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e FIG. 44.—Microscopical cross-section of the tibia illustrating the result of Mayer and Wehner's “cap experiment.' Specimen recovered 48 days after the operation. The cap successfully prevented the ingrowth of regenerated periosteal cells and consequently no bone growth whatever occurred beneath it, in marked contrast to the excessive production of new bone on the outer surface of

a, Denuded cortex beneath the cap; b, the grooves into which the cap was firmly fastened; c, newly formed bone on the outside of the cap; d, regenerated periosteum; e, detritus.

the cap.

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b
Fig. 45.—Microscopical cross-section of the tibia illustrating the effect of Mayer and Wehner's “cap experiment.' Speci-
men recovered 15 days after the operation. On one side the cap was not fastened sufficiently firmly to prevent the
ingrowth of regenerated periosteum. A formation of new bone has therefore occurred beneath the cap. a, Cortex of tibia;
b, grooves into which the cap was set. Note that on the left side the periosteum has obliterated the groove; c, new bone
formation outside of cap; d, regenerated periosteum; e, newly formed bone beneath the cap.

transplantation, macroscopically without periosteum, is unquestionably due to the adhesion of these osteogenetic cells to the surface of the graft. Endosteal cells of the marrow cavity and of the Haversian canals are also capable of osteogenesis, though to a diminished degree.

Animal research and secondary operations on human beings, coupled with autopsy findings have given a clear conception of what occurs after a transplantation of living bone. The

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spinous process Fig. 46.—Cross-section of a tibial graft inserted between the halves of a cleft spinal process. Magnification, X4. Specimen recovered 60 days after operation. For the higher magnifications, see the following figures.

theory that the transplanted bone acts merely as a scaffolding is as incorrect as Macewen's conception of the bone cells proliferating with the rapidity of epithelial transplants. Figs. 46, 47, 48, 49 and 50 illustrate the course of events. They were derived from a case of transplantation of the tibia for spinal disease (typical Albee operation in male 40 years old). Death occurred 60 days after the operation. The greater part of the transplanted bone shows no evidences of life. On the surface where the tip of the transplant projects into the sur

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Graft surface, showing absorption Fig. 47.—Camera lucida drawing of microscopical section of the transplanted bone, at a point where it projects into the soft parts. Section shows extensive bone absorption due to the ingrowth of capillaries.

Young, newly-formed bone on surface of graft in contact
with the fractured spinous process

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Young, newly-formed bone about a Haversian canal Fig. 48.—Camera lucida drawing of microscopical section of the transplanted bone where it is in contact with the cancellous tissue of the split spinous process. In this section, in contra-distinction to the preceding, there is conclusive evidence of new bone formation, not only on the surface of the graft, but also surrounding the Haversian canals. In these are visible the "capillaries which have invaded the graft and typical osteogenetic cells which have evidently been derived from the adjacent bone of the spinous process.

rounding connective tissues, bone destruction bas taken place. The bone cells have lost their normal staining qualities and the lacunæ are empty. In that portion of the graft, however, where cancellous bone was transplanted, a large proportion of nuclei have retained their normal appearance. Where the

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Fig. 49.—Camera lucida drawing of the periosteal surface of the bone graft. Here, although there is no contact with the spinous process, a new formation of bone has occurred, unquestionably due to the Osteogenetic function of the transplanted periosteal cells.

graft is in intimate contact with the living bone of the spine a deposit of young osseous tissue is visible on the surface and the enlarged Haversian canals near this area are surrounded by zones of similar young bone differing sharply in appearance from the old bone of the graft.

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