If there be extensive disease in the medullary canal of a bone, several perforations may require to be made, and these may be connected by the use of a small saw, or the cutting forceps. The diseased cancelli, thus exposed, can be readily removed by the scoop or graver, as recommended by Mr. Hey, primus, in his excellent work. If, with the probe, it is ascertained that a portion of the cancellated texture has become dead and loose, it is to be removed after dilatation of the external opening. It may frequently be difficult to distinguish in the effused blood, between what is diseased and what is not; it will often be necessary afterwards to cauterise freely the exposed surface, and for this purpose the oxidum hydrargyri rubrum ought generally to be preferred. The slough will soon be thrown off, and healthy granulations fill up the breach. The application of the actual cautery may be by some considered necessary: at one time I employed this remedy very extensively in caries, and occasionally with very good success; I have since, however, been led to change my opinion, and am now inclined to prefer the potential cautery already mentioned. By the application of the red-hot iron, the diseased portion is destroyed effectually, but at the same time the vitality of the surrounding parts is often very much weakened and their power of reparation diminished, so that they are incapable of assuming a sufficient degree of action for throwing off the dead part; their action being increased whilst their power is diminished, they may become affected with caries, and thus, instead of being arrested, the original disease will either be increased, or extensive necrosis may take place. The red oxide of mercury is not calculated to produce such bad effects; it does not spread or insinuate itself into the bony tissue, as liquid caustics are apt to do; and it is sufficiently powerful for complete destruction of the diseased parts. It will be necessary to keep the wound open, by proper dressings, till all the dead portions of bone be discharged, and every part of the parietes of the cavity produce healthy granulations: if the discharge be offensive, its fetor may be corrected by the use of spirituous applications, such as the tinctures of myrrh, opium, or aloes, separately or combined. After healthy granulations have appeared, and the cavity has begun to contract, light dressing is all that is necessary.