To discuss fully the subject and laws of health would require a whole treatise, and would be beyond the scope of this text-book. There are, however, some outstanding conditions for the preservation of health which are plain to everyone, and which may be summed up in the three words Temperance, Exercise, and Rest. These have been well termed the three great physicians, whose prescriptions are painless and cost nothing. 1. _Temperance_.--Man needs a certain amount of food to sustain him, but if that amount be increased beyond the proper quantity it is dangerous to health. It overtasks the power of digestion and is injurious. We need therefore to be constantly on our guard as to what we eat and drink lest we run into excess. Every one must study his own constitution, find out its need, and suit the supply of food to its wants. According to the old proverb, "We should eat to live, not live to eat." It is a great matter for health when we are able to strike the proper medium and neither eat nor drink too much nor too little. To lay down rules on this subject for the individual is impossible. "One man's food is another man's poison." A man must determine from his own experience what he ought to take, and how much, as well as what he ought to avoid. The word intemperance is generally employed as applying to the abuse of strong drinks. On this subject much has been written, some advocating total abstinence and others judicious and moderate use. Into this region of controversy we cannot enter. The evils of drinking habits, as they are called, are plain to all. They are a terrible curse to society, and a terrible danger to the individual. They have ruined many a promising career. For many, perhaps we may say for most, entire abstinence is their only safety. He who finds that he can do his work well by drinking only water will be wise if he drinks nothing else. That will never harm him, though other liquids may. We must judge for ourselves, but "Temperance in all things" is a rule binding on every Christian man. We cannot have health unless we strictly and constantly practise temperance.