186 HANDBOOK OF PHYSIOLOGY. 



such as the elephant (eight or nine times per minute). These facts may 

 be explained as follows : The heat-producing power of any given animal 

 depends largely on its bulk, while its loss of heat depends to a great ex- 

 tent upon the surface area of its body. If of two animals of similar 

 shape, one be ten times as long as the other, the area of the large animal 

 (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 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 indivi- 

 duals 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 great measure due to the power exerted by the elastic reaction of 

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

 tionate 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 Hut- 

 chinson. ) 



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 ef- 

 fort 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 " . . Ordinary, . . 2,5 " 



2.5 " . . . Strong, . . . 3.5 " 



3.5" . . Very strong, . 4.5" 



4.5 " . . . Eemarkable, . . 5.8 " 



5.5 " . . Very remarkable, 7.0 " 



6.0 " . . . Extraordinary, . 8.5 " 



7.0" . . 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 res- 



