222 HEALTH AND DISEASE 



temperature, poverty of blood, irritation of the mucous membrane of 

 the stomach, sometimes solution of the walls of the organs by the 

 action of the gastric juice, fever and delirium — in short the ordinary 

 indications of starvation. This condition is, of course, extremely rare 

 in relation to horses, excepting as the result of accident or the presence 

 of .some disease in the mouth or swallow which prevents the animal 

 from taking food. 



Excessive exertion has already been considered among the predispos- 

 ing causes, and in order to become an exciting cause it must be pushed to 

 such an extent as to induce acute congestion of the vessels of the lungs or 

 brain or some other organ, a condition which will be quickly followed by 

 interference with the action of the heart and total stagnation of the cir- 

 culation. Short of this condition, which will necessarily be fatal, congestion 

 of the important organs referred to may be followed by inflammation, 

 which, though not necessarily fatal in its effects, is not unlikely to leave 

 serious structural changes in the parts which are affected. The other 

 exciting causes of disease of a cognizable kind are nervous excitement, 

 excessive or defective secretion, impure atmosphere, and climatic changes. 

 The action of all these has been described under the head of predisposing 

 causes of disease. It is easy to understand that they all of them become 

 exciting causes when pushed to an extreme. Thus, violent nervous 

 excitement may result in a fatal shock, or it may induce an attack of 

 apoplexy. Excessive secretion may under certain circumstances cause 

 fatal syncope; while deficient secretion not only impairs the function of 

 the organ for which it was intended, but leads to the accumulation of 

 poisonous matters in the system, which, if not immediately fatal, may 

 lead to serious organic disease. Defective ventilation, uncleanliness, 

 and drainage leading to the accumulation of large quantities of septic 

 matter in the air may occasion rapidly fatal septic poisoning or various 

 forms of disease, which may be commonly classed as low fevers presenting 

 all the indications of typhoid. Climatic changes involving sudden 

 transitions from cold to heat not only render the system liable to various 

 disorders, but are also capable of immediately producing affections of 

 the respiratory system from simple catarrh to bronchitis and pneumonia, 

 in addition to internal congestion of other important organs. The 

 immediate effect of extreme cold is rapidly to reduce the vital powers; 

 the action of heat, on the other hand, tends to cause internal congestion 

 of the liver and other organs, and even extreme congestion of the brain, 

 which may be fatal. 



Specific causes Of disease relate to all those maladies which only 

 occur under the influence of a particular virus or poison. It has been 



