336 



J. F. DASHIELL 



also unlike all the results which the writer and his students had 

 previously gotten in work with these animals and this material. 

 It was soon after discovered that wild gray rats had lately found 

 their way into the building where the experiments were being 

 conducted and had even left their trail in the mazes. 



The exact form and degree of disturbance produced in the 

 white rats by the presence of the traces of the gray pests is a 

 thing yet to be made out in precise terms, but that there is a 

 general disturbance produced seems unquestionable from the 

 writer's observations. It may be mentioned incidentally that 



O. 



before the gray rats had been completely disposed of a few of 

 them had forced their way into nests of the white rats, wounding 

 or killing some of the inmates. 



The average rates of learning of the test maze Q for the eight 

 trials mentioned is given for the various groups in figure 7. 

 The hump in the curve for group III on the second trial is due to 

 the irregular performance of two of the five subjects of this group, 

 and does not seem significant inasmuch as (a) the three other 

 rats showed decrease in time in the second over the first trial, 

 and (b) four of the five subjects showed decrease in errors on the 

 second trial. 



Comparing records for groups I and II, little difference is 

 brought to light except a slight superiority for group II in both 

 the matter of time and the matter of errors after the fourth trial. 



