Literary Notices. 337 



The mice displayed ability, varying with the individual, to discriminate different 

 shades of gray paper, though their capacity in this direction was less than that of 

 a human being. One mouse was subjected to tests of the validity of Weber's 

 Law, in discriminations of the degree of illumination in different compartments; 



D R 

 and the law was found to hold, the proportion -~ lying between i-io and 1-15. 



These discriminations were greatly improved by practice. 



As regards color discrimination, much of the behavior superficially to be classed 

 under this head appeared on further investigation to be really based on the bright- 

 ness value of the colors. This value is apparently quite different in the case of the 

 mouse from what it is in the human subject. The red end of the spectrum is 

 much darker to the mouse, being indistinguishable* from black and darker than 

 any green or blue. There is some evidence that the mice can discriminate green 

 and red "by some other factor than brightness," but on the whole the problem of 

 their color vision is not solved. The dancer was found to be incapable of distinguish- 

 ing between two equal illuminated areas of equal brightness but different form. 

 Mice that have learned a labyrinth path are little disturbed in traversing it by 

 being made to do so in darkness, by washing the labyrinth so as to destroy smell 

 clues, or by moving the labyrinth to one side so that the former track is removed. 

 They were a good deal disturbed when the fioor was covered with smoked paper, 

 but Dr. Yerkes thinks this disturbance was a general one and not the result of 

 loss of a clue. The role of the senses of sight, smell, and touch in the learning of a 

 labyrinth path, quite a different problem from the effect of eliminating a sense after 

 the animal has learned the path, was not experimentally tested; observation of the 

 general behavior of the animals led to the conclusion that these senses are all used, 

 but in different degrees by different individuals. 



2. The results that bear especially on the mouse's learning capacity are as fol- 

 lows. The dancer is capable of forming habits that involve turning in one direc- 

 tion or another (labyrinth habits), and habits that require in addition visual dis- 

 crimination, but the former are acquired much more rapidly than the latter. A 

 regular labyrinth, involving turns alternately in two directions, is learned with espe- 

 cial speed. Useless habits occasionally persist for some time, a fact which several 

 other investigators have noted. The mice did not learn by imitating each other. 

 Putting the animals through one of the reactions which they learned, that of climb- 

 ing a ladder, did aid the learning process. Dr. Yerkes's conclusions regarding 

 sex differences in learning capacity are less convincing than his other inferences 

 from results. He says, "In labyrinth tests the female is as much superior to the 

 male as the male is to the female in discrimination tests." Yet in the tables upon 

 which the first part of this statement is based, although the average number of 

 tests which had to be given before the labyrinth was perfectly learned was 18.7 for 

 the males and 13.8 for the females, five of the ten males learned with fewer tests 

 than did five of the females. "Of the five pairs of individuals whose records in 

 white-black training appear in Table 43," says the author,"not one contradicts" 

 the statement that the males are superior to the females in discrimination experi- 

 ments. This table contains the results of tests of black-white discrimination 

 made at the rate often per day; but Dr. Yerkes himself points out that the 

 females did better than the males when twenty tests per day were given. 



The experiments on the relation of docility to age were not completed. As 



