RESPIRATION AND BODY HEAT 241 



comfort does the same; reflex stimuli are absent, the system is 

 relaxed and all processes slow down. 



The breathing of normal sleep is slow and regular. Depressing 

 emotions tend to diminish the frequency and disturb the rhythm of 

 respiration. (Witness the "long breath" and frequent sighing of 

 the morbidly depressed person.) 



In certain cerebral and other conditions, the respiratory 

 center seems to be dulled, so that it responds sluggishly or irregu- 

 larly, as in meningitis and apoplexy ; also in disease of the 

 myocardium. 



Action of Drugs. Certain drugs are called respiratory stimu- 

 lants. Among the best known are strychnine and atropine. 

 Others are respiratory depressants: as opium (in sufficient dose), 

 ether, chloroform, and many others. 



Respiration is one of those involuntary processes in the body 

 which we may voluntarily regulate. We may, whenever we choose, 

 modify the rate and depth of respirations, breathing slowly or 

 rapidly, deeply or superficially at will. We may even cease to 

 breathe for a time, because the residual air always present will sus- 

 tain the demand for oxygen temporarily, although soon we lose con- 

 trol and respiration will proceed with or without any effort of ours. 



Respiration contributory to body heat by providing oxygen 

 for tissue change in all parts of the body. 



Muscle tissue is constantly at work; by rapid oxidation the 

 muscles generate much heat, but only so long as the respiratory 

 organs keep pace with the demand for rapid breathing. 



It is natural to breathe more rapidly as well as more deeply on 

 a cold day, because a low temperature of the surrounding air 

 stimulates (reflexly) the various activities of the body to meet the 

 call for warmth, and the respiratory process must be among the 

 first to respond. (The subject of body heat is considered in 

 Chapter XVIII.) 



The tissues which are most active require most oxygen. Con- 

 sequently we can create a demand and obtain a supply by volun- 

 tary muscle exercise in good air, thus feeding the blood and through 

 it the viscera where also much heat is generated, and the entire 

 body, with this most important element for tissue change. 



Summary. Respiration is a nutritive process, an eliminative 

 process and a contributing source of body heat. 



16 



