THE MACHINE WITH INPUT 4/22 



less alike. In this system various properties, if they exist in one 

 place, can also exist in other places. It follows that the basic 

 properties of the biological world will be of the types to be described 

 in the following sections. 



4/22. Self-locking properties. It is a general property of these 

 systems that their behaviour in time is much affected by whether 

 there can, or cannot, develop properties within them such that the 

 property, once developed, becomes inaccessible to the factors that 

 would "undevelop" it. Consider, for instance, a colony of oysters. 

 Each oyster can freely receive signals of danger and can shut close; 

 once shut, however, it cannot receive the signals of safety that would 

 re-open it. Were these the only factors at work we could predict 

 that in time the colony of oysters would pass entirely into the shut 

 condition — an important fact in the colony's history! 



In many other systems the same principle can be traced more 

 seriously, and in almost all it is important. Consider, for instance, 

 a solution of reacting molecules that can form various compounds, 

 some of which can react again but one of which is insoluble, so that 

 molecules in that form are unreactive. The property of "being the 

 insoluble compound" is now one which can be taken by part after 

 part but which, after the insolubility has taken the substance out of 

 solution, cannot be reversed. The existence of this property is 

 decisive in the history of the system, a fact well known in chemistry, 

 where it has innumerable applications. 



Too little is known about the dynamics of the cerebral cortex for 

 us to be able to say much about what happens there. We can 

 however see that if the nerve cells belong to only a few types, and if 

 the immediate effects between them are sparse, then if any such 

 "self-locking" property can exist among them it is almost certain 

 to be important — to play a major part in determining the cortex's 

 behaviour, especially when this continues over a long time. Such 

 would occur, for instance, if the cells had some chance of getting 

 into closed circuits that reverberated too strongly for suppression 

 by inhibition. Other possibilities doubtless deserve consideration. 

 Here we can only glance at them. 



The same principle would also apply in an economic system if 

 workers in some unpleasant industry became unemployed from time 

 to time, and during their absence discovered that more pleasant 

 forms of employment were available. The fact that they would pass 

 readily from the unpleasant to the pleasant industry, but would 

 refuse to go back, would clearly be a matter of high importance in 

 the future of the industry. 



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