Estimating the number of organisms in quantal assays.

It has been demonstrated by virologists that, when procedural difficulties can be overcome and host variation can be eliminated, dosage-response data from virus assays conform with the one-particle theory of infection for both plaque counts and tissue cultures. Based on this theory, the number of virus particles from quantal virus assays can be estimated. Here a set of tables is presented from which the number of estimated particles can be obtained directly for several dilution factors and a number of dilution levels. Maximum likelihood estimation of particle counts is also illustrated using a computer program that we have prepared.