66 Veterinary Elements. 



the one gas for the other. Here then we have in a nut- 

 shell the reasons for ventilation: (1) to remove impure 

 air and (2) fetch in pure air, and by carrying out these 

 two important things give (3) the means of warmth to 

 the animal. 



The processes of taking in food, using it and discharg- 

 ing the waste, have been described, there remains, how- 

 ever, the consideration of the respiratory (breathing) 

 organs dual-purpose in character because, as intimated 

 above, not only do they remove the waste poisonous gas 

 (carbon di-oxide), but also are the means by which that 

 valuable gas oxygen, without which no animal life can 

 exist, is brought into the system. 



The Organs of Respiration. The organs going to make 

 the respiratory system are the nostrils, nasal cavities, 

 pharynx, larynx, trachea, bronchi, bronchial tubes and 

 lungs. The nostrils are situated at the anterior extremity 

 of the nasal chambers, they are made up of cartilages, 

 which are dilated by muscles, and lined by mucous mem- 

 brane. At the upper part of the nostrils are two blind 

 pockets, called false nostrils; just inside the nostrils are 

 small openings, the point of exit of tears, brought from 

 the eyes by the lachrymal duct. A large nostril is much 

 desired, as the nostrils control the amount of air taken 

 in. The nasal chambers are two cavities separated by a 

 piece of cartilage (gristle), the septum nasi, in each cav- 

 ity are thin delicate curled bony plates, the turbinated 

 bones, covered with mucous membrane, which is thin 

 and contains delicate blood vessels, consequently the air 

 is warmed as it passes over these bony plates before 

 being taken into the lungs. Fine nerves, constituting the 



