Quarterly Journal of Microscopical Science, Vol s3-98, 281-290, Copyright © 1957 by Company of Biologists

The Shrinkage of Air-dried Bacteria prepared for the Electron-microscope

¹ Department of Biological Science, Wye College, University of London
² Department of Zoology, University of Edinburgh

Values for the mean thickness of living bacilli in a number of different cultures of Lactobacillus bulgaricus were obtained from phase-change measurements. These were made with an interference microscope. The bacilli were mounted in media of several different refractive indices. The accuracy of these measurements is not limited by the wavelength of the light used, so that the mean thickness of bacteria can be measured more critically in this way than by an eyepiece micrometer scale.

The values obtained for the mean thickness of the living bacilli were compared with the mean width of similar bacilli measured in electron-micrographs, after they had been prepared for electron-microscopy by drying them in air on formvar. The method used for preparing the bacteria for the electron-microscope is described in detail.

It was found that osmium-fixed air-dried L. bulgaricus so prepared shrink linearly in the plane of the formvar film by 59%±5%, and similar unfixed bacilli by 51%±5%. Phase-change measurements through these air-dried bacilli indicated a similar degree of shrinkage, or a slightly greater shrinkage, in the direction at right angles to the formvar film.