METHOD Excised strands of the ventricular conductive system of the kid ('false tendons') were studied in a bath of Tyrode solution as described in an earlier paper (Draper & Weidmann, 1951). Single Purkinjefibres could sometimes be found in the finest arborizations ofthe false tendons, immediately before their entry into the ventricular wall. These had a thickness of 40-100 t and measured a few mm between their peripheral cut end and the point of fusion with a thicker branch of the false tendons. Thepreparation was mounted as seen in Fig. 1 with the single fibre underneath