VITAL CAPACITY 



345 



into the respiratory chambers at each ordinary quiet inspiration, 

 and somewhat less than this amount is expelled at each expiration. 

 One may say, in round numbers, that the tidal air of the average 

 adult is about 500 c.c. The tidal air at various ages and weights 

 is given below (Table L.) : 



TABLE L 



Age. 



0-6 months. 

 6-12 months. 

 3- 7 years. 

 8-14 years. 

 Adult. 



48 



85-130 

 124-220 

 220-400 

 300-550 



If a very deep inspiration is taken, more than 500 c.c. can be 

 sucked into the lungs. This extra quantity, which varies with 

 the " build " and expertness of the subject, but which usually is 

 about three times the tidal volume, is called the complemental air. 

 By a forced expiration after a normal expiration the reserve air 

 may be expelled from the lungs. The volume so expelled varies 

 very much, and may markedly be increased by practice. Some 

 people can breathe out only an additional 500 to 700 c.c, while 

 singers, physical training experts and others who practise abdomino- 

 thoracic breathing, may register a volume of 1,500 to 2,500 c.c. 

 These three quantities together give the vital capacity of an 

 individual, i.e. the amount of air that a person can expire after a 

 deep inspiration. It is not possible completely to empty the lungs. 

 As we shall see later, a mechanism exists in the air vesicles which 

 prevents their total collapse. They retain about a litre of air — the 

 residual air. 



To summarise, taking average figures : 



Vital capacity 



Residual air 



Tidal air 



Complemental air 

 Reserve air 



500 c.c. 

 1,500 c.c. 

 1,500 c.c. 



3,500 c.c. 

 1,000 c.c. 



Volume of fully distended respiratory apparatus . 4,500 c.c. 



This volume of 4,500 c.c. includes not only the volume of the 

 lungs but of the approaches to the lungs — the nasal cavity, 

 the trachea, the bronchi and the bronchioles. These constitute the 



