Analysis of freeze-fracture electron micrographs by a computer-based technique.

A procedure is described for deriving a numerical characterization of membrane particle patterns revealed in freeze-fracture electron micrographs. Rectangular coordinates of the particles are obtained with high precision by means of an electronic digitizing device. These coordinates are fed into a large computer and analyzed in terms of (alpha) a local particle density function in terms of variable subdivisions of the membrane, and (beta) an interparticle distance function describing describing all particle pairs within the membrane. It is found that the particle density function gives the most useful description of clustering provided that particle-free patches are monitored along with nonvanishing particle densities. Theoretical particle patterns are generated with the computer by means of a random number generator to provide defined aggregation states which serve as standards of comparison for observed particle patterns.