CHAPTER 13 



Disturbed Systems and Habituation 



13/1. We have seen that ultrastable systems are subject to two 

 conflicting requirements : complexity and speed. The system 

 with abundant internal connections, though able to represent 

 a complex and well-integrated organism and environment, 

 requires, at least in the form so far studied, almost unlimited time 

 for its adaptation. On the other hand, the same number of main 

 variables, divided into many independent parts, achieves adapta- 

 tion quickly, but cannot represent a complex biological system. 

 There are, however, intermediate forms that can combine, to 

 some extent, the advantages of these two extremes. Since the 

 properties of the intermediate forms are somewhat subtle we 

 shall have to proceed by small steps. As a first step I shall 

 examine in this chapter the properties of ultrastable systems that 

 are no longer completely isolated, as has been assumed so far, but 

 are subject to some slight disturbance from the outside. 



13/2. Before entering the subject, I must make clear a point of 

 method that will be used frequently. In Chapter 8, the discussion 

 of the ultrastable system necessarily paid so much attention to the 

 process by which the terminal field was reached that some loss of 

 proportion occurred; for the focusing of attention suggested 

 that the system spent most of its time reaching a terminal field, 

 whereas in the living organism this process may occupy only a few 

 moments — a time unimportant in comparison with the remainder 

 of the organism's life during which the terminal field will act 

 repeatedly to keep the essential variables within limits. 



From this point of view the terminal field is more important 

 than the preceding fields simply because it is permanent while 

 the others are transient. As we increase the time over which the 

 system is observed, so do the transient fields become negligible. 

 The same principle is used in the Darwinian theory of natural 



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