46 GARDNER CHENEY BASSET 



and the number of days required to relearn after sixty days' 

 rest. But most of the rats relearned very quickly without 

 reference to trie number of days required for learning ; in numbers, 

 too, the rats were too few for such mathematical consideration. 

 An investigation along such a line should consist of but one 

 relatively simple experiment; several hundred rats of one sex 

 only should be used; and the period of time between the corii- 

 pletion of learning and the beginning of relearning should be 

 lengthened to, at the least, ninety days. 



The general results of the experiments here set forth may be 

 summed up as follows: On the average, the strain of inbred rats 

 having a less than normal relative brain weight did less well in 

 learning to form habits than did the normal control series. 



From these results the following may be formulated: A less 

 than normal brain weight in a strain of rats is accompanied by a 

 less than normal ability to form habits. 



ADDENDUM 



The tables of individual daily averages, from which the tables 

 of group averages contained in this monograph are derived, are 

 so extensive as to preclude publication. If, however, any may be 

 interested in them, the original copy is deposited with the library 

 of the Wistar Institute of Anatomy and Biology, Philadelphia, 

 Pennsylvania; and a duplicate is in the private library of the 

 author'. 



