_a._ The _marasmic_ forms are due to essential alterations in the constituents of the blood, which are due mainly to starvation or wasting disease. Marasmic thrombi seldom give rise to serious disturbance during life until the condition is so complex and grave that the patient is at death’s door. Postmortem evidences of marasmic thrombi, however, are often found, and yet have but little surgical significance. They are seen perhaps as often in the cranial sinuses as anywhere. _b._ Thrombi of _mechanical or traumatic_ origin are those, for instance, which are due to the presence of foreign bodies, to stagnation of blood as the result of ischemia or local anemia, to compression by tumors, etc. _c._ _Infective_ thrombi are those distinctly due to the injurious effects of micro-organisms, and are those mainly concerned in the various manifestations of sepsis which are of interest to surgeons. While the ordinary evidences of thrombosis are most often looked for in the veins of the extremities, in the lungs, and in the cranial sinuses, it must not be forgotten that thrombosis may occur equally easily in the portal system of vessels; in which case we find the most marked expressions in this system and in the liver. In cases also of pyemia proceeding from lesions in the rectum or in the bowels there are evidences of infection, abscess, etc., in the liver, but not in the lungs, to which point infective thrombi from other sources are promptly carried. The _ultimate fate of a thrombus_ depends entirely upon the presence or absence of bacteria. If septic, it invariably breaks down. If aseptic, it may undergo one or more of the following metamorphoses: A. _Decolorization._--This is noted particularly in the red thrombi, and is due to disintegration of the red corpuscles, their coloring matter being diffused and resorbed or transformed into hematoidin. It would be a mistake, however, to suppose that all light-colored thrombi are those which, originally red, have been decolorized. The possibility of white thrombi must always be remembered.