I struck a spark and tried to read the paper. It went out before I could actually read anything, but I caught a glimpse of something rather long written on the back.
I went south and threw a bunch more rocks down the shaft, including the one I was carrying.

Inventory

@Stratn - The first aid kit does have an antivenom, but it's not fast-action enough for whatever very strong poison used in the air vents.
@MSB - That would take us to the collapsed gate room. I'm pretty sure that's not what you wanted.