VISION IN THE MOUSE 



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In the next experiment, light gray paper was substituted for 

 the white with the following results. 



The strips were now taken up and the tin boxes were covered 

 respectively with light gray and dark gray papers. No back- 

 grounds were used. 



The experiment resulted as follows: By mouse D, in 40 trials, 

 the light gray was chosen 19 times, the dark gray 21 times. 



Experiment (d). Selection of yarns. 



Preference of mice for light or dark yarns obviously depends 

 upon their power of discrimination. 



Method : Neither food nor electric shock was used in this 

 experiment. Advantage was taken of the opportunity afforded 

 by the instinct of a mother mouse to make a warm nest for her 

 litter. A black mouse, X, about six months old, with five little 

 ones, was taken as subject. When the young mice were a little 

 over a week old, pieces of yarn were hung in the cage and some 

 of the cotton was removed from the nest. The order in which the 

 mouse took the different yarns to replenish the nest was recorded. 



Theyarnsused were white, black, and two shadesof gray. These 

 were hung in the cage in a row, 4 cm. apart and at a distance of 

 15 cm. from the entrance to the nest. The lower ends rested on 

 the floor of the cage. After a set had been pulled down by the 

 mouse and taken into the nest, four other pieces were hung up in 

 a different order. After three or four sets had thus been taken they 

 were removed from the nest and the experiment was repeated. 



In anentire series all the possible arrangements of the four shades 

 were made. There being six possible permutations of the four 

 yarns and four places, there were 96 selections in the series, each 

 yarn appearing in each place six times. The order in choosing the 

 four positions was recorded also, in order to show what influence 

 the habit of first seeking a certain locality might have. 



