Necrosis once formed is variable in its pro gress and indefinite as to the tirne that may be necessary to its completion. Sometimes the affection of the bone is exceedingly acute, ac compa.nied by external inflammation resemb ling plilegmonoid erysipelas : in these cases the bone 'soon dies, the sequestrum separates and protrudes very rapidly, perhaps even before the new deposit has attained strength to sup port the limb, so that it is necessary to preserve it artificially as to shape and length until the process is complete. Within the last year we have seen a ease in which, through neglect of this precaution, the tibia is bent nearly into the shape of the letter C. In other instances the disease is extremely tedious, requiring years before the sequestrum is either removed or ab sorbed : we possess a preparation exhibiting a. specimen of necrosis of more than six years' duration, in which the sequestrum is of a more than ordinary size. I3etween these extremes of great rapidity and as great tediousness there is every possible variety, and perhaps these me dium cases are the most unfavourable, for the very rapid are over before the &Institution is broken down, and the very slow produce their effects on the system so gradually as not. to make any decided or severe impression ; whilst those which exhibit the symptoms of abscess, with an extraneous body working to gain the surface and not able to accomplish it quickly, occas:on much suffering, and if there is ever danger to life or limb from the disease, such cases are most likely to produce it.
The sequestrum or dead bone is disposed of either by presenting externally and permitting of its removal by the process of ulceration or by manual operation, or else it is never seen, and is entirely carried off by the absorbent vessels. Mr. Russell accounted for the disap pearance of the sequestrum in a very unsatis factory manner. Ile considered the dissolution of the dead bone to be "greatly accelerated by the solvent poWer of the purulent matter," a property, the existence of which in pus both observation and experiment render question able : and when thus macerated, he conceived it to be prepared to be removed by absorption or washed out by the discharge of the matter. But, if the surfaces of a sequestrum are exa mined, that which is next to the granulations of the new bone will be found to be irregularly marked and indented, as if by the action of the mouths of the absorbents, whilst the other is comparatively smooth ; and as every part ex posed to the action of the fluid should suffer equally if the removal of the osseous particles was effected by maceration, there are strong reasons for believing that the disappearance of the sequestrum depends not on any power chemical or mechanical, but on some vital pro cess, and therefore probably on the action of the absorbents.
When the sequestrum presents externally, either one end of the bone (almost always the superior one) protrudes through the soft parts and remains there dry, hard, and dead for a longer or shorter time, until it becomes de tached by the slow process of nature, or is separated by a surgical operation; or else the middle of it presents, and can be seen or felt through an . aperture in the surrounding new
bone whilst its extremities are confined. In either case the process of removal is extremely tedious. When the end presents, it is gene rally moveable, and seems as if very little force would be sufficient to detach it altogether ; yet if an attempt is made to pull it away, it is by no means easily accomplished, and a con siderable time elapses between the first pro trusion and its final and complete separation. When the middle presents, the process is still more protracted. All bones do not seem equally liable to necrosis. Perhaps the tibia is as fre quently attacked as all the other bones of the skeleton taken together ; next in frequency is the humerus, the bones of the fore-arm, the thigh, the clavicle, and lastly the lower jaw.
Thus far, it will be seen that we have con sidered necrosis as a disease, distinct and dif ferent from every other affection of the bones whatever, and that its chief and most marked characteristic is the process of regeneration. Regarded in this point of view, it is as much and even more an action of health than of dis ease, and it can easily be understood why the constitution suffers so little, why the hectic fever is of so mild and mitigated a form, and why in a simple and uncomplicated case re covery is nearly certain. It is also evident that this disease will not be likely to occur in a constitution contaminated with syphilis, scro fula, scurvy or any of those other vices which the continental surgeons not only think it may be united with, but which they adduce as its occasional exciting causes. Doubtless, if the death of a bone from any cause or under any circumstances—if caries, exfoliation, and other such destructive maladies ace to be included as species under the generic name of necrosis, such affections may not be inconsistent with the existence of any poison or any taint ; but if the idea of a process of repioduction co existent with that of disease must be admitted as appertaining to this affection, it will be im possible to recognise scrofula or syphilis as connected with it in the remotest possible de gree. Perhaps we shall incur censure for thus attempting to limit the signification of the term, but it has been observed that the nomen clature of surgical pathology is too loose and undefined, and in no instance is the remark more applicable than with reference to the dis eases of the osseous system; and again, patho logy to be useful must be practical, and we can by no means assimilate caries which is so des tructive of the limb or fatal to life— or exfo liation, which is always attended with loss of substance—with necrosis, the essential cha racter of which is a process of reproduction, and its natural termination recovery.