Bone-formation comprises various new growths, which, in their developed stage, are readily divided into two classes, according to the analogy which their texture bears to that of normal bone. Still the line of demarcation is not sharply drawn, owing to the multiplicity of transition forms from the one to the other. The one category comprises new growths identical, or nearly identical with, the other, a series of new growths less or more widely discrepant from the texture of normal bone. On a closer scrutiny, however, this series again separates into the osteoid, and into the bony concretion, which latter manifests itelf, more especially in fluid blastemata, as cretefaction.

It is, indeed, worthy of preliminary remark, that not alone solid blastemata and perfected textures, but also fluid blastemata. afford the basis of, and are liable to, so-called ossification.

The process which involves the conversion of the substances here alluded to into bone, is commonly termed ossification, and thus brought into kindred relation with the bony conversion of cartilage.

We have here to observe:

1. In the first place, amongst the pathological growths with which we are here more especially concerned, are ossifications for the most part not constructed upon a preformed cartilaginous base, whilst many of them deviate from the course and the results of the ossifying process of bone-cartilage. It will be seen that in these last referred to, there is an absence of the vascularization proper to the cartilage in its transition to bone, an absence of that lamellated structure-development, with that grouping of the cartilage-cells, and that resulting arrangement of the bone-cells, which both exhibit in common. In isolated cases, as, for instance, in the ossifying of enchondroma, it is not in the intercellular substance, but in the cartilage-cell, that the ossification first commences. That ossified enchondroma differs in essential points from the texture of true bone, we have already seen.

"Where no preformed cartilage, but rather a rude, firm, sod-like, and fibrous, or a fluid blastema, or, again, an anomalous, mostly fibroid texture, constitutes the groundwork of the ossification, the result is a concretion more or less uniformly penetrated by bone-earths, and presenting scarcely any analogy with the texture of bone.

2. The characters of ossification differ according to certain differences in the implicated textures; or, where the textures are identical, according to certain peculiarities in the process itself.

The ossification of a cartilaginous base has frequently, although not always, an import coequivalent with that of ossified bone-cartilage - in other words, the import of a progressive metamorphosis into a complex vascularized texture. Genuine bone-texture, on the other hand, can, in the present state of our knowledge, be traced to a cartilaginous base alone, the pre-existence of which, if not obvious, must be taken for granted.

The ossification of other textural bases, on the contrary, has, if we take into account other collateral changes which these bases, and more especially the fibroid textures, undergo, the import of a retrogressive metamorphosis, of a decay, of a destruction of the base. With the display of lime-earths in the shape of black molecules, the textures lose their color, their succulence, and their elasticity, waste, shrivel, toughen, dry up, and become more or less lardaceous. Not alone do no new bloodvessels make their appearance, but old ones, if there be any, become obliterated. Fluid blastemata in the course of cretefaction become turbid, chalky, gritty to the feel. Under the development of fat, they form into a pap, and eventually thicken down to a mortar-like concre-ment. Even in cartilaginous bases, ossification is often so modified as to represent rather a retrogressive than a progressive metamorphosis (compare enchondroma).

3. A most important and comprehensive question relative to ossification generally, and therefore to bone-cartilage inclusive, is: whence are the lime-earths which incrust and penetrate the various soft textural bases derived?

A narrow scrutiny of the ossifying process, especially in fibroid textures, and of the cretefaction in soft and fluid blastemata, will speedily convince us that the appearance of lime-earths is not essentially due to their deposition out of either a pre-existent or a new-formed and special system of bloodvessels within the ossifying growth. For, when we see growths ossify, which are almost, if not entirely devoid of bloodvessels, and which are, at the same time, remote from the vascular system of other formations (for instance, free bodies within serous sacs); when we see the process of ossification often attended, not with any new growth of bloodvessels, but with the obliteration of existing ones; when, again, we reflect upon the concomitant changes wrought in textures during their osseous conversion, their wasting and discoloration, the interlarding of their shrivelling substance with free fat, we are fain to look upon the entire process as the result of the total transformation of the chemical constituents; as, in fine, an elimination of pre-existent lime-earths out of their primitive connections.

Even in the normal ossifying of boife-cartilage, the process is the same at the commencement, the lime-earths appearing long before the development of any vascular system. This, then, offers at least one connecting link for all processes of ossification.

In the revolutions effected by the ossifying process, a most important part is without doubt assignable to the accession of fat. It is common to all processes of ossification, and probably results both from a release of pre-existing fat from its primitive combinations, and of a simultaneous conversion of protein substances into fat.

From these preliminary remarks, we may at once proceed to a muster of the new growths belonging to this category, premising, however, that much relating to them will have to be discussed more at large in later chapters of the present work.