168 RESPIRATION. 



that, for example, while a man of five feet six inches, and 

 weighing less than Hi stones, should be able to expire 217 

 cubic inches, one of the same height, weighing 12 stones, 

 might expire only 203 cubic inches. 



By age, the capacity appears to be increased from about the 

 fifteenth to the thirty-fifth year, at the rate of five cubic inches 

 per year; from thirty -five to sixty-five it diminishes at the 

 rate of about one and a half cubic inch per year ; so that the 

 capacity of respiration of a man of sixty years old would be 

 about 30 cubic inches less than that of a man forty years old, 

 of the same height and weight. 



Mr. Hutchinson's observations were made almost exclusively 

 on men ; and his conclusions are, perhaps, true of them alone ; 

 for women, according to Bourgery, have only half the capacity 

 of breathing that men of the same age have. 



The number of respirations in a healthy adult person usually 

 ranges from fourteen to eighteen per minute. 



It is greater in infancy and childhood ; and of course varies 

 much according to different circumstances, such as exercise or 

 rest, health or disease, &c. Variations in the number of res- 

 pirations correspond ordinarily with similar variations in the 

 pulsations of the heart. In health the proportion is about 

 one to four, or one to five, and when the rapidity of the heart's 

 action is increased, that of the chest movement 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 proportion than that of the respirations. 



According to Mr. Hutchinson, the force with which the in- 

 spiratory 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 stat- 

 ure 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 ex- 

 erted 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. 



