But have we any evidence that the fibrin of the blood may be deposited, forming clots within the vessels during life? In proof of this, we have only to refer to the result of the application of a ligature to an artery; where the interval between the point of application and the first vessel coming off above, will be filled with a fibrinous clot, which performs an important part in the closing up of the vessel; or, to the well-known deposits of fibrinous layers within aneurismal tumors, sufficient, in many cases, to so fill up the sac as to result in a cure; therefore, the favoring conditions being present, it is not unreasonable to claim that fibrinous clots _may_ form within the heart, of such size and in such positions as to be an immediate cause of death. _Causes._ In looking for the causes, or conditions promoting the formation of these fibrinous deposits, we have to consider, first, variations in the character of the blood itself; and secondly, peculiarities in its circulation and in the circulatory apparatus. Fibrin, one of the normal constituents of the blood, is estimated by physiologists as forming from 2 to 3 parts in 1000, while it may fall as low as 1, or rise to 7½ parts. We find it reduced to the minimum quantity in all diseases which present a hæmorrhagic tendency, as in true typhus, yellow fever, certain malignant forms of disease, and as the effect of many poisons, both animal and vegetable. In these cases, the loss of fibrin results in the effusion of blood into the tissues, producing petechial spots, or upon the mucous surfaces, giving rise to epistaxis, black vomit, hæmaturia, etc., while very feeble, if any, coagulation of the blood will be found after death. In scurvy, however, where we have a condition of the blood not unlike that above referred to, there appears to be a marked tendency to the formation of clots, as has been noticed by many observers, and as has been verified by Dr. J. C. Morgan, in several cases which came under his notice while in the army. But it is in cases where there is at least a _relative increase_ of fibrin, that heart clots are more liable to form. Such a condition we find in cases where, while the fibrin remains normal in quantity, the water of the blood, the menstruum in which the fibrin is held in solution, is below the normal standard, this reduction favoring the tendency to deposit. Thus, in all cases where there has been an exhausting and rapid flux from the bowels, as in cholera, or excessive purging from drastic cathartics, or from the colliquative sweating of phthisis, we have the favoring condition, and death may be the immediate result of a fibrinous clot in the heart.