236 THEORY AND PRACTICE 



by apposition on the part of the osteoblasts on the other hand. 

 In this way is produced a more soHd dense bone — the definitive 

 callus. 



When great dislocation of the fragments has occurred, it may 

 take several months or even years before the reparative pro- 

 cesses are fully complete. In case of great dislocation the me- 

 dullary canal is usually not restored. 



Bones unite all right if given a chance. They are stronger 

 at the point of fracture after healing than before. It is a pop- 

 ular idea that horse's bones will not unite well. Dogs, sheep 

 and young steers take care of themselves and assist us but the 

 horse never does, that is why we have such poor success in the 

 healing of a horse's fracture. When the bones fail to keep in 

 position they become intensely inflamed and this is kept up until 

 gangrene sets in and ends the life of the animal. 



DISEASES OF THE NERVOUS SYSTEM. 



Diseases of the brain and nervous system are not as com- 

 mon in the lower anin:ials as in the human. The lower animals 

 are less liable to fatal results from shocks, as from fright or 

 operations. These diseases are divided into three classes — (1) 

 cerebral, when applied to the brain; (2) spinal, to the cord; 

 (3) peripheral, to the nerves. 



On account of the decussation of the nerves in the medulla, 

 and in fact all along the spinal cord, injuries on one side of the 

 brain produce paralysis on the other side of the body. The ef- 

 fects of sudden injuries to the brain are very noticeable, but 

 slowly encroaching injuries are very puzzling in the effects which 

 they produce. Any derangement of the nervous systein has a 

 tendency to produce either an increased functional activity or a 

 depression, that is, hypersesthesia or paralysis. 



Cerebr.\l Congestion. — This disease is called vertigo, 

 megrims, and sometimes blind staggers. It is due to a disturb- 

 ance of the circulation resulting in a hypersemic condition of the 

 brain. It is more or less sudden in its attacks and it is usually 

 due to pressure on the large veins of the neck by ill-fitting har- 

 ness. It may be due to a plethoric condition of the animal and is 



