ULTRASTABILITY IN THE LIVING ORGANISM 9/5 



ment ' is simple, for it means that some sensory organs or nerve 

 endings have been stimulated with an intensity high enough to 

 cause step-function changes in the nervous system (S. 7/6 and 

 10/2). The concept of c reward ' is more complex. It usually 

 involves the supplying of some substance (e.g. food) or condition 

 (e.g. escape) whose absence would act as ' punishment '. The 

 chief difficulty is that the evidence suggests that the nervous 

 system, especially the mammalian, contains intricate and special- 

 ised mechanisms which give the animals properties not to be 

 deduced from basic principles alone. Thus it has been shown 

 that dogs with an oesophageal fistula, deprived of water for some 

 hours, would, when offered water, drink approximately the 

 quantity that would correct the deprivation, and would then 

 stop drinking ; they would stop although no water had entered 

 stomach or system. The properties of these mechanisms have 

 not yet been fully elucidated ; so training by reward uses 

 mechanisms of unknown properties. Here we shall ignore these 

 complications. We shall assume that the training is by pain, 

 i.e. by some change which threatens to drive the essential vari- 

 ables outside their normal limits ; and we shall assume that 

 training by reward is not essentially dissimilar. 



It will now be shown that the process of ' training ' necessarily 

 implies the existence of feedback. But first the functional rela- 

 tionship of the experimenter to the experiment must be made 

 clear. 



The experimenter often plays a dual role. He first plans 

 the experiment, deciding what rules shall be obeyed during it. 

 Then, when these have been fixed, he takes part in the experi- 

 ment and obeys these rules. With the first role we are not 

 concerned. In the second, however, it is important to note that 

 the experimenter is now within the functional machinery of the 

 experiment. The truth of this statement can be appreciated 

 more readily if his place is taken by an untrained but obedient 

 assistant who carries out the instructions blindly ; or better still 

 if his place is taken by an apparatus which carries out the pre- 

 scribed actions automatically. 



When the whole training is arranged to occur automatically 

 the feedback is readily demonstrated if we construct the diagram 

 of immediate effects. Thus, a pike in an aquarium was separated 

 from some minnows by a sheet of glass ; every time he dashed 



113 



