300 THEORETICAL BIOLOGY 



have to distinguish an internal equihbrium within each 

 functional building-stone from the internal equilibrium con- 

 trolling the function as a whole. According to external 

 conditioning by the injury and the internal conditioning by 

 the reserve-material present, now the one and now the other 

 comes into evidence. 



EQUILIBRIUM IN TIME 



The instances dealt with hitherto all refer to spatial 

 equilibrium, which expresses itself, now in one functional 

 building-stone and now in all together. But it cannot be 

 denied that there are also rules connecting into unities factors 

 separated from one another in time. The notes of a melody 

 . that we have heard immediately appear to us connected to- 

 gether by a rule. But the melody is not just a rule discovered 

 afterwards (which would be merely passive) : on the contrary, 

 it is active in the extreme, as soon as we ourselves sing a 

 song ; and, in a way unknown to us, it controls the impulses 

 in the actions of our larynx, which produces the notes. In 

 this case we are fully justified in assuming an impulse-system 

 corresponding to the melody, and in seeking for its internal 

 equilibrium. In the same way, active rules, referable to 

 impulse-systems, lie behind all those of our actions that are 

 not reflexes. They must all possess an internal equilibrium. 



The way in which we have to picture the invasion of 

 impulse-systems has already been set forth in detail. Accord- 

 ing to this conception, there is every time a regeneration of 

 the central mesh-work. By this means we are enabled to 

 consider the whole process from outside, without entering on 

 psychological questions. Before our eyes a natural process 

 is taking place, which follows an autonomous rule. It owes 

 its autonomy to an impulse-system, which is held together by 

 an internal equilibrium. 



