A STUDY OF RESPIRATION 221 



3. CHANGES IN AIR AND BLOOD DUE TO 



Temperature of Inspired and of Expired Air. The tem- 

 perature of a room in which we are living and working 

 should be kept as near to 68 F. as possible. Under these 

 conditions the air that enters the body is about 30 cooler 

 than the normal temperature within the body (98 J F.). 

 Let one breathe upon the bulb of a thermometer, however, 

 and the mercury soon registers over 90 F. (some heat being 

 lost to the surrounding air). This means that the air is 

 heated to a considerable extent within the body, and to do 

 this the body must give up a corresponding amount of heat. 



Composition of Inspired and of Expired Air. The air that 

 enters the lungs consists of about one fifth oxygen and four 

 fifths nitrogen. The latter is of no use to the body, and 

 practically all of it is sent forth in expired air. About one 

 fourth of the oxygen of fresh inspired air is taken up by 

 the blood for use in the tissues (one and four fifths pounds 

 each day). 



By the simple experiments suggested on p. 210, we dem- 

 onstrated that the air coming out of the lungs contains 

 considerable quantities of water and carbon dioxid. In 

 twenty-four hours the body rids itself by this means of 

 over half a pound (more than a half pint) of water, and of 

 something less than two pounds (422 quarts) of carbon 

 dioxid gas. 



At the same time, the air that leaves the lungs carries 

 with it minute quantities of ill-smelling, poisonous organic 

 compounds. It is the latter that give the smell of closeness 

 to an occupied room that is poorly ventilated, and these 

 make expired air unwholesome and dangerous. 



Changes in the Blood while passing through the Lungs -- 

 Whatever the expired air has gained in the lungs is, of 

 course, lost by the blood; the blood also takes in the 

 ingredients given up by inspired air. The change of color 



i See "Laboratory Exercises," No. 40. 



