8/14 THE HOMEOSTAT 



In animals, though we cannot yet say much about their critical 

 states, we can observe failures of adaptation that may well be due 

 to a defect of this type. Thus, though animals usually react 

 defensively to poisons like strychnine — for it has an intensely 

 bitter taste, stimulates the taste buds strongly, and is spat out 

 — they are characteristically defenceless against a tasteless or 

 odourless poison: precisely because it stimulates no nerve-fibre 

 excessively and causes no deviation from the routine of chewing 

 and swallowing. 



An even more dramatic example, showing how defenceless is 

 the living organism if pain has not its normal effect of causing 

 behaviour to change, is given by those children who congenitally 

 lack the normal self-protective reflexes. Boyd and Nie have 

 described such a case: a girl, aged 7, who seemed healthy and 

 normal in all respects except that she was quite insensitive to 

 pain. Even before she was a year old her parents noticed that 

 she did not cry when injured. At one year of age her arm was 

 noticed to be crooked: X-rays showed a recent fracture-disloca- 

 tion. The child had made no complaint, nor did she show any 

 sign of pain when the fragments were re-set without an anaesthetic. 

 Three months later the same injury occurred to her right elbow. 

 At the seaside she crawled on the rocks until her hands and knees 

 were torn and denuded of skin. At home her mother on several 

 occasions smelt burning flesh and found the child leaning uncon- 

 cernedly against the hot stove. 



It seems, then, that if an imperfectly formed ultrastable system 

 is, under certain conditions, defenceless, so may be an imperfectly 

 formed living organism. 



8/14. Even if the ultrastable system is suitably arranged — if the 

 critical states are encountered before the essential variables reach 

 their limits — it usually cannot adapt to an environment ' that 

 behaves with sudden discontinuities. In the earlier examples of 

 the Homeostat's successful adaptations the actions were always 

 arranged to be continuous; but suppose the Homeostat had con- 

 trolled a relay which was usually unchanging but which, if the 

 Homeostat passed through some arbitrarily selected state, would 

 suddenly release a powerful spring that would drag the magnets 

 away from their 'optimal ' central positions: the Homeostat, if 

 it happened to approach the special state, would take no step 



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