ELEMENTS OF EIPPOLOQY. 155 



CHAPTER XIII. 



THE HEART, LUNGS, AND AIR-PASSAGES. 



The heart is the organ by which the blood is circulated 

 through the body. It hangs a little to the left of the center of 

 the forward part of the chest, suspended from the vertebra; of 

 the withers, the small end downwards. Its average weight is 

 from seven to eight pounds. 



The heart is of interest to the amateur horseman because of 

 the influence disease has on its action. In health, the heart of 

 the ordinary horse pulsates from thirty-five to forty times a 

 minute; the thoroughbred horse, from forty to forty-five. These 

 pulsations of the heart send the blood through the arterial 

 system in a series of waves, each wave corresponding to one 

 pulsation of the heart. These waves constitute what is called 

 the pulse, and it is by counting the pulse and by observation of 

 the relative strength and frequency of the waves of the pulse 

 that the heart-action of the horse is verified. 



It must be understood that the number of pulsations above 

 noted is for the animal at rest, or when not undergoing any 

 special exertion. The pulse will become higher during exertion, 

 the amount of the increase depending on the extent of the ex- 

 ertion. The pulse will be higher in horses kept in fine condition, 

 in warm stables, and fed on selected forage, than in animals 

 more roughly stabled and fed. It is higher in young horses 

 than in old ones. Fear or excitement also tend to augment 

 the pulse. 



When the animal is at rest, a pulse of from 50 to 55 indi- 

 cates a feverish condition, the cause of which should be inves- 

 tigated. From 70 to 75 beats a minute indicates a very serious 

 condition, demandingorompt and energetic action. 



