EXTREME BREATHING CAPACITY. 403 



Extreme Breathing Capacity. By the extreme breathing 

 capacity is meant the volume 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. Hutchin- 

 son the vital capacity, 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 appropriate apparatus, the spirometer, 1 and compari- 

 sons 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 rela- 

 tion to the stature of the individual. Hutchinson com- 

 mences with the proposition that in a man of medium height 

 (5 feet 8 inches], it is equal to two hundred and thirty cubic 

 inches. He has shown that the extreme breathing 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 ca- 



The tidal or breathing air, he estimates at 30 cubic inches. 



The observations of Dr. Grehant are as yet so few in number that we prefer 

 to adhere to the results of the greatly extended observations of Hutchinson ; 

 though the new method is very ingenious, and further experiments will probably 

 lead to important results. 



1 The spirometer consists of a vessel containing water, out of which a receiver 

 is raised by breathing into it through a tube ; the height to which the receiver is 

 raised indicating the volume of the vital capacity (Cyclop, of Anat. and Phys., 

 vol. iv., part 2, p. 1068). In all the observations of Dr. Hutchinson, he has taken 

 care to see that the level of the water was the same in the receiver and the reser- 

 voir, and to carefully correct the volumes of air for temperature. All observa- 

 tions were made with the subject erect, and every thing carefully avoided which 

 could interfere with the free action of the respiratory muscles. 



