114 MENTAL EVOLUTION IN ANIMALS. 



our chapter on the Physical Basis of Mind, that conscious 

 memory may become degraded into unconscious memory by 

 repetition; associations originally mental lapsing into asso- 

 ciations that are automatic. 



Thus much being premised touching the physical basis of 

 memory, we may next pass on to consider the evolution of 

 memory on its psychological side. 



The earliest stage of true or conscious memory may, I 

 think, be regarded as consisting in the after-effect produced 

 upon a sensory nerve by a stimulus, which after-effect, so 

 long as it endures, is continuously carried up to the sensorium. 

 Such, for instance, is the case with after-images on the retina, 

 the after-pain of a blow, &c.* 



The next stage of memory that it appears to me possible 

 to distinguish by any definite interval from the first-named, 

 is that of feeling a present sensation to be like a past sensa- 

 tion. In order to do this there may be no memory of the 

 sensation between the two successive occasions of its occur- 

 rence, and neither need there be any association of ideas. 

 Only this takes place ; when the sensation recurs the second, 

 third, or fourth time, &c., it is recognized as like the sensa- 

 tion when it occurred the first time — as like a sensation 

 which is not unfamiliar. Thus, for example, according to 

 Sigismund, who has devoted much careful attention to the 

 psychogenesis of infants, it appears that the sweet taste of 

 milk being remembered by newly-born infants, causes them 

 to prefer sweet tastes in general to tastes of any other kind. 

 This preference of course endures long after the time of 

 weaning is past, and generally continues through childhood ; 

 but the interesting point in the present connection is that it 

 occurs too early in the life of the child to admit of our sup- 

 posing that any association of ideas can take part in the 

 process. For Sigismund says that the memory of the taste of 

 milk becomes attached to the perception '' immediately," 

 and Preyer states, from independent observations of his own, 

 that the preference shown for sweet tastes over tastes of all 

 other kinds may be clearly seen as early as the first day. 



The next distinguishable stage of memory is reached 

 when, still without any association of ideas, a present sensa- 

 tion is perceived as unlike a past one. Thus, again turning 

 to the observations of Sigismund and Preyer, it appears from 



* Compare Wundt, Qrundziige der philosophischen Psychologie, p. 791. 



