150 × 8 = 1,200 ————- W + W^1 = 1,630 1,630 × 25 × 5,280/(20 × 2,240) = 4,802·7 foot-tons. This being the total work done, the work per man = nearly 600.3 foot-tons. _A hill-coolie weighing 150 lbs. goes 30 miles with an ascent of 5,500 feet in three days, carrying 80 lbs. in weight. What is the work per day? (Parkes.)_ Work of the ascent = (150 + 80) × 5,500∕2,240 = 564·7 foot-tons. Work of 30 miles walk = 230 × 30 × 5,280/(20 × 2,240) = 813·2 foot-tons. Total work = 564·7 + 813·2 = 1,377·9. Total work per day = 1,377·9∕3 = 459·3 foot-tons. _Suppose a man weighing 150 lbs. in his clothes, carries a load of bricks weighing 35 lbs. up a perpendicular ladder 30 feet high, 100 times daily, what amount of work does he do; and what will it equal in miles walked upon a flat road at the rate of 3 miles an hour?_ ((150 + 35) × 30 × 100) / 2,240 = 247·8 foot-tons (185 × D) / (20 × 2,240) = 247·8. Therefore D = 60,056 feet = about 11·4 miles. _Suppose a man strikes 12,000 strokes in 5 hours with a 14-lb. hammer, raising it at each stroke 4 feet, how much work does he do? Compare this with a walk of 15 miles on a level ground at 3 miles an hour, the weight of the man and what he carries being 180 lbs._ (_a_) 12,000 × 14 × 4 = 672,000 foot-lbs. of work = 300 foot-tons. (_b_) (180 × 15 × 5,280) / (20 × 2,240) = 318·2 foot-tons. The two amounts of work are related as 300: 318·2. CHAPTER XXXVIII. PERSONAL HYGIENE (_continued_)—REST AND SLEEP. =Physiological Considerations.=—Life is made up of alternations of rest and action. The exercise of any organ is followed by a necessary period of repose, during which the oxidised materials produced by functional activity are removed by the blood, and carried to the excretory organs; while at the same time fresh nutritive material is supplied by the blood to make good the losses thus sustained. The only apparent exceptions to this rule of alternation of rest and exercise are the heart and lungs, and some less important organs acting out of the control of personal volition. But even these organs obey the universal law. The difference is that their rest is very frequent and momentary; the heart having to contract sixty or seventy times per minute, rests 6∕11 of a second each second, or more than thirteen hours in the twenty-four. The lungs and respiratory muscles rest a shorter time than this, but probably about three hours per day. The necessity for rest is well shown by the sense of taste. If salt is kept in the mouth for a considerable time, the power of tasting it disappears, and only returns in its original strength after several hours. The gustatory nerve has been exhausted.