ANIMAL GRAFTS AND REGENERATIONS. 337 



the middle, and, on examining the organ some months after- 

 ward, he observed complete reunion between the separated 

 parts, and ascertained that the solution of continuity was 

 filled up by a fresh growth of muscular tissue. Thus all 

 the tissues of the animal system can be reproduced in the 

 grown-up subject, and these regenerations are uniformly 

 identical operations with those which have as their result 

 the first formation and the development of the very same 

 tissues in the embryo or in the young animal. 



In the practice of the surgical art the knowledge of 

 these facts of reproduction has been the occasion of more 

 or less remarkable inventions and operative methods, some 

 of which are as yet under investigation. Those which re- 

 late to the renovation of bony tissue have interested the 

 public peculiarly of late years. It has always been known 

 that, when a bone is broken, the solution of continuity in 

 it is filled up, after a certain time, by a portion of bone of 

 fresh formation, a true bony scar, a callus. It was not be- 

 fore the middle of the last century that a French physiolo- 

 gist, Duhamel, and after him a Neapolitan physician settled 

 at Paris, Troja, investigating the phenomenon of callus 

 closely, discovered its physiological mechanism. They 

 believed they could observe that the chief agent in the 

 elaboration of bone is a thin fibrous sheath applied and 

 adhering closely all around the bones, the membrane called 

 the periosteum. 1 Their experiments were neither numerous 

 nor striking enough to disclose to surgeons the advantage 

 that might be gained from the knowledge of the bone- 

 making property peculiar to the periosteum. The atten- 

 tion of practitioners did not begin to be drawn to this point 

 until later, toward 1830, by the labors of a professor at 



1 The bones may be regarded as formed of three concentric layers, 

 each inner one sheathed in another the inmost one the marrow, next 

 the bony substance properly so called, which is coyered by the perios- 

 teum. 



