306 Problems of Organic Adaptation 



samer, goes "ballooning" to new lands; the tremendous 

 power of flight of the albatross and eagle; the apparently 

 effortless soaring of the buzzard and frigate-bird; the flight 

 of the arctic tern and golden plover from pole to pole, or 

 the world-wide flight of the tiny humming-bird. Long ages 

 before man had appeared on the earth, animals had con- 

 quered the land, the water, and the air; and although by 

 means of his machines man can now surpass them in speed 

 and strength in these three elements, they can still teach 

 us much in skill and efficiency of locomotion. 



The heart, with its valves, is a remarkably efficient 

 pump; the strength and thickness of the muscular walls of 

 the auricles and ventricles are nicely adjusted to the "load" ; 

 the valves are ideally constructed for quick, simple, and 

 efficient action; the sequence of the beats in auricles and 

 ventricles is usually perfect. Even more remarkable are 

 adaptations to increased "load" during violent exercise or 

 in high altitudes. In man the resting heart pumps about 

 five pints of blood a minute, but in violent exercise it pumps 

 seven times as much as this. The structures of arteries, 

 veins, and capillaries are admirably suited to the needs of 

 efficient circulation, and the mechanism for regulating blood 

 pressure is extraordinarily efficient. 



The efficiency of the living machine in the production of 

 light, as for example in the firefly and glowworm, is incom- 

 parably greater than in the case of any lighting system of 

 human invention. In electric lighting from 90 to 95% of the 

 energy is wasted in heat and only 5 to 10% produces light, 

 whereas these proportions are reversed in living things. 



The mechanism for heat regulation in warm-blooded 

 animals is wonderfully perfect. Irrespective of extreme 

 changes in external temperature, the internal temperature 

 is frequently maintained for years at a time within a few 



