Passive Dilatation, in its lesser degrees, is of frequent occurrence. It attacks the ventricles as well as the auricles, especially the cavities on the right side of the heart, and the right auricle most frequently. When it affects the left ventricle it is most commonly and most decidedly seen at its apex, where it first manifests itself. Intense degrees of this form of disease are unusual, although the auricles in particular are capable of remarkable dilatation.

These different forms may be variously combined. Where disease has attacked the whole of the cavities of the heart, one cavity is usually dis-proportionally affected beyond the others, and heterogeneous forms are observed to arise and exist in conjunction with one another, as for instance hypertrophy and active dilatation on the left side, together with passive dilatation of the right. In most cases the disease predominates in that portion of the heart's cavity which was first and, from some obvious cause, most intensely affected. Such is, however, not invariably the case, since consecutive disease occasionally supervenes, which fully equals or even exceeds that in the cavity originally attacked.

Dilatation of the openings usually exists in conjunction with dilatations of the heart generally, corresponding in intensity with the various degrees of the latter, and depending most probably on one common cause. In active dilatations, the arterial openings are more prominently affected, whilst in passive dilatation the auriculo-ventricular openings more frequently participate in the disease. In this form of dilatation the valvular apparatus very commonly remains sufficient, in consequence of an enlargement of the valves, attended by a striking attenuation and an elongation of the tendons of the papillary muscles. - We must, however, be careful not to confound these forms of dilatation with dilatation of the commencement of the aorta, which is of very frequent occurrence, and depends on a diseased condition of its coats, for the latter will occasion dilatation of the left side of the heart, with a frequency proportional to the association of dilatation of the vessel with insufficiency of its valves.

It is important to notice that there is a relaxed condition of the heart after death, which is very similar to passive dilatation. In the rapidly decomposing bodies of those who have died of acute dyscrasiae, the heart is very commonly collapsed, visibly dilated, easily torn, and characterized by thinness of the walls, various discolorations of the muscular substance, and imbibition of haematin in the endocardium and along the coronary veins. It is very probable that a similar condition of the heart manifests itself in every case at a certain period after death. The above-named requirements of its occurrence enable us to recognize this phenomenon as the result of decomposition, but the difficulty attending its diagnosis in the dead body reminds us of that which attaches to the question of the existence of concentric hypertrophy in so far as this condition is undoubtedly very frequently to be referred to the agonia mortis.

In simple dilatation we also occasionally meet with a condition of the muscular substance of the heart, which gives it a passive character.

In cases of active dilatation (eccentric hypertrophy) the trabeculae are frequently so completely atrophied as not only to be attenuated by elongation, but even entirely severed, their existence being indicated » along the greater and middle part merely by the inner cardiac investment surrounding them, and by the muscular substance of which their terminations are composed.

We are not yet able to explain why, under analogous or very similar conditions, dilatation of the heart will be developed in one case in a passive, and in another in an active form. We will append to our enumeration of the causes of these diseases of the heart the form of disease that is usually dependent on each, merely remarking here, in general terms, that, in our opinion, considerable mechanical obstructions generally, and sometimes with great rapidity, induce an excessive degree of dilatation, whilst, on the other hand, lesser and more slowly developed obstructions give rise to hypertrophy.

The form of the heart undergoes various alterations in consequence of these enlargements. Its malformation is the more important in proportion to the enlargement, and the more it is confined to, or preponderates in one single cavity of the heart. It affects the external as well as the internal form. In simple, and still more manifestly in eccentric hypertrophy (active dilatation) of the left ventricle, where the chief seat of disease is at the base and the middle portion, the heart assumes a round wedge-like form, while in the more advanced stages of the disease, the whole ventricle is swelled into a pad-like shape. The malformation which especially consists in dilatations of the left ventricle, expands towards the right ventricle, into which the septum is bent in an arched form; its space being so considerably contracted, that it appears like a mere appendix to the heart, while its conus arteriosus appears dilated and hypertrophied. Dilatations of the right ventricle widen the heart at its base, and from thence down to the apex. Where there is simultaneous dilatation of the left ventricle, the heart acquires the form of an obtuse triangular pyramid, or a discoidal mass. Active dilatations of the conus arteriosus of the right ventricle, which are of frequent occurrence, lead to malformation of the heart by enlarging its circumference near the base, etc.

