Illness?
If there were harmful bacteria aboard the ship, they should have struck many days ago. There was no disease in space itself.
Gas?
If such ships as the By Jove! carried any sort of gas, Albrekt didn't know about it. He had been briefed on the weapons he might face. Surely gas would have been mentioned.
Perhaps it was chance, or perhaps some part of his mind was swiftly scanning what he had learned through his reading of the last few days: his eyes fell on a bank of dials ranged side by side on the control board. The hands of all of them were lined up at the same angle—all but one. It had sunk far to the left.
The legend above the bank of dials read: "OXYGEN." The plate below the lagging dial read: "Control Room."
Albrekt unstrapped himself from the chair with nervously fumbling hands. Somehow the crew of the By Jove! was interfering with his oxygen supply.
Albrekt was beginning to feel a little nauseated. His head throbbed. He pushed himself across the control room and grabbed the helmet of the spacesuit that hung there. He did not take time to put on the suit itself, but pulled the helmet down over his head and switched on the suit's oxygen supply.
In a moment his head cleared, leaving only a slight headache.
As well as Albrekt remembered from the reading tapes, the ship's oxygen supply was on one of the lowest decks. The crew evidently had blocked the line to the control room.