Abstract
Summary: A technique has been devised to estimate virus yield per cell in cultures of trypsin-dispersed monkey kidney cells infected with different strains of the three immunologic types of poliomyelitis virus. Under the conditions employed, the range of variation in plaque-forming units produced per cell by 7 type 1 strains was from 132–612 (mean 256); for 6 type 2 strains from 68–270 (mean 151) and for 5 type 3 strains from 36–127 (mean 87).