2 CHARLES A. COBURN 



number of mice used was about 1300 and consisted of wild 

 mice, tame mice, and hybrids of the first, second, and third 

 generation. 



Professor Yerkes mentioned in the report of his investiga- 

 tion the difficulty he experienced in always being sure he was 

 distinguishing between wildness and timidity in rats. He 

 says: "It is indeed extremely doubtful whether it can with 

 sufficient certainty be distinguished from wildness to render 

 measurements significant." The characteristics of rats are 

 so different from those of mice that it would be all the more 

 difficult to make this distinction in the case of the latter. For 

 this reason timidity was omitted in this study and only the two 

 behavior-complexes, wildness and savageness, were investigated. 



MATERIAL AND METHODS 



From the beginning of the work in December, 1911, until 

 June 7, 1913, the mice were kept in one of the large, well-venti- 

 lated rooms of the Harvard Psychological Laboratory. Upon 

 the latter date the mice were taken to the Franklin Field Station 

 at Franklin, New Hampshire, where the excellent facilities 

 allowed even greater progress during the summer than in the 

 quarters at Harvard although in no way were the methods of 

 the experiment changed. Upon the return from the Franklin 

 Field Station in October, 1913, the study occupied one of the 

 rooms of the newly-completed Harvard Laboratory of Animal 

 Psychology where it remained until the completion in May, 

 1914. This room was well lighted through the glass ceiling 

 but possessed no direct connection with the outside, hence had 

 to be ventilated by a system of fans. This, however, seemed to 

 have no effect upon the work as the mice throve equally as 

 well here as in the former quarters. 



In the beginning the mice were kept in the large cages used 

 by Professor Yerkes in his work with the dancing mice (1907) 

 from the report of which a description may be obtained. Later, 

 when the large number of mice compelled the use of more cages, 

 the type of cage used by Professor William E. Castle and his 

 associates at the Bussey Institute, Forest Hills, Mass., was 

 adopted. A description of this cage, to the knowledge of the 

 writer, has never been printed. It is made entirely of woven 

 wire of one-quarter inch mesh and is, in form, a truncated rec- 



