STUFFY ROOMS 377 



The pressure of the blood in the veins and arteries nnder the influ- 

 ence of gravity varies with every change of posture. The respiratory 

 pump, too, has a profound influence on the circulation. Active exer- 

 cise, 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 contractions and relaxa- 

 tions of the muscles, and a vastly increased pulmonary 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 constipation. At the same time the surplus food 

 metabolic products, such as sugar and fat, stored in the liver, are 

 consumed in the production of energy, and the organs swept with a 

 rapid stream of blood containing other products of muscular metab- 

 olism 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 thou- 

 sand was covered by the food eaten. 



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

 for the other four thousand calories comes from the consumption of 

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

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

 against 140 liters and 3,000 c.c. while doing very hard labor. The call 

 of the muscles for oxygen through such waste products as lactic acid 

 impels the formation of red corpuscles and hemoglobin. The products 

 of muscular metabolism in other ways not yet fully defined modify the 

 metabolism of the whole body. 



Exposure to cold, cold baths and cold winds has a like effect, accel- 

 erating the heart and increasing the heat production, the activity of 

 the muscles, the output of energy, the pulmonary ventilation and 

 intake of oxygen and food. In contrast with the soft pot-bellied, over- 

 fed city man the hard, wiry fisherman trained to endurance has no 

 superfluity of fat or tissue fluid. His blood volume has a high rela- 

 tive value in proportion to the mass of his body. His superficial veins 

 are confined between a taut skin and muscles, hard as in a race-horse 

 trained to perfection. Thus the adequacy of the cutaneous circula- 

 tion and loss of heat by radiation rather than by sweating is assured. 

 His fat is of a higher melting-point, hardened by exposure to cold. 

 In him less blood is derived to other parts such as adipose tissue, skin 



VOL. LXXXI. — 26. 



