294 



ADA \Y. YERKES 



In order to compare these data with those obtained by Basset 11 

 in his work on habit formation in albino rats, the averages for 

 these seven rats are given in table 12. Like Basset's rats, these 

 inbred animals have a somewhat greater body length and body 

 weight than the stock rats, and have a larger per cent of water 

 in the brain and cord. Unlike his rats the brain weight of the 

 inbred rats is greater, not less, so that the relations of brain 

 weight to body length and to body weight are very nearly alike 

 for stock and inbred rats, and very close to Basset's averages 

 for normal animals, a little less in the former case, a bit greater 

 in the latter. 



Stock . . 

 Inbred. 



Stock.. 

 Inbred. 



The data of these experiments differ, therefore, from Basset's 

 in that these rats inbred for thirteen generations did not show 

 a brain weight much less than that of normal rats of an entirely 

 different strain. The results of Basset's experiments showed 

 that his inbred rats of the seventh and eighth generation, having 

 a less than normal brain weight, showed a less than normal 

 ability to form habits, less retention of the habit when formed, 

 and took a longer time to relearn than the normal rats. In 

 the experiments whose results are presented in this paper, a 

 smaller number of animals were tested. Of the rats for which 

 anatomical data were obtained, the inbred learned a trifle more 

 slowly than the stock rats, both in the maze and in the discrim- 

 ination experiments, but they carried discrimination of lightness 

 and darkness further, and showed the most pronounced differ- 

 ence only in their greater timidity and instability of behavior. 



11 Bassett, G. C. Habit formation in a strain of albino rats of less than normal 

 brain weight. Behavior Monographs, 1914, vol. 2, no. 4, p. 11. 



