AND DEVELOPMENT OF BONK. 199 



In another experiment the rabbit operated upon was eight months 

 old, the periosteum was detached as in the former experiment, but 

 was coiled around the bone, and its detached extremity kept in posi- 

 tion by means of a ligature. Four days after the operation the wound 

 was re-opened and that portion of the periosteum which had been left 

 attached to the bone was now severed from it. At the end of twenty- 

 three days, the periosteum had become wholly converted into bony 

 matter. 



In a subsequent experiment a portion of periosteum from the tibia 

 was dissected off, and placed beneath the skin of the back ; thirteen 

 days afterwards, complete ossification had taken place. 



The bones thus obtained have all the characteristics of normal 

 bone. Examined microscopically, they exhibit the lacunee and can- 

 aliculi, and the Haversian canals are disposed in the direction of the 

 axis of the bone. 



These experiments prove to demonstration that cartilage is not 

 absolutely necessary for the formation of bone, and are strongly 

 corroborative of the opinion set forth by Sharpey, that the shaft of 

 the bone increases in diameter by the direct ossification of the sub- 

 periosteal layer. An examination of this layer by the microscope 

 reveals the presence of a blastema composed of cells and free nuclei, 

 such as are to be met with in embryonic tissues, together with some 

 exceedingly fine fibres. 



When the periosteum is transplanted this subperiosteal layer is the 

 germ whence bony tissue is developed. 



In proof of this assertion it has been found experimentally that if 

 the inner surface of a detached piece of periosteum be scraped with a 

 scalpel and the sub-periosteal layer of nuclei, nucleated cells and 

 accompanying fine fibres be thus removed, the osteogenetic power of 

 the membrane is thereby wholly destroyed. 



It may be asked whether bone thus developed continues to grow 

 indefinitely. To be able to satisfactorily answer this question would 

 require the experience of several years ; but, reasoning from analogy, 

 it may be presumed that these heterotopical bones would continue to 

 increase in size so long as the normal osseous framework is augment- 

 ing in volume. 



From a surgical point of view the importance of the knowledge 

 «obtained by means of these experiments is very great, and must have 



