It is unnecessary to quote any farther autho rities to shew that no universality of opinion prevails as to the pathology of this important disease, and that it still requires careful and accurate investigation. It seems, however, to be agreed on, that when the patient begins to recover, a great activity may be observed in the deposition of the earthy material, and that it is principally deposited where it is most wanted, viz. on the concave surfaces of the curves.
Fragilitas.—We have classed a brittle con dition of the bones under the head of a dispro portionate abundance of the earthy substance, rather in compliance with a doctrine that was once universally believed, and perhaps is still pretty generally admitted, than as the statement of a fact that may be supported by evidence. It was supposed that the presence of a greater quantity of phosphate of lime rendered the bone short-grained and dry, and therefore more liable to snap across ; and this condition of bone, as peculiarly appertaining to old age, has been placed by Boyer among the predis posing causes of fracture.f The opinions of Ribes on this subject, and the doubt cast by chemical analysis on the ordinary explanations of a softened condition of bone on the one hand, and of its fragility on the other, have been already noticed, and, notwithstanding some attention to the subject, we are obliged to leave it without even attempting a solution of the difficulty ; the results even of several series of experiments, which were instituted in the years 1831 and 1832, with a view to the elucidation of this difficult question, scarcely deserve to be stated, as they were in every respect unsatis factory. We compared the respective thick ness of the thigh-bone in the adult and the aged, the section being made exactly in the middle : we weighed equal lengths of similar bones—we softened equal lengths and equal weights by means of dilute muriatic acid— and we burned equal portions and weights also, with a view of comparing them under these different circumstances, but could never arrive at any fixed or certain conclusions. In one remarkable instance the bone of a wo man, who must have been seventy or eighty years of age, was thicker, stronger, and con tained more both of the animal and earthy materials than any adult bone with which it was compared. We were, therefore, obliged to adopt M. Ribes' theory of " a change of action," just as we see the muscle of an old man incompetent to such a display of strength as would be -easy to that of a younger person, although the latter may be smaller, and pos sessed apparently of less toughness of fibre.
Fragility seems to exist under two different conditions, one derived from, or having rela tion to, some defect or imperfection in the bone itself; the other being rather a symptom of some other disease than a disease itself, and arising from some vice or taint in the constitu tion. The former of these is exhibited in the
fragility occasionally observed in the bones of some young persons, and more constantly in those of the old ; but it may be remarked that the causes that produce this fragility (whatever they are) do not interfere with the restorative powers of the part. True, a fractured bone is tedious in uniting, and is frequently followed by unpleasant consequences in aged persons, but in such all the vital powers exhibit evi dence of sluggishness and debility; whilst in youth, so far from fragility interfering with the process of union, fractured bones have been observed to be consolidated in even less than the usual period. But when any particular condition of constitution or any disease seems to be the exciting cause of fragility, it may also be regarded as a cause of subsequent non union. Of these, cancer, fungus haarnatodes, and sea-scurvy, seem to furnish the most nu merous and best authenticated instances ; sy philis has been added, probably from the fact of some fractures remaining disunited until the patients had been subjected to a course of mercury; its influence, however, is question able, unless where it had previously produced caries. A state of pregnancy or of lactation has been mentioned as predisposing to fracture, and impeding or delaying the process of re union ; but however the observation might have been occasioned by a few solitary cases, it is not borne out by general experience.
In the fragility of early youth, and where union would take place quickly and kindly, it is not to be expected that the bone (if there was an opportunity of examining it) should present any morbid appearances unless the evidences of its physical weakness in the small ness of its diameter and the thinness of its walls should be so considered. In the aged, as all persons are not afflicted with this fragility, so are there some whose bones cannot be dis tinguished from those of the healthy adult. .As to the ordinary characters of the bones of old persons, Mr. Wilson remarks they are never found so friable and fragile as to crumble like a calcined bone, but, on the contrary, they contain a large quantity of oil; and when dried after death, they are so greasy as to be unfit to be preserved as preparations. Their organized vascular part is diminished, but their oily animal matter is increased.