It will thus be seen that embolism constitutes often a distinctly surgical condition for which unfortunately only radical measures are suitable. Many cases of gangrene of the toes and feet, extending to the legs, are produced by embolism of the femoral and popliteal arteries, similar conditions being noted less often in the upper extremities. Amputation offers the only resource in such instances, at the same time affording no guarantee against any similar embolic disturbance elsewhere. In only most exceptional instances is it possible, by resorting to moist heat, position, etc., to encourage circulation to such an extent as to obviate the necessity of amputation. (See Chapter V.) =Fat Embolism.=--Fat embolism as a distinct, sometimes fatal, surgical condition has received of late so much study as to be entitled to consideration by itself. By this term is meant a plugging of small arteries by minute drops of fat, which, having been set free somewhere about the periphery, are carried into the venous circulation and thence distributed to various parts of the system. Inasmuch as the capillaries of the lungs are often their first lodging place, fat embolism here is most often met with, and consequently recognized and studied. But it may occur in the brain, the choroid, the kidneys, or other parts, provided only that there has been sufficient _ris a tergo_ on the part of the heart to force the fat globules through the pulmonary capillaries and into the systemic circulation. [Illustration: FIG. 2 Fat embolism of lungs. Large branching pulmonary artery filled with spherical, oval, cylindrical, and branching masses of fat. Fresh mashed preparation in potassium hydrate. (Kaiserling.)] Fat embolism occurs frequently, and to a slight extent in nearly every case of fracture and laceration. So common is it, and so closely allied are some of its most prominent symptoms to those of shock, that as a matter of fact many cases heretofore considered shock are to be regarded as instances of this condition. Indeed, even in a miscellaneous series of 260 dead bodies fat embolism was found in 10 per cent. The injuries most likely to be followed by it are simple, and particularly compound fractures of bones; laceration of soft parts, especially of adipose tissues; certain surgical operations; acute infections of bone and periosteum; rupture of fatty liver; and certain pathological conditions where the phenomena are not so easily explained, _e. g._, icterus gravis, diabetes, etc.