4:00 RESPIRATION. 



which are changed in any of the operations connected with 

 breathing. 



Reserve Air. This name is appropriately given to the 

 volume of air which may be expelled and changed by a vol- 

 untary effort, but which remains in the lungs, added to the 

 residual air, after an ordinary act of expiration. It may be 

 estimated, without any reference to the residual air, by for- 

 cibly expelling air from the lungs, after an ordinary expira- 

 tion. The average volume is 100 cubic inches. 1 



The reserve air is changed whenever we experience a 

 necessity for a more complete renovation of the contents of 

 the lungs than ordinary. It is encroached upon in the unu- 

 sually profound inspiration and expiration which occur every 

 five or six acts. It is used in certain prolonged vocal efforts, 

 in blowing, etc. 



Added to the residual air, it constitutes the minimum 

 capacity of the lungs in ordinary respiration. As it is con- 

 tinually receiving watery vapor and carbonic acid, it is always 

 more or less vitiated ; and when reenforced by the breathing 

 air, which enters with inspiration, is continually in circulation, 

 in obedience to the law of the diffusion of gases. Those who 

 are in the habit of arresting respiration for a time, as the 

 pearl-diver, learn to change the reserve air as completely as 

 possible by several forcible acts, and then fill the lungs with 

 fresh air. In this way they are enabled to suspend the re- 

 spiratory acts for from one to two minutes without inconven- 

 ience. The introduction of the fresh air with each inspira- 

 tion, and the constant diffusion which is going on, and by 

 Svhich the proper quantity of oxygen finds its way to the air- 

 cells, gives, in ordinary breathing, a composition to the air 

 in the deepest portions of the lungs which insures a constant 

 aeration of the blood. The slight difference in the rapidity 

 of oxidation between inspiration and expiration is only suffi- 

 cient to give rise to the involuntary reflex acts of respiration, 



1 HUTCHINSON, IOC. dt. 



