36. The mere reduction of a fracture of the os femoris, is but one step towards the cure. In this, more than in the fracture of any other bone, causes which act incessantly (13) tend to subvert the momentary work of art; it is here, then, in particular, that means ought to be devised for maintaining this work. But, the first of these means is a suitable position of the limb. I have already mentioned the inconveniences that result, both as to the reduction and subsequent treatment, from that proposed by Pott (24 ... 26). The patient must, then, be laid horizontally on a plain exactly even, and not capable of being affected or rendered uneven by the weight of the body. Instead of feather beds generally used in other cases at the Hotel-Dieu, Desault, in cases of fractures, substituted firm and hard mattresses, which, not sinking in the least, by the pressure of the body, give no cause to apprehend those continual displacements, to which a soft bed exposes the patient. These mattresses supersede the advice of certain authors who direct a plank to be placed under the patient. 37. The second means, not less efficacious than the first, consist in the forms of apparatus, in which the limb is placed, and which, being differently modified according to the fancies of their different authors, present us with an assemblage of various splints, compresses, &c. To appreciate, with accuracy and correctness, the advantage and disadvantage of these, let us first unfold the curative indications which they ought to fulfil; we will then compare their mode of action with these indications, from whence will result, as necessary inferences, the object of our research. 38. The intention of every form of apparatus being, to prevent the displacement of the fragments, the causes of this displacement ought to be the basis or foundation of its mechanism and construction. But these causes in the present case are, 1st, the muscular action drawing the inferior fragment upwards (10); 2dly, the weight of the body pushing the superior fragment downwards (14); whence every form of apparatus intended to keep the os femoris in place when fractured obliquely, ought, 1st, to draw the lower fragment downward and retain it there; 2dly, to draw and retain upwards the superior fragment, and the trunk which bears on its upper end. This principle is applicable generally, and subject only to a few exceptions which I shall notice when treating of transverse fractures, where the displacement is lateral, or in the direction of the cross-diameter of the bone, or where no displacement at all exists. 3dly, The apparatus must also be so constructed as to prevent the rotatory motions of the lower fragment (18), and secure the immobility of the limb, lest by means of some motion being communicated to it, the fragments might be deranged. § VII. OF THE MANNER IN WHICH THE DIFFERENT PIECES OF THE APPARATUS ACT.