DR. LEGEAB'S STOCK BOOK. 19 



CHAPTER V. 

 ORGANS OF RESPIRATION (BREATHING). 



The principal organs of breathing are the nostrils, nasal cham- 

 bers, larynx, windpipe, and the lungs. Owing to the large size 

 of a horse's soft palate, he can not breathe through his 

 mouth, but must breathe through his nostrils entirely. The 

 mucous membrane lining the nostrils and the chambers in 

 a horse's head is very delicate and sensitive, and by a 

 horse breathing through his nostrils exclusively explains why a 

 horse catches cold, distemper, etc., so easily. The larynx is situ- 

 ated in the throat, and is the entrance to the windpipe. It be- 

 comes affected in the d:\sease called roaring. The windpipe is 

 the tube that conveys the air from the larynx to the lungs. It 

 can be felt plainly in the front of a horse's neck. The lungs are 

 the principal organs of breathing. They consist of two light, 

 soft, spongy masses, one on either side, commonly called the 

 "lights," being situated entirely in the cavity of the chest. On 

 the outside, the lungs are completely covered by a thin, shining 

 membrane, called the pleura, which also lines the chest cavity. 

 The healthy lungs of any animal, after birth, will float on wa- 

 ter, but will not before birth. It is in the lungs that the blood is 

 purified the oxygen in the pure air that the animal breathes 

 comes in contact, as it were, with the impurities in the blood, 

 burning it up, and converts it into a substance called carbon 

 dioxide, which is thrown off from the lungs as a poisonous gas. 



