Autoradiographic Observations on the Silk Glands of Bombix mori

Brachet (1) first called attention to the correlation between tissue R N A content and protein synthesis and to the R N A richness of the silk glands of B. mori. This high R N A content (2), cytological characteristics (3), and synthesis of a specific protein-fibroin--with peculiar properties .and aminoacid composition (4)--suggested an autoradiographic study of the incorporation of radioactive amino acids into the silk glands. Fibroin is synthetized by the posterior part of the silk glands (5). The tubular silk glands are lined by large cells, filled with ergastoplasm erroneously interpreted as secretion by Lesperon (3). In their apices are found hyaline globular masses and complex structures constituted by a filamentous grid, stainable by phosphotungstic acid hematoxylin. This apical structure is presumably related to the secretion of fibroin into the lumen of the gland. Cell nuclei are branched and contain numerous nucleoli.