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J Virol. 1967 October; 1(5): 1074-1081
Copyright © 1967 American Society for Microbiology. All Rights Reserved.

A New Procedure for Quantitative Measurements of Virus Particles in Crude Preparations

Federal Research Institute for Animal Virus Diseases, Tuebingen, Germany

ABSTRACT

A new method is described for the quantitative measurement of virus concentration in crude preparations by density gradient centrifugation and electron microscopy. The centrifugation is carried out in a specially designed centrifuge tube which permits separation and sedimentation of virus particles at different levels according to their sedimentation velocity. The gradient of a mixture of heavy and normal water (D₂O-H₂O) is designed to sediment the virus particles with constant velocity so that the optimal time of centrifugation can easily be calculated. The virus particles are collected on carbon-coated nickel grids floating on mercury at the bottom of the centrifuge tube and are counted by means of electron microscopy. The efficiency of the method is demonstrated with a crude plant extract of tobacco mosaic virus.