DESIGN FOR A BRAIN 3/3 



Table 2/4/1 , for instance, contains a variable ' part of skin stimu- 

 lated ' which, in Pavlov's Table, takes only two values: 'usual 

 place ' and ' new place '. Even more complicated variables are 

 common in Pavlov's experiments. Many a Table contains a 

 variable ' stimulus ' which takes such values as ' bubbling water ', 

 1 metronome ', ' flashing light '. A similar difficulty occurs when 

 an experimenter tests an animal's response to injections of toxins, 

 so that there will be a variable ' type of toxin ' which may take 

 the two values 4 Diphtheria type Gravis ' and ' Diphtheria type 

 Medius '. And finally the change may involve an extensive 

 re-organisation of the whole experimental situation. Such would 

 occur if the experimenter, wanting to test the effect of the general 

 surroundings, tried the effect of the variable ' situation of the 

 experiment ' by giving it alternately the two* values' ' in the 

 animal house ' and ' in the open air '. Can such variables be 

 represented by number ? 



In some of the examples, the variables might possibly be speci- 

 fied numerically by a more or less elaborate specification of their 

 physical nature. Thus ' part of skin stimulated ' might be 

 specified by reference to some system of co-ordinates marked on 

 the skin ; and the three intensities of the electric heater might be 

 specified by the three values of the watts consumed. But this 

 method is hardly possible in the remainder of the cases ; nor is it 

 necessary. For numbers can be used cardinally as well as 

 ordinally, that is, they may be used as mere labels without any 

 reference to their natural order. Such are the numberings of the 

 divisions of an army, and of the subscribers on a telephone system ; 

 for the subscriber whose number is, say, 4051 has no particular 

 relation to the subscriber whose number is 4052: the number 

 identifies him but does not relate him. 



It may be shown (S. 21/6) that if a variable takes a few values 

 which stand in no simple relation to one another, then each value 

 may be allotted an arbitrary number; and provided that the 

 numbers are used systematically throughout the experiment, and 

 that their use is confined to the experiment, then no confusion 

 can arise. Thus the variable ' situation of the experiment ' 

 might be allotted the arbitrary value of ' 1 ' if the experiment 

 occurs in the animal house, and ' 2 ' if it occurs in the open air. 



Although ' situation of the experiment ' involves a great number 

 of physical variables, the aggregate may justifiably be treated as 



32 



