hooklets of echinococcus cysts; and, perhaps most often of all, the _microorganisms_ clinging to some minute fragment of thrombus which has been dislodged. Embolism is also produced experimentally by the artificial introduction into the circulating blood of cinnabar or small particles of pith or other material. Emboli differ in number and size from the smallest appreciable up to the largest, which may be met with in the larger venous trunks. They are _dislodged_ from their primary site sometimes by _accident_, as by rude manipulation, injury, etc.; sometimes by _undue cardiac activity_, as when detached from a valve wall; sometimes by the _process of softening_ of thrombus and a subsequent introduction into the blood stream as a result of some trifling motion; or even by _spontaneous processes_. Emboli also differ in numbers according to the nature of the primary lesion. In cases of so-called fat embolism fluidified fat is taken into the returning blood stream, carried to the heart, churned up with the contained blood, and distributed to the lungs in such a way that myriads of minute fat masses are distributed throughout the capillaries of the lungs, and free circulation of blood through them is thereby impeded. It will thus be seen that the relations between thrombosis and embolism are most intimate, but that either one may occur without the occurrence of the other. Among the viscera, with the exception possibly of the brain, the disastrous consequences of such processes as those just described are more apparent and indicative than in _thrombosis and embolism of the mesenteric bloodvessels_--a condition not so rare as journal articles would imply, yet, nevertheless, one seldom recognized either during life or after death. Its principal symptoms consist of intense abdominal pain, bloody diarrhea, subnormal temperature, sometimes with vomiting, perhaps in the latter stages vomiting of blood. Shock is usually also extremely marked. The consequence of this condition is almost inevitably gangrene of the intestine supplied by that particular portion of the mesenteric vessels. The pain comes on within a short time after the occurrence, and under the peculiar circumstances gangrene may be practically determined within a few hours. Some two hundred and fifty cases of this kind are now on record, and the condition is one well worth the prompt attention of the surgeon, because only by surgical intervention--_i. e._, by resection of the necrotic mass of intestine--can life possibly be saved. That when a limited portion of the intestine is involved the gangrenous part may be successfully removed has been proved by several operators. (See Chapter LII.)