抄録
The dark contrast microscopy, in which a dark image can be seen against somewhat bright background, is especially suited for examining details of biological specimens. However, objective lenses recently made in Japan for this purpose are designed at rather small values of transmission factor so as to obtain a sharp image especially with extremely thin specimens like animal cells. This caused another problem: the deterioration of phase contrast image with specimens which have rather thick optical path but can be clearly contrasted with short-barrel objective lenses once supplied. In this study, the authors tried to improve such image by mounting specimens with a liquid medium having refractive index larger than water so as to reduce the phase difference between specimens and the medium. Among various hydrophilic substances examined using Type 021N filaments as specimens, PVA was found to be most suited for this purpose. When filamentous bacteria in activated sludge are of concern, PVA solutions at different concentrations around 5%w/w to 15%w/w can be recommended on the basis of fact that the objective lens employed in this study has fairly a small value of transmission factor, and at the same time, there exist few filaments that have cells dimension greater than those of Type 021N in activated sludge.
