RESPIRATION. I 9 1 



(representing its loss of heat) is 100 times that of the small one, while its 

 bulk (representing production of heat) is about 1000 times as great. 

 Thus in order to balance its much greater relative loss of heat, the smaller 

 animal must v have all its vital functions, circulation, respiration, etc., 

 carried on much more rapidly. 



Force of Inspiratory and Expiratory Muscles. The force with 

 which the inspiratory muscles are capable of acting is greatest in individ- 

 uals of the height of from five feet seven inches to five feet eight inches,, 

 and will elevate a column of three inches of mercury. Above this height, 

 the force decreases as the stature increases; so that the average of men 

 of six feet can elevate only about two and a half inches of mercury. The 

 force manifested in the strongest expiratory acts is, on the average, one- 

 third greater than that exercised in inspiration. But this difference is 

 in u'reat measure due to the power exerted by the elastic reaction of the 

 walls of the chest; and it is also much influenced by the disproportionate 

 strength which the expiratory muscles attain, from their being called into 

 use for other purposes than that of simple expiration. The force of the 

 inspiratory act is, therefore, better adapted than that of the expiratory for 

 testing the muscular strength of the body. (John Hutchinson.) 



The instrument used by Hutchinson to gauge the inspiratory and ex- 

 piratory power was a mercurial manometer, to which was attached a tube 

 fitting the nostrils, and through which the inspiratory or expiratory 

 effort was made. The following table represents the results of numerous 

 experiments: 



Power of Power of 



Inspiratory Muscles. Expiratory Muscles. 



1-5 in. Weak 2'0 in. 



2-0 



3-5 

 4-5 

 5-5 



6-0 



7-0 



Ordinary . . 2'5 



Strong . . . 3'5 



Very strong . .4*5 



Kemarkable . . 5'8 



Very remarkable . 7*0 



Extraordinary . 8 '5 



Very extraordinary . 10 '0 



. . 



The greater part of the force exerted in deep inspiration is employed 

 in overcoming the resistance offered by the elasticity of the walls of the 

 chest and of the lungs. 



The amount of this elastic resistance was estimated by observing the 

 elevation of a column of mercury raised by the return of air forced, after 

 death, into the lungs, in quantity equal to the known capacity of respira- 

 tion during life; and Hutchinson calculated, according to the well-known 

 hydrostatic law of equality of pressures (as shown in the Bramah press), 

 that the total force to be overcome by the muscles in the act of inspiring 

 ;200 cubic inches of air is more than 450 Ibs. 



