Internal Respiration. 109 



air. 5. Both give off gases, consisting mainly of carbon 

 dioxid and water vapor. 



How the Body differs from a Locomotive : i . The body 

 does not get hot enough to burn ; i.e. the oxidation is 

 relatively slow, and is not combustion. 2. The oxidation 

 of the body never produces light. 3. The oxidation in the 

 body is always in the presence of moisture. 



The Amount of Carbon Dioxid given off. When the 

 breath is held for some time, the carbon dioxid in the 

 expired air may reach 7 or 8 per cent. During violent 

 exercise the amount of carbon dioxid given off may be 

 more than twice as much as when we are at rest. In 

 ordinary respiration there is one hundred times as much 

 carbon dioxid in the air we breathe out as there was when 

 it was taken in. Oxygen is carried chiefly in the cor- 

 puscles, but the carbon dioxid is carried in both plasma 

 and corpuscles. 



Effect of Re-breathing Air. Every one knows how 

 unpleasant it is to breathe the air of a close room where 

 many people are present. In many persons such air 

 causes headache and drowsiness. This effect is not due 

 to the reduced amount of oxygen, nor is it due to the 

 increase of carbon dioxid. It is believed to be due to 

 the " organic impurities" which are thrown out in the 

 expired breath. It is this matter that gives the offensive 

 odor to a room which is kept close and warm after a crowd 

 has been in it. If in a crowded lecture room you divide 

 the space by the number of people present, you find that 

 each one has really very little room. In such rooms 

 special attention to ventilation is necessary, or great injury 

 will be done. When we learn how many cases of lung 



