90 CHEMICAL ACTION. 



A. Hard bodily labour in the open 

 air causes much oxygen to be conveyed 

 into the lungs by inspiration; the com- 

 bustion of the food is carried on quickly ; 

 animal heat increased; and need for 

 nutritious food more quickly indicated 

 by craving hunger. 



Q. Why have persons who follow SEDENTARY 

 PURSUITS less APPETITE than ploughmen and masonst 



A. 1st The air they inhale is not 

 so pure, because its oxygen is partly 

 exhausted : and 



2ndly Their respiration is neither so 

 quick nor strong, and therefore the 

 combustion of their food is carried on 

 more slowly. 



Q. Why do we like strong MEAT and GREASY 

 food when the WEATHER is very COLD ? 



A. Strong meat and grease contain 

 large portions of hydrogen, which (when 

 burned in the blood) produce a larger 

 amount of heat than any other kind of food. 



Q. Why do persons EAT MORE food in COLD 

 weather, than in hot ? 



A. In cold weather the body requires 

 more fuel to keep up the same amount of 



