3 Eugenics Record Office, Bulletin. 



least of the direct ancestors as far back as possible; the fraternities 

 to which the parents belong; the offspring of all members of such 

 fraternities and the parents of each consort when there are children. 

 Likewise, each of the members of the four grand parental fraternities, 

 their consorts and their children, their children's consorts and the 

 children's children. If the patient has brothers and sisters these to- 

 gether with the patient are studied with the greatest possible care; 

 also their consorts and children, if any. 



If the trait is one that never appears in the children unless one 

 parent shows it, then it is desirable to carry back the direct line as 

 far as possible and less attention need be paid to the descendants of 

 certainly normal collaterals beyond what is necessary to establish with 

 certainty the law of inheritance. 



4. METHODS O^ ANAI^YSIS. 



A brief statement of the Mendelian rules of heredity. So many 

 traits are inherited in accordance with the Mendelian rules that a 

 brief statement of them is appended. But the field worker is warned 

 against being so prejudiced by these rules that her, or his, judgment 

 is warped. The exact facts are to be sought; their interpretation 

 must come later. So far as possible all statements should be verified. 

 In general a statement may be regarded as verified when made by a 

 second, independent witness. 



With this caution in mind the Mendelian rules will be found 

 useful in directing the field worker in her inquiries. First, it is im- 

 portant to disabuse the mind of the popular error that traits are in- 

 herited from ancestors. Strictly, traits are not inherited at all; what 

 is inherited is a condition of the reproductive or germ cells which 

 determines the development of the trait — the trait depends on the 

 presence or absence of a determiner in the germ cells. 



Some defects that the field worker will study, such as albinism 

 and feeble-mindedness, are known as recessive defects, i. e., they are 

 defects due to the absence of the determiner making for normality 

 in respect to these traits. Other defects, such as cataract and brachy- 

 dactylism, are dominant defects, which means that they are due to the 

 presence of some germinal determiner in addition to all the determiners 

 for normality in respect to these characteristics. Thus, in respect to 

 one character there are three gametic and two somatic types of 

 individuals. Somatically, the individual has or has not the defect; 



