Measurement of capillary basement membrane thickness by magnification on a rear opaque projection screen

2190 measurements of capillary basement membrane thickness were obtained from the images of magnified micrographs using a rear opaque projection screen. This method proved to be reproducible and reliable. The electron microscope magnification used, 2500x, permits sharp definition of structures in the resulting micrographs. Projection on the opaque rear screen magnified the image 16x, yielding a final magnification of 40,000x. This high final magnification of micrographs of good quality minimized the error in measurement. The use of a special dial caliper with pins attached allows an open field and decreases the subjective components of measurements. Moreover, this technique results in less stress for the persons performing the measurements.