ADAPTATIONS 



whole world of human mechanical devices, 

 and proceed to what seem to be much 

 simpler arrangements for doing special 

 work. Thus as to the intake of oxygen 

 and the outgo of carbonic acid in breath- 

 ing. Professor Haldane, whose researches 

 on this subject are highly rated, remarks: 

 " Liebig believed that the rate of respira- 

 tory change was regulated by the supply 

 to the body of oxygen and of food 

 material. If one breathed faster, the re- 

 spiratory exchange was assumed to be also 

 increased, just as ordinary combustion 

 outside the body would be increased by 

 an increased supply of oxygen. If, again, 

 one took more food, it was supposed that 

 the excess went to increase the rate of 

 combustion in the blood, just as a fire is 

 increased when more fuel is supplied. We 

 now know that these assumptions were 

 wholly mistaken, and that the respiratory 

 movements, respiratory exchange, and cor- 

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