THE PLATINUM-CARBON REPLICATION OF A HOMOGENOUS POPULATION OF GOLD PARTICLES MAKES LOG-NORMAL DISTRIBUTIONS OF SHADOW WIDTHS AND LENGTHS

Gold particles were prepared, dried on grids and shadowed at 45 degree s with a 1.2 nm platinum-carbon (Pt-C) film using the shadowing condit ions previously described for the freeze-fracture of gastric parietal cell membranes. The particle diameters and the particle shadow widths and lengths were measured using an image analysis system. Statistical analysis of 2000 diameters, shadow widths and shadow lengths indicated that a homogenous population of particles had a normal frequency dist ribution of diameters (mean diameter 14.5 +/- 1.5 nm) and that the Pt- C shadowing transformed that normal curve into a log-normal frequency distribution of shadow widths. The frequency distribution of shadow le ngths was log-normal too. We conclude that a statistical partition of experimental frequency distributions of particle shadow widths and len gths of natural membranes to determine the number and parameters of in dividual components should involve log-normal subdistributions rather than normal ones.