_Swimming_.--A word of warning is necessary in regard to those learning to swim in rivers. Boys at school, when they take to river bathing, often carry it to a dangerous extent. They get into the water, and now in, now out on the bank, sometimes remain for hours. This may take place day after day, and if the weather continues warm and the holidays last long enough, the boy may reduce himself to the lowest ebb of feebleness, and possibly develop the seeds of latent disease. He may even die from the effects of this prolonged immersion and madcap exposure. The muscular exertion undergone during swimming, especially by those who swim only occasionally, is very great. The experienced swimmer conserves his strength, as do proficients at all feats, but the occasional swimmer, like the occasional rower, puts forth treble the energy required, and soon becomes exhausted. In the first place, it is a new act for the muscles to perform; they are taken off from the beaten tracks, and are grouped together in new associations; hence they lack adjustment and adaptation. Again, as in other feats for which one is untrained, the heart and lungs do not work in time. Ease and speed in swimming depend upon the attainment of harmony in the working of the muscles, heart, and lungs. Diving is an accomplishment attached to swimming, which involves many dangers, and is well-nigh useless. The customary dive off a springboard into the shallow water of a swimming bath is dangerous in the extreme. The only place where diving should be attempted is into deep water, at least fifteen or twenty feet, where there is no danger of striking the bottom. _Lawn Tennis_.--Of all modern inventions in the way of games, lawn tennis is the best. The dangers attendant on lawn tennis are:-- 1. Overexertion, causing rupture and deranged circulation, especially in the case of those with weak hearts, or those who, being out of condition, or too fat, suddenly engage in the game too long or too violently. 2. Rupture of the _tendon of Achilles_, from taking a sudden bound. In such an accident the subject falls down, with a sensation as if struck with a club on the leg. 3. Rupture of one of the heads of the biceps in the arm. Here the arm drops helplessly, and a muscular knob rises up on the inner and upper part of the arm. 4. The tennis arm. This trouble arises from the method of manipulating the bat. The pain is felt over the upper end of the radius. Many of the strains, ruptured tendons, and torn muscles in tennis players are caused by the want of heels to tennis shoes. As, ordinarily, we walk on heels which vary from half an inch to an inch, there must be a considerable extra strain thrown on the muscles of the calf of the leg, when the heels are left off. Especially during a sudden spring is this apparent, when to rise from off the heels on to the toes requires a greatly increased force. Tennis shoes should therefore have fairly deep, broad heels.