254 TiMEHRI. 



shown that respiration is carried on by the lungs for the 

 great part, and to a lesser extent, but still one of great 

 importance, by the skin. In ordinary lung respiration 

 the oxygen is taken from the air in exchange for 

 the carbonic acid added to it with a trace of nitrogen, 

 ammonia, a large quantity of water and other bodies. 

 This is the exa6l analysis. 



Unrespired dry A ir. Expired A ir. 

 Oxygen ... 20*94 1 6*033 



Nitrogen ... 79*02 79*02 



Carbonic Acid... '04 3-'^ to 5.5 



Ammonia, a trace. 



Water. 

 Organic matter. 

 This interchange of gases goes on continuously, and in 

 24 hours amounts to the consumption of 744 grammes of 

 oxygen and the excretion of 900 grammes of carbonic 

 acid which measures from twelve to sixteen cubic feet 

 (at ordinary pressure and temperature) of gas per diem 

 or '6 cubic feet added to the air per hour. Males from 

 eight years onwards to old age, give off more carbonic acid 

 than females, and as might be expefted from a study of 

 chemistry, muscular and energetic persons use more 

 oxygen than the less a6live. The amount of carbonic 

 acid gas excreted during sleep is diminished by about a 

 fourth and it is stated the quantity of oxygen consumed 

 is increased ; but this is open to question. 



The excretion of water varies a good deal, amounting 

 from the lungs and skin together to as much as from 25 

 to 40 ounces in 24 hours. It is subje6l to great varia- 

 tion depending on the work done and the temperature 

 of the surrounding medium. 



