THE STORY OF THE LUNGS, SKIN AND KIDNEYS 77 



CHAPTER V 



THE STORY OF THE LUNGS, SKIN AND KIDNEYS 



THE WORK OF THE LUNGS. The function of breath- 

 ing, or respiration as it is also termed, is discharged 

 in the body with a double aim in view. Even a casual 

 study of our breathing movements reveals at once 

 the fact that by the one movement, inspiration or 

 breathing in, we inhale air from the atmosphere, and 

 by the succeeding and opposite movement of expira- 

 tion or breathing out, we exhale air from the lungs. 

 A very casual examination of the difference between 

 the air breathed in and that breathed out further 

 serves to show that the two movements represent two 

 distinct phases of the work of the lungs. We breathe 

 in atmospheric air, the composition of which will be 

 presently noted, whilst we breathe out in addition to 

 the air, somewhat altered in its composition, certain 

 other matters representing part of our bodily waste. 

 By inhaling air we supply the body with the oxygen 

 gas, which has already been noted to be essential for 

 all the processes of life, this gas being conveyed with 

 the pure blood circulated through the body to every 

 cell of the frame. On the other hand the matters 

 breathed out from the lungs include air which shows 

 a far larger proportion of carbonic acid gas than the 

 air breathed in, whilst the exhaled air is found like- 

 wise to be loaded with watery vapour and also to be 

 much warmer than the air which is inspired. We 

 thus learn in the first place regarding the duties of 



