These specimens plainly teach that in the cranial vault, where fissures occur without disturbance in bone, osseous callus is not deposited, but instead there are found very evident osseous clefts. These facts lead to the conclusion that the neoplasm which originates from the contents of the canals of Havers cannot of itself alone possess a true osteo-plastic value. The causes, which would seem to have led to the absorption in a manner not unlike that seen upon the rounded ends of misplaced long bones, may be referred to the destruction of the periosteum at the place of injury, and will be discussed as we examine in detail the part which is taken by the periosteum in the process of repair.

Professor Ercolani stated in 1866 "that repeated observations had demonstrated to him, that the periosteum underlying the soft neoplasm surrounding the fractured bone was shortly attacked by a complete process of destruction."

In 1867 Billroth wrote, "that the periosteum disappears in the new tissue, and in the callus in the course of ossification.” After this clear and precise statement, he asserted, "the periosteum has not a very important share in the formative process of the callus." When we remember the emphasis which he placed upon the osteo-genetic function of the irritative exudation from the Ilaversian system, we are led to believe he meant the periosteum in general, for he did not describe a metamorphosis of periosteum taking place in the callus, hence, we conclude that he must refer to destructive changes, when he stated that the periosteum disappears.

This is an important conclusion, and one to be carefully reviewed even when taught by so illustrious a master.

We may assume that it is an unquestioned fact, that to the integrity of the periosteum corresponds the integrity of the bone which it covers, and that to lesions of the periosteum correspond alterations in the bone; also that a moderate degree of irritation in the periosteum suffices to determine an excessive production of osseus substance, while a serious and profound lesion of the periosteum produces an opposite effect, the destruction of the substance of the bone.

Let us compare these observations so universally accepted, with the specimens before described. In these several examples, along the fissures there is found scarcely the slightest trace of neo-formation of osseus substance, yet a little way therefrom

appears a more or less abundant deposit. It would seem a fair interpretation, that in the place where the fissures of the bone occurred, the lesion of the periosteum was so serious as to produce a sudden cessation in its osteo genetic function, while in the neighboring parts, where the irritating and inflammatory process became necessarily less severe, there the process of osseous neo-formation was active. If the injury to the periosteum in simple fractures, or even fissures, is followed by results so serious as to put an end to its osteo-genetic function, it must, in a yet larger measure, be true in the more severe injuries and in compound fractures; this is abundantly proved in the long bones, either human or animal, which have consolidated with displacement of their extremities. We have already shown that the osseous substance at the apices in displaced fractures after a time undergo a marked atrophy, and, in the series of microscopic preparations from the rabbit to be described presently, we think it is demonstrated that these changes by absorption of the old bone commence within a few days after the injury.

This is in direct evidence that the exudation from the Haversian system, as earlier remarked, has not, in these instances at least, an osteo-genetic function. From these observations, and equally important ones derived from the study of fractures in flat bones, and especially from the demonstrations in the microscopic preparations referred to, it seems a conclusion from which there is no escape, that the periosteum at the place where the fracture occurs takes no part in the neo-formative process, but is actually destroyed. One following thus far in the analysis of the different factors which enter into the regeneration of bone, and finding that each may be excluded as non-essential, will be led to inquire: what then is the physico-pathological process by means of which the callus is formed? This differs in a great measure according to the form of the bone, whether flat, spongy, or long; the kind of fracture, whether simple or compound; and the position which the fragments of the bone assume and retain during the period of repair.

The results of careful study of these processes in the long bones of the rabbit we now give as the best possible illustration of what we believe occurs in the long bones of all animals when placed under similar favorable circumstances.

The series comprise twenty animals, from the third to the twenty-fourth day inclusive, all having been submitted to the

same treatment. The animals were etherized, the leg fractured, and at once secured in a plaster splint. They were then chloroformed at the desired period, a canula was inserted through the left ventricle into the aorta, and the blue gelatine solution injected quite warm. After repeated experiments, we have determined that the best means of injection is by the continuous stream under steady, but not too great, atmospheric pressure.

Third Day.'

The preparations of the third day after the injury, the appo sition having been nearly perfect, show very few marked changes. The edges of the fractured bone, which upon one border were considerably splintered, have scarcely altered, the neighboring vessels are not enlarged and only a few red and white blood-cells are to be seen. There is a small quantity of plasmatic fluid about the fractured ends which, magnified five to six hundred diameters, is shown to be composed of fine granules. The Haversian system appears unaltered and the periosteum is infiltrated with red corpuscles.

