50 Heredity. 



idea is perceived all the more vividly in proportion as the 

 mind is less occupied at the same moment with anything else. 

 When a person is deeply occupied, a new idea makes little im- 

 pression on his mind, because before it can lay hold of the con- 

 sciousness it has expended all its force. On the other hand, it is 

 well known that persons who are altogether idle interest them- 

 selves much about trifling details, and that an empty mind breeds 

 hypochondria. 



An idea that has passed away from the consciousness is not 

 destroyed, but only transformed. Instead of being a present idea, 

 it becomes a residuum, representing a certain tendency of the mind 

 exactly proportioned to the energy of the original idea. The 

 existence of ideas in the unconscious state might, therefore, be 

 regarded as a state of perfect equilibrium. ' Forgetfulness means 

 that the idea of a thing is in equilibrium with other ideas, and 

 recollection that this idea quits the state of equilibrium, and enters 

 the state of motion. No idea is lost ; and every operation of the 

 mind in virtue of which a latent idea passes to the active state 

 is a state of recollection.' x 



Amid all these hypotheses, which the future, perhaps, will show 

 to be truths, this remains certain and unquestionable, that the 

 phenomena of recollection are to be referred to the grand law of 

 the conservation of force, of which it is only a particular case. If, 

 now, we pass from this very general law to one that is less general 

 from a formula embracing all changes which occur in the universe 

 to a formula restricted to the domain of life we shall see memory 

 under another aspect. 



This biological law is habit. In the first place, habit, considered 

 in its essence, is referable to the law of the conservation of force, 

 for its cause is the primordial law or form of being that is, the 

 tendency of beings to persevere in the act which constitutes them. 

 As has been already seen, every act leaves in our physical and 

 mental constitution a tendency to reproduce itself, and when- 

 ever this reproduction occurs the tendency is strengthened ; and 

 thus a tendency, often repeated, becomes automatic. This 

 automatism is the link between memory and habit, and gave rise 



1 Miiller, Psychologic, ii. p. 517. 



