DESIGN FOR A BRAIN 5/6 



reactions. Take the type-problem of the kitten and the fire. 

 When the kitten first approaches an open fire, it may paw at the 

 fire as if at a mouse, or it may crouch down and start to ' stalk ' 

 the fire, or it may attempt to sniff at the fire, or it may walk un- 

 concernedly on to it. Every one of these actions is liable to lead 

 to the animal's being burned. Equally the kitten, if it is cold, 

 may sit far from the fire and thus stay cold. The kitten's 

 behaviour cannot be called adapted, for the temperature of its 

 skin is not kept within normal limits. The animal, in other words, 

 is not acting homeostatically for skin temperature. Contrast this 

 behaviour with that of the experienced cat: on a cold day it 

 approaches the fire to a distance adjusted so that the skin tempera- 

 ture is neither too hot nor too cold. If the fire burns fiercer, the 

 cat will move away until the skin is again warmed to a moderate 

 degree. If the fire burns low the cat will move nearer. If a red- 

 hot coal drops from the fire the cat takes such action as will keep 

 the skin temperature within normal limits. Without making any 

 enquiry at this stage into what has happened to the kitten's brain, 

 we can at least say that whereas at first the kitten's behaviour 

 was not hom'eostatic for skin temperature, it has now become so. 

 Such behaviour is ' adapted ' : it preserves the life of the animal 

 by keeping the essential variables within limits. 



The same thesis can be applied to a great deal, if not all, of 

 the normal human adult's behaviour. In order to demonstrate 

 the wide application of this thesis, and in order to show that even 

 Man's civilised life is not exceptional, some of the surroundings 

 which he has provided for himself will be examined for their 

 known physical and physiological effects. It will be shown that 

 each item acts so as to narrow the range of variation of his 

 essential variables. 



The first requirement of a civilised man is a house; and its 

 first effect is to keep the air in which he lives at a more equable 

 temperature. The roof keeps his skin at a more constant dryness. 

 The windows, if open in summer and closed in winter, assist in 

 the maintenance of an even temperature, and so do fires and 

 stoves. The glass in the windows keeps the illumination of the 

 rooms nearer the optimum, and artificial lighting has the same 

 effect. The chimneys keep the amount of irritating smoke in the 

 rooms near the optimum, which is zero. 



Many of the other conveniences of civilisation could, with little 



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