This section of the book is from the "Household Companion: The Family Doctor" book
Little thought is needed, for every one to see that for good breathing there must be sound lungs and air tubes, and strength in the muscles of the chest, as well as pure air. Our breathing muscles can be strengthened by exercise. All active muscular movements of any part of the body, but especially brisk walking or running, quicken the action of the heart; and, as the blood then goes more rapidly through the lungs, it needs to be, and is, aired by quicker breathing.
Using the voice a great deal (as in speaking or singing) in early life, promotes the growth of the lungs and the strength of the breathing muscles. Those who belong to consumptive families should, while young, be accustomed to active out-of-door habits; and for them, reading or speaking aloud or singing (vocal gymnastics) will be wholesome exercise; that is, so long as they are well. When the lungs are actually diseased, active efforts of all kinds should be avoided.
Pure air, and plenty of it, is a constant necessity for health. The application of this truth belongs in many ways to our every-day life, especially, of course, within doors. Out of doors we can usually trust to nature to supply us a fair share of wholesome air, if, of course, we keep away from localities in which the air is vitiated by bad sanitation or other unwholesome surroundings.