EXERCISE is the subject that next claims our consideration, and we shall briefly notice its effects on the different systems of organs. (1) The most important effect of muscular exercise is produced uu the ittafin, the quantities of inspired air and of exhaled carbonic acid being very much increased. Taking the air inspired in a given time in the hori zontal position as unity, a man walking 3 in. per hour inspires 8.22; and if carrying 34 lbs., 3.5; a man walking 4 in. per hour inspires 5; and when walking 6 m. per hour, no less than seven. Almost twice as much carbonic acid is exhaled during exercise as dur ing rest. Hence. muscular exercise is necessary for the due removal of the carbon; and it is obvious that in a state of prolonged rest, the carbonaceous food must be diminished, or the carbon will he liable to accumulate in the system; and further, it is clehr that, for strong exercise, carbonaceous food should be freely given. (2) The action of the heart rapidly increases in force and frequency during exercise. The increase in the number of beats may range from 20 to 30, and is sometimes much more. After exercise, the heart's action is diminished. Excessive exertion may do harm by inducing pulmonary congestion, and even Ihumoplysis, palpitation, hypertrophy, valvular disease, and occa sionally rupture; while deficient exercise probably tends to induce tuberculous disease of the lung, weakness of the heart's action, and probably dilatation and fatty degenera tion. From these facts we learn, that when a person commences any new form of exer cise or gymnastics, the heart's action should be watched, and lithe pulse rise to 120 or more, the exercise should for the time cease. (3) The skin becomes red from increase of blood in the capillaries, and the perspiration is increased, being at least doubled. The bodily heat is kept down by cutaneous evaporation, winch reduces the temperature. During exertion, there is very little danger of chill, but the danger becomes great when the exertion is over, because there is then a rapid fall in the heat of the body, while the evaporation of the skin continues. Hence, while the skin may be freely exposed during exercise, it must be covered immediately iifterward in order to prevent any feeling of coolness on the surface. (4) The muscles grow to a certain limit, but over-exercise of any special group may produce wasting. Care must be taken that the exercise is of such a nature that all the muscles, and not single groups, should be brought into play; and that in curly training, long intervals of rest should intervene betty en the periods of exer cise. (5) The effect of exercise on the mind is not clearly determined; great bodily activity is often observed in association with full mental sctivity; but there is a fear that, in our great public schools and universities, boating and cricket are supplanting more useful subjects, and leaving too little lime for the due performance of intellectual work. (6) 1 hgestion is improved hy exercise. The appetite increases, and nitrogenous
substances, fats, and salts, especially phosphates and chlorides, are required in greater quantity than in a state of rest. (7) The change of /issues is increased by exercise, or, in other words, the excretions give off increased quantities of carbon, nitrogen, water, and salts. The muscles require much rest for their reparation after exercise. and they then absorb and retain water, which seems to enter into their composition. So completely is the water retained in the muscles, that the urine is not increased for some hours. hence, observes Dr. Parkes, there is an absolute necessity of water for the acting muscles, and time old rule, field bi trainers, of only allowing the smallest possible quantity of fluid, must be wrong.
The amount of exercise which should be taken by an adult healthy man is a subject Of great importance. Prof. Houghton, in his New Theory of Muscular Action, calculates that a laboring man daily exerts a muscular force to a degree which may be expressed by saying, that he would raise to the height 1 foot from 250 to 350 tons. For pet:ion:I not obliged to labor, the force expended, including that required for the avoca tions of life, should average 150 tons, which is equivalent to walking about 9 in. daily. It is unfortunately impossible to arrange scales of exercise for invalids, women, and children. Prof. Houghton has shown that walking on a level surface is equivaleut to raising the -hilt part of the weight of the body through the distance walked. When ascending a height, a man of course raises his whole weight through the height ascended.
' Using his formula W+ W D (where W is the weight of the person, W' the weight ear 20 X 2240 ried, D the distance walked, 20 the coefficient cf traction (see FRICTION), and 2240 the number of pounds in a ton), we obtain as a result the number of tons raised 1 foot; and on applying it, we get the following table: done in tons Kind of exercise.
lifted one foot.
1 mile. .. . 17.67 20 miles.. 353.4 " 1 mile, and carrying 60 lbs 21.75 " 20 miles " 495.
Thus, a march of 10 m., with a weight of GO lbs. (which is about the weight a soldier car ries when in marching order, but without blankets and rations), is a moderate day's work. A 20 miles' march with this weight is a very hard day's work. As a continuous effort, prof:Houghton believes that walking 20 m. a day without a load (Sundays excepted) is good work.—For a discussion on the various forms of exercise, as horse exercise, boat ing, dancing, and gymnastics, we may refer the reader to Mapother, op. cit., pp. 263-268. Iu connection with the subject of exercise, the reader is referred to the article MUSCULAR FORCE, ORIGLN OF.