By these conditions we purpose indicating a thickening of the true endocardium (which, in respect to the main character of its composition, corresponds to the inner coat of the vessels), by a morbid deposition from the blood of a substance which becomes metamorphosed into the layers of the epithelium and longitudinal fibres composing the endocardium. This excessive deposition of new layers of the endocardium is a process which occurs in its most fully developed form in the arteries, and more especially in their main trunks, and will be duly considered in the appropriate place. Its proximate result is a thickening of the endocardium.

This morbid condition acquires additional importance from the facility with which it may be, and no doubt very frequently is, confounded with endocarditis and its products, which it greatly resembles, and with which it is often found associated. We have, on this account, thought it best to devote the closing part of the present section on endocarditis, to the consideration of this subject, however unusual such an order of arrangement may appear. (See p. 123.) The following remarks on the peculiar characteristics of this affection will clearly exhibit the differences which distinguish it from the endocarditic process and its products.

In the lower degrees it is only by a careful investigation that we can discover any undue thickening of the endocardium. The color of the muscular substance is less clearly discernible, while more strata than usual must be removed before we reach the layer of cellular tissues interspersed with elastic fibres, which is situated under the endocardium; moreover we clearly observe that the innermost layers are lighter and softer, and that the tissue which constitutes the longitudinal fibrous coat is less developed and more moist.

In this manner new depositions of layers of endocardium, either with or without an epithelial investment, are frequently found to cover one or more of the cavities of the heart (the ventricle or auricle of the left or both sides), together with the corresponding valves.

When this process of deposition has been frequently repeated, and the thickening of the lining membrane of the heart is correspondingly increased, this condition will be easily recognized. In these higher degrees of intensity we very frequently observe, as in the arteries, that the endocardium exhibits, at more or less well-defined spots, portions of thicker surface in the form of islands or patches, while we at the same time remark that the valves, more especially those of the aorta, have been considerably thickened and enlarged by the deposit.

The opalescent translucence and stratification of the deposit and the uniform texture of the combined lamellae, distinguish it from the products of endocarditis, from the loosely-attached, bluish-white, opaque milk-spots, and from the fibroid thickening of the endocardium, which cannot, without extreme difficulty and effort, be separated into strata, and which exhibits greater density and dryness of its tissue, and evidently consists of fibrous or areolar tissue. The absence of redness and injection in every stage and of vegetations and secondary processes (metastases) in the capillary system, distinguishes it from the endocarditic process. The existence of the process of deposition in the trunk of the aorta affords us further diagnostic aid in determining hypertrophy of the endocardium.

A correct diagnosis, which has for its object to determine both processes generally, and to distinguish the special share taken by each in the anomalies under consideration, is rendered more difficult in those cases in which, as we have already observed, the products of endocarditis occur simultaneously with the condition we term "excess of endocardiac formation," and which is indeed very commonly favored or even occasioned by the residua of endocarditis. A peculiar difficulty presents itself, when the deeper or older deposits lose their transparency, and become completely opaque, white or faded, in consequence of an atheromatous process, or of a metamorphosis tending to ossification. They may be distinguished from endocarditic products on a closer inspection, by the occurrence of a large quantity of molecules, consisting of albumen, fat, and calcareous salts, deposited in the different strata.

This metamorphosis never, so far as we know, proceeds on the walls of the heart, beyond the incipient stage above indicated; we have never found it developed in the true atheromatous process, nor have we ever been able to ascertain that this process formed the basis of any of the numerous cases of aneurism of the heart which we have examined. The valves, however, occasionally present the appearance of an incipient atheromatous disintegration of the deposit, while ossification of the deposit on the valves, more especially on those of the aorta, is very frequently a final result. It is highly probable, moreover, that all the forms of ossification of the valves which become developed in the advanced periods of life, belong to this class.

Hypertrophy of the endocardium is limited almost exclusively to the left side of the heart, and of the two arterial trunks it only attacks the aorta. The aortic valves and the left ventricle are more frequently and more intensely affected than the auriculo-ventricular valves and the auricle. The aorta is at the same time diseased in like manner, but generally in a very preponderating degree. The endocardium of the left auricle is, however, excessively thickened in some few cases where there is contraction of the mitral valve.