1890 SALLY 257 



the difference between two quantities of sensuous 

 perceptions, and distinguishing between numbers of 

 any amount by marking each sensuous perception 

 with a separate sign. Of course, in the above in- 

 stance of animals counting it must be the former 

 method alone that is employed, and, therefore, I have 

 not sought to carry the ape beyond the number 5 

 lest I should spoil the results already gained. But a 

 careful research has been made to find how far this 

 method can be carried in the case of man. The 

 experiments consisted in ascertaining the number of 

 objects (such as dots on a piece of paper) which admit 

 of being simultaneously estimated with accuracy. It 

 was found that the number admits of being largely 

 increased by practice, until, with an exposure to view 

 of one second's duration, the estimate admits of 

 being correctly made up to between 20 and 30 objects. 

 (Preyer, ' Sitzungsber. d. Gesell. f. Med. u. Naturwiss.,' 

 1881.) In the case of the ape it is astonishing over 

 how long a time the estimate endures. Supposing, 

 for instance, that she is requested to find five coloured 

 straws. She perfectly well understands what is 

 wanted, but as coloured straws are rare in the litter, 

 she has to seek about for them, and thus it takes her 

 a long time to complete the number ; .yet she remem- 

 bers how many she has successively found and put 

 into her mouth, so that when the number is com- 

 pleted she delivers it at once. After having consigned 

 them to her mouth she never looks at the straws, and 

 therefore her estimate of their number must be formed 

 either by the feeling of her mouth, or by retaining a 

 mental impression of the successive movements of her 



s 



