DISEASES OF THE EESPIRATORY ORGANS. 625 



increased and elevated, whereby it is enabled to pump an in- 

 creased supply of blood to all parts of the body, in order to 

 maintain their strength and integrity during the time they are 

 so greatly taxed. In fact, it may be said that the horse's respira- 

 tory organs — wind — circulation, and muscular action, are elevated 

 into a high state of functional perfection by careful training, 

 and a horse in this condition will perform during a long run 

 with the hounds or on the race-course, without danger to his 

 health and life. But if a horse that is not thus trained — not in 

 condition, no matter how good its health might be — is suddenly 

 put to severe and prolonged exertion, when neither its muscular, 

 pulmonary, nor circulatory systems are fit to undergo the fatigue 

 consequent thereon, it will be seen that, first of all, the breathing 

 becomes frequent and distressed ; the heart beats tumultuously, 

 but with little impulsive force ; the voluntary muscles, conse- 

 quent upon want of tone and exhaustion, obey the will im- 

 perfectly. It goes " all abroad," as the horseman says. The 

 breathing becomes more and more distressed, and at last it 

 falls, and perhaps dies from actual suffocation, consequent upon 

 the pulmonary vessels being overloaded with non-oxidized 

 blood ; and after death the lungs are found gorged with blood, 

 black in colour, and prone to rapid decomposition, giving origin 

 to the expression " black as your hat, and rotten as a pear," 

 and to the idea that the animal had suffered from some chronic 

 disease. In giving an opinion on a case of this kind, the 

 veterinarian must bear in mind that the blackness, tendency to 

 putrescence, or even deliquescent condition of the lung tissue, 

 are results of acuteness of attack, and not of any previous dis- 

 ease ; and it may always be accepted that mere engorgements 

 and blackness, without the formation of an exudate, are positive 

 evidence that the disease is not of long standing. 



Another cause of congestion of the lungs is actual want of air 

 in badly ventilated stables, the congestion here arising from the 

 stop-cock action of the pulmonary capillaries already described 

 — (see Death hy Siiffocation) — which contract, and prevent, as it 

 were, as much as possible the passage of impure blood into the 

 left side of the heart and systemic circulation. Pulmonary 

 apoplexy is also termed hcemorrhagic infarction, and, as ex- 

 plained by Dr. Yeo, is " universally admitted to depend on a 

 local impediment to the circulation, such as an embolus impacted 



2s 



