CONTENTS 



Page 



Acknowledgments v 



Introduction 1 



Historical 1 



Apparatus and Procedure 4 



Experimental Results: 



Twenty-five day rats 15 



Sixty-five day rats 23 



Two hundred day rats 29 



Three hundred day lats 33 



Five hundred day rats 38 



Comparison of Results for Different Ages 42 



Incidental Tests: 



Effect of Sex on Rapidity of Learning 46 



Day and Night Work ; . 47 



Continuation of Work after Problem has been Learned 48 



Blood Relationship and Learning 51 



Retention 52 



Resume of Conclusions . . 54 



iii 



