What They Saw
The tritium was ditritium gas, similar to dihydrogen. They purified and fractionated protein from the bacteria and tested the fractions for tritium uptake, methylene blue reduction, and acetylene reduction. They found that acetylene reduction and the other two were found in separate fractions (makes sense; one's nitrogenase and the others hydrogenase). Tritium uptake could be stimulated with ATP somehow.
Tritium uptake and methylene blue reduction mostly went together in terms of fractionation, but there was a little of the latter in some fractions where the former wasn't observed. So there could be something else reducing methylene blue.
They found that carbon monoxide (CO) inhibited tritium uptake, though it was less inhibitory when ATP was present.
What This Means
This supports the idea that nitrogenase produces hydrogen while hydrogenase oxidizes it and reduces electron acceptors such as methylene blue. It's weird that ATP should stimulate that though, and also weird that some fractions had reduction activity but not hydrogen oxidation.