The membrane microscope method (MM) may be applied to samples of both large-volume and small-volume parenteral injections, as well as ophthalmic solutions. This test enumerates solid particulate matter that is ≥10 µm after collecting, rinsing, and drying on a microporous membrane filter. Semisolid substances may also be isolated, although all liquid and sub-micrometer material will pass through the membrane. Because a wide range of test aliquots may be utilized, particle counts may be determined on a per-volume or a per-container basis without dilution or extrapolation.