ACKNOWLEDGMENTS . 



Before entering upon the body of this presentation I desire 

 to express my obligations to those without whose co-operation 

 my experiments would have been of less value. 



Above all am I indebted to Professor John B. Watson, Direc- 

 tor of the Johns Hopkins Psychological Laboratory, who has 

 kept himself informed of the progress of my experimentation 

 and who has been ready at all times with helpful suggestions 

 and encouragement. 



To Dr. Henry H. Donaldson I owe much: for suggesting 

 the experiment; for placing the facilities and materials of the 

 Wistar Institute at my disposal; for much helpful advice as 

 to the evaluation of my results. 



To Dr. Shinkishi Hatai for preparing the anatomical data 

 referring to the rats used in my experiments. 



To Dr. Helen D. King for keeping her sequences of in- 

 breeding moving so perfectly that it was possible at any time 

 to procure inbred rats of the desired age. 



GARDNER CHENEY BASSET. 



IV 



