I have often found (I presume, therefore, that it is not an uncommon occurrence) coagula of an irregularly laminated texture having their colouring matter not entirely discharged, but unequally distributed through them, which have been most intimately adherent to some part of the lining of the heart. Of these some have admitted of separation, while the surface of the membrane and the surface of the clot were left rough at the place of contact, and others were incapable of being detached without the membrane being detached along with them. The appendix of the left auricle is a situation in which they are apt to occur, and they are generally accompanied by an extensively diseased condition of the lining membrane. These coagula, from their laminated texture, and from the intimacy of their union with the internal lining, seem to be essentially different from polypi of the heart. They appear to be connected with a process of disease in the membrane, and to have obtained their union with it long before the death of the patient. I once saw two separate tumors, entirely resembling what are called polypi, between the carneæ columnæ of the left ventricle, and firmly adherent to the heart; and in the centre of each a distinct formation of pus. The heart was otherwise healthy[9]. There are three preparations in the museum of the College of Surgeons, put up by Mr. Hunter himself, and noted by him as exhibiting "Tumors on the inner surface of the right ventricle, seemingly composed of layers of coagulable lymph one upon another, the central part having the appearance of glary mucus." This last appearance (the mucus) no longer remains in any of the three, but in its stead there is a cavity. The tumors which I have mentioned as originally containing in their centre a distinct formation of pus, also now present in its stead a cavity. The preparation preserved at St. Bartholomew's, and those at the College of Surgeons, are probably specimens of the same disease. Here what in the recent parts seemed to be pus or glary mucus, and the cavities still remaining in the preparations, must suggest the suspicion, that these tumors, whether they grew from the surface or were deposited from the blood, had become organized, and afterwards inflamed; and that the inflammation had terminated in the formation of an abscess. ESSAY III. _Morbid Anatomy of the Muscular Substance of the Heart._