THE ANIMAL AS MACHINE 3/12 



Their behaviour at first suggested that there was no feedback. 

 But on the third day their change of behaviour showed that, in 

 fact, the change in the bath had had some effect on them. 



The importance of feedback lies in the fact that systems which 

 possess it have certain properties (S. 4/14) which cannot be shown 

 by systems lacking it. Systems with feedback cannot adequately 

 be treated as if they were of one-way action, for the feedback 

 introduces properties which can be explained only by reference 

 to the properties of the particular feedback used. (On the other 

 hand a one-way system can, without error, be treated as if it 

 contained feedback : we assume that one of the two actions is 

 present but at zero degree (S. 2/3). In other words, systems 

 without feedback are a sub-class of the class of systems with 

 feedback.) 



3/12. As the organism and its environment are to be treated 

 as a single system, the dividing line between 4 organism ' and 

 4 environment ' becomes partly conceptual, and to that extent 

 arbitrary. Anatomically and physically, of course, there is a 

 unique and obvious distinction between the two parts of the sys- 

 tem ; but if we view the system functionally, ignoring purely 

 anatomical facts as irrelevant, the division of the system into 

 4 organism ' and ' environment ' becomes vague. Thus, if a 

 mechanic with an artificial arm is trying to repair an engine, 

 then the arm may be regarded either as part of the organism that 

 is struggling with the engine, or as part of the machinery with 

 which the man is struggling. 



Once this flexibility of division is admitted, almost no bounds 

 can be put to its application. The chisel in a sculptor's hand 

 can be regarded either as a part of the complex biophysical mechan- 

 ism that is shaping the marble, or it can be regarded as a part of 

 the material which the nervous system is attempting to control. 

 The bones in the sculptor's arm can be regarded either as part of 

 the organism or as part of the ' environment ' of the nervous 

 system. Variables within the body may justifiably be regarded 

 as the ' environment ' of some other part. A child has to learn 

 not only how to grasp a piece of bread, but how to chew without 

 biting his own tongue ; functionally both bread and tongue are 

 part of the environment of the cerebral cortex. But the environ- 

 ments with which the cortex has to deal are sometimes even deeper 



39 



