CHAPTER 9 



Ultrastability in the 

 Living Organism 



9/1. The principle of ultrastability has so far been treated as 

 a principle in its own right, true or false without reference to 

 possible applications. This separation has prevented the possi- 

 bility of a circular argument ; but the time for its application 

 has now come. I propose, therefore, the thesis that the living 

 organism uses the principle of ultrastability as an automatic 

 means of ensuring the adaptiveness of its learned behaviour. 

 At first I shall cite only facts in its favour, leaving all major 

 criticisms to Chapter 11. We shall have, of course, to assume 

 that the animal, and particularly the nervous system, contains 

 the necessary variables behaving as step-functions : whether this 

 assumption is reasonable will be discussed in the next chapter. 



Examples of adaptive, learned behaviour are so multitudinous 

 that it will be quite impossible for me to discuss, or even to 

 mention, the majority of them. I can only select a few as 

 typical and leave the reader to make the necessary modifications 

 in other cases. 



The best introduction is not an example of learned behaviour, 

 but Jennings' classic description of the reactions of Stentor, a 

 single-celled pond animalcule. I shall quote him at length : 



4 Let us now examine the behaviour [of Stentor] under 

 conditions which are harmless when acting for a short time, 

 but which, when continued, do^ interfere with the normal 

 functions. Such conditions may be produced by bringing a 

 large quantity of fine particles, such as India ink or carmine, 

 by means of a capillary pipette, into the water currents 

 which are carried to the disc of Stentor. 



1 Under these conditions the normal movements are at 

 first not changed. The particles of carmine are taken into 

 the pouch and into the mouth, whence they pass into the 

 internal protoplasm. If the cloud of particles is very dense, 



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