IV 



ORGANIC REGULATION AS THE ESSENCE 

 OF LIFE. INADEQUACY OF MECHAN- 

 ISTIC AND VITALISTIC 

 CONCEPTIONS 



In the previous lecture we saw that the internal 

 environment is kept constant as the result of a con- 

 tinuous and extraordinarily delicate regulation of the 

 balance between opposing activities. What general 

 conception can we form of this balancing process? 



An obvious possible interpretation is that each of 

 the various organs concerned in the balancing process 

 has such a physical and chemical structure that it 

 reacts to a given small deviation in the internal en- 

 vironment so as to prevent further deviation in this 

 direction. As the combined result of the reactions of 

 all the organs the internal environment as a whole 

 remains constant. It is evident, for instance, that the 

 respiratory centre reacts to very small differences in 

 the hydrogen ion concentration in the blood, in such a 

 way as to prevent larger differences from occurring. 

 The temperature-regulating centre reacts to small dif- 

 ferences in the blood-temperature. The kidneys react 

 in a similar way to very small differences in the con- 

 centrations of water, urea, and numerous other inor- 



