194 NON-INFLAMMATORY DISEASES OF BONES. 



Occasionally the periosteum will be thicker, more vascular 

 and more easily stripped off; the fractured surfaces, however, 

 or such as are exposed, on making a section through the shaft, 

 disclose great general vascularity, and consequent heightening 

 in colour. 



" The medulla appears not only to contain an extra amount of 

 blood-vessels loaded with blood, but at many parts these seem 

 to have ruptured, and extravasation to have occurred. This 

 heightening in colour and extravasation of blood is not only 

 present in the large nutrient canal, but distributed throughout 

 the entire nutrient system of the bone. Obvious alteration of 

 structure in all these cases is found to exist both in the compact 

 tissue of the shaft, and in the entire cancellated and compact 

 tissue of the extremities. In the former, the bony laminae 

 surrounding the Haversian canals are expanded, opened out, 

 and thinner, resulting in a consequent dilatation of these latter ; 

 the same conditions exist to an equal extent in the cancellated 

 tissue of the extremities. 



" Although this rarefaction of the true bone tissue may have 

 proceeded to a great extent, leaving merely a thin shell of com- 

 pact bone around the great medullary canal, in no case is there 

 an entire want of bony matter, or a replacement of this by 

 cartilaginous or fatty tissue. The bone will not cut with a 

 knife, but may be fragile enough to admit of being crushed on 

 the application of even moderate force. 



" It is no doubt from this apparent condition of the extra 

 amount of blood contained in the vessels and nutrient canals, 

 its effusion, and the very dark colour imparted to the bones, 

 which has led ordinary observers to speak of them as being in a 

 state of rottenness and decay. 



" Although all breeds and ages of sheep, wdien circumstanced 

 as stated, seem liable to be thus affected, I have met with it 

 most frequently amongst cross-bred sheep, and in these when 

 under two years of age, most probably because they are the 

 class of sheep most frequently subjected to the adverse in- 

 fluences mentioned. 



" In regard to the treatment of this disease, we can, from ex- 

 periments which have been carried out, speak with tolerable 

 certainty as respects the efficacy of preventive measures. When 

 sheep are placed either on pasture or on roots, with such con- 



