108. The insufficiency of these forms of apparatus, arises from their not being constructed with a proper view or reference to the general principle that ought to be observed in the treatment of every fracture; namely, that the means intended to prevent displacement, ought to be founded on the causes that produce it. But, these causes here, are, 1st, The action of the muscles which draw the lower fragment upwards: 2dly, The weight of the body which pushes the pelvis downwards: 3dly, The weight and direction of the foot and leg, which tend to carry the toes outwards by a rotatory motion. Hence, the threefold indication or end of every apparatus, is, 1st, To keep the body of the bone down: 2dly, To retain the pelvis up: and 3dly, To secure the foot nearly in a right line with the leg. 109. The first consideration leads us naturally to the second. The means destined to fulfil this three-fold indication, must be constant in their action, since the causes which they have to combat act without remission. Hence the necessity of an apparatus for permanent extension. See what has been said on the nature of this expedient (46 ... 51), on the different modes of effecting it (52 ... 57), and particularly on the mode pursued by Desault (58 ... 70). 110. The mechanism of his apparatus for permanent extension is the same here as in fractures of the body of the bone. The limb is secured against a strong splint, to the two ends of which two rollers, running one from the pelvis, and the other from the foot, are firmly tied. The first of these rollers holds the pelvis up, and the second draws the foot down: hence the two first indications are fulfilled. The third is also fulfilled by the extension of the limb, which prevents its rotation outwards, by means of the outside splint, which passing beyond the sole of the foot keeps it immoveable. 111. The bandage of strips and compresses, which in fractures of the body of the bone, are previously applied round the limb, and oppose in some measure its motions laterally, are here entirely useless. Being all indeed applied on the lower fragment, what purpose could they answer towards fixing it against the upper one? They could do nothing but compress the muscles, and by that means diminish their power of contraction: but extension alone produces this effect. Desault rejected the bandage altogether, and contented himself with the use of splints and bolsters, as appears from the following case reported by Couteau. CASE VI. Maria Nof, as she was running on the ice, in the severe winter of 1788, slipped, and falling on the great trochanter, fractured the neck of the os femoris. She was immediately carried to the Hotel-Dieu, where the signs formerly mentioned (60 ... 66) disclosed at once the nature of her disease. The shortening of the limb was less than in ordinary cases.