[The use of family trees and the notion of heredity: a case study of hereditary chorea].

This paper analyzes the development and use of visual tools known as "family trees" that allow medical practitioners to see hereditary family diseases. Family trees, consisting of family names and a tree diagram on personal traits, became popular among neurologists during the late 19th century. However, social scientists have devoted only scant attention to the historical and social processes through which, before the rediscovery of Mendelian laws, medical practitioners came to use family trees as scientific devices for nosographical classification of hereditary diseases, such as hereditary chorea (one of the initial terms used to describe Huntington's disease). The purpose of this paper is to trace the complex processes by which family histories, namely the descriptive nosography of family members and family trees became distinct during the late 19th century. This paper argues that family trees of hereditary chorea became and important clinical tool, with the establishment of teaching hospitals, although, in the case of hereditary chorea, family trees were used to support different interpretations of the notion of heredity. The use of family trees was made possible by three conditions including the centralization of medical care, the standardization of medical records, and the circulation of medical information among medical practitioners.