8 MANUAL OF EQUINE MEDICINE. 



found that navicular disease is rare in cart-horses, though 

 it is a common affection among the more highly bred 

 animals. Again, roaring is very often associated with 

 certain shapes of neck. 



5. Colour. — Melanoid sarcoma is frequent in grey or 

 white horses. 



6. Temperament predisposes to certain diseases. The 

 sanguine temperament is especially shown in the highly 

 bred horses, whereas in lower bred animals the lymphatic 

 temperament is predominant. The sanguine temperament 

 predisposes to diseases of an inflammatory type. 



7. Diathesis. — By this term we mean a special liability 

 to certain diseases ; for example, a rheumatic or tubercular 

 susceptibility. 



8. EiFects of Previous Disease. — Some diseases when 

 once acquired tend to recur ; others, again, are jprotedive 

 against themselves. 



EXTRINSIC CAUSES of disease are : 



1. Dietetic. — Food and water are frequently sources of 

 disease, when excessive or deficient in amount, or when the 

 quality is unsuitable. 



2. Atmospheric or Telluric Influences. — These are of 

 much importance in the production of disease, as are also 

 the locality and geological formation. 



3. Imperfect Sanitation. — Defective drainage and im- 

 j)erfect ventilation are fertile sources of disease ; indeed ^ 

 there is no more i^otent cause of disease among horses titan in- 

 sufficient or vitiated supply of air. 



4. Work. — When too severe, work is a cause of disease, 

 as also it is when insufficient. 



5. Temperature. — Heat and cold are of much influence 

 in the causation of disease. 



6. Mechanical Causes. — Injuries of various kinds. 



7. Poisons. — Mineral poisons, as arsenic, antimony, and 