Sixth Day.

The changes from the third to the sixth day are instructive. There are seen a few blood vessels already formed in the new callus, which is distinct, and the exudate between the fragments is blended with the old bone. A nearly amorphous or finely granular material fills the interspace. This is under the most favorable conditions, as the fracture was not complete.

Ninth Day.

The changes which have taken place in the specimen of the ninth day are of much greater importance. The blood effused into the medullary canal has been largely absorbed, and we see in the finely granular matrix loops of new vessels rapidly forming. Many of them are ectasic in character and inosculate with the medullary vessels. The borders of the fractured bone.

1 The microscopic preparations were exhibited by means of the oxy-hydrogen or calcium light, representing upon a screen the sections at different diameters. This article was intended to have been illustrated by photographic representations, but after several attempts by one of our best artists, they failed to be sufficiently satisfactory. We much regret it, for it is impossible to substitute a description which, at the best, is simply the observer's opinion.

are somewhat softened and cemented by the same finely granular material as seen in the specimens from the third and sixth day.

The vessels of the Haversian canals remain unchanged. The periosteum presents marked modifications at the side of the fracture, upon both borders of the bone, there is a distinctly defined disintegration of the periosteum with absorption, less extensive where the fragments are in close apposition. Extending several lines in either direction there is an abundant deposit of the formative callus, or grume of the earlier writers, which infiltrates and incorporates into itself certain fibres of torn muscular tissue. This contains a few red and white blood cells. Upon one border of one of the preparations of this date there is an extensive fissure, which shows no effort at repair, but on the contrary an active process of absorption has taken place upon the osseous borders, and the interspace is filled with amorphous material. There is considerable displacement.

Tenth Day.

The specimens of the tenth day are described because they exhibit the development of the so-called internal callus. There was no displacement of the fragments, and hence a less active periosteal development. The new material upon the medullary borders is distinctly ossific, and is carried forward in diverticuli separated from each other by loops of vessels, surrounded by a bed of germinal matter. Upon the inner border of the fractured ends, there is a very considerable layer of cartilage cells. The capillaries are chiefly prolongations of the medullary vessels, although some are traced directly into the Haversian canals, and there doubtless inosculate with each other. The injected Haversian vessels are no larger than in the bone quite remote from the fracture, and the active part taken by the Haversian system, as claimed by Billroth, is not found. The medullary vessels in the vicinity of the fracture are considerably enlarged. There is also a trace of the necrosis of the old periosteum, and the overlapping of the new periosteal growth is well shown.

Twelfth Day.

The specimens of the twelfth day show beautifully the more perfectly developed series of vessels in the formative callus, both of the periosteum and of the medullary canal, many of the loops

are ectasic, cartilage cells are abundant, and osteoblasts have formed in the new periosteum. The point of destruction of the old periosteum is replaced by layers of cartilage cells. Here is first seen in the series, the process described by Billroth, namely the absorption of the bone about the Haversian canals, and a granular amorphous deposit on the line of their vessels. These changes are confined principally to the borders of the shaft beneath the new periosteal development; the vessels in the central portion of the old bone have undergone no change.

The separated edges of the fractured bone have a granular appearance, and are cemented by a protoplasmic mass, which reveals no cellular development even when magnified to eight hundred diameters.

Fourteenth Day.

In this radius which was simply fissured, the periosteal development is reduced to the minimum, while the finely granular material, filling the fissure, the edges of which have undergone distinct absorptive changes, is more clearly nuclear and highly refractory. The Haversian canals are being rejoined through the deposited material. The injection failed to enter the fiuer vessels.

Sixteenth Day.

The specimen from the sixteenth day shows especially well the injection of the vessels in the developed callus, which is in a great measure ossific. The place of the old destroyed periosteum is refilled with cartilage cells.

Nineteenth Day.

The specimens of the nineteenth day show yet more interesting changes than any of the previous ones. The displacement of the fragments is very considerable, and the callus is in proportion developed. The changes in the shaft of the old bone are less marked, and are chiefly confined to its periosteal surface. The Haversian canals are very little altered, the medulla, although the bone is displaced by half its diameter, has taken, equally with the periosteum, an active share in the reparative process.

Twentieth Day.

The displacement in the specimens of the twentieth day was very slight, and the process of repair is much more advanced than in the preceding one.