In flooded cells, the gases escape before they can recombine, so water must be periodically added.

At present, many other previously unseen episodes are being added periodically.

An online version is available on a subscription basis, and new entries are added to this periodically.

Water must be periodically added to the bath, with proper controls to prevent a steam explosion.

Additional studies will be added to this collection periodically.

Additional translators have been periodically added in other cities.

Symptoms were periodically added to the clinical picture.

Community discussion tools will be added periodically to encourage idea sharing.

Since initial release new free missions are periodically added by the developers.

A second wave of titles was released in early 2007, with additional games being added periodically.