USE OF THE HANDS IN THE RHESUS MONKEY 185 



transfer occurred and differentiating them from the others was 

 the presence of the wire netting of the cage between the experi- 

 menter and the animal. When on the leash the monkey was 

 directly exposed to attack and in taking food from the table 

 in front of the cage he had to put his hands between the wires 

 of the front of the cage and so expose them to attack. The 

 stimuli from the presence of the wire netting between the mon- 

 key and the experimenter seem, then, to have formed the limit- 

 ing condition for the transfer of training. 



An attempt at a further analysis of the role of these stimuli 

 in determining the transfer is hardly justified by our present 

 knowledge. In their cages the animals frequently give more 

 threatening reactions than when held by a leash, so it may be 

 that a certain physiological tone or emotional reaction, common 

 to a part of the situations, reinforced the habit and led to its 

 transfer to all of them in which it was present. The transfer 

 might also be looked upon as the result of an analysis of the 

 situations in ideational terms, but this and the concept of physio- 

 logical tone are, themselves, so badly in need of experimental 

 analysis as to amount to nothing more than a restatement of 

 the problem when applied as explanatory principles. We can 

 say safely only that the habit of using the left hand was condi- 

 tioned by a complex group of stimuli. 



The ease with which the predominance in the use of the 

 hands may be altered by training will make it very difficult 

 to establish the existence of any hereditary predominance. We 

 never know the complete history of an animal or can exclude 

 the possibility of a severe trauma which might condition the 

 use of one or the other hand. Only the observation of the 

 predominant use of one hand in a wide variety of situations 

 and in situations entirely new to the animal could furnish reliable 

 evidence for an hereditary predominance. 



The possibility that the use of the hands by human infants 

 may be equally easily modified by training makes the existing 

 data upon handedness in young children of very doubtful value. 

 Mrs. Woolley ('10) believed that the predominant use of the 

 left hand by the infant which she studied was the result of the 



