ETIOLOGY. 



h. Temperature. — Excess of heat or the opposite, and more 

 certainly sudden alternations from the one to the other, act 

 both systemically and locally. 



c. Telluric. — This acts variously, as through the character of 

 the materials of the food-supply grown from particular soils, 

 by the nature of its geological formation as to its capability of 

 retaining or discharging moisture, its reception and treatment 

 of the sun's rays, or the amount of organic matter which it 

 holds undergoing decay. The breaking up of soils has a 

 marked and often peculiar influence in determining the appear- 

 ance of serious maladies amongst animals. 



d. Dietetic. Food and Water. — The food may be wrong as 

 to quantity or quality, or given at improper intervals, and 

 under unfavourable conditions of animal health and work- 

 Water, either in excess or deficiency, but most frequently from 

 its contamination with poisons, mineral or vegetable, or organic 

 germs, may act injuriously. 



e. Work. — This operates both in respect of its amount, or 

 its amount in relation to other conditions of health and adapta- 

 bility; and when thus operating, may do so both constitution- 

 ally and locally, more often in the latter direction. 



/. Defective Sanitary Conditions. — Of these the chief are 

 defective ventilation, imperfect light, bad drainage, and want 

 of cleanliness of body. 



g. Mechanical Causes. — Under this head may be placed im- 

 properly fitting harness, continued pressure from other external 

 objects, bad shoeing, all probably operating in inducing local 

 injury rather than direct constitutional disease. 



Besides these, there are other causes which operate in 

 inducing altered states of healthy activities, and which usually 

 act in a definite and determmate manner. A large class of 

 these are the so-called poisons, mineral and vegetable ; but in 

 addition there are others not usually ranked as such. These 

 •latter may be roughly grouped : 1st, as originating within the 

 animal itself, developed within the organism through faulty 

 digestion and perversion of assimilation ; 2nd, agencies con- 

 nected with the vegetable kingdom, as parasitic plants de- 

 veloped in both external and internal parts of the body ; 

 3rd, such as belong truly to the animal kingdom, including 

 (a) all poisons of a purely animal material, (h) animal para- 



