INHERITANCE OF TEMPERAMENT. 75 



5. GENERAL FACTS OF HEREDITY. 



An examination of the family histories of the hyperkinetic and hypo- 

 kinetic indicates that in some families there is a prevailing tendency for 

 the one condition, in other families for the other, while still other 

 families show the mixed state or a stable mood scattered among the 

 other moods. Examples of these families are given in the pedigree 

 charts. Attention may be drawn to Nos. i, 3, 22, 31, 35, and 45 as 

 examples of prevailing hyperkinesis, and Nos. 25, 34, 36, 52, and 80 as 

 of mixed or circular types, while 17, 55, 58, 61, 65, and 74 show a large 

 proportion of stable or near-stable individuals. 



III. HYPOTHESIS AS TO HEREDITY. 



How can we bring under one general scheme the inheritance of these 

 various types of mood? After several preliminary trials the following 

 hypothesis was selected for detailed testing: 



There is in the germplasm a factor, E, which induces the more or less 

 periodic occurrence of an excited condition (or an exceptionally strong 

 reactibility to exciting presentations) and its absence, e, which results in 

 an absence of extreme excitability. There are also the factor C, which 

 makes for normal cheerfulness of mood, and its absence, c, which permits 

 a more or less periodic depression. Moreover, these factors behave as 

 though in different chromosomes, so that they are inherited independently 

 of each other and may occur in any combination. 



What the nature of these factors is, whether they affect primarily the 

 development of certain parts of the nervous system or the secretions 

 of certain glands, is not known and is not involved in the hypothesis. 

 It is even conceivable that each state may be due to more than 

 the pair of factors here suggested; but if the hypothesis fits the facts 

 it would indicate that in the factors E and C we have the predomi- 

 nating influences that control mood. 



IV. TEST OF THE HYPOTHESIS. 



1. METHOD. 



The general method employed in the test of the hypothesis is as 

 follows : From the family histories available for the study of mood, 89 

 were finally selected as sufficiently full for the purpose. There was no 

 selection of these family histories because it was foreseen that they 

 would supply facts fitting the hypothesis, and no rejections of any 

 histories because they afforded statements opposed to the hypothesis. 

 In these 89 family histories were found 146 matings that could be 

 used because the mated pair, their parents (usually), and certain of 

 their offspring were sufficiently described for the purposes of the test. 



Let us consider, first, the case where a person of pure, excitable 

 strain (2) marries one of a pure unexcitable strain (62). The gametes 

 are respectively E, E, and e, e, and the zygotes are E e. This is the 



