been flying around here."

"Well, you'll be in your element now. We know that Denberg is loose
and their capture of Thelma is no coincidence. I was pretty sure that
Saranoff and his gang were at the bottom of this; now I am certain.
They must have introduced something onto the marshes last night which
caused the trouble. They could not have come overland very well, for
the place is too well patrolled. Had they come by air, they would have
attracted attention, even had they used a Bird silencer on their
motor, for they couldn't muffle their propeller, especially on a
takeoff, and there are plenty of men here who would have recognized
it. You might check up on that, but I am confident that they came by
water. Launches and boats are continually passing up and down the
Chesapeake and its tributaries and one more could easily have escaped
notice. The Bush River is at the far end of the Michaelville range and
it is navigable for craft of light draft at high tide. Find out
whether any strange craft were seen in the vicinity of the proving
ground last night. If you draw a blank, go to Perryville and Havre de
Grace and see what you can find out there. I have a hunch that their
base is more likely to be up the Susquehanna than down toward the
coast. Above all, Carnes, don't approach the proving ground by water
to-night and don't get near the mouth of the Bush River."

"All right, Doctor. What are you going to do?"

"I'm going down on the swamp and collect samples. Oh, don't look so
worried. I know just what I am up against and I will have adequate
protection. I'll be in no danger and you would just be in the way.
Toddle along, old dear, and report to me by telephone as soon as you
have learned anything."

"As you say, Doctor. You'll hear from me the minute I do."

* * * * *

When Carnes had left, Dr. Bird climbed into the waiting car and was
driven back to the hospital. Captain Murdock greeted him with a
smiling face.

"I don't know how you got on to that treatment, Dr. Bird," he said,
"but it is doing the men good. The worst cases haven't been affected
much, one way or the other, but the progress of the malady in the mild
cases from the stables has been completely checked. I think they have
a chance now."

"They'll be all right if the destruction and coagulation of tissue
hadn't progressed too far before you checked it, Captain. Treat them
now for simple lung cauterization and they ought