There is comparatively little to be found in medical literature relative to the =pathology= of sprains. Probably Moullin in his excellent monograph on Sprains has given as good an outline as can be found[41]. He says that “generally speaking, the tissues on one side of a joint are overstretched and torn; those on the other compressed and crushed together; but there is always so much twisting, and such a difference in the strength and power of resistance of various structures, that unless the part is examined with the greatest care it is almost impossible to say what actually has given way.” Hemorrhage due to torn vessels is the cause of most of the swelling within the first few hours. Later on, there is considerable lymph mixed with the blood. There is not only extravasation of blood into the surrounding tissues but also into the synovial wall and cavity. This causes considerable irritation and pain owing to the roughening of the membrane, and the joint becomes inflexible. And if the joint or any strained tissue is kept too long at rest the mass becomes organized and is the cause of much discomfort and annoyance. Similar changes may occur in the bursæ due to the extravasated blood. Strong ligaments may be torn across, but not frequently. The tear is usually a separation from the bone. Occasionally interosseous ligaments, as for instance in the knee, may be injured. The muscles may be severely torn, but more often they are “hurt by their own sudden and spasmodic effort at recovery than by anything else.” In a few cases the tendons and muscles will be found bruised, lacerated, and dislocated. The veins occasionally rupture and thus results more or less effusion, so that rigidity and edema may persist for a long time. The bones are very frequently damaged. This may be a simple bruising of the tissue but more often, as osteopathic diagnosis shows, there is partial displacement of the bony structure. A point of great importance that every experienced osteopath will agree to is the following from Moullin: “Diseases of the spine, hip, and other joints in children may be due, in great measure, to some constitutional taint, though it is open to question whether the influence of this is not overrated; but it is quite certain that the immediate starting point in nine cases out of ten is some chance sprain, often so slight as scarcely to have been noticed at the time.” Before treating a sprain there are one or two points the osteopath should carefully note: first, that there is no complicative fracture; second, in children that there is not an epiphysial separation; and, third, note peculiarities of a constitutional character that would complicate matters. Whatever is done, always give the patient the benefit of the doubt.