OBSERVATIONS ON THE PREFERENTIAL USE OF 

 THE RIGHT AND LEFT HANDS BY MONKEYS 



SHEPHERD IVORY FRANZ 



From the Psychological Laboratory of the Government Hospital for the Insane, 



Washington, D. C. 



In the course of a series of observations on the formation of 

 simple habits by monkeys careful records were kept of the 

 number of times each hand was used by an animal in taking 

 the food which was presented. These observations are the data 

 used in the preparation of the present communication. Six 

 years previously I had observed that among a dozen monkeys 

 certain ones tended to hold to the wire netting of the cage with 

 one hand and to grasp with the other the food which was pre- 

 sented to them outside the cage. It appeared that there were 

 marked individual differences, one animal apparently almost 

 always using the right hand and arm for holding to the wire 

 front of the cage and the left hand for taking the food, while 

 another animal would reverse the hands in these two acts. 

 These early observations were not systematically collected, but 

 observations were made to determine whether or not it would 

 be difficult to change the actions so that the animal which 

 habitually used the right arm and hand to steady itself on the 

 wire of the cage would learn to use that hand for grasping. 

 It was found that after a few tests, twenty to thirty, in which 

 the righthanded monkey was refused food when this hand 

 grasped for it, and was given food in the left hand, this animal 

 learned to hold with the right hand to the wire and to grasp for 

 the food with the left. The ease with which the apparent habit- 

 ual reaction was replaced by one of a different tendency led me 

 to the belief that the apparent proneness to the exclusive, or 

 almost exclusive, use of either hand might be due to any one 

 of a number of extraneous factors, such as the position of the 

 experimenter, his use of the right hand in delivering the food, 

 etc. Further experiments to determine the truth or falsity of 

 this belief were not made. Subsequently, the data presented 

 in this paper were collected. 



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