=Amount of Exercise Desirable.=—According to Parkes, the average daily work of a man engaged in manual labour in the open air is equivalent to the work involved in lifting 250 to 350 tons one foot high; this is a moderate amount, 400 tons being a heavy day’s work. The amount of muscular exercise involved in this may be easily known by remembering that a walk of 20 miles on a level road is equivalent to about 353-2∕3 tons lifted 1 foot; and that a walk of 10 miles while carrying 60 lbs. is equivalent to 247½ tons lifted 1 foot. (Haughton). The _amount of work done_ by a healthy adult per diem is stated by M. Foster to be about 150,000 metre-kilogrammes (_i.e._, 150,000 kilogrammes lifted 1 metre). Metre-kilogrammes can be converted into foot-pounds by multiplying by 7·233; into foot-tons by multiplying by ·003229; 150,000 metre-kilogrammes therefore equal 484·35 foot-tons. This is considerably in excess of Parkes’ estimate, but in certain laborious occupations this high amount is reached. In addition to this amount of external work, there is the internal work of the heart, muscles of respiration, digestion, etc. This is estimated by Parkes at about 260 foot-tons. The internal and external muscular work of the body together amount to about 1∕7th to 1∕8th of the total force obtainable from the food. Every healthy man probably ought to take an amount of exercise represented by 150 tons raised 1 foot, which is equal to the work done in walking 8½ to 9 miles on a level road. A certain amount of this exercise is taken in performing one’s daily work; but apart from this, out-door exercise should be taken equivalent in amount to a walk of five or six miles. It is impossible to lay down rules to suit all cases, but a less amount of exercise than that named is probably incompatible with perfect health. =Effects of Deficient Exercise.=—The _muscles_ themselves become enfeebled and wasted. Some wasting of muscle occurs after a few days’ confinement to bed; and a limb confined in a splint speedily loses its healthy, rounded contour. _Oxidation processes_ are diminished; less carbonic acid is eliminated, and it tends to accumulate in the system, owing to the diminished activity of respiration. In consequence of the diminished oxidation, the temperature of the body is not well maintained, and the heat is not uniformly distributed. Cold feet are a common complaint of those who lead sedentary lives, though seldom complained of by others. Along with the other muscles, the _heart_ becomes enfeebled and the circulation less perfect. _Digestion_ is enfeebled; the appetite is poor. The _nervous system_ also suffers; nervous irritability is a common result, while sleeplessness—a thing almost unknown among those who live by the sweat of their brow—is becoming much more common among the worried and ill-exercised inhabitants of our towns.