Caries (Lat. caries, decay), a chronic inflammation of bone, accompanied generally by the formation of matter, which tends to make its way externally. The so-called spongy tissue, of which are composed the bones of the Avrist and ankle and of the spine, and the ends of the long bones of the limbs, is that usually affected. It is to be distinguished from necrosis. In the latter disease a part of the bone has its blood supply cut off, dies, and acts as a foreign body, until thrown off by nature or removed by the surgeon. In caries the disease is, so to speak, centrifugal, the bone being gradually absorbed by the growth of a soft newly formed tissue, composed chiefly of microscopic cells, which is formed in the spaces of the spongy tissue normally filled by marrow. In necrosis therefore the cause, being generally local, soon ceases to act, and the bone or piece of bone which has died, if not extruded by nature or removed by the surgeon, will act, as would a splinter, as a foreign body and to be expelled. In caries, the disease, being constitutional, tends to spread and finally to implicate the whole bone or district of bone, and very frequently those which are contiguous. Necrosis may be compared to a slough of the soft parts, caries to an ulcer of the same.

Scrofula and syphilis are the most frequent causes of caries. It may be excited by a local injury, but in such a case it is an expression of some constitutional disturbance or condition; the same injury in a healthy person not being followed by a like result. The symptoms are those of a chronic inflammation: pain and tenderness, followed sooner or later by swelling, redness, and heat of the superficial parts; the formation of matter, which tends to make its way by one or more (often sinuous) tracks to the nearest surface, and continues to be discharged so long as the disease lasts. A probe passed to the bottom of such a track would come in contact with roughened bone, or more often would impinge upon the new tissue spoken of above, through which it would have to be thrust in order to touch the bony wall of the cavity in which the disease existed. In caries of the spine the matter would make its way downward and present itself as an abscess in the groin. If near a joint, as for instance in caries of the upper end of the leg bone, this may by implication become disorganized. The patient's general health would probably indicate a constitutional disturbance other and greater than could be accounted for by the local trouble.

The prognosis would depend on the cause and situation of the disease, and the age, constitution, and civil condition of the patient. Though nature might in many cases effect a cure, the process would usually be tedious, and assistance on the part of the surgeon be necessary. Good food and air, proper exercise, and perhaps cod-liver oil, iron, and quinine, form the appropriate general treatment. Locally, mechanical support to counteract deformity and prevent the pressure of one ulcerated surface upon another, the judicious opening of abscesses, injections along the abscess tracks to induce a more healthy action, and finally, where practicable, the removal of the diseased parts, are indicated.