HABIT FORMATION IN ALBINO RATS 7 



five consecutive days. During this period the centre was barred 

 from the rest of the maze at entrance 6. At the age of seventy 

 days the experiment began. Eleven males and ten females 

 from the inbred strain were used and, as control, an equal num- 

 ber of males and females from the normal control series. Of 

 the inbred rats, fourteen were from the sixth generation and 

 seven from the seventh. The stimulus used was the food to 

 which they had become accustomed, bread soaked in milk. 



From the beginning of the experiment each rat was required 

 to run from E to F five times daily. At the end of the fifth trial 

 it was allowed to feed in the centre, F, for five minutes, but 

 permitted no more food until the completion of the next day's 

 experiment. Each rat was used daily until it had learned the 

 course perfectly, the criterion of perfection being five perfect 

 trials for each of three successive days. A perfect trial consisted 

 in running the course within six seconds, a period of time so 

 short that it was practically impossible for the rat to make a 

 detectable error and reach the centre within that time. Those 

 rats failing to learn within one hundred days (five hundred 

 trials) were no longer used for experinjentation. Such rats as 

 learned the maze were, at the conclusion of the experimentation, 

 fed for sixty days in a runway twenty-five feet long with a feed- 

 ing-box at the right of the far end. At the end of this period 

 they were tested for retention and relearning. 



The shortest period of time required by an inbred rat to 

 learn the maze perfectly was twelve days; for a control rat, 

 ten days. Two inbred rats and one control failed to learn the 

 maze habit within the one hundred days allowed. During the 

 process of learning certain of the normal control series showed 

 peculiarities of behavior similar to those exhibited by the inbred 

 strains. These peculiarities, for the greater part, consisted in 

 disorientation and persistent errors. All the normal control 

 series, with the exception of five rats containing germ-plasm of 

 the B strain, had perfected the maze habit by the twenty-fourth 

 day. The control rat mentioned above as having failed to learn 

 the maze within one hundred days was from this group. So 

 erratic in behavior and so slow in learning were the B strain 

 rats that the investigator suspected them to be of less than 

 normal brain weight; and, when the returns were received from 

 the Wistar Institute, this was indeed found to be the case. 



