496 REGENERATION OF BONE. 



(Legrand, Ewetzky, Schklarewsky); but usually when a part of a 

 cartilage is removed, it is replaced by connective-tissue. 



8. When a tendon is divided, proliferation of the tendon cells 

 occurs, and the cut ends are united by connective-tissue. 



9. The reproduction of bone takes place to a great extent under 

 certain conditions. If the articular end be removed by excision, it 

 may be reproduced, although there is a considerable degree of 

 shortening. Pieces of bone which have been broken off or sawn off 

 heal again, and become united with the original bone (Jakimowitsch). 

 If a piece of periosteum be transplanted to another region of the body, 

 it eventually gives rise to the formation of new bone in that locality. 

 If part of a bone be removed, provided the periosteum be left, new 

 bone is rapidly reproduced; hence, the surgeon takes great care to 

 preserve the periosteum intact in all operations where he wishes new 

 bone to be reproduced. Even the marrow of bone, when it is 

 transplanted, gives rise to the formation of bone. This is due to the 

 osteoblasts adhering to the osseous tissue (P. Bruns, MacEwen). 



In fracture of along bone, the periosteum deposits on the surface of the ends of 

 the broken bones, a ring of substance which forms a temporary support, the 

 external callus. At tirst this callus is jelly-like, soft, and contains many corpuscles, 

 but afterwards, it becomes more solid and somewhat like cartilage. A similar 

 condition occurs within the bone, where an internal callus is formed. The 

 formation of this temporary callus is due to an inflammatory proliferation of the 

 connective-tissue corpuscles, and partly to the osteoblasts of the periosteum and 

 marrow. According to Rigal and Vignal, the internal callus is always osseous, and 

 is derived from the marrow of the bone. 



The outer and inner callus becomes calcified and ultimately ossified, whereby 

 the broken ends are reunited. Towards the fortieth day, a thin layer of bone is 

 formed (intermediary callus) between the ends of the bone. When this begins to 

 be definitely ossified, the outer and inner callus begins to be absorbed, and ultimately 

 the intermediary callus has the same structure as the rest of the bone. 



There are many interesting observations connected with the growth and meta- 

 bolism of bones. 1. The addition of a very small amount of phosphorus (Wagner) 

 or arsenious acid (Maas) to the food causes considerable thickening of the bones. 

 This seems to be due to the non-absorption of those parts of the bones which are 

 usually absorbed, while new growth is continually taking place. 2. When food 

 devoid of lime salts is given to an animal, the growth of the bones is not arrested 

 (v. Voit), but the bones become thinner, whereby all parts, even the organic basis of 

 the bone, undergo a uniform diminution (Chossat, A. Milne-Edwards). 3. Feeding 

 with madder makes the bones red, as the colouring matter is deposited with the 

 bone salts in the bone, especially in the growing and last formed parts. In 

 birds, the shell of the egg becomes coloured. 4. The continued use of lactic acid 

 dissolves the bones (Siedamgrotzky and Hofmeister). The ash of bone is thereby 

 diminished. If lime salts be withheld at the same time, the effect is greatly 

 increased, so that the bones come to resemble rachitic bones. The normal de- 

 velopment of bone is described in vol. ii. 



When a lost tissue is not replaced by the same kind of tissue, its 

 place is always taken by cicatricial connective-tissue. 



