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original medullary tissue is transformed into adipose tissue: the fat, however, is always contained in the interior of the marrow-cells, as it is in the cells of the panniculus adiposus. But this yellow, fatty marrow does not occur in all bones. In the bodies of the vertebrae we almost always find the small cells. In the long bones of the adult the fatty marrow always occurs normally, but in pathological conditions it may very rapidly yield up its fat, the elements may divide and we then again have red, but inflammatory, marrow.
In this whole series of allied processes from the first development of marrow out of cartilage until the production of inflammatory marrow—the last disturbance which manifests itself in injured bones (as we see in amputations)—there at no time exists any amorphous substance, blastema or exudation; we can always trace the descent of one cell from another; every one of them has been directly developed from an earlier one, and will have, as long as the proliferation continues, a direct progeny of cells.
The second series of transformations in the longitudinal axis of the cylindrical (long) bones is furnished by the osseous tissue, which may arise out of marrow and cartilage. In the one case the marrow-, in the other, the cartilage-cells, become the subsequent bone-cells. This act of real ossification, the production of the osseous tissue, is extremely difficult to observe, chiefly for the reason, that what first takes place in the course of these processes, is not the production of real osseous tissue, but only the deposition of calcareous salts. Generally, namely, there first of all takes place in the immediate vicinity of the border of the bone a calcification of the cartilage, which gradually advances, first along the borders of the larger groups of cells and then around the individual cells, always following the substance of the capsules, so that every individual cartilage-cell is surrounded by a ring of cal
Fig. 127. Horizontal section through the growing cartilage of the diaphysis of the tibia of a seven months' fcetus. Cc. The cartilage with groups of cells that have undergone proliferation and enlargement; pp, perichondrium. i. Calcified cartilage, in which the individual groups of cells, and cells, are enclosed in calcareous rings; at k larger rings, at W progress of the calcification along the perichondrium. 150 diameters.
Fig. 128. Right corner of Fig. 127, more highly magnified, co. Calcified cartilage, eo' commencement of calcification, p perichondrium. 350 diameters.
careous substance. But this is not yet bone, it is nothing more than calcified cartilage, for, upon dissolving the calcareous salts, the old cartilage is again brought into view—and indeed it offers no analogy to bone in any other respect excepting in the presence of calcareous salts.
Now, in order that this calcified cartilage may become real bone, it is necessary that the cavity in which every cartilagecell lies, be converted into the well-known, radiated, jagged bone-cavity [lacuna]. This process is so extremely difficult to obtain a sight of, because on making sections the masses of lime crumble away before the knife, and furnish debris within which it is impossible to see well what really is present. In this circumstance you must seek for an explanation of the fact, that up to the present time there are still, and probably still will be for several years, continual disputes with regard to the mode of origin of bone-corpuscles. I hold that view to be correct, according to which the bone-corpuscles1 in certain places directly originate out of the cartilage-corpuscles, and indeed in this way, that in the first place the cavity of the capsule which invests the cartilage-cell, becomes narrower, manifestly because fresh capsular matter is deposited on the inside. But in proportion as this takes place, the inner border of the capsular cavity begins to assume a distinctly indented appearance2 (Fig. 133, c) and the space occupied by the
1 Cartilage-corpuscle=capsule+cartilage-cell; bone-corpuscle=bone-cell.— Traiul.
1 The lacunae may be said really to have no existence in living bone (or osteoid tissue); they are merely the gaps (holes) in the intercellular substance in which the bone- (or osteoid-) cells lie, and are normally so entirely filled by these cells, that it is impossible to give the outlines of both in a drawing. The outline of the cell is the outline of the lacuna. Who, in drawing a deal-board, would ever think of giving a second contour to every knot, in order to represent the outline of the gap which would result from the falling out of the knot! Hence Authors have come to speak of the nuclei of lacuna', whereby of course they mean the nuclei of the cells which fill the lacunae, but which, thanks to the deeply rooted but erroneous impression left upon their minds by microscopical sections of macerated bone, they have failed to recognize, or have not even sought for, taking for granted they had lacunae before them. In the preparation of sections, however, the cells frequently shrink, so that an interval is left between them and the walls of the lacunae.
. FORMATION OF BONE-CORPUSCLES. 417
original cell is thereby considerably diminished. In rare cases, we still succeed in finding cartilage-corpuscles, in which the capsular cavity has (without the occurrence of calcification) become diminished in consequence of the deposition of new capsular matter, so as to assume the form of a bone-cavity (lacuna)—which it generally assumes only after ossification—whilst the old cellular element (the cartilage-cell with its nucleus) still remains in it. After this — still without the occurrence of any calcification—the boundary disappears which originally existed between the capsules of the cartilage-cells and the basis-substance, and we find jagged elements1 (the future bone-cells) in an apparently entirely homogeneous substance—in other words, a tissue still soft, though in structure like bone (osteoid tissue, Fig. 133, o). Usually this process is concealed by means of the early calcification of the cartilage and only certain processes, for example, rickets, give us the opportunity of seeing the osteoid transformation take place in just the same manner in those parts of the cartilage also which are beginning to calcify.
But the old limits of the capsule still represent the real district which is under the sway of the bone-corpuscle, and, as I pointed out to you at the commencement of my lectures (p. 15) with an especial reference to this point, in pathological conditions this district comes again not only in force but also into view. Within these limits we see
What is here said of the lacunae of course equally applies to the canaliculi. Both represent the margins of the calcified intercellular substance, where it comes into contact with the bone-cells and their processes —Bated upon MS. notet by the Author.
1 The cartilage-cells (and the same holds good of the marrow-cells) during ossification throw out processes (become jagged) in the same way, that connective-tissue corpuscles, which are also originally round, do, both physiologically and pathologically. These processes—which in the case of the cartilage-cells are generally formed after, but in that of the marrow-cells frequently before, calcification has taken place—bore their way into the iuterccllular substance, like the villi of the chorion do into the mucous membrane and into the vessels of the uterus, or like the pacchionian granulations (glands) of the pia mater of the brain into (and occasionally through) the calvarium.—From a MS. note of the Author.
Fig. 129. Line of demarcation in a piece of necrosed bone from a case of paedarthrocace ;2 a, a, a the necrosed bone with very much enlarged osseous corpuscles and canaliculi; here and there slight indications of excavations upon the surface, b, b. The vacuities, which have taken the place of the cell-districts of the bone (Cf. Fig. 134), seen at the side of the object on a different level; here and there enlarged bone-corpuscles still to be seen through a layer of basis-substance which covers them, c, e. Completely empty cavities. 300 diameters.
1 The drawing was made from a somewhat thick preparation, and does not represent one level surface, but three different planes which form, as it were, terraces, one above the other. Of these e is distinctly in focus; b is on a lower (or higher) level, and is less distinctly seen; a is lower (or higher) still, and is therefore still more out of focus. Hence it is that the canaliculi (which besides are badly represented), are not clearly seen.—From a MS. note by the Author.
'Necrosis (scrofulous) of the fingers in children.