16 LAMENESS OF THE HORSE 



more intense in the process and pressure of standing than when 

 the mem])er is swung or advanced. 



Certain bones are so well protected by muscular structures 

 that they are not frequently injured except as a result of vio- 

 lence w'hich may produce fracture. However, there are certain 

 bones which receive the constant shock of concussion when the 

 animal is subjected to daily, rapid work on hard road surfaces. 

 Splints, ringbones and spavins are the most general examples 

 produced by these conditions. 



Varying pathological developments often result from concus- 

 sion, contusion or other violent shocks to the bony structuras. 

 In such cases there either follows a simple periostitis which may 

 resolve spontaneously with no obvious outward symptom, or 

 osteitis, which may occur with tissue changes, as in exostosis; or 

 the case may produce any degree of reaction between these two 

 ])Ossible extremes. 



Rarefying Osteitis, or Degenerative Changes. 



Certain bone alfections, such as osteonudacia or osteoporosis, 

 are in the main, responsible for distortions and morphological 

 changes of bone, causing lameness, permanent blemish and even 

 resulting in death of the affected animal. The climatic condi- 

 tions in some localities favor these occurrences but they may 

 also be ascribed to improper food constituents and to possible 

 infective agencies. 



Rarefying degenerative changes manifested by exostosis involv- 

 ing the phalanges of the young, causing ringbone, are fairly com- 

 mon in occurrence throughout this country. This is due, sup- 

 posedly, to a lack of mineral substance in the bony structure of 

 the affected animals, and is known as rachitis — commonly called 

 rickets. Since the affected subjects suffer involvement of several 

 of the extremities at the same time, the theory of rachitic origin 

 seems well supported. 



Fractures. 



Fractures of bones constitute serious conditions and are always 

 manifested by lameness. A sub-classification is essential here 



