Internal Respiration. 107 



when it is at work. The more rapid stream brings the 

 muscle more oxygen. This it needs, for it is by the oxida- 

 tion of the muscle (or substance in it) that the muscle 

 produces heat and motion. The oxidation in our tissues is 

 a slow oxidation, more like the rusting of iron than the 

 burning of a candle. Oxidation in our bodies never pro- 

 duces a high degree of heat and never produces light. 



Increased Blood Flow is the Result of Exercise. When 

 we exercise, the muscles need more oxygen. They also 

 need to have removed the waste matters that they are so 

 rapidly producing at this time. How is the oxygen brought 

 and the waste removed ? By the blood, you answer. True ; 

 but what makes the blood come and go faster at this time ? 

 By reflex action, you reply. The muscles send a message 

 to a nerve center, and this nerve center sends back a mes- 

 sage to the blood tubes, making them widen, and the heart 

 also may be made to beat faster. 



Increased Respiration from Exorcise. But would it do 

 any good to have the blood flow through the muscles faster, 

 if it could not bring more oxygen, and take away and get 

 rid of more wastes ? You will say no. To give the extra 

 oxygen and take out the carbon dioxid, the lungs cannot, 

 of themselves, take in and send out air. The work of 

 pumping air depends on the muscles of respiration, the 

 diaphragm, and the muscles that elevate the ribs. These 

 muscles will not work faster unless they are ordered to do 

 so. A message must be sent to them telling of the need. 

 Thus, by a series of reflex actions, all these processes are 

 kept in close relation to each other. It must be borne in 

 mind that increased blood flow is the result, and not the 

 cause, of the increased activity of the tissues. 



Temperature of the Body. Insert the bulb of a thermometer into 

 the mouth, and keep it there three or four minutes to find the tempera- 



