The softening of the thrombus, on the contrary, is always a source of danger. This is partly due to the nature of the products of the softening, whether bland or septic, and partly to the mechanical disturbances produced by the transfer of portions of the softened thrombus to remote parts of the body. All thrombi may become softened. When the process of organization advances normally, the softened parts are absorbed as rapidly as the formation of vascularized fibrous tissue progresses. If this formation is checked or stopped, the process of disintegration still continues. White corpuscles undergo fatty degeneration; red corpuscles give up their coloring matter and become converted, like the fibrin, into granules, and there results a granular detritus. This is present as a viscid, semi-fluid material, either red, gray, or yellow, according to the color of the thrombus. This simple softening is to be regarded as essentially chemical in character, and begins at the oldest portion of the thrombus and advances toward the periphery. Its products are capable of absorption without the production of serious disturbances, and are usually prevented from direct entrance into the blood-vessel containing the thrombus by the continuation of the latter from new coagulation or deposition upon its surface. The thrombus is thus extended as the softening progresses. When the thrombus is comparatively free from red blood-corpuscles, the softened product, in consequence of its yellowish color, opacity, and viscidity, resembles pus. The so-called encysted abscesses projecting into the cavity of the heart, from its wall, are parietal and globular thrombi, in the interior of which softening has occurred. This form of softening is called simple or bland, as it is free from any evidence of local suppuration, inflammation, or general constitutional disturbance attributable to an absorption of poisonous material. Septic softening is accompanied by general evidences of a blood-poisoning, and by the local phenomena of purulent inflammation. A suppurative thrombo-phlebitis or arteritis, occurs; that is, an acute inflammation of the wall of the vessel, corresponding in its origin to the seat of the thrombus, and characterized by the formation of pus. In the earliest stage the softened thrombus need not present products differing in appearance from those occurring in simple softening, but their effect is manifested by a rapidly-advancing inflammation of the vascular wall and by the evidence of septicæmia. Inoculation with such material produces a group of symptoms classified under the head of blood-poisoning.