164 OF THE DEATH OF BONE, 



tlie cliaBges succeed each otlier in the most gradual, 

 orderly, and regular manner. 



In rickets the bioplasm grows fast, and a very soft 

 kind of formed material results, which is not hardened, 

 or only very imperfectly hardened by the infiltration of 

 calcareous salts. The bone is, therefore, not resisting 

 enough to support the superincumbent weight of the 

 body, and yields, becoming bent and distorted, ac- 

 cording to the direction of the pressure. In caries, 

 the bioplasm of a part of a bone receives too large 

 a supply of nutrient matter; it grows too fast, ard 

 lives upon the surrounding tissue which has been 

 already formed. 



224. Of the death of bone. — In necrosis, the death 

 of the bioplasm of many lacunee takes place. It is 

 easy to conceive that such a result must ensue if the 

 supply of blood be cut off; for the currents of fluid, 

 which during life flow through the canaliculi, and 

 permeate every part of the bone, cease, and the bio- 

 plasts die. Changes in the small trunks which supply 

 the Haversian vessels, ending either in their obstruc- 

 tion, as, for example, by clots, or their obliteration by 

 pressure, exerted upon them, as from the growth 

 of adventitious tissue around, may cause necrosis of 

 a considerable extent of osseous tissue. Thus effusion 

 into the deeper and more spongy portion of the 

 periosteum, as occurs in the formation of a node, may 

 cause the occlusion of sonae of the vessels passing 

 from this membrane into the compact tissue. The 

 passage of blood through these vessels being inter- 

 fered with, the bioplasm of all that portion of bone 

 receiving nutriment from them must die, and a piece of 

 bone of considerable size become " necrosed." Imme- 

 diately around this the nutrient matter would flow 

 more freely, but of course less regularly. In conse- 

 quence, the bioplasm of the neighbouring lacunae 

 would grow much faster, and thus a vast number of 

 bioplasts would result. These would even eat away, 



