DISEASES OF RESPIRATORY PASSAGES AND ORGANS. 



39 



twelve per minute, varying, however, according to the tempera- 

 ment of the animal and the condition he may be in at the time 

 of making the observation ; while in horses the respirations are 

 more frequent, varying in health, and when at rest, from fourteen 

 to twenty-five ; yet, under excitement and disease, they sometimes 

 number over one hundred. 



THE CONTENTS OF THE THOBAX. 



HULahatioh.— Fig. 1, Trachea ; 2, Bifurcation of the carotid artery ; 3, Internal carotid artery ; 

 4 4, Anterior lobes of the lungs: 5 5 Posterior lobes of the lungs; 6, The heart; 7, Coronary 

 artery; 8, Cartilages of the false ribs; 9, The diaphragm. 



When an animal is located in a pure atmosphere, and the 

 lungs are in good working condition, all the impurities contained 

 in venous blood are brought into the presence of oxygen through 

 the lining membrane of the air-cells, and thus a change in the 

 color and character of the blood is immediatelv effected. In the 

 irist place, the venous blood, as it appeared before having been 

 submitted to the action of the atmosphere, was of a dark purple 



