The membrane which lines the cavities of the heart is very liable to disease, but not equally so in every part. Where it is thin and transparent, and admits the colour and character of the muscular structure upon which it is spread to be seen through it, it is seldom found diseased; but where it is of a denser texture, either in itself or from an admixture of other structures, whether cellular or fibrous, with its own, it is frequently, and often exclusively diseased. This latter character of a denser texture belongs to it where it forms the tough white circles which surround the apertures of communication between the auricles and ventricles; also where it is reflected upon itself, and forms the loose duplicatures of membrane, which are given off, as it were, from the internal surface of the heart, either at the fibrous circles intermediate between the auricles and ventricles, constituting the tricuspid and the mitral valves, or at the commencement of the pulmonary artery and aorta, constituting the semilunar valves.
It is remarkable how curiously disease is apt to limit itself to the spaces just pointed out. Of the fibrous circle between the auricle and ventricle, of the valves which originate from it, and of the tendinous cords which connect the valves with the carneæ columnæ, there will not be the smallest space free from disease; but the disease will abruptly stop where the tendinous cords cease and the carneæ columnæ begin[1].
The membrane, however, where it covers the fleshy columns of the heart, is not exempt from the possibility of disease: but when disease actually affects it, it has seldom originated there, but has generally spread from other parts of the same membrane, although (as we have just remarked) it is apt to stop short before it reaches this.
Of the two sides of the heart, the membrane which lines the left is unquestionably the more liable to disease. But my own observation would never have led me to conclude that the membrane of the right side was so far exempt as it is commonly thought to be. Speaking from the best recollection I have of the specimens which have fallen under my examination, I should say that, in one-third of the cases where disease has been found on the left side, it has existed on the right side also, and been essentially of the same character. But there has been a remarkable difference in the extent to which it has proceeded on each side respectively: while on the left it has gone so far as to be the undoubted cause of death, on the right, although essentially of the same character, it has been only just beginning.
It very seldom happens that disease appertains to the lining of the right cavities of the heart exclusively; and, where it affects both, the disease in the right cavities is very seldom found in advance of that in the left.
It should seem, indeed, according to the ordinary course of things, that disease does not begin in the lining of the right cavities of the heart, until it has already advanced to an extreme degree in the left.
The internal lining of the heart, as well as of the arteries, is often found to have become of a red colour. This redness, so well known to all who are accustomed to examine dead bodies, used to be regarded as a mere stain imparted to it by the colouring matter of the blood after death. Yet a due consideration of various circumstances connected with it will hardly warrant this conclusion.
It has been found whether the heart or artery be full or empty of blood; and if blood be present it has been found, whether it is liquid or clotted; and if it be clotted, whether it does or does not retain its colouring matter. External temperature, and length of time between the death of the patient and the dissection of his body, have not made any difference in the frequency with which this peculiar appearance occurs. Lastly, no artificial methods, such as washing of any kind, can get rid of it; nor will inclosing blood within an artery for any period produce it[2]. This simple redness is sometimes seen universally in both sides of the heart and throughout the whole arterial system, and sometimes in patches only, of greater or less extent, whether in the arteries or in the heart.
Now, when all these circumstances are considered, although in some instances it may be a mere stain imparted by the colouring matter of the blood after death, it is plainly impossible that it should be of that nature in any large proportion of the numerous instances in which it is found.