Walking gives movement to every portion of the body, and ensures vigorous circulation of the blood; for, when we walk fast, fresh air is inhaled into the lungs. Then there is the inestimable joy that natural objects give us, the joy that comes from a contemplation of the beauties of nature. ... Let those who are suffering from indigestion and kindred diseases try for themselves, and they will at once realise the value of walking as an exercise. (Chapter VII, Exercise)