The growth curve resulting from these stage of virus replication is illustrated in figure 9.9 in the first few minutes after infection the virus is said to undergo an eclipse. During this period infectious particles cannot be detected in the culture medium. The eclipse begins as soon as infectious particles are removed from the environment by absorbing to host cells. Once attached to host cells,the virions are no longer available to infect other cells. This is followed by the entry of viral nucleic acid (or intact virions ) into the host cell. If the infected cell breaks open at this point,the virions no longer exists as an infectious entity since the viral genome is no longer inside its capsid. Maturation begins as the newly synthesized nucleic acid molecules become packed inside protein coats. During the maturation phase,the titer of active virions inside the host cell rises dramatically. However,the new virus particles still cannot be detected in the culture medium unless the cells are artificially lysed to release them. Because newly synthesized virions have not yet appeared outside the cell,the eclipse and maturation periods together are called the latent period.