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- 
