EXTREME BREATHING CAPACITY. 137 



inson, in perfect repose, when the respiratory movements are hardly perceptible, not 

 more than from seven to twelve cubic inches are changed ; while, under excitement, he 

 has seen the volume increased to seventy-seven cubic inches. Of course the latter is 

 temporary. Herbst noted that the breathing volume is constantly increased in pro- 

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

 capacity of the chest. 



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

 spiratory effort as to contain a quantity of air much larger than after an ordinary in- 

 spiration. 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. 



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

 temporary arrest of respiration. Brief and violent muscular exertion is generally pre- 

 ceded by a profound inspiration. In sleep, as the volume of breathing air is somewhat 

 increased, the complemental air is encroached upon. A part or the whole of the com- 

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

 inspiration which precedes sneezing, in straining, etc. 



Summary. In a healthy male of medium stature, the residual air, which cannot be 

 expelled from the lungs, amounts to about one hundred cubic inches. 



The reserve air, which can be expelled but which is not changed in ordinary respi- 

 ration, amounts to about one hundred cubic inches. 



The tidal air, which is changed in ordinary respiration, amounts to about twenty 

 cubic inches. 



The complemental air, which may be taken into the lungs after the completion of an 

 ordinary act of inspiration, amounts to about one hundred and ten cubic inches. 



Extreme Breathing Capacity. By the extreme breathing capacity is meant the vol- 

 ume of air which can be expelled from the lungs by the most forcible expiration, after 

 the most profound inspiration. This has been called by Dr. Hutchinson the vital capa- 

 city, as signifying " the volume of air which can be displaced by living movements." 

 Its volume is equal to the sum of the reserve air, the breathing air, and the complemental 

 air, and represents the extreme capacity of the chest, deducting the residual air. Its 

 physiological interest is due to the fact that it can readily be determined by an appro- 

 priate apparatus, the spirometer, and comparisons can thus be made between different 

 individuals, both healthy and diseased. The number of observations on this point made 

 by Dr. Hutchinson is enormous, amounting in all to little short of five thousand. 



The extreme breathing capacity in health is subject to variations which have been 

 shown to bear a very close relation to the stature of the individual. Hutchinson com- 

 mences with the proposition that, in a man of medium height (five feet eight inches), it 

 is equal to two hundred and thirty cubic inches. He has shown that the extreme breath- 

 ing capacity is constant in the same individual, and that it is not to be increased by habit 

 or practice. 



The most striking result of the experiments of Dr. Hutchinson, with regard to the 

 modifications of the vital capacity, is that it bears a definite relation to stature, without 

 being affected in a very marked degree by weight or the circumference of the chest. 

 This is especially remarkable, as it is well known that height does not depend so much 

 upon the length of the body as upon the length of the lower extremities. 



It has been ascertained that for every inch in height, between five and six feet, the 

 extreme breathing capacity is increased eight cubic inches. 



