I published a paper upon this subject, whence some of the following account is taken. The first object was to obtain bone in certain different and early stages of inflammation, and for this purpose the legs of several rabbits were broken, the animals killed at certain dates from the receipt of the injury, and the condition of the osseous tissue examined. I found that the first effect of an inflammation, or perhaps one should rather say the first organic change producing an inflammation, was enlargement of the lacunæ and their canaliculi. The annexed plates represent sections of the bones of rabbits, in different states. The first is a section simply in the normal condition, the relative sizes and appearances of the parts being strictly preserved; the

Section of the femur of a rabbit-normal-magnified 500 diams.

last is a section six days after fracture, equal care being taken in the representation.

Section of femur of a rabbit, close to fracture, magnified 500 diams.
The lacunæ may be seen large and round.

Inflammation producing simple induration commences by some enlargement of the lacunæ; those of the Haversian systems, which, on transverse sections, appear normally long and narrow, assume under the disease an oval shape; they remain dark, except in rare instances. In the spongy texture, in which the lacunæ are ordinarily larger and more broadly oval than in the solid substance, the increase is not so marked, but is not less real. The appearance of the sections shows, therefore, an unusual crowding together of the bone cells; but the observer will be principally struck by the increased development of the canaliculi; these channels are not only more plainly marked, but are more numerous than natural, so much so, that the bone, except for the lacunæ, assumes almost the appearance of dentine. The portion of tissue thus affected may be detected by the naked eye: if a section, simply filed tolerably smooth or rubbed on a stone without being ground thin, present any white opaque portion, the canaliculi will, in those parts, be certainly thus affected. The section looks so very nearly like human bone in the same state under less magnifying power that the same cut will suffice. Passing onwards to the focus of the inflammation, where suppuration is taking place, a further series of changes becomes apparent. The lacunæ have increased still more in size and breadth; even those of the Haversian systems are very broad ovals, or are rudely circular; their interior, instead of remaining dark, has, as it were, opened out into a light space marked by light-coloured round spots, surrounded by dark lines, or vice versa, according to the focus and direction of the light; some of them are very granular, others, more rare, are crowded with round celllike bodies, forming a mulberry mass, which appears to stand out above the bone surface. The canaliculi remaining, large in

Represents a lamina taken out of the spongy portion at the upper end of a human tibia-normal. The light semicircular portion at the side represents the edge of a cancellus. The longest lacuna is line length; the largest oval has a long diam. of line.

number, have increased in size, chiefly at their commencement in the lacuna, so that they appear to open into that space by a broad mouth, like an estuary. They are throughout more marked than the normal tube; they branch also in many instances into three or four channels, and sometimes at the spot whence these branches diverge a considerable enlargement in the main trunk is perceptible, as though at that point a new lacuna were being formed.

During these changes in the appearance of the cells and their branches the intercellular substance begins to suffer a peculiar transformation, which commences first in the parts next the Haversian canal, or cancellus, as the case may be; the bony substance becomes perfectly granular, that is to say, it looks as though it were composed of dark and light coloured dots placed close together. As this change spreads from the Haversian canal or cancellus outward, the margins of the cavity lose their distinctness of outline and become very irregular; in parts the edge is gone, the cavity is therefore on that side increased; in other parts the spotted bone tissue appears to mingle, or to be continuous with some granular contents of the cavity. It is quite evident that in these places the bone tissue is softened; one can trace the gradual completion of the process from some point which is only slightly spotted to the part next the cavity, which is a mere pultaceous granular mass, in which many of the dots have the appearance of nuclei.

Represents a lamina taken out of the spongy portion of the upper end of a human tibia in a carious condition. The upper portion of the cut shows a mere pultaceous mass into which the bone has become converted, and in which dark cells from the bone are scattered. In the lacunæ many nucleated cells are frequently to be seen; one, in the lower right corner, is conspicuous for its size and appearance; it measures 85 line in diameter.

