This disease corresponds to ulceration in the soft parts. It is sometimes the immediate result of an inflammatory process of low type (dyscrasia), the product of which exerts a solving power upon the bony tissue: the scrofulous and syphilitic ulcerations of bone are of this kind. Sometimes it arises out of simple suppuration in a bone in consequence of local or general (internal) causes. It is, moreover, frequently set up by ulcerative processes going on in adjoining soft parts; a frequent instance of which is presented by the caries of the articular ends of a bone, which ensues upon disorganization (Verjauchung) of the soft tissues of a joint. Lastly, it results also from the softening and ulcerative inflammation of morbid growths in bone, such as tubercle, cancer, etc.

Caries is sometimes situated at the surface (caries superficialis, peri-pherica), and sometimes originates in the interior of a bone - in its medulla (caries centralis, profunda). In its extent it may be total or partial: it may involve a whole bone, as one or more of the vertebrae, of the carpal or tarsal bones, or the whole of a finger or toe; or it may attack a portion only of one of the larger bones, such as the end of one of the long bones composing a joint, or a circumscribed spot on the shaft of a bone.

Though it chiefly affects spongy bones and parts of bones, it is not altogether rare in the compact tissue; indeed, certain forms of dyscrasia establish their ulcerative inflammation by preference in that tissue: generally speaking, we may say that there is no bone which may not be the seat of the disease. It is most frequently met with in young persons as a scrofulous affection.

It may come on whether the tissue of the bone in which it occurs be in its original healthy state, or have been previously diseased; it may occur, for instance, in a rickety bone.

Its course is generally chronic; but in the extensive devastations which it commits, and the fatal exhaustion which it sometimes produces within a short period, it frequently exhibits the character of an acute disease. It often threatens life, moreover, less by its own progress than by exciting inflammation in neighboring important organs; it does so, for example, when it occurs in the skull.

An ulcer in bone presents numerous varieties corresponding with the kind of constitutional affection which gave rise to it. I shall, however, first treat of the process of ulceration in bone generally, without reference to its varieties, as there will be an opportunity in another part of detailing the characters and differences which the ulcer obtains from the several processes of dyscrasia in which it originates.

The appearances presented by an ulcerated bone when examined in the recent state, vary according to the progress which the disease has made; and in every stage of the affection its characters are far better marked in a spongy than in a compact bone.

When caries is superficial, the compact bone is found covered with ichor, and rough, as if it had been gnawed: this appearance is given by the unequal loss of substance which the outward lamellae have sustained. The Haversian canals are enlarged, but not uniformly: the tissues contained within them form in part a disorganized soft and shreddy mass, infiltrated with ichor; or spongy granulations which easily bleed, grow from them luxuriantly, and advance outwards over the rough surface of the bone, whilst internally they partially or completely fill the enlarged Haversian canals. In both cases the bone appears porous or cancellous, but its color differs in the two: in the former, it is discolored by the contents of the Haversian canals; in the latter, it obtains various tints of red from the color of the granulations.

When caries affects cancellous tissue, the bone acquires a livid red color, especially if the granulations be at all abundant; it becomes soft, resembles a mass of flesh traversed by a delicate and brittle bony skeleton, and is easily cut with a knife, or yields to light pressure with the finger: lastly, it becomes swollen.

In cases of central caries, the swelling sometimes produces expansion of the bone, especially if it be a spongy bone, for the thin wall gives way and becomes distended.

The loss of substance which the bone sustains is occasioned by its solution in the sanious product which is effused by the inflammation into the Haversian canals. These canals enlarge in all directions, though not uniformly, and contain in different proportions, on the one hand, sanies and the soft parts which naturally fill them, discolored and disorganized (verjaucht); and on the other hand, granulations. It is thought by Delpech and Berard, Pouget and Sanson, and by Mouret, that a peculiar fatty matter is generated in carious bones; Mouret differs from the others, however, in believing that the organic principle (the gelatinous portion) does not disappear from the bone.