PHYSIOLOGY OF TO-DAY 



little blood and oxygen that they almost cease to function, 

 while the same thing has been shown for the kidneys, 

 which almost cease to secrete urine. 



It has also been found quite recently that the spleen 

 contracts during muscular exercise and shunts considerable 

 concentrated blood, which has been stored here, into the 

 general circulation. This helps in two ways, by increasing 

 the amount of circulating blood and by allowing the 

 blood to carry more oxygen. 



Even now, if the exercise is maximal, the contracting 

 muscles will not get enough oxygen, so the body goes 

 into oxygen debt — borrows oxygen, so to speak, on further 

 credit; that is, does work without oxygen — and the blood 

 may get into such an acid condition as is seen in disease 

 just before death. After a bout of violent exercise of only a 

 few minutes' duration, it may take an hour or so to pay 

 back the oxygen debt and restore things to normal. In 

 this example we have followed only briefly the integration 

 necessary to supply sufficient oxygen to the active 

 muscles. 



Closely bound up with this integration of the various 

 organs and parts, so that the body can act as a harmonious 

 unit, is the stability and constancy of the organism. 

 Claude Bernard may well be said to have formulated this 

 idea in his theory of the constancy of the composition of 

 the internal environment of the organism, the blood 

 plasma and lymph. It is found that physiological mecha- 

 nisms exist which tend to maintain the constancy of the 

 organism when its normal state is disturbed. There takes 

 place an increase or decrease of some function in the nature 

 of an adaptation which tends to restore things to normal. 

 The study of such adaptations would seem to be one of 

 the central problems of physiology. Lawrence Henderson 

 has written: "The law of adaptation in organisms, founded 

 upon the fact of survival, seems to be quite as well estab- 



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