Jean Brachet, l'hérédité générale and the origins of molecular embryology.

Jean Brachet's research on microsomes and the role of RNA in protein synthesis during the 1940s and 50s is placed in the context of embryological views about the role of the cytoplasm in development, and plasmagene theory based on studies of non-Mendelian inheritance in microorganisms. I show how Brachet's subsequent conception of messenger RNA evolved in the context of his conceptions of the relations between plasmagenes and nuclear genes. His theorizing on cytoplasmic organelles and viruses is further situated in the bio-political controversy over the inheritance of acquired characteristics during the Lysenko controversy.