Short communications 8Ihave the ring-like appearance and the central nucleoid may have been particles of rubella virus (Fig. I).The failure of Chatterji et al. to observe similar particles in the large amount of control material examined is difficult to explain, as both the strains of virus which they used had been passed in the same line of RK I3 cells just before the experiments which they describe and one of the strains, I7L had only been passed in these cells since it was isolated. This, together with the observation that many of the virus harvests from the untreated Australian cells show higher infectivity titres of mycoplasma than of virus, must raise the possibility that even though the mycoplasma does not influence the virus, the converse might not always be true. However, studies to date have not indicated any difference between titres of mycoplasma attained in rubella-infected and control cultures.We are grateful to Professor B. P. Marmion for his advice and for the isolation of M. orale, Type I, from the Manchester line of RK 13.

SUMMARYA striking feature of the development of rubella virus in RK 13 cells was the presence of virus-like particlcs at the surface of the infcctcd cells. Thcse particles were not scen inside the cell cytoplasm or nucleus, nor were they identified in uninfected cultures. They wcrc pleomorphic, with some evidence of substructure. Their appearance coincided with thc dcvclopmcnt of ncw infective virus; they may, therefore, bc mature virus particles.