7 

 done because it was early noticed how eager the rats were 



to feed when the operator first entered the room and how 

 this eagerness subsided after he had been present any 

 length of time. This connection of the operator with the 

 getting of food was seized upon as indicating a timely 

 moment for work. Of course, when there were from five to 

 ten groups of rats to work with.it was impossible to reach 

 the last of them before this eagerness subsided, there- 

 fore a system of rotation in handling the groups was • 

 adopted, whereby the same group was not taken first every 

 morning but every second or third morning. If the rats 

 had been kept apart from the room in which the work took 

 place, rotation would probably have been unnecessary. 



The time for each trial was taken by a stop watch in 

 minutes, seconds and half seconds, later the seconds were 

 converted into decimals of a minute. The time spent by 

 the rats in nosing about in the entrance box was not 

 considered, but from the moment when the rats entered the 



