Particle Counting of Partially Purified RNA Tumor Viruses by a Thin Sectioning Technique

Abstract

Most of the available methods for counting virus particles in the electron microscope require the sedimentation or spreading of particles on an electron transparent film and their visualization by negative staining or replica techniques. Two problems are encountered in these methods. Uniform distribution of particles on support films is difficult due to surface tension effects. Unless the virus preparation is highly purified, recognition of virus particles among cell debris may be difficult. This can be largely eliminated by the use of thin sections. Counting virus particles in thin sectioned pellets requires large quantities of purified virus. Membrane filters serve as suitable substrate for pelleted virus particles which can be examined in thin sections.