The Growth of Asibi Strain Yellow Fever Virus in Tissue Cultures. Ii. Modification of Virus and Cells.

A number •of primary and established tissde cultures were examine& for their susceptibility to yellow fever virus, with-the.most intensive study directed to HeLa cells. The following resultsqwere obtained: Of those cultures that were susceptible, three different patterns of-dose response were obtained' that were interpreted as different possible mantfestations of interference. HeLa cells, which were among the least-sensitive to low infection multiplication, h~ad the greatest capacity (highest yields). Subjecting cultuIres to wash cycles betwien 15 minutes and 2, hours post-inoculation increas~d the sensitivity. (detectable virus) of suchcultures'100-fold, increased the tate of virus multiplication, and had-' no effec~t on the peak titer (capacity). The HeLa cultures werd found to be composed of different (morphological) clonale typteL. Three of these that wereýstudied were all susceptible, comparable in capacity, but varid in their sensitivity.