144 NOTES 



A similar device has been used by Professor Casteel in his study of visual dis- 

 crimination in turtles. 1 He placed white designs on pendulums and caused them 

 to swing slowly back and forth in order that they might "attract and concentrate 

 the attention of the animals." 



Another important variation in the method is to present a single stimulus thus 

 having only one object upon which attention is to be concentrated. The organism 

 may be trained either to seek or to avoid the given object. Later, this object 

 may be presented with a more or less similar object and discrimination on the 

 basis of certain characteristics demanded. 



Other variations may be introduced as seems desirable by the employment of 

 stimuli for different senses. Visual and olfactory stimuli may be employed simul- 

 taneously, or olfactory and auditory, or visual, olfactory, and auditory. In cer- 

 tain cases, it may prove very advantageous to introduce stimuli which are naturally 

 interesting to an organism even although those stimuli are not to be used other- 

 wise than to control the attention and encourage the organism to effort. 



Every experimental study of an organism emphasizes the importance of knowl- 

 edge, insight, and ingenuity on the part of the investigator. He can not know 

 too much about the habits, instincts, and environmental relations of the organism 

 under consideration. Nor can he be too much given to distrusting and discounting 

 the value of human experience as a guide in the study of animal behavior. 



Finally, it may not be superfluous to emphasize the importance of avoiding 

 the overworking of animal subjects, for especially in the higher organisms it is 

 clear that too frequent necessity for reaction to a situation, even although the 

 reaction can be made appropriately, has a bad effect upon the organism. It is 

 extremely important, also, to avoid discouragement on the part of the animal. 

 This may result from too frequent experimentation, too prolonged experimenta- 

 tion, or demands for discrimination under conditions which are overdifficult. 



In connection with these dangers of experimentation, overfeeding is a frequent 

 mistake on the part of experimenters. It is a good laboratory rule to supply 

 animals with an abundance of sunlight, fresh air, to make them work for a living, 

 and to restrict the amount of food obtained to that necessary to keep them strong 

 and active. ROBERT M. YERKES 



1 Casteel, D. B. The discriminative ability of the painted turtle. Journal of 

 Animal Behavior, 1911. vol. 1, p. 15. 



