PARAMETERS 



6/4 



300- 



200 



state and change of field, can hardly be over-estimated. In 

 order to make the distinction clear I will give some examples. 



In a working clock, the single variable defined by the reading 

 of the minute-hand on the face is absolute as a one-variable system ; 

 for after some observations of its behaviour, we can predict the 

 line of behaviour which will follow any given state. If now the 

 regulator (the parameter) is moved to a new position, so that the 

 clock runs at a different rate, and the system is re-examined, it 

 will be found to be still absolute but to have a different field. 



If a healthy person drinks 100 g. of glucose dissolved in water, 

 the amount of glucose in his blood usually rises and falls as A 

 in Figure 6/4/1. The single variable c blood -glucose ' is not 

 absolute, for a given state 

 (e.g. 120 mg./lOO ml.) does 

 not define the subsequent 

 behaviour, for the blood- 

 glucose may rise or fall. 

 By adding a second vari- 

 able, however, such as ' rate 

 of change of blood-glucose ', 

 which may be positive or 

 negative, we obtain a two- 

 variable system which is 

 sufficiently absolute for 

 illustration. The field of 

 this two-variable system 

 will resemble that of A in 

 Figure 6/4/2. But if the subject is diabetic, the curve of the 

 blood-glucose, even if it starts at the same initial value, rises 

 much higher, as B in Figure 6/4/1. When the field of this 

 behaviour is drawn (B, Fig. 6/4/2), it is seen to be not the same 

 as that of the normal subject. The change of value of the 

 parameter 4 degree of diabetes present ' has thus changed the 

 field. 



Girden and Culler developed a conditioned reflex in a dog which 

 was under the influence of curare (a paralysing drug). When 

 later the animal was not under its influence, the conditioned reflex 

 could not be elicited. But when the dog was again put under its 

 influence, the conditioned reflex returned. We need not enquire 

 closely into the absoluteness of the system, but we note that two 



75 



2 3 



Figure 6/4/1 : Changes in blood-glucose 

 after the ingestion of lOOg. of glucose : 

 (A) in the normal person, (B) in the 

 diabetic. 



