due to the proliferation of the cartilage and constitute simple inflexions; and it is easy to conceive that parts, which are so entirely deprived of their regular development (as they are in rickets), and ought, properly, to be densely impregnated with calcareous salts, must retain great mobility.

The enlargement and multiplication of the individual cells takes place in the same manner, as in the cases we have already considered; but inasmuch as at a later period individual parts in the cartilages, that properly ought to have become bone, do not calcify, and especially a formation of medullary spaces often takes place a long way up above the border of calcification-in many of these rhachitic parts the whole history of the development of bone is clearly revealed in a connected form. Large and often very vas

RICKETTY CARTILAGE.

435

cular conical processes of fibrous medullary tissue are seen extending upwards from the bone into the cartilage, and it may be very distinctly perceived, that these processes do not force their way into the cartilage from without, but that they owe their origin to a fibrillation of the intercellular substance of the cartilage itself. It is around them chiefly that the osteoid transformation of cartilage also can best be seen, and particularly that the gradual conversion of a cartilage-corpuscle into a bone-corpuscle can very distinctly be witnessed. Out of the cartilage-corpuscle which has a moderately thick capsular membrane, arises a structure, provided with a capsule continually increasing in thickness, within which the space for the cell constantly grows smaller, and which, when it has attained a certain degree of thickness, acquires indentations on its inner wall, like the socalled dotted canals of vegetable cells. Such is the mode in which the first rudiments of the bone-corpuscle are traced, after which a fusion of the capsule with the basissubstance very generally ensues, and with the production of anastomosing processes from the cells the formation of the bone-corpuscle is completed. At times isolated osteoid cartilage-corpuscles calcify alone without the occurrence of any fusion; and whilst between them lies the ordinary intercellular substance of cartilage, the capsules of the osteoid corpuscles fill themselves completely with calcareous salts. In other places on the contrary the fusion of the capsules with the intercellular substance takes place very rapidly; the new intercellular substance formed by this fusion assumes a coarsely fibrous appearance, and in

ing tibia from a child two years old. A large conical process of medullary tissue, sending out a lateral band on the left side, extends from m up into the cartilage; it consists of a fibrous basis-substance with spindle-shaped cells. At the circumference, at c, c, c the cartilage in a state of proliferation with large cells and groups of cells; at e, e commencing thickening and internal indentation of the cartilage-capsules which at o, o coalesce and form osteoid tissue. 300 diameters.

the place of several groups of cartilage-cells we see a fibrous mass, containing jagged osseous (bone-), or osteoid corpuscles. There is therefore no sharply defined boundary in the tissue, but the condensed or fibrous substance, which surrounds the jagged bodies, is directly continuous with the translucent substance which holds the cartilage together. Essentially, however, it is the same structure.1

This isolated transformation of single cartilage-cells into bone-corpuscles is obviously of the greatest importance to the cellular theory in general. In this specimen (Fig. 134) the whole series of these processes is seen at a glance. Where the completely ossified portion, in which the bone

Fig. 134. Insular ossification in ricketty diaphysal cartilage c, c. Ordinary growing (proliferating) cartilage, d, increasing thickening of the capsules with formation of an indented cavity (osteoid cartilage-cells), co', calcification of similar, still isolated cartilage-cells, co, commencing fusion of the capsules of calcified cartilage-cells, o, osseous substance. 300 diameters. (Cf. Archiv f. path. Anat., Vol. XIV, Plate I.)

The following section, including the history of the formation of callus, has been transferred to this place from the next lecture, inasmuch as a better understanding of it is thus ensured.

OSSIFICATION IN CARTILAGE.

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corpuscles are developed with perfect regularity, adjoins the cartilage, you see a zone where the conversion of cartilage-corpuscles into perfect osseous substance may be viewed within the limits of a very short space. At the point of transition a number of corpuscles are found lying close to one another like hazel-nuts-distinguished from ordinary cartilage-corpuscles by their dark contours, hard appearance, and unusually great brilliancy, and enclosing in a small, indented cavity a little cell; these little cells are the still isolated' bone-corpuscles with calcified capsules which they have retained from that earlier period in their existence when they were cartilage-cells. It is especially important that you should see these bodies thus isolated—in situ, in order that you may comprehend those other processes, in which in bone the territories2 belonging to the bone-cells fall out (p. 418, Fig. 129). When an object of this kind has once been accurately examined, it is impossible that doubts can any longer arise as to whether cartilage-cells can become bone-corpuscles, and I cannot conceive how it is that even the most recent (and those very careful) observers still start the question, whether bone-corpuscles are not in all cases structures obtained by a circuitous route, and not directly produced from cartilage-corpuscles. It is no doubt true, that in the case of the normal growth in length of bone most of the bonecorpuscles do not directly proceed from cartilage-corpuscles, but are immediately derived from marrow-cells and only mediately from cartilage-cells; but it is just as true that cartilage-cells also can be transformed straightway into

1 Isolated, because their capsules have not yet become fused with the basissubstance.-From a MS. note by the Author.

2 In bone formed directly (i. e., without the intervention of medullary tissue) out of cartilage, the territories of the bone-cells correspond to the cartilage-capsules. But when bone is developed out of any other tissue, the limits of these territories cannot be distinguished at all during growth, and it is only when gaps arise (through disease) in the bone around the bone-cells that these limits are defined. From a MS. note by the Author.

bone-corpuscles. It is now a long time since I called attention to one spot in particular, where the conversion of cartilage into osteoid tissue can be very distinctly viewed, namely at the points of transition from cartilage to perichondrium in the neighbourhood of the border of calcification in growing bones. Here the boundaries between the different forms of tissue are completely obliterated, and all sorts of transitions between round (cartilaginous) and jagged (osteoid) cells are seen.

The next preparations have reference to the pathological new formation of bone, or, if you will, to the physiological formation of callus. They are derived from a very recent fracture of the ribs, around which a thick mass of callus has been deposited. In reference to this process I will add a few words, as it is one that has been much discussed and is very important in a surgical point of view.

You have seen from what I have just been describing to you, that there are several ways in which the new formation of bone is effected, and that the old supposition that either the one or the other mode must be considered as the only prevailing one, is incorrect. The pre-existence of cartilage is by no means necessary for the formation of bone; on the contrary, an osteoid substance is very frequently formed by a direct sclerosis in connective tissue, nay, ossification is thus really more easily effected than when it takes place in real cartilage. We see also by the history of the theories concerning callus, that the endeavour to shew that it is always developed in the same way or out of the same substance (e.g. extravasated blood, periosteum, medullary tissue, exuded fluids, &c.) has proved the greatest obstacle to the true perception of the real state of things, and that all have really had right upon their side, inasmuch as new bone in fact builds itself up out of the most different materials. Unquestionably, when the case runs a very