212 POrLTRY DISEASES 



JNIany of the bones of the fowl, as the head, vertebrae and 

 humerus, contain air cavities. The air sacs send extensions 

 into these cavities. 



Bones of fowls nearly always develop from a connective 

 tissue foundation. The inorganic substance of the bone is 

 compressed in or between the fibers of the connective tissue, 

 while the cells of the latter are transformed into bone cells. 

 Between fibers are calcified bone cells, each of which rests 

 in a cavity of the matrix, called lacuna. 



The bone cells have processes that anastomose with the 

 processes of other cells. They lie in special canals known as 

 canaliculi. 



The histological structure of the bone of the domestic fowl 

 is similar to that of mammals, with the exceptions given 

 above, and the reader is referred to any histology for further 

 study. 



II. Reparative Processes of Bone 



A fracture of bone may be defined as a sudden solution of 

 continuity in a bone. The cause of fractures in a fowl are: 

 first, injury or trauma, receiving a blow as from a stick or 

 stone or bejng stepped upon by a large animal, as a horse 

 or cow, or by the infliction of a gun shot wound; second, 

 muscular action. Bones are most resistant to traction, next 

 to pressure and less resistant to flexion or bending and least 

 of all to torsion. External violence may be direct or indi- 

 rect. In fracture from direct violence the bone is broken at 

 or near the spot where violence is applied. As a rule the 

 soft structures surrounding the fracture are more or less 

 injured and more serious results may follow than in frac- 

 tures by indirect violence. In this kind of fractures the bone 

 may be comminuted or fissured and perhaps driven into vital 

 organs, as the liver or lungs, if the fracture be near these 

 regions, or into the brain if in the cranial region. 



External violence is \]u^ most common cause of fracture in 

 the fowl. The most common bones tlint are fractured are 

 those of the legs and next those of the wings. 



Fractures may be chissified as follows: first, simple frac- 

 tures those breaks in the continuity (vF the bone where the 



skin is not broken; second, comixmnd. also called open, or 

 complicated fractures — those where the ])reak is accompanied 

 by a break through the skin ;ind soft i^arts extending to the 



seat of fracture. 



A series of studies was uindc in this laboratory of repaired 

 fractures of fowls of long standing, after which a series was 

 made of the nature and rapidity of repair of fractured bones 



