264 ESSENTIALS OF BIOLOGY 



we positively know about the nervous system suggests that a 

 complex motor habit is made possible by some structural changes 

 involving cerebral tracts and groups of synaptic connections. 

 Apparently when these neurone-patterns have been established 

 the activity becomes an automatic one, is performed with facility 

 and, it may be, with an entire absence of consciousness of its 

 performance — that is, the acquired activity has become a habitual 

 one. The above statements apply particularly to neuro-muscular 

 activities, but they may be extended so as to include what is called 

 organic functioning. Thus a conditioned reflex w^hich involves 

 the secretion of saliva may be regarded as a glandular habit. 

 Acquirements, whether made spontaneously or as the results of 

 training, thus may become habits in the individual animals that 

 make them. 



Habits become instinctive activities a?id thus transformism is 

 effected. This is, of course, the doubtful step in the argument. 

 The acquirement, made spontaneously, or by imitation, or by 

 training, must be " transmitted by heredity " so that it occurs 

 again (without being " evoked " by imitation or training, and in 

 such a way as to suggest that it is not " spontaneous " in the sense 

 used above) in the progeny of the animal in which it first appeared. 

 That is, the habit, which depended on random fluctuations of 

 the behaviouristic mechanisms, now involves the developmental 

 organization so that the ability to do something, and the corre- 

 sponding changes of structure, are " congenital," " inborn," or 

 have become instincts and morphological changes. It is difficult 

 to resist coming to such a conclusion, which seems to be the natural 

 one. It is difficult to avoid thinking that the continual repetition 

 of an acquired habit, from generation to generation, will, by and 

 by, come to affect the developmental organization so that the 

 activity will be displayed '' instinctively," or without being 

 acquired. Such views have always been held both by laymen and 

 naturalists. (" The fathers have eaten sour grapes and the teeth 

 of the children are set on edge.") Much in human affairs suggests 

 that acquired activities (mental, or motor, or functional) tend to 

 become transmitted by heredity. For instance, the phenomena 

 of immunity to some diseases that follows upon prophylaxis seems 

 to point to such a conclusion. It has been said to be " inconceiv- 

 able " that the acquirement of some activity, or morphological 

 change, can affect the " germ-plasm " so that the acquirement 



