flow microfluorometry instrument such as a facs analyzer or a facs iv cell sorter facs division of becton dickinson and company sunnyvale calif may be used the sample is preferably passed through the beam at a rate of from about 0 05 ml min to about 0 3 ml min preferably about 0 1 ml min in accordance with the method of the invention wherein fluorescence emission is observed using a flow microfluorometer data may be obtained using multiple parameters of analysis as for example forward and 90 u00b0 light scatter and red and green fluorescence emission the data may be presented and studied using a linear scale or preferably a logarithmic scale or if desired some parameters may be studied using a linear scale while others are studied using a log scale the determination of suitable parameters of analysis and instrument settings are well known to those skilled in the art and no further details in these respects are needed for a complete understanding of the invention the data collected may be analyzed for example by dividing log green fluorescence emission by log red fluorescence emission to give a ratio gram negative microorganisms show a ratio of 40 or less and gram positive microorganisms show a ratio of 45 or more the gram sign of an unknown microogranism may thus be assigned by the magnitude of the ratio the following examples are provided to further illustrate.