132 RESPIRATION RESPIRATORY MOVEMENTS. 



More or less of the reserve air is changed whenever there is a necessity for 

 a more complete renovation of the contents of the lungs than ordinary. It is 

 encroached upon in the unusually profound inspiration and expiration which 

 occur once in every five to eight acts. It is used in certain prolonged vocal 

 efforts, in blowing etc. Added to the residual air, it constitutes the mini- 

 mum capacity of the lungs in ordinary respiration. As it is continually re- 

 ceiving watery vapor and carbon dioxide, it is always more or less vitiated, 

 and when reenforced by the breathing air, which enters with inspiration, is 

 continually in circulation, in obedience 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 completely as possible by several forcible acts and 

 then fill the lungs with fresh air. In this way they are enabled to sus- 

 pend the respiratory acts for two or three minutes without inconvenience. 

 The introduction of fresh air with each inspiration, and the constant 

 diffusion which is going on arid 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 a constant aeration of the 

 blood. 



Tidal, or Ordinary Breathing Air. The volume of air which is 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 great care is necessary to avoid error in estimating the vol- 

 ume 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 c.c.). According to Hutchin- 

 son, in perfect repose, when the respiratory movements are hardly perceptible, 

 not more than seven to twelve cubic inches (114*7 to 196-6 c.c.) are changed ; 

 while, under excitement, the volume may be increased to seventy-seven cubic 

 inches (1,261-8 c.c.). The breathing volume progressively increases in pro- 

 portion to the stature of the individual, and bears no definite relation to the 

 apparent capacity of the chest (Herbst). 



Complemental Air. The thorax may be so enlarged by an extreme vol- 

 untary 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 which 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 Hutchinson 

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

 mean complemental volume is one hundred and ten cubic inches (1,802-9 c. c.). 



The complemental air is drawn upon whenever an effort is made which 

 requires a temporary arrest of respiration. Brief and violent muscular exer- 

 tion is generally preceded by a profound inspiration. In sleep, as the vol- 

 ume of breathing air is somewhat increased, the complemental air is en- 

 croached upon. A part or the whole of the complemental air is also used in 

 certain vocal efforts, in blowing, in yawning, in the deep inspiration which 

 precedes sneezing, in straining etc. 



