9/4 ULTRASTABILITY IN THE ORGANISM 



the street alike build up their ideas of how things are connected in 

 the simple material or anatomical sense. So the child learns that 

 when he picks up one end of a rattle the other end comes up too ; 

 and so the demonstrator of anatomy shows that if a certain tendon 

 in the forearm is pulled, the thumb moves. These operations 

 specify a diagram of immediate effects, a pattern of connectivity, 

 of great commonness and importance. But we must beware of 

 thinking that it is the only pattern; for there are also systems 

 whose parts or variables have no particular position in space 

 relative to one another, but are related dynamically in some 

 quite different way. Such occurs when a mixture of substrates, 

 enzymes, and other substances occur in a flask, and in which the 

 variables are concentrations. Then the ' system ' is a set of con- 

 centrations, and the diagram of immediate effects shows how the 

 concentrations affect one another. Such a diagram, of course, 

 shows nothing that can be seen in the distribution of matter in 

 space; it is purely functional. Nothing that has been said so 

 far excludes the possibility that the anatomical-looking Figure 

 7 1 5 /l may not be of the latter type. We must proceed warily. 



9/3. The chief part of Figure 7/5/1 that calls for comment is the 

 feedback from environment, through essential variables and step- 

 mechanisms, to the reacting part R. The channel from environ- 

 ment to essential variables hardly concerns us, for it will depend 

 on the practical details for the particular circumstances in which, 

 at any particular time, the free-living organism finds itself. 



The essential variables, being determined by the gene-pattern 

 (S. 3/14), will often have some simple anatomical localisation. 

 Some of them, for instance, are well known to be sited in the 

 medulla oblongata; and others, such as the signals for pain, are 

 known to pass through certain sites in the midbrain and optic 

 thalamus. More accurate identification of these variables demands 

 only detailed study. 



Step -mechanisms in the organism 



9/4. Quite otherwise is it with the step-mechanisms. We have 

 at present practically no idea of where to look, nor what to look 

 for. In these matters we must be very careful to avoid making 

 assumptions unwittingly, for the possibilities are very wide. 



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