THE RESPIRATORY SYSTEM Itf 



in old age. The weight of the lungs is about 42 ounces, 

 the right lung being 2 ounces heavier than the left. 



The lungs, like the other organs, are supplied with nerves 

 and vessels for their nutrition and support. 



Respiration. The respiration in health is free, easy, 

 and noiseless. The number of respirations a minute 



FIG. 71. Larynx, trachea, and bronchi (Morrowj. 



varies, averaging about 35 during the first year of life, 

 25 during the second, 20 at puberty, and 18 in the adult. 

 The air which is contained in the pulmonary lobules and 

 vesicles, being used for the purpose of arterializing the 

 blood, becomes rapidly vitiated in the process of respira- 



