Fine structure of changes produced in cultured cells sampled at specified intervals during a single growth cycle of polio virus

PHmary suspended cultures of rhesus monkey kidney cells were infected with poliomyelitis virus, type 1 (Brunhilde strain). The release of virus from these cells over a one-step growth curve was correlated with th ir change in fine structure, as seen in the electron microscope. Most of the cells were infected nearly simulta-neously, and morphological changes developed in the cells were suflidently syn-chronous to be classified into three stages. The earliest change (stage I) b came visible at a time when virus release into the culture fluid begins, some 3 hours after adsorption. Accentuation of the abnormal characteristics soon occurs, at 4 to 7 hours after adsorption, andresults in stage II. Stage IH represents he appear-ance of cells after their ate of virus release had passed its maximum, and probably the abnormal morphology of these cells reflects non-specific physiological damage. There seems to be consistency between th previously described cellular changes as seen under the light microscope and the finer scale changes reported here. Cytoplasmic bodies, called U bodies, were seen i large number at the time when the virus release was the most rapid (stage II). While these bodies are not of proper size to be considered polio virus, they seem to be specifically related to the in-fection. No evidence was found for the presence of particles that could even be presumptively identified with those of polio virus