Abstract: Laboratory investigations in vitro of destruction and damage of living cells frequently involve labeling of the tissue cells in question with a radioactive isotope and subsequent dispersion of the cells in a suitable liquid. The dispersion is allowed to settle in a test tube, whereby a column of supernatant liquid is formed above precipitated cell particles. The radioactivity of said supernatant liquid is considered to be a measure of cell destruction and in order to measure the same while completely separated from the precipitated cell tissue, either the total amount or an accurately known fraction of the liquid must be collected, yet at the same time avoiding any collection of the precipitated particles.