1 86 ANSWERS TO PRACTICAL QUESTIONS 



23. What causes the pylorus to open and close at the right 

 time ? 



The reflex action of the nerves which preside over that 

 organ. In a similar way, a tickling in the throat excites 

 coughing. 



24. Why is pleasant exercise most beneficial'} 



A chief condition of keeping the brain healthy is to 

 keep the unconscious nervous functions in full vigor, and 

 in natural alternations of activity and repose. Thus it is 

 that (besides its effect in increasing the breathing and the 

 general vigor of the vital processes) muscular exercise 

 has so manifest a beneficial influence on a depressed or 

 irritable state of mind. The bodily movement, by afford- 

 ing an outlet to the activity of the spinal cord, withdraws 

 a source of irritation from the brain ; or it may relieve ex- 

 citement of that organ by carrying off its energy into a 

 safe channel. HINTON. 



25. Why does grief cause one to lose his appetite ? 

 Through the action of the sympathetic system. 



26. Why should we never study directly after dinner ? . 



The blood then sets toward the stomach, and the whole 

 strength of the system is needed to properly digest the 

 food. 



27. What produces the peristaltic movement of the 

 stomach ? 



The presence of the food which, through the sympa- 

 thetic system, acting involuntarily, sets in motion the 

 complicated apparatus of digestion. 



