The P-Base is one of three ingredients used to culture the Daylight vaccine. It must be transported very carefully as exposure to air will cause it to dissolve.[1] A sealed P-Base sample can be found in the water treatment plant below Raccoon University; this area is also used to house Hunter γ B.O.W.s, it should be noted.
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The player can find an opened P-Base which will eventually dissolve that can be used instead of the sealed P-Base but it is unknown if the player can find it and put it into the machine before it fully dissolves.