6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



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

 call of the muscles is for more oxygen, and their waste products 

 stimulate the formation of haemoglobin, and in other not fully defined 

 ways influence the metabolism. 



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 

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

 overfed city man, the hard, wiry fisherman 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 

 are assured. His fat is of a higher melting point, hardened by 

 exposure to cold. In him less blood is contained in adipose tissue 

 and skin, and the circulation through the brain muscles and viscera 

 is more active. 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 (Krogh) ; 

 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 efficient action 

 of his skin and cutaneous circulation — the radiator of the body — he 

 performs the work with far 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 demands a 

 rapid flow of blood, and his heart has to do the circulatory work, as 

 he sits still or stands at his desk, against the influence of gravity. 

 Hence a high blood-pressure is maintained for long periods at a time 

 by vaso-constriction of the arteries in the lower parts of the body and 

 increased action of the heart. Hence, perhaps, arise those degenera- 



