OSTEOPOEOSLS. 



263 



lands where the thermometer occasionally registers freezing point. 

 Owing to the lack of nutritious forage there are no breeding 

 establishments in the rainy districts, and of the few foals born, 

 nearly all succumb to the disease before attaining maturity. The 

 geological fornuition of the island is similar throughout its whole 

 extent, and is purely volcanic. The recoveries resulting from 

 change of locality contrast strongly with the inadequacy of drugs. 

 Two thorough-bred animals, each four years old, were in the last 





Fig. lOo. — Ilor-se's head suffeving from osteoporosis, 



stages of this disease ; they were removed to a dry district, well 

 fed, and allowed the run of a small paddock. Restoratioii to 

 normal health was effected in three months. 



NATURE OF THE DISEASE.— Osteoporosis appears to be a specific 

 inflammation of bone by which a portion of the earthy matter becomes dis- 

 solved. Its course closely resembles that of human " rarefying ostitis," 

 which was described as follows : A portion of compact bone undergoirrg 

 this charige is iir the earliest stages slightly redder than natural ; the 

 openings of the Haversian canals after a time become somewhat increased in 

 size, and consequently a larger number are visible to the naked eye. As 

 the process advances, the Haversian canals increa.se at the expense of the 



