Attack of the Giant Germ sounds like the title of a Powerpuff Girls short subject but it's the plot synopsis of Immunity Syndrome, an episode of the original Star Trek TV series. This slightly ludicrous premise actually turns out better than one might reasonably expect.
The story: a protozoan of planetary size and capable of interstellar flight destroys wherever it goes, its negative energy field draining the power of both machines and things living. Kirk's orders from Starfleet Command: Destroy it!
It's a weary crew aboard USS Enterprise and this motive seems to be projected a bit too effectively, exhausting the viewer as well. Just as well, then you won't worry how the ship and shuttlecraft manage to manoeuvre in a colloidal mass. Or why the ship doesn't turn about while on the retreat. A few maudlin scenes in Act II, culminating in the plan, daringly executed as always, to strike the nucleus with a ballistic missile with an anti-matter warhead. A fair conclusion, I suppose, but I would have enjoyed it more if Bones had quickly synthesized a super-antibiotic and Spock flew a shuttlecraft with a huge needle attached to the bow into the nucleus.
No new sets, no guest stars, no new wardrobe, no new miniature shots, incidental music largely recycled from The Doomsday Machine are factors likely to have been critical in the selection of this script as it helped Desilu Studios recoup budget overages on certain previous episodes.
Of the original 79 episodes, I would rank Immunity Syndrome around number 40.