PART I. INSTINCTIVE REACTIONS 

 I. Introduction and Statement of the Problem 



The experimental work reported in this monograph was car- 

 ried on during the years 1907, 1908, and 1909 in the Harvard 

 Psychological Laboratory. The variety of chick used in all the 

 work was the Barred Plymouth Rock. It is usually considered 

 by poultry breeders a hardy chick, and for this reason more 

 than any other was selected for these tests. The program of 

 research began with a cursory study of the first activities of 

 the animals, preliminary to a more detailed study of certain 

 instinctive modes of response such as drinking, pecking, and 

 "imitating." In the case of drinking, interest centered in the 

 nature of the stimulus; in the case of pecking, in the accuracy 

 of the reaction; as for imitation, the question was asked. In 

 how far is social influence a means to improvement in the accu- 

 racy of pecking? After some knowledge of the natural tenden- 

 cies of the chicks had been gained, an attempt was made to 

 trace the course of development of certain habits of response 

 to optical stimuli, as well as to study the interrelation and 

 persistence of these habits. Quantitative methods were devised 

 and applied wherever they suggested themselves to the ex- 

 perimenter. 



The investigation was pursued under the immediate direction 

 of Professor Robert M. Yerkes. What I owe to his searching 

 criticism and fertile suggestions, a mere word of acknowledgment 

 will not suffice to say. I shall be- only too glad if my immature 

 effort reveal some trace of his admirable scientific spirit. I am 

 also much indebted to my colleague. Professor Charles Scott Berry, 

 for a critical reading of the manuscript, and to Dr. William F. 

 Hauhart, Instructor in German, University of Michigan, for 

 valuable assistance in reading the proof. 



II. Previous Experimental Work on Chickis 



Attention is limited in this r^sum^ to the conclusions of inves- 

 tigators in regard to the accuracy of the pecking response. The 

 results of some previous studies of the drinking reaction will be 



