(From to abrade, or from karah, to dig in, a Chaldee word); according to Mr. Sharp, it is a partial mortification of the bone, which separates from the sound part sooner or later. Dr. Cullen places this disease in the class locales and order dyalyses, and names it exulceratio ossis. But as every species of caries, attended with loss of substance, may be termed an ulcer, Mr. Bell, to prevent confusion, considers caries as an accidental symptom of ulcers, and speaks of it under the general name of carious ulcer. It is an ulcer, however, of a gangrenous kind, but differing from mortification of the bone, which will be considered under the term necrosis. In short, these diseases bear the same relation to each other as a foul putrid ulcer and a sphacelusthis disorder, called caries, sphacelus, teredo, or tredon, happens when the bone is deprived of its periosteum, and, having lost its natural colour, becomes oily, yellow, brown, and at last black. This state, which is the first degree of the disorder, was called by the ancients os vitiatum, ossis nigrities. When the disease advances the bone is corroded, discharging a sanies which consumes the adjacent flesh. Of the many names given to the caries, which are collected under spina ventosa, the following are only necessary: When the cause is external, it is the spina ventosa; or, with Severinus, when it happens to children, it may be called paedarthrocaces: when the cause is external, caries.
That an inflammation of the periosteum is tending to a caries of the bone, is known, first, from the signs of inflammation preceding; secondly, a freedom from, pain in the affected part, without a manifest cause, and from a dense, slow, increasing, and not very painful, tumour of the incumbent parts. But among the signs of a beginning caries, the sudden removal of pain is fallacious; for this happens in inflammation of the periosteum, when this membrane is corroded so as to admit the matter to escape betwixt the muscles, though, in general, when pain is relieved by a resolution of inflammation, it goes off gradually only; for a perfect resolution hardly, if ever, happens after a violent inflammation. Again, when a caries is threatened, the taint is propagated through the cellular membrane, which, by slight causes, is often raised into a large tumour: but, as all the symptoms of an inflammation lessen when a caries is present, the tumour will not have the hardness and resistance observable in a phlegmon, but will be flaccid, and hardly sensible of pain. If the incumbent part changes to a livid colour, or a dark sanious discharge issues from a part in the direction of a bone, the bone is then, without doubt, in a mortifying state.
Celsus, the best ancient author, at least on the cure of caries, observes, lib. viii. cap. 3. "We may soon, by-means of a probe, discover a caries of the bone, since the probe will penetrate less or more, according as the caries is superficial or deep."when the probe comes to the sound part of the bone, it is resisted. Wiseman, vol. i. p. 296. edit. 5. says, "If the bone be bare, its corruption is easily discerned, though sometimes it be covered with a grumous or viscous matter, which rubbed off, the bone appeareth white, brown, or black. If the white be porous, the caries may be deeper and more dangerous than if it were black and hard. If the bone lies so hid as that you cannot feel it with your probe, yet you may judge it carious from the quantity or quality of the matter. If the bone lies near, and the flesh is lax and white, it is strongly suspicious that the bone is carious: but if the matter stinks, or is oily, it is a more certain sign of rottenness. Ulcers of long continuance near a bone do also foreshow a caries, according to Hippocrates. Also the difficulty of cicatrizing them, and the frequent and sudden eruption of them after they are cured, give a suspicion of a foul bone. But if the bone is much corrupted, the matter is fetid, and the probe will penetrate into it."
The friability of carious bones is occasioned by the acrimony of their humours, and chiefly of their corrupted medullary oil; for since its separation destroys the cohesion,"by decompounding the bony substance, the peculiarly disagreeable fetid smell, which arises from carious bones, is from this corrupted medullary oil.
When a caries is under an ulcer, the flesh over the caries is soft, flaccid, and fungous; the lips of the ulcer inverted, the sanies clear, fetid, and full of small black scales. The ulcer heals only superficially, and soon breaks out again. Ulcer has been accused of producing caries, but the latter is more frequently the cause of the former. See Ulcer with a caries, under Ulcus.
In the Edinb. Med. Essays, Dr. Monro gives a particular account of several species of this disorder, viz. 1. The dry or gangrenous caries, which is, where the bone is smooth and firm, and throws out little matter; its surface at first is not of a very dark colour, but before exfoliation it turns very brown or black. This kind exfoliates with less difficulty than any other. 2. The worm eaten caries, or Ulcer of the bones, hath not such a dark colour as the former, it discharges more matter; the cavernous or spongy texture of the bone becomes conspicuous. 3. The carneous caries, or ulcer of the bones with hypersarcosis: this sort differs from the worm eaten caries only in the addition of spongy flesh growing in the cells of the bone; this spongy flesh often bleeds, if touched with the greatest caution. 4. The phagedenic caries with hypersarcosis: in this case the periosteum is thickened, the bone softened, and its surface is eroded, a yellow red spongy substance sprouts out; the difference betwixt this and the carneous caries is, that in the latter the spongy flesh grows out of the caverns, while their grey or brown coloured spongy bony sides still remain; but in the former, the bony fibres disappear wherever the spongy flesh comes, so that one can scarcely determine by the probe whether or no the bone is carious: upon scraping away the flesh, so destructive to the bone, its surface appears rough indeed, but not much eroded, nor greatly altered in its colour. 5. The scrofulous caries is sometimes observed when an abscess is opened; the bone at the bottom of it appears white and smooth, without its periosteum or any connection to the neighbouring parts, except by its ligaments at the extremities; and this kind of caries most commonly happens in scrofulous habits. 6. The scirrho-cancerous caries: in one species of exostosis the tumefied bone is softer in one part than in the other, and is not composed of regular fibres, nor cavernous, but as if the ossifying juice had been thrown out irregularly, over which a cartilaginous or tendinous substance had spread; and from this a firm shining smooth flesh grows out, which, after the teguments are removed, tends forth a thin stinking acrid sanies. The patient complains often of throbbing pains in the part, and sometimes considerable haemorrhages are made from imperceptible vessels on its surface. 7. The spreading cancerous caries: in the spreading eating cancers the bones are wasted, as well as the soft parts, and the appearances are the same in both, unless that the bones do not consume quite so fast. 8. The syphilitic caries affects chiefly the tibia, frontal bone, the ossa nasi and palati, and the sternum. 9. The aneuris->iatic caries affects any bones in the neighbourhood of an aneurism.