216 STUDIES IN ADVANCED PHYSIOLOGY. 



In addition to these gases there was recently discovered 

 another gas resembling nitrogen in some of its properties, 

 and called "Argon" by its discoverer, but as this gas does 

 not figure in the processes of respiration a consideration of 

 it may be for our purposes omitted. 



If now with such inspired air we compare expired air, 

 we find that a number of changes have occurred in the 

 lungs. First, the expired air is warmer, due to its having 

 remained for some time in the warm lung. Second, as a 

 consequence of this increase in temperature it has expanded 

 slightly in volume, so that the expired air seems at first a 

 little larger than inspired air, and for this reason it tends 

 to rise. However, when expired air is reduced to the same 

 temperature and pressure as the inspired air, it is found to 

 be a little less in volume, showing that a part of the air has 

 actually been taken into the body and kept there. Third, ex- 

 pired air contains a much larger amount of moisture. This 

 is especially evident on a cold day when the breath, as we 

 say, becomes visible, due to the condensation of the large 

 amount of moisture in it. So far the changes are merely 

 physical changes. There is, however, fourth, quite a dif- 

 ference in the chemical composition of the two. The ex- 

 pired air has lost five per cent, of oxygen and gained about 

 four per cent, of carbon dioxide, and finally, fifth, the 

 expired air contains traces of volatile organic substances, 

 and possibly particles of disintegrated tissue to which the 

 vitiation of respired air is due. 



It requires special chemical experiments to show that 

 five parts of the twenty parts of oxygen have been removed. 

 On the other hand, the addition of the four parts of carbon 

 dioxide to expired air may be easily shown in a very simple 

 experiment. If a person breathe, by means of a glass tube, 

 "through a flask or bottle containing lime-water, the carbon 

 dioxide will unite with the lime-water, and a white precipi- 

 tate will form insoluble in the water which soon settles to 

 the bottom. 



