[Illustration: FIG. 48.--CAPILLARIES among fibers of voluntary (cross striped) muscle. (Peabody.)] A grave danger from athletics is that of developing the muscles, including the heart, to an enormous extent by training; then _when training ceases the muscles undergo fatty degeneration from disuse_. Heart disease and other diseases may follow. Many athletes die young, killed by trying to turn their bodies into mere machines for running, boxing, or rowing, instead of living complete lives. _The athletic ideal is not the highest ideal of health_; general activity, resembling the occupations of hunting and farming by which the early race supported itself, is best for health. Many kinds of factory work use only one set of muscles. The savage did not lead a monotonous life, and monotony is bad for both muscles and nerves. =Advantages of Work and Play over Gymnastic Exercises.=--The interest that comes from doing something useful, makes muscular exertion doubly beneficial to the health. The lifting of dumbbells, Indian clubs, and pulley weights, and letting them down again, tends to become very irksome, even though done with the knowledge that the exercise will benefit the health. _Useful labor and games place definite objects in view and do not require so great an effort of the will nor exhaust the nerves so much as mere exercise._ The interest in the work or the game serves to arouse all the nerves and muscles to work in harmony. [Illustration: FIG. 49.--DESK TOO LOW. (Jegi.)] [Illustration: FIG. 50.--CORRECT POSITION.] [Illustration: FIG. 51.--SLIPPING DOWN IN SEAT.] =An Advantage of Gymnastics over Work and Play.=--Gymnastics can furnish any required variety of exercises and _can develop exactly the muscles that need development and leave those idle that have become overdeveloped_ by doing constantly one kind of work or playing continually the same game. The _deformity of a flat chest_ (and round shoulders which always accompany it) does not so often indicate a weak chest or small lungs as it indicates weak or relaxed muscles of the back and the habit of sitting in a relaxed position at work (Figs. 49, 50, 51). _Gymnastic exercise is not wholly an artificial custom._ Cats stretch themselves, stretching each leg in succession; many animals gambol and play. A gymnastic drill, taken to music and with large numbers of pupils in the drill, is interesting as work or play, and should not be neglected for any study, however important.