626 TRANSACTIONS OF SECTION I. 
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. 
ach 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 con- 
tractions and relaxations 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 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 come from the consumption of surplus food pro- 
ducts stored in the tissues. While resting a man breathes some seven litres of air, 
and uses 300 c.c. of oxygen per minute, against 140 litres and 3000 c.c. while 
doing very hard labour. 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, accelerating 
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 fisher- 
man trained to endurance has no superfluity of fat or tissue fluid. His blood 
volume has a high relative 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 circulation 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, and viscera. He uses up 
the oxygen in the arterial blood more completely and with greater efficiency ; for 
the output of each unit of energy his heart has to circulate much less blood 
(Kreogh); his blood is sent in full volume by the well-balanced activity of his 
vaso-motor system to the moving parts. Owing to the perfect co-ordination 
of his muscles, trained to the work, and the efticient action of his skin and 
cutaneous circulation—the radiator of the body—he performs the work with 
tar greater economy and less fatigue. The untrained man may obtain 12 
per cent. of his energy output as work, against 30 per cent. or perhaps even 
50 per cent. obtained by the trained athlete. Hence the failure and risk 
suffered by the city man who rushes straight from his office to climb the Alps. 
On the other hand, the energetic man of business or brain worker is kept by his 
work in a state of nervous tension. He considers alternative lines of action, but 
scarcely moves. He may be intensely excited, but the natural muscular response 
does not follow, His heart is accelerated and his blood pressure raised, but 
neither muscular movements and accompanying changes of posture, nor the- 
respiratory pump materially aid the circulation, The activity of his brain 
