8 GARDNER CHENEY BASSET 



For greater convenience in making a comparative study, I 

 have placed together in Table I a summary consisting of the 

 daily averages of the entire inbred group and, directly beneath, 

 the corresponding daily averages of the entire normal control 

 group. From this table, too, are constructed the comparative 

 curves of learning. 



Table I compares: (a) the progress of learning by days; 

 (b) the ' 'absolute retention" (this being a term used here to 

 represent the time required to complete the first trial of the 

 relearning series after the sixty days' rest; the greater the re- 

 tention, the less is the time) ; (c) the progress of relearning by 

 days; (d) the anatomical data. 



Table la shows that two of the inbred and one of the control 

 rats (the latter from the" B strain) failed to learn the maze habit. 

 The inbreds required, on the average, 36.62+ days to learn; 

 the control but 24.67+ days. The absolute retention of the 

 inbred rats (Table Ib) was, on the average, 81.558 seconds; 

 of the control series, 59.640 seconds. The two inbreds and one 

 control failing to learn the maze were not, of course, tested for 

 retention and relearning. Of the inbreds so tested (Table Ic), 

 two failed to relearn within fifty days, in consequence of which 

 it was thought useless to carry them further. All the control 

 series had relearned at the end of twenty-two days. The inbreds 

 required, on the average, 12.68+ days to relearn; the normals 

 but 5.75 days. 



In all these criteria of ability: learning, absolute retention, 

 and relearning, the rats of the normal control series are shown, 

 on the average, to be superior to those of the inbred series. 



There are two methods in use for estimating the relative 

 brain weight: in reference to body length and in reference to 

 body weight. In a healthy normal rat the difference between 

 body weight in grams and body length in millimeters is slight; 

 but, under conditions of overfeeding, underfeeding, or of sick- 

 ness the body weight varies greatly while the body length 

 remains constant. For this reason Dr. Donaldson of the Wistar 

 Institute has accepted body length as the better method. I 

 have laid greater stress on the body length criterion, although 

 both are presented in the tables of anatomical data. Both 

 body length and body weight of the inbred rats used in the 

 maze (Table Id) are, on the average, slightly greater than is 



