Reliability of 50% Egg Infectivity Titrations with Suspensions of Influenza Viruses Prepared from Mouse Lungs. ∗

Summary

1. The use of 2 different methods for analyzing the reliability of 50% end point determination has been illustrated. The data were available because duplicate titrations of a number of virus suspensions were required for the purposes of other experiments. Data of comparable significance could have been obtained by a similar number of replicate titrations of the same virus suspension. The latter type of procedure is tedious, expensive, and is seldom carried out. It would seem likely that the records of other investigators would contain data suitable for analysis by the methods used in this report. 2. In the present study the reliability of 50% egg infectivity titrations was determined with crude suspensions of lungs infected with recently isolated strains of Type A-prime and Type B influenza viruses. The reliability of these determinations was similar to that previously described for titrations of infectivity for mice or for eggs with purified suspensions of the PR8 strain of influenza virus.