2 GARDNER CHENEY BASSET 



insufficient nourishment during the first four generations; but, 

 the rats used for purposes of inbreeding produced a strain hav- 

 ing a lesser relative brain weight on the average. This strain 

 of rats I shall hereafter, for convenience, refer to as the Inbred 

 Strain. The object, then, of the following experiments is to 

 compare the habit-forming ability of ' the inbred strain with 

 lesser brain weights, with the ability of a normal control series. 



Owing to the fact that experimental work on the brain weight 

 problem has not before been attempted there is no history and 

 little literature to be presented. Donaldson 1 reproduces tables 

 from Manouvrier 2 showing the brain weights of eminent men 

 to be, on the average, greater than those of average Parisians. 

 It is not necessarily true that the specific individual with greater 

 brain weight is more intelligent or will contribute more to the 

 world's arts and sciences than the specific individual of lesser 

 brain weight; but, if the conclusions of Manouvrier are to be 

 believed, individuals of brain weight above the average are 

 more liable to be of superior intelligence and to do the world 

 greater service. 



The results of the experiments described in this paper agree 

 closely with Manouvrier 's conclusions. Tables of distribution 

 of brain weights of the inbred strain and normal control series 

 overlap; but the normal series, having a greater brain weight 

 average, show greater ability t in habit formation. 



All the experiments here described were carried out at the 

 Psychological Laboratory of the Johns Hopkins University. 



II. METHODS 



All the inbred rats used in this investigation were bred at 

 the Wistar Institute of Anatomy and Biology by Dr. Helen 

 D. King. Two strains were used, referred to in this paper as 

 strains A and B. The original parents of each strain were taken 

 at random, a male and female from each of two unrelated lit- 

 ters. The A male was mated to his sister, A female, and the 

 B male to his sister, B female. Their respective litters consti- 

 tuted generation 1A and IB. From this point inbreeding was 

 carried on by selecting from the litter the healthiest appearing 



1 Donaldson: The Growth of the Brain. London and New York, 1909, pp. 

 128 ff. 



2 Manouvrier, Sur Interpretation de la quantite dans 1'enc^phale, etc., Paris, 1885. 



