10/9. To summarise: — Let it be given that the organism has adapted to P1 by trial and error, then it adapted similarly to P2, and that when P1 was given for the second time the organism was adapted at once, without further trials. From this we may deduce that the step-mechanisms must be divisible into nonoverlapping sets, that the reactions to P1 and P2 must each be due to their particular sets, and that the presentation of the problem (i.e. the value of P) must determine which set is to be brought into functional connexion, the remainder being left in functional isolation.
Thus if the diagram of Figure 7/5/1 is taken as basic, it must be modified so that the step-mechanisms are split into sets, there must be some gating mechanism ? to determine which set shall be on the feedback circuit, and the gating mechanism ? must be controlled (usually through R, as this is the organism’s structure) by the value of P.
Figure 10/9/1 presents the diagram of immediate effects, but the Figure is best thought of as a mere mnemonic for the functional relations, lest it suggest some anatomical form too strongly. The parameter P can be set at various values, P1, P2 … The stepmechanisms are divided into sets, and there is a gating mechanism ?, controlled by P through the environment and the reacting part R, that determines which of the sets shall be effective in the second feedback via the essential variables.