So, I decided my top-level cavern was a little too full of forgotten beasts for a few reasons. I sent the 63 soldiers to deal with them.
The eyeless dimetrodon went down without much trouble.
The clear salamander knocked a dwarf unconscious, but he went down too.
The hairless three-tailed giant lemur gave a dwarf a broken bone, and the three-eyed giant salamander strangled one to death on its way down. No big deal yet. That's what the red shirts are for.
Finally we fought the giant slate winged humanoid. Beware his poison blood.
I would never have fought the giant slate winged humanoid, if I knew what the poison blood would do.
He killed two dwarves who were too eager to engage before the rest of the soldiers caught up. This is a loss I could accept.
An injured dwarf--shall we call him Urist McVictim--lay unconscious in a pool of the beast's blood after we killed it.
Some idiot went to rescue that dwarf.
Urist McVictim's body swelled up and he bled all over the stairway while being rescued, and continued to bleed out in the hospital. He succumbed to the strange illness soon after. So did his rescuer.
Then four children who'd been wandering around in the stairway all died at once of the strange swelling illness. They died on contact, on the spot.
Then two more children.
Six adults who'd walked through the main stairway caught it too, and lay in the hospital. A few lived long enough for the surgeons to try and remove the rot and ease the swelling. This wasn't a good thing.
The surgeons cancelled surgery as they fell ill as well.
Then the wound dressers and suturers caught it when they tried to patch up the bleeding patients. And everybody who tried to clean up pools of infected blood in the hospital succumbed to it as well. I had to disable the cleaning labor for all the dwarves. I wish I had realized all the sources that were spreading it, sooner.
And then the diagnosticians who came to look at the dwarves stepped in puddles of illness and caught it.
So far about 25 dwarves have fallen to the swelling blood-sickness, and 15 others have been murdered by well-armed, tantrumming dwarves. Children die almost instantly when they catch it. Almost everyone in the fortress is either insane, having a tantrum, or Miserable.
That is, everyone but the duke. He sits calmly in the mason's shop, making coffins. He's not worried at all.
I decided not to let any more dwarves use doctor skills, since that just causes them to catch the illness and die. If I can keep everybody who doesn't have the sickness yet out of the hospital, maybe I can close it off and stop the spread. I'm not sure what to do about the stairway at all, though. If I use any constructions to seal off small areas, the builders will touch the blood and catch the sickness.
I think I have to seal off the entire stairway to make the fortress safe again, but I'm not sure how. I'm very low on workers because most of them have gone nuts, and when they work they come in contact with dwarves who've gone nuts and have swords and morning stars and such. Also, how many people are tracking the bad blood around? I can't tell. There's a lot of blood around the place because nearly everyone is going around murdering each other and our livestock.
This is bad. Back to trying to salvage it.