In the early 1950's, a series of improvements in preparation procedures made possible the full-scale application of electron microscopy to the study of cells and tissues. That was about 25 years after research had started in electron optics1 and about 15 years after electron microscopes had become available for research.2,3 The long lag gives an idea about the magnitude of the difficulties encountered in working out such procedures as well as about the important role played by appropriate techniques in research progress.
Once secured, these technical improvements opened for investigation a new and rich layer of biological organization which stretched from the limit of resolution of the light microscope, ie, about 0.2μ, to that of the electron microscope. The latter has reached at present about 5 angstroms and is still progressing. From one microscope to another there is, therefore, a gain of about 400 times in the ability