276 THEORETICAL BIOLOGY 



automatically. We even call our own actions instinctive, 

 when a series of movements in conformity with plan are per- 

 formed by us according to a law of their own, which adapts 

 itself to the external conditions without being automatic. 



TTn7 mAQTTr ArTinxT ^ ^^I AO E 

 THE PLASTIC ACTION = j ~ ~~ T ~ T 



The plastic action, in the narrower sense, refers only to 

 the plasticity of the mark-organ, while the course of the pro- 

 cesses in the action-organ is reflex. I would remind you of 

 the dogs in which Pawlow managed to connect the secretion of 

 saliva with new indications of an optical or acoustic nature. 

 In this case also there can be no doubt that new framework 

 appears. The presumption, of course, is that the indications 

 brought into fresh prominence were already there. But 

 there is introduced a new kind of connection between these 

 indications and effector processes not hitherto under their 

 influence. 



The plasticity in this case depends, not on a mere in- 

 fluencing of the rhythm of a given impulse-series, but on the 

 introduction into this law of impulses hitherto unused. Not 

 merely is the rule of working governed by a rule of direction, 

 but a new one makes its appearance. In such a case, after 

 formation of the new framework in the mark-organ, this rule 

 may withdraw, leaving behind it merely a new reflex action 

 as evidence of a plasticity that once was there. 



THE ACTION BASED ON EXPERIENCE = j - — -j 



When, by whistling to his bull-finch, a boy gets it to pipe 

 a new tune by itself, that is an action of experience on the 

 part of the bull-finch. It is characterised by there arising, 

 not merely a new combination of indications in the mark- 



