A simple method for total particle counts of trachoma and inclusion blennorrhoea viruses.

Abstract

DARK-GROUND illumination has been used to examine the elementary bodies of large viruses in stained and unstained preparations1,2. We find that unstained crude suspensions of chick embryo yolk sacs infected with the viruses of trachoma and inclusion blennorrhœa, examined under dark-ground illumination, contain particulate host material which obscures the virus particles and which can be confused with them. However, when such suspensions are dried, fixed and stained with Giemsa, many bright yellow-green particles are seen by dark-ground illumination, resembling elementary bodies stained with acridine orange and viewed by ultra-violet microscopy. Their colour and intensity clearly distinguish them from background material, even if they are enveloped by it. They resemble virus particles in size and shape, and their distribution in yolk sac smears is the same as that of the purple elementary bodies in films stained by Giemsa viewed by ordinary illumination; they are not present in smears of normal yolk sacs. Our conclusion that these are virus particles is also supported by dark ground microscopy of inclusions found in HeLa cells infected with trachoma or inclusion blennorrhœa viruses3. The inclusions contain numerous yellow-green particles similar to those in yolk sac smears and suspensions. Large forms of virus are also recognizable, but are much less bright, and reddish in colour.