ULTRASTABILITY IN THE LIVING ORGANISM 9/1 



repeatedly and violently while still enclosed in its tube. In 

 this way the attachment of its foot to the object on which 

 it is situated is broken and the animal is free. Now it 

 leaves its tube and swims away. In leaving the tube it may 

 swim forward out of the anterior end of the tube ; but if 

 this brings it into the region of the cloud of carmine, it 

 often forces its way backwards through the substance of 

 the tube, and thus gains the outside. Here it swims away, 

 to form a new tube elsewhere. 



1 . . . the changes in behaviour may be summed up as 

 follows : 



(1) No reaction at first ; the organism continues its normal 



activities for a time. 



(2) Then a slight reaction by turning into a new position. 



(3) ... a momentary reversal of the ciliary current . . . 



(4) . . . the animal breaks off its normal activity com- 



pletely by contracting strongly . . . 



(5) ... it abandons its tube . . . ' 



The behaviour of Stentor bears a close resemblance to the 

 behaviour of an ultrastable system. The physical correspon- 

 dences necessary would be as follows : — Stentor and its environ- 

 ment constitute an absolute system by S. 3/9 ; for Jennings, 

 having set the carmine flowing, interferes no further. They 

 consequently correspond to the whole ultrastable system, which 

 is also absolute by the definition of S. 8/4. The observable 

 (here : visible) variables of Stentor and its environment corre- 

 spond to the main variables of the ultrastable system. In Stentor 

 are assumed to be variables which behave like, and correspond 

 to, the step -functions of the ultrastable system. The critical 

 states of the organism's step-functions surround the region of 

 the normal values of the organism's essential variables so that 

 its step-functions change value if the essential variables diverge 

 widely from their usual, normal values. These critical states 

 must be nearer to the normal value than the extreme limits of 

 the essential variables, for these critical states must be reached 

 before the essential variables reach the extreme limits compatible 

 with life. 



Now compare the behaviour of the ultrastable system, de- 

 scribed in S. 8/7, with the behaviour of organisms like Stentor, 

 epitomised by Jennings in these words : 



1 Anything injurious to the organism causes changes in 

 its behaviour. These changes subject the organism to new 



105 



