66 HUMAN BIOLOGY 



Hygiene of the Circulati 



on 



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 ma- 

 terials 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 in- 

 creased, changing the blood to a brighter red. Sleep gives 

 time for the exhausted cells and depleted blood to be re- 

 plenished. 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 puri- 

 fiers " 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. 



