Mi. 23 INFLUENCE OF ATMOSPHERE ON HEALTH 5 



become soldiers, may develop a physique and bodily health and vigor 

 in striking contrast to their brothers who become clerks, shop assist- 

 ants, and compositors. 



Too much stress cannot be put on the importance of muscular 

 exercise in regard to health, beauty, and happiness. Each muscle 

 fills with blood as it relaxes, and expels this blood on past the venous 

 valves during contraction. Each muscle together with the venous 

 valves forms a pump to the circulatory system. It is the function 

 of the heart to deliver the blood to the capillaries, and the function 

 of the muscles — visceral, respiratory, and skeletal — to bring it back 

 to the heart. The circulation is contrived for a restless mobile 

 animal ; every vessel is arranged so that muscular movement furthers 

 the flow of blood. 



The pressure of the blood in the veins and arteries, under the 

 influence of gravity, varies with every change of posture. The 

 respiratory pump, too, has a profound influence on the circulation. 

 Active exercise, such as is taken in a game of football, entails endless 

 changes of posture, varying compressive actions — one with another 

 struggling - in the rough and tumble of the game — forcible contrac- 

 tions and relaxations of the muscles, and a vastly increased pulmon- 

 ary ventilation ; at the same time the heart's action is accelerated and 

 augmented and the arterial supply controlled by the vaso-motor 

 system. The influence of gravity, which tends to cause the fluids 

 of the body to sink into the lower parts, is counteracted ; the liver 

 is rhythmically squeezed like a sponge by the powerful respiratory 

 movements which not only pump the blood through the abdominal 

 viscera, but thoroughly massage these organs, and, kneading these 

 with the omentum, clean the peritoneal cavity, and prevent constipa- 

 tion. At the same time the surplus food products, such as sugar 

 and fat stored in the liver, are consumed in the production of energy, 

 and the organs are swept with a rapid stream of blood contain- 

 ing other products of muscular metabolism which are necessary 

 to the inter-relation of chemical action. The output of energy is 

 increased very greatly ; a resting man may expend two thousand 

 calories per diem ; one bicycling hard for most of the day expended 

 eight thousand calories, of which only four thousand were covered 

 by the food eaten. 



Such figures show how fat is taken off from the body by exercise, 

 for the other four thousand calories came from the consumption of 

 surplus food products stored in the tissues. While resting, a man 

 breathes some 7 liters of air, and uses 300 cc. of oxygen per minute, 