The position of the diseased heart becomes the more anomalous in proportion to the volume and weight which it acquires. In a slight degree of enlargement, the heart inclines less to the left side of the thorax, while in excessive forms of enlargement and dilatation, it has its base almost diagonally inclined to the right and its apex to the left side, whilst its right half rests on the anterior thoracic wall, contracting both thoracic cavities in the region of the lower lobes of the lungs, and causing them to press in one large surface on the diaphragm, which is thus more or less pushed downwards on the epigastrium.

The color, consistence, and texture of the muscular substance of the diseased heart, present numerous differences.

The color of the hypertrophied heart is most frequently dark, and of a brownish-red hue; the consistence is generally greatly increased, and the texture apparently normal. It must here be remarked that the consistence of the right ventricle presents a striking anomaly in the more highly developed forms of hypertrophy, the texture acquiring a toughness which is never observed under any condition in the left ventricle. The walls which become rigid and retract on being cut, exhibit extreme resistance and hardness, and yield, when struck, a sound which, according to Laennec, resembles the tone emitted from hard leather. A similar relation is observed in active dilatation of the auricles, when excessively hypertrophied. This increase of consistence seems to depend on the deposition of a great quantity of organic matter in the form of a finely granular substance, and in the production of new flat muscular fibres without transverse striae.

In other, and very frequent cases, the hypertrophied tissue of the left ventricle presents another character. Its color appears to be faded, and of a dirty brown or yellow tint, either in separate points in the form of foci, or over a layer, generally an internal one, whose thickness varies, or finally throughout the whole thickness of this portion of the heart. The consistence then becomes modified in a peculiar manner, the walls of the heart become rigid, tough, and capable of resistance, while their tissue loses its proper firmness, is fragile, and easily broken down. The texture is perceptibly altered, although in what manner the change is effected is not known. According to our investigations, this disease of texture must be regarded as a form of morbid fatty degeneration of the heart, similar to that treated of under Form 2 of Diseases of the Muscles; and we will therefore consider the subject more at large under the head of Anomalies of Texture. We are moreover of opinion, that it associates itself with hypertrophy as a consecutive disease; that is to say, that after being once developed in the hypertrophied tissue, it favors the dilatation of the hypertrophied portion of the heart, and very frequently gives rise to those spontaneous ruptures which occur in this organ.

Traces Of Inflammation

Traces Of Inflammation not unfrequently occur, either with or without the above-named alterations of texture in the muscular substances of the left ventricle, when it is the seat of active dilatation. One or more points or foci of limited extent, either on the surface or lying deep in the texture, occasionally exhibit a redness and injection of the bleached and flabby tissue, which is infiltrated with gelatinous, fibrinous or purulent matter. More frequently these are the residua of a former inflammation, - spots at which we find the muscular substance replaced by a white ligamentous (fibroid) texture. (See the section on "Inflammation of the Muscular Substance of the Heart.") These latent and recurring processes of inflammation are in some instances connected with the residua and secondary effects of pericarditis and endocarditis, and undoubtedly would appear to promote the origin and further development of cardiac disease.

In passive dilatations, the color of the tissue of the heart is occasionally purplish-red, but more frequently it is darker and bluish-red, owing to the imbibition of the haematin, which is greatly favored by the dissolved condition of the blood, and the relaxation of the whole tissue. The muscular substance of the heart is in these cases extremely flabby and easily torn, while its walls collapse when they are cut open. In the higher stages of dilatation the muscular bundles in the auricles are forced asunder, so that the wall of the heart appears between them as a mere membrane.

In dilatations arising in pericarditis, the muscular substance has a dirty rusty brown, or yellow leather-like color, is easily torn, and appears as if half boiled; in other cases, it is pale, flabby, and abnormally fat, the surface of the heart being frequently covered by an accumulation of adipose matter.

The knowledge of the causes of the origin of these diseases of the heart is of the highest interest. Many admit of being discovered and made apparent without any great difficulty, but many others are partly problematical and partly uninvestigated. We will consider them in such an order as to proceed from those which are obvious to those which are less apparent, and finally to the problematical and hypothetical, giving special attention to the practically important ones comprised under each category.

These causes are as follow: