EXTREME BREATHING CAPACITY 113 



to the law of the diffusion of gases. Those who are in the habit of 

 arresting respiration for a time, learn to change the reserve air as com- 

 pletely as possible by several forcible acts and then fill the lungs with 

 fresh air. In this way they are enabled to suspend the respiratory acts 

 for two or three minutes without much inconvenience. The introduc- 

 tion of fresh air with each inspiration and the constant diffusion which 

 is going on and by which the proper quantity of oxygen finds its way to 

 the air-cells give, in ordinary breathing, a composition to the air in the 

 deepest portions of the lungs, which insures constant aeration of the 

 blood. 



Tidal, or Ordinary Breathing Air. The volume of air changed in 

 the ordinary acts of respiration is subject to certain physiological varia.- 

 tions; and the respiratory movements, as regards their extent, are so 

 easily influenced, that care is necessary to avoid error in estimating the 

 volume of ordinary breathing air. As a mean of the results obtained by 

 Herbst and by Hutchinson, the average volume of breathing air, in a 

 man of ordinary stature, is twenty cubic inches (327. 7 cubic centimeters). 

 According to Hutchinson, in perfect repose, when the respiratory move- 

 ments are hardly perceptible, not more than seven to twelve cubic inches 

 ( 1 14.7 to 196.6 cubic centimeters) are changed ; while, under excitement, 

 the volume may be increased to seventy-seven cubic inches (1261.8 

 cubic centimeters). The breathing volume progressively increases in 

 proportion to the stature of the individual and bears no definite relation 

 to the apparent capacity of the chest (Herbst). 



Complemental A ir. The thorax may be so enlarged by an extreme 

 inspiratory effort as to contain a quantity of air much larger than after 

 an ordinary inspiration. The additional volume of air thus taken in may 

 be estimated by measuring all the air that can be expelled from the 

 lungs after the most profound inspiration, and deducting the sum of the 

 reserve air and breathing air. This quantity has been found by Hutch- 

 inson to vary in different individuals, bearing a close relation to stature. 

 The mean complemental volume is one hundred and ten cubic inches 

 (1802.9 cubic centimeters). 



The complemental air is drawn upon whenever an effort is made 

 which requires a temporary arrest of respiration. Brief and violent 

 muscular exertion usually is preceded by a profound inspiration. In 

 sleep, as the volume of breathing air is somewhat increased, the comple- 

 mental air is encroached upon. A part or all of the complemental air 

 also is used in certain vocal efforts, in blowing, in yawning, in the deep 

 inspiration which precedes sneezing, in straining etc. 



Extreme Breathing Capacity. By the extreme breathing capacity 

 is meant the volume of air that can be expelled from the lungs by the 



