CELLS OF THE RAT, AS SHOWN BY ELECTRON MICROSCOPIC RADIOAUTOGRAPHY’

Raohioactive gahactose was intjected intravenously into rats and localized itt thy-void folhicular cells by electron microscopic radioautographty at intervals ranging from 2.5 to 30 mm after injection. The galactose label was mostly presenit in the Golgi apparatuss at 2.5 mm, with some of it in the adjacent rough enudoplasmic reticuhtum. By 30 mint, the label was found in apical vesicles and colhoid. It was con-cluded thtat galactose is added to the carbohydrate side chains of incomplete thuyro-globulin molecules during thteir travel through the cisternae of the endoplasmic reticulum into thte (;olgi apparatus; the uptake begins as this organelle is ap-proachued, but predominates within it. Thte thtyroglobuhin molecule whuich Itas thtus been labeled is transported by the apical vesicles to the colloid. ‘[‘lie )oly)eptide chains of thyroglobuiint are synithuesized iii the rough enudoplasmic reticu!uuit (RER) of thyroid follicular cellsand later nttigrate through the RER cisterntae toward the Golgi ap-paratus, where thtey are packaged into “apica