17/1 DESIGN FOR A BRAIN 



possibility makes the homeostat unrepresentative ; for a man 

 does not, like a prince in a fairy tale, pass instantaneously from one 

 world to another, but has rather a series of environments that are 

 interrelated, neither wholly separate nor wholly continuous. We 

 are, in fact, led again to consider the properties of a system whose 

 connections are fluctuating and conditional — the type encoun- 

 tered before in S. 11/8, and therefore treatable by the same 

 method. I suggest, therefore, that many of the environments 

 encountered on this earth by living organisms contain many part- 

 functions. Conversely, a system of part-functions adequately 

 represents a very wide class of commonly occurring environments. 

 As a confirmatory example, here is Jennings' description of an 

 hour in the life of Paramecium, with the part-functions indicated 

 as they occur. 



(It swims upwards and) ' . . . thus reaches the surface film.' 



The effects of the surface, being constant at zero throughout the 

 depths of the pond, will vary as part-functions. A discontinuity 

 like a surface will generate part-functions in a variety of ways. 



1 Now there is a strong mechanical jar — someone throws a 

 stone into the water perhaps.' 



Intermittent variations of this type will cause variations of part- 

 function form in many variables. 



(The Paramecium dives) ' . . . this soon brings it into water 

 that is notably lacking in oxygen.' 



The content of oxygen will vary sometimes as part-, sometimes as 

 full-, function, depending on what range is considered. Jennings, 

 by not mentioning the oxygen content before, was evidently 

 assuming its constancy. 



4 ... it approaches a region where the sun has been . . . 

 heating the water.' 



Temperature of the water will behave sometimes as part-, sometimes 

 as full-, function. 



(It wanders on) ' . . . into the region of a fresh plant stem 

 which has lately been crushed. The plant- juice, oozing out, 

 alters markedly the chemical constitution of the water.' 



Elsewhere the concentration of these substances is constant at 

 zero. 



4 Other Paramecia . . . often strike together ' (collide). 



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