Separation of Measles Virus Particles in Density Gradients

The chemical and physical properties of measles virus have been difficult to ascertain due to the instability of the virus and low yields obtainable in tissue culture. Whether by a chance adaptation of the virus to our line of HEP 2 cells or as a result of modifications in growth conditions, we have been fortunate in our laboratory in producing measles virus in concentrations which lend themselves to quantitative analysis. Preparations with complement fixing (CF) titers of 1:16 or greater and containing from 10 7 to 10 8 tissue culture infectious doses per milliliter have been obtained regularly. Further concentration could be effected by osmotically forced dialysis using polyethylene glycols 1 or by sedimentation. The present study was initiated in the hope that fractionation of measles virus concentrates, with respect to density, might reveal the presence of specific viral substances or particles differing not only in density but also in