Q. Why do we perspire when very hot?
A. The pores of the body are like the safety valves of a steam-engine; when the heat of the body is too great, the combustible gas and grease flow out in perspiration, instead of burning in the blood.
Q. Why do persons feel lazy and averse to exercise, when they are half-starved or ill-fed?
A. Animal food contains great nourishment, and produces a desire for active occupations; but when the body is not supplied with strong food, this desire for muscular action ceases, and the person grows slothful.
Q. Why have persons, who follow hard out-of-doors occupations, more appetite than those who are engaged in sedentary pursuits?
A. Hard bodily labour in the open air causes much oxygen to be conveyed into the lungs by inspiration; the combustion 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 masons?
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.