2i 4 RESPIRATION. 



varies much according to different circumstances, such as 

 exercise or rest, health or disease, etc. Variations in the 

 number of respirations correspond ordinarily with similar 

 variations in the pulsations of the heart. In health the 

 proportion is about i to 4, or i to 5, and when the rapidity 

 of the heart's action is increased, that of the chest move- 

 ment is commonly increased also; but not. in every case 

 in equal proportion. It happens occasionally in disease, 

 especially of the lungs or air- passages, that the number of 

 respiratory acts increases in quicker proportion than the 

 beats of the pulse ; and, in other affections, much more 

 commonly, that the number of the pulses is greater in pro- 

 portion than that of the respirations. 



According to Mr. Hutchinson, the force with which the 

 inspiratory muscles are capable of acting, is greatest in 

 individuals 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 mer- 

 cury. The force manifested in the strongest expiratory acts 

 is, oh 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. 



The following table expresses the result of numerous 

 experiments by Mr. Hutchinson on this subject, the instru- 

 ment used to gauge the inspiratory and expiratory power 

 being a haemadynamometer (see p. 164), to which was 

 attached a tube fitting the nostrils, and through which the 

 inspiratory or expiratory effort was made : 



