[Sidenote: 17. Of violent and spasmodic efforts? Strength, how attained? Give the particulars.] 17. Violent exercise is not beneficial; and spasmodic efforts to increase the muscular strength are not calculated to secure such a result. Strength is the result of a gradual growth, and is most surely acquired if the exercise be carried to a point short of fatigue, and after an adequate interval of rest. To gain the most beneficial results, the exercise should be at regular hours, and during a regular period. The activity of the exercise, and the time devoted to it must vary, of course, with the strength of the individual, and should be carefully measured by it. [Sidenote: 18. What may walking be called? What further is said of walking?] 18. DIFFERENT MODES OF EXERCISE.--There are very few who have not the power to walk. There is required for it no expensive apparatus, nor does it demand a period of preliminary training. _Walking may be called the universal exercise._ With certain foreign nations, the English {32} especially, it is a very popular exercise, and is practised habitually by almost every class of society; by the wealthy as well as by those who have no carriages; by women as well as by men. [Sidenote: 19. What is said of running, and other like movements? What, as related to childhood? What instances are alluded to? Example?] 19. Running, leaping, and certain other more rapid and violent movements, are the forms of exercise that are most enjoyed in childhood. For the child, they are not too severe, but they may be so prolonged as to become injurious. Instances have been recorded where sudden death has resulted after violent playing, from overtaxing the heart: for example, we have the case of a young girl who, while skipping the rope, and endeavoring to excel her playmates by jumping the greatest number of times, fell dead from rupture of the heart. [Sidenote: 20. Carriage-riding? Horseback-riding?] 20. Carriage-riding, as a means of passive exercise, is particularly well suited to invalids, and persons advanced in life. Horseback exercise brings into use a greater number of muscles than any other one exercise, and with it there is an exhilaration of feeling which refreshes the mind at the same time. It is one of the manliest of exercises, but not less suitable for women than for men. To be skilful in riding, it is best to begin its practice in youth; but there are very few kinds of exercise of which the same is not equally true. [Sidenote: 21. Boating, swimming, and skating?]