The Sanies Produced By The Bone is an acrid fatty fluid, itself discolored in various ways, and which, as is well known, blackens silver probes and linen. It almost always contains small particles of bone, discolored and brittle, which look as if they had been calcined, and are, in fact, loosened remains of the bony tissue, which is being destroyed. They are, without doubt, minute portions of necrosed bone; for in every form of caries, small imperceptible particles of bone die and are cast off. More rarely it happens, that necrosis of a larger piece of the ulcerating bone takes place (caries necrotica). In that case the portions of bone die sometimes without partaking at all in the inflammatory process, and simply from the access of their fluids being cut off by the carious destruction which is going on around them; and sometimes they die from the inflammation and disorganization.

Whilst this disorganizing process (Jauchung) is going on in the bone, more or less of the adjoining osseous tissue and soft parts are always inflamed to a greater or less distance. The inflammation is sometimes chronic, and the soft parts become infiltrated with a gelatinous or gela-, tinous and lardaceous product, and indurated; at other times it is acute, and leads to suppuration and ulceration. The periosteum, and the ligamentous tissues connected with the bone, are, of course, involved in this change in the soft parts. The mode in which the ulcer of the bone opens externally, varies according to circumstances: sometimes one large abscess is formed; at other times, one or more straight or tortuous, single or branching, long canals (fistulae, sinuses), either lead directly outwards, or not unfrequently pass to very remote distances; the orifices of the sinuses are usually marked by rather a hard margin, which surrounds them like a rampart.

The carious bone, when macerated and dried, looks rough, and as if corroded: from being perforated in various ways by the unequally-enlarged Haversian canals, it has a spongy, porous, worm-eaten appearance; the cells of its cancellous structure are enlarged; its walls and network are attenuated or demolished; and hence it is lighter than natural, discolored, expanded, and very brittle.

New osseous substance, which assumes the form of some of the different osteophytes, is sometimes deposited around the ulcerated spot, both on the surface of the bone, in its medullary canals, and in the cells of its spongy substance. And bone is deposited not only on the diseased bone, but on others also which are near it.

In other cases the neighboring bones are found in a state of rarefaction (osteoporosis), of areolar expansion, combined with hypertrophy, or inflammation of the soft parts of the bone, and, at length, of atrophy of their tissue.

Caries will heal, even in cases where it has committed great devastations, by a change of the ulcerative into a healthy suppurating and granulating process. The subsequent reproduction of bony substance is small in proportion as the amount of destruction has been great, and hence there will be more or less deformity, as well as variety of size, in the cicatrix.

Caries, as has been partly mentioned already, and will also be further pointed out hereafter, must be carefully distinguished from several other losses of substance in bone.