one another, and the valve is pressed against the septum by the blood in the left auricle.

Symptoms of cyanosis do not occur even in cases of considerable deficiency of the valve of the Foramen ovale, without or even with the persistence of the foetal condition of the Eustachian valve, which carries a portion of the blood of the Vena cava to the Foramen ovale, although in the latter case there is necessarily an admixture of venous and arterial blood.

In those cases, however, in which the patency exists conjointly with or is dependent upon the above-named anomalies, the symptoms of cyanosis are necessarily present, although this admixture of both kinds of blood is not invariably effected, as is commonly assumed, by the afflux of venous to arterial blood. The mode of admixture depends upon the nature of the accompanying anomaly in the vessels or heart. If for instance there is abnormal narrowness or obstruction of the pulmonary artery, the blood of the right auricle will be mixed with that of the left auricle in consequence of the obstruction to the escape of the blood from the right ventricle of the heart; but if, on the other hand, the aorta be the seat of the anomaly in question, the arterial will be carried to the venous blood. Either of these conditions will be induced in alterations of the ostia, occasioned by foetal endocarditis, according as the right or the left side of the heart has been the seat of this process.

The patency of the Ductus arteriosus involves patency of the Foramen ovale from the right auricle, although not always in the manner usually assumed. It is supposed that the quantity of the blood in the left auricle diminishes with the width of the latter, as it flows into the aorta, and that a continued current of blood from the right auricle prevents the closure of the Foramen ovale. There are cases, however, in which the form of the open Ductus Botelli, and its two mouths, as, for instance, its expansion from the direction of the aorta, render it highly probable that the blood flows from the aorta towards the pulmonary artery, and, in such cases, the transmission of the blood of the right auricle, and the patency of the Foramen ovale, are the result of the excessive fulness of the former, arising from the passage of the aortic blood into the pulmonary artery, and the consequent obstruction to a free discharge of blood from the right side of the heart. In either case, whether the venous blood passes into the arterial, or the arterial blood into the venous, the presence of cyanosis will occasionally be manifested, in consequence of the inability of the blood in the Venae cavae to pass into the diseased heart when already in a state of dilatation.

Very considerable deficiency, or even the entire absence of the auricular septum, although necessarily accompanied with the admixture of the venous and arterial blood, does not give rise to cyanosis where the arterial trunks are normal. Numerous observations testify, however, that this deficiency very probably seldom exists unaccompanied by an anomaly of the vascular trunks, although its presence may frequently be overlooked. This consists in an obvious narrowness of the trunk of the aorta, which gives rise to a remarkable degree of cyanosis, although the arterial blood obviously passes into the venous. Narrowness of the trunk of the aorta, like contraction of the aortic opening, occasions active dilatation of the left ventricle, extending to the left auricle, and lastly, to the right side of the heart, through the capillary system of the lungs. The immediate consequence of the obstruction to the passage of the blood from the left ventricle and the auricle, occasioned by the narrowness of the trunk of the aorta, is undoubtedly to carry a portion of the arterial blood of the left towards the right auricle. A more remote consequence of the obstruction to the discharge of the blood from the left side of the heart, is to impede the passage of the blood of the Venae cavae into the right side of the heart, and we then have cyanosis as the result of the overloading of the capillaries from the Venae cavae.

It is evident that in these cases there will generally be a considerable degree of active dilatation of the right ventricle, especially of the Conus arteriosus and the trunk of the pulmonary artery. Bouillaud is unable to explain this circumstance, otherwise than by assuming that the right ventricle becomes arterialized from contact with the arterial blood, which enters it from the left auricle.

It would appear, from numerous observations, that a deficiency of the ventricular septum - as its perforation - and the communication consequently established between the two ventricles do not, in all probability, give rise to cyanosis, unless there exists a simultaneous anomaly of the arterial trunks. For, in the absence of this predisposing cause, and only under certain conditions, such as mental emotion, bodily exertion, or disease of the lungs, cyanotic symptoms are of rare occurrence and of a transient character. It must, however, be observed, that important anomalies of the vascular trunks are of such common occurrence with deficiency of the ventricular septum, that the latter condition is almost constantly associated with excessive cyanosis.