Page:First course in biology (IA firstcourseinbio00bailrich).pdf/532



Effects of Work, Fresh Air, and Rest on Corpuscles and Plasma.—Work uses up the nutritious elements in the blood. A few hours after food is eaten the nutritious materials in the blood are found to be increased. By the breathing of fresh air the carbon dioxid in the plasma is diminished and the oxygen in the colored corpuscles is increased, changing the blood to a brighter red. Sleep gives time for the exhausted cells and depleted blood to be replenished. Loss of sleep means longer hours of activity and greater consumption of nutriment with shorter hours for replacing the nutriment. The pale skin of one who has lost sleep tells of the exhausted condition of the blood.

How the Muscles help the Circulation.—The imperative need of muscular exercise to keep the body sound exists because of the lack of other means to cause movement in the veins and lymphatics. Good food, pure air, and plenty of exercise are necessary for healthy blood. Many so-*called "blood purifiers" are advertised to entrap the ignorant. It is impossible to imagine how "blood purifiers" can aid the blood. The blood is purified, not by putting anything into the blood, but by something going out of it as it passes through the skin, kidneys, liver, and lungs. These organs all send out impurities brought to them by the blood.

The one great hygienic effect of muscular exercise is an active circulation, and from an active circulation nine chief effects may be traced. The effects upon the body will be given in order, beginning with the surface—skin, fat, muscles, bones; and the effects upon the internal organs are given in order of position, beginning with the highest—brain, lungs, heart, digestive organs.