DESIGN FOR A BRAIN 7/23 



variables are outside their normal limits. Thus if the main 

 variables were as few as two (for graphical purposes), the dis- 

 tribution might be as the* dots in I of Figure 7/23/1. The dis- 

 tribution means that the organism is in tolerable physiological 

 conditions if the representative point stays within the undotted 

 region. 



Ill 



Figure 7/23/1 : Changes of field in an ultrastable system. 



states are dotted. 



The critical 



Suppose now that the first set of values on the step-functions S 

 gives such a field as is shown in I, and that the representative 

 point is at X. The line of behaviour from X is not stable in the 

 region, and the representative point follows the line to the 

 boundary. Here (Y) it meets a critical state and a step-function 

 changes value ; a new field, perhaps like II, arises. The representa- 

 tive point is now at Y, and the line from this point is still unstable 

 in regard to the region. The point follows the line of behaviour, 

 meets a critical state at Z, and causes a change of a step-function : 

 a new field (III) arises. The point is at Z, and the field includes a 

 state of stable equilibrium, but from Z the line leads further out 

 of the region. So another critical state is met, another step- 

 function changes value, and a new field (IV) arises. In this field, 



96 



