In this case, an attempt is made to reduce the luxation: the capsule is pressed in folds against the glenoid cavity, and, interposing itself between it and the head of the humerus, renders fruitless the efforts of the surgeon who would replace the bone. Desault was the first who observed this practical fact, two instances of which are recorded in his journal, and which has frequently since occurred in the Hotel-Dieu. In such a case, the head is in general extremely moveable, because, being entirely without the capsule, there is nothing to impede its motion. 25. When, to a primitive luxation a consecutive one succeeds, several causes may concur in its production. If a second fall happen, the arm, being separated from the body, the head of the humerus having nothing to retain and secure it, obeys, with great facility, the power tending to displace it in that direction, and suffers a fresh removal from the bed which it accidentally occupies. CASE I. A man fell in descending a ladder, and luxated his humerus in a downward direction. Desault being immediately called, discovered the nature of the disease, but deferred the reduction till evening. In the interval, the patient went to get into a chaise: his foot slipped, and he fell a second time. The pains became more severe than at the time of the first accident; and Desault, on his return, instead of finding, as in the morning, the head of the humerus under the hollow of the arm-pit, discovered it to be behind the pectoralis major. 26. Muscular action is one permanent cause of a new displacement. Suppose the humerus luxated downward, the pectoralis major, and the deltoid muscles draw its superior extremity upward and inward, which, offering to their action but a feeble resistance, changes its position and that in a two-fold direction. 27. The different motions of the arm may also, according to their direction, produce the same effect. Thus we have often witnessed a luxation inwards succeeding to a luxation downwards, in consequence of unskilful attempts to reduce it. § IV. OF THE SIGNS. 28. The diagnosis of luxations of the humerus, presents in general, but few difficulties. Whatever may be the mode or seat of the displacement, there always exists, as Hippocrates has observed, a manifest depression under the acromion, which exhibits a prominence more perceptible than in its natural state. The motions of the part are almost all accompanied with pain; the greater part of them are impracticable; all of them very much confined. The arm cannot move, without a synchronous motion of the shoulder, because, the articulation being no longer able to exercise its functions, these two parts constitute, so to speak, but one body.