FORMATION OF CALLUS AFTER FRACTURE.

439

favourable course, that path is chosen in which the new formation can be most conveniently effected, and it is by far the most convenient way, when the periosteum produces very large portion of the whole. This takes place in the following manner: the periosteum grows dense towards the edges of the fracture, and there gradually swells up, the swelling being of such a nature, that separate layers or strata can afterwards pretty clearly be distinguished in it. These continually become thicker and more numerous, in consequence of the constant proliferation of the innermost parts of the periosteum-and of the formation, by means of a multiplication of their cellular elements, of new layers, which accumulate between the bone and the relatively still normal parts of the periosteum. These layers may become cartilage, but it is not necessary, nor yet the rule. For we find that, in the greater number of favourable cases of fracture, where cartilage is produced, not the whole mass of the periosteal callus is produced from cartilage, but a greater or less portion of it is always formed out of connective tissue. The layers of cartilage generally lie next to the bone, whilst the farther we proceed outwards, the less does the formation out of cartilage, and the more a direct transformation of connective tissue, prevail.

The formation of bone is, however, by no means restricted to the limits of the periosteum-very commonly it extends beyond them in an outward direction, and often penetrates, in the form of spicula, nodules, and protuberances, to a very considerable depth into the neighbouring soft parts. It is self-evident that in these cases we have by no means to deal with any proliferation of the periosteum in an outward direction, but that an ossifiable tissue arises out of the interstitial connective tissue of the neighbouring parts. Of this it is very easy to convince oneself, because osscous spicula are found shooting up in the interstitial tissue of the neighbouring muscles. In the preparation from the

fractured ribs, places are still to be found in the external parts, where fat has been included in the ossification. It cannot be said therefore that the formation of callus around fractured parts is altogether a periosteal formation; in all cases where it takes place with a certain abundance, it transgresses the limits of the periosteum, and invades the connective tissue of the surrounding soft parts.

There is a second kind of callus-formation completely different to this-that namely, which takes place in the midst of the bone from the medullary tissue.

At the moment when the bone in a case of fracture is shivered, a number of little medullary spaces are naturally opened. In the neighbourhood of these, the still

Fig. 135. Transverse fracture of the humerus with formation of callus, about fourteen days old. On the outside is seen the porous capsule of the callus produced from the periosteum and soft parts, the innermost layer on the right side being still cartilaginous. On the left lies detached a fragment shivered off from the cortex of the bone. The two fractured ends are connected by a (dark-red) fibrinous layer of hæmorrhagic origin; the medulla on both sides is very dark (owing to hyperæmia and extravasation), in the lower fragment several porous islands of callus are seen which have been produced by the ossification of the medulla.

DESTRUCTIVE NATURE OF NEW-FORMATIONS.

441

time a larger or smaller new layer of bone is found, filling up the end of the medullary canal of each fragment so as to occasion its occlusion. This is a kind of new formation which has nothing in common with the former one, as far as their starting-points are concerned, but has its origin in quite another tissue, and is altogether different in its palpable result, inasmuch as it produces, within the confines of the old bone, a condensation of that portion of the marrow which lies in the immediate vicinity of the fracture. Even in cases where the ends of the bones perfectly coincide, an internal formation of bone such as I have described takes place in the medullary canal of each fragment, producing its occlusion.

These two kinds are the usual and normal ones. Around the two fractured ends the swelling takes place, in the interior, the condensation. Gradually-in proportion as the extravasated blood is absorbed the new masses of tissue which have been developed between the broken ends draw nearer to one another, and round about the fracture forms a bridge- or capsule-like communication by means of the ossification of the soft parts. There is therefore but little reason to ask whether the callus proceeds from free exuded or extravasated matter. No doubt an extravasation takes place in the first instance into the space between the fractured ends, but the extravasated blood is generally pretty completely reabsorbed, and it contributes comparatively but very little to the real formation of the subsequent uniting media.

We discussed, gentlemen, last time, the chief points in the history of new-formations. You remember that, according to our ideas, every kind of new-formation—inasmuch as it has its origin in pre-existing cellular elements and takes their place-must necessarily be connected with a change in the given part of the body. It is no longer

possible to defend an hypothesis such as that which, based upon the supposed existence of plastic matters, was formerly maintained, namely, that a substance was deposited between and upon the existing elements of the body, which produced a new tissue out of itself and thus represented a clear accession to the body. If it is true that every new-formation proceeds from definite elements and that usually divisions of the cells are the means by which the new-formation is produced, it becomes of course self-evident, that where a new-formation takes place, certain histological elements of the body must generally also cease to exist. Even a cell, which simply divides and out of itself produces two new cells like itself, thereby ceases to exist, even though the whole result is only the apparent apposition of a cell. This holds good for all kinds of new-formations, both for benignant as well as for malignant ones, and it may therefore in a certain sense be said, that every kind of new-formation is really destructive, and that it destroys something of what previously existed. But we are, as is well known, accustomed to judge of destruction according to the more obvious effects produced, and when we speak of destructive formations, we do not so much mean those, in which the result of the new-formation is analogous to the old one, as some product or other deviating more or less from the original type of the part. This is the point of view to which I have already (p. 64) directed your attention when treating of the classification of pathological new-formations. By it is a reason, sensible and in correspondence with the facts, afforded for the separation of all new-formations into homologous and heterologous ones.

Heterologous we may call not only malignant, degenerative neoplasms, but we must also thus designate every tissue which deviates from the recognized type of the part, whilst we should call all that homologous, which, although new-formed, still reproduces the type of its parent soil.

HOMOLOGOUS AND HETEROLOGOUS NEW FORMATION. 443

We find, for example, that the so extremely common form of uterine tumour, which has been designated fibrous or fibroid, has in every respect the same structure that the walls of the "hypertrophied" uterus has, inasmuch as it consists not only of fibrous connective tissue and vessels, but also of muscular fibre-cells. The tumour may, as is well known, become so large, as not only to embarrass the uterus in all its functions in an extreme degree, but also to exercise through pressure the most injurious influence upon the neighbouring parts. In spite of this, it must always be considered an homologous structure. On the other hand we cannot help employing the term heterologous formation, as soon as, by means of a process which at first seems to represent a simple multiplication of the parts, a result is obtained which is essentially different from the original condition of the spot. A catarrh for example in its simple form may be attended by a multiplication of the cellular elements on the surface of the mucous membrane, without the new cells' being essentially different from the pre-existing ones. Thus I brought along with me for you last time a vagina with very marked leucorrhoea. You there saw no doubt that the cells in leucorrhoea very closely resemble those of the epithelium of the part, although they no longer entirely retain the typical form of pavement epithelium. The less, however, they approach in their development the typical forms of the epithelium of the part, the more incapable do they become of performing their functions. They are moveable upon a surface, to which they ought properly to adhere, they flow down' and produce results which are incompatible with the integrity of the parts.

In a narrower sense of the word heterologous newformations are no doubt alone destructive. The homo

1 Καταρρέω (catarrh).