486 PULMONARY CONGESTION. 



and prolonged exertion. The muscular system must by steady 

 and at first slow work be gradually accommodated to exertion, 

 while in the developing of the muscular power, properly so 

 called, botli the respiratory and circulatory systems become 

 strengthened and rendered capable of performing their work 

 under the exacting conditions of rapidity and continued 

 duration. Unless these points are attended to, no horse, how- 

 ever good in health, and in however high spirits, can be ex- 

 pected to perform an ordinary day's work at an average horse's 

 pace, far less such severe and sustained exertion as we require 

 in the hunting-field, without the risk of pulmonary conges- 

 tion. 



In horses of any class this may occur wlien put to severe 

 exertion or prolonged Avork, for which they are unprepared by 

 a certain amount of previous work and by proper feeding. It 

 is common in horses brought from dealers' stables, when suffi- 

 cient care is not exercised in putting them to the work for 

 which they may be intended. 



In the same way, animals suffering from catarrh, or only 

 recently recovered from some respiratory disturbance, are 

 more susceptible of an attack of pulmonary hypera3mia than 

 others. 



Instances, also, may be encountered in cases of collapse of 

 lung-structure from pressure by fluid contained in the pleural 

 sac, on the sudden removal of this fluid by operative inter- 

 ference. 



Further, pulmonary congestion may occur without direct 

 over-exertion in cases where horses are confined to defectively 

 ventilated stables after having undergone active exertion in 

 the open air ; this is apparently from a deficiency of respirable 

 air and consequent non-oxygenation of the blood. 



Whenever the amount of oxygen or carbonic acid in the 

 blood, or the relationships which ought to subsist between 

 these, are permanently disturbed, the consequences are either 

 asphyxia or apnoea : asphyxia, when the Avant of oxygen is 

 very marked, and the irritability of the nerve-centres, which 

 require for their functional activity so much oxygen, cease ; 

 apncea, when the blood is too rich in oxygen and poor in car- 

 bonic acid, respiration becoming arrested because of the want 

 of the normal excitant of the respiratory centre. 



