C. _Temperature_ has also an influence in the same direction, and extremes in either direction, or drying of vessels which may happen to be exposed to the air for some time, lead to the same results. D. _Inflammatory and degenerative processes_ occurring in and about the vessel walls tend always to produce coagulation. This is well seen in the influence exerted by the so-called _atheromatous ulcers_--_i. e._, the degeneration of certain areas in the walls of large vessels. E. _Microörganisms and their products_ are perhaps the most frequently effective of all the accessory causes of thrombosis. In other words, in all the surgical infectious diseases we may expect to find more or less, sometimes extensive, thrombosis in the vessels of the affected part. This may so far shut off circulation as to produce temporary or permanent edema, or it may lead to gangrene, which may be local or may terminate the life of the patient. _Thrombi are classified_ as: 1. _Primary_; and 2. _Propagated_. The _primary_ thrombus is one which has originated at the spot where it has been first produced, and is usually co-extensive with its cause. The propagated thrombus may be one which has been carried to a considerable distance, and is met with at a point widely different from that where it originated, or one which has extended along the vascular channel in which it was first formed, but far beyond the limits of its prime cause. When a thrombus attaches itself to a part of the vessel wall it is called _parietal or valvular_, because it does not completely occlude the vessel; when it involves the entire circumference of the vessel, but does not completely occlude it, it is spoken of as _annular_. The _obstructive_ thrombus is that which completely fills a given vessel and shuts off all circulation through it. The _propagated_ thrombus extends usually in both directions, and always much farther in veins than in arteries. Thus, thrombi may be met with extending from the ankles even into the inferior vena cava. The venous valves may on one hand excite coagulation, or on the other tend to fix the coagula more firmly in their place. In arteries thrombi usually extend only to the first collateral channel on the cardiac side, but occasionally they spread farther. The _cause of a primary thrombus_ is to be _sought at the site of its lodgement_; the _cause of propagated thrombi_ is often observed _at a wide distance from the effect_. Thrombosis is, again, to be spoken of as-- _a. Marasmic;_ _b. Mechanical or traumatic;_ _c. Infective._