Abstract
1. An improved technique for measuring the protoplasmic viscosity of certain types of cell is described. 2. It is shown that the viscosity of Paramecium is not greater than 0.5 c.g.s. unit, and that it may be much less. 3. A simplified type of microscope centrifuge has revealed several sources of error in the centrifuge method customarily employed for the determination of protoplasmic viscosity.