Another change in the cell forms part of this softening process, viz., that as the dotted or granular condition reaches a certain stage, so do the canaliculi disappear; therefore of course from that side first, which is turned towards the cavity

(Haversian or cancellar), they vanish by simple shortening, by recession from the entirely softened bone, until they are reduced to mere little rudimentary projections on the surface of the cell. At this time the cell itself is visible as a granulated dark bag, more or less transparent, and very highly refracting, which projects from the wall of the scarcely resistent bone, and is of large size; it bulges out, and seems swollen; projects more and more, and at last breaks away from its attachment, and lies among the softened débris in the cavity, still retaining its dark colour. In breaking away, however, it often leaves behind those of its canaliculi which were turned away from the cavity, and which may often be seen on the edge, but which soon disappear as softening goes on spreading outwards. Frequently several smaller cells come out of the lacuna, instead of one large one. In this way a lamina between two cancellous cavities very soon disappears from softening on both sides: in this way also circlet after circlet of cells around an Haversian canal cave into the cavity, and thus the system melts away and leaves around the vessel only a soft granular and cellular mass.

That portion of osseous tissue, which lines within and without the shaft of a long bone, may be regarded as having the same relations in the one case to the periosteum, in the other to the medullary membrane, as the Haversian system has to the canal, or as the lamina bear to the cancelli. The ordinary cells of this tissue have certainly this relation, but those very long cells already described as peculiar to this situation (p. 4) are not so analogous. These cells appear destined to aid quickly and uniformly in the circumferential growth, and therefore also in the internal absorption of the bone, their action under inflammation is so rapid that, unless by experiment, one has hardly any chance of detecting their agency, for as soon as disease commences at the outer layers of the bone, they begin to swell in thickness, loosening thin flakes of the structure, even before it is softened, so that in stripping off the periosteum, however gently, such pieces will (if the attack be sufficiently recent) remain adherent to the membrane. If, however, the loosened flakes be not disturbed, they soften with great rapidity, and add their quota to the thickened state of the periosteum. It was said (p. 229), that if the periosteum be stripped off a bone inflamed on the surface, "it does not merely

drag away thin fibres (capillaries), but thick, sodden, plugs and ridges, which, as they come out of the tissue, leave it marked by deep holes and grooves, giving it the appearance of being wormeaten." If one or more of these plugs be examined, it will be found to consist of a vessel surrounded by a pultaceous mass of granules, among which are some scattered cells. If the wormbitten looking holes be studied they will each be found to represent the absence of an Haversian system, and the parts left between them the Haversian interspaces. Some of these holes run obliquely into the substance of the bone, and from these the plug is drawn out with the periosteum; others run along the new surface, and from these the ridges come; thus, it is evident, that the pultaceous granular mass which surrounds the vessel is a molten and altered Haversian system. It does not always happen, however, that the whole circle is thus dissolved, and comes out with the vessel; frequently, only its inner layers are sufficiently softened to do so, and it is by no means necessary that every Haversian canal on the inflamed surface should be in the same state of advanced softening.

Necrosis presents to our consideration three conditions of osseous tissue-necrosis, caries, and induration-the two last have been described; but the relative positions in which the three occur must claim attention. When a portion of bone dies ulceration must separate the dead mass. This action does not take place immediately on the surface of the necrosis, but a little beyond it. In soft parts the slough becomes separated by ulceration, which occurs on both sides of the demarcating line, at the edge of the sloughed portion as well as at the edge of the part to be preserved: that is to say, that a certain portion of the tissue separated is not dead, since on its surface ulceration and granulation occur. Thus also, in osseous structure, the ulcerating action continues in still living bone on the surface of the dead material; the inter-relation of diseased parts proceeding from the healthy to the necrosed portion may be thus stated :-healthyindurated-ulcerated-indurated-necrosed; the two last together constitute the mass separated; hence in all sequestra are two portions, the actually necrosed, and the indurated but living tissue; if the slough have occurred in the centre of a bone it is surrounded by the hardened material; if only on the surface, with