HABIT FORMATION IN THE ALBINO RAT 5 



and care for in large numbers than any other small mammal. 

 For reasons which will appear later, we adopted the circular 

 maze as our problem since it is generally conceded that the rat 

 is pre-eminent among animals in his ability to thread a labyrinth, 

 while his satisfactoriness as a subject for experimental work 

 is attested by the number of experimenters who have employed 

 him in various capacities. 



The rats were bred in our own laboratory as needed, inbreeding 

 being carefully avoided and all possible care being taken to 

 maintain uniformity of breeding conditions. All of the rats 

 were weaned at from eighteen to twenty- three days, 15 and the 

 sexes were separated at thirty-five to forty days and kept sepa- 

 rate thereafter. The living cages were protected from mice and 

 gray rats by screened compartments constructed of pine and 

 one fourth inch wire mesh. Every two weeks the cages were 

 thoroughly cleaned, the shelves washed with a disinfecting solu- 

 tion, and the rats dipped in a one per cent solution of " Kreso" 

 to prevent the rise and spread of vermin. The animals were 

 carefully watched and treated immediately upon the appear- 

 ance of parasites, so that they were kept continually in a healthy 

 condition. The diet consisted of milk-soaked bread given every 

 day, and a mixture of cracked corn and sun-flower seed every 

 other day. They seemed to thrive on this somewhat restricted 

 diet, so that no additions were made to it although both Basset 

 and Ulrich used carrots and fruit occasionally. 



The rats were handled freely from birth, and consequently 

 were perfectly tame and evinced no fear of the experimenter. 

 Special care was taken to tame any rat seeming a little wild, 

 before beginning work with him; since it was believed that fear 

 and timidity might cause irregularities in behavior, a belief 

 which was substantiated during the course of the experiment. 



It was desired in this work to obtain not only a record of 

 time but also a distance record of the learning process, since 

 it was felt that this might throw considerably more light on the 

 factors involved in learning than had yet been obtained. The 

 maze problem seemed to offer greater possibilities in this line 

 than either sensory problems requiring a long and tedious course 

 of preliminary training, or problems of manipulation permitting 



15 No bad effects were noticed from this early weaning and the rats were found 

 to be extremely active as early as the sixteenth day. See Slonaker, op. cit., p. 350. 



