108 PHYSIOLOGY. 



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 message to the blood tubes, making 

 them widen, and the heart also may be made to beat 

 faster. But would it do any good to have the blood flow 

 through the muscles faster, if it could not bring more oxy- 

 gen, 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 will not work faster unless 

 they are ordered to do so. A message must be sent to 

 these telling of the need in the muscles that we are con- 

 sidering, say one of the large muscles of the lower limbs. 

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

 kept in harmonious relation to each other. It must be 

 borne in mind that increased blood flow is the conse- 

 quence, 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- 

 ture of the inside of the body. For this it is better to use a clinical 

 thermometer, if one can be obtained. The average temperature of the 

 tissues within the body is about 98.5 F. 



How the Body is like a Stove. The body may be 

 compared to a stove. Into one we put fuel and produce 

 heat. In the other we get heat from food. 



How the Body differs from a Stove. But the body is 

 not like the stove in burning the fuel (food) directly. The 

 food is first made into tissues, or " storage compounds " in 

 the tissues. It is as though we were to build a stove 



