An integrating microdensitometer for biological cells

Abstract

A photoelectric method for the rapid determination of the total absorption of biological cells is described. The image of the cell, formed by a microscope, is scanned by a mechanically-driven aperture behind which is mounted a photomultiplier. A logarithmic circuit is used in conjunction with an electric integrator giving a meter reading linearly related to the total absorption. The scanning time is three seconds and it is possible to measure at least forty cells per hour. The mean random error is not more than 2% for most objects studied, and the error due to inhomogeneous distribution in one plane is negligible. Systematic error due to glare and other optical effects is of the order of 2%.