292 ADA W. YERKES 



the food box, a trick none of the others attempted. All four 

 of the stock rats ate readily on returning to the food box, even 

 after having been punished. 



In the discrimination experiments one peculiarity was early 

 noticed. Five of the eight rats developed the habit, on enter- 

 ing the space in front of the discrimination chambers, of run- 

 ning immediately to one side or the other, right or left, but 

 always the same for each rat. When discrimination was easy, 

 if that chanced to be the side on which was the light box they 

 would enter at once or stop for a brief comparison of the two 

 boxes. Four of the five always went to the right, one to the 

 left. A sixth one showed a tendency to go first to that side 

 on which the light box had been in the previous trial. 



4. ANATOMICAL DATA 



Under the conditions of these experiments it was found im^ 

 possible to have a large number of rats finish at the same time 

 and anatomical data were obtained, therefore, for only the seven 

 rats which survived at the close of the memory tests given after 

 the discrimination experiment. These data are given in table 1 1. 



The section of the table marked W. I. R T. (Wistar Insti- 

 ture Reference Tables) gives data compiled at the Institute, 

 from many rats having the same body length, and serves as a 

 standard for comparison. If we examine the first horizontal 

 line we find that No. 80, stock female, had a body length of 

 179 mm.; tail length, 144 mm.; body weight 133.5 grms.; brain 

 weight 1.6805 grms.; spinal cord weight .4578 grms.; we'ght of 

 water in the brain 1.3212; in cord .3296; per cent of water in 

 brain 78.619; in cord, 71.997. Comparing this with the Wistar 

 average of rats having the same body length, we find that in 

 No. 80 the tail length is low, body weight low, brain and cord 

 weights low, and the per cents of water in the brain and cord 

 are high. This is uniformly the case with all seven animals, 

 but it is noticeable that especially in the inbred rats is the per 

 cent of water high. For their age all the rats were under 

 weight, as the Wistar average for males of that age was over 

 200 grams., and for females nearly 200 grams. It is probable 

 that in feeding the animals only once a day, at the close of the 

 experiments, they did not get enough food for normal growth, 

 although they did keep in good physical condition. 



