RESPIRATION 127 



and deeper until a maximum is reached, after which they 

 gradually become shallow again. The intervals between the 

 groups last from thirty to forty-five seconds. The time ratio 

 of inspiration to expiration may be put at 5 to 6. In infants 

 the ratio is 1 to 2 or 3. The rate of respiration varies with 

 the most diverse internal and external conditions. In the 

 normal adult the rate is about 18 cycles a minute when the 

 body is in repose. The ratio to the pulse rate may be put 

 at 1 to 4. During quiet respiration the inflow and outflow 

 of air, which amounts to about 500 c.c., is known as the tidal 

 air. The volume of expired air, owing to its increased tempera- 

 ture, is greater than that inspired, but the actual quantity 

 is less. Complemental air (about 1500 c.c.) is the .amount 

 that can be inspired after an ordinary inspiration. The supple- 

 mental or reserve air (about 1500 c.c.) is the amount that can 

 be expelled after an ordinary expiration. Residual air is the 

 volume that remains in the lungs after the most forcible expira- 

 tion (1500 c.c.). Vital capacity is equal to the sum of the 

 complemental, tidal, and supplemental air. Stationary air 

 is the amount that remains after the ordinary expiration, 

 and is equal to the sum of the reserve and the residual air. 

 The lung capacity is the total quantity of air that can be held 

 after the most forcible inspiration, and is equal to the sum of 

 the vital capacity and residual air (4500 c.c.). 



It may easily be calculated that man, in twenty-four hours, 

 respires about 10,800 liters of air, which is equal to a space 

 eight feet in three dimensions. The air, thus breathed, should 

 be kept as nearly as possible of the composition of the atmos- 

 phere outside. The relative purity of room air may be most 

 easily judged by a quantitative determination of carbon 

 dioxide. Ordinary air contains 4 parts per 10,000. Ventila- 

 tion should be sufficient to keep the carbon dioxide down to 

 6 parts per 10,000, giving a permissible degree of vitiation of 

 0.02 volume per cent. On this basis the air necessary for 



each person can be determined from the formula d = -, in 



r 



which d represents in liters the delivery of fresh air per 

 hour; e, the carbon dioxide expired per hour in liters; and r, 

 the ratio of permissible vitiation. The value of d, then, is 

 equal to 100,000 liters of air per hour for each person. The 



