ed out of the garage and took
the four-mile winding ribbon of concrete which separated the
Michaelville water impact range from the main front of the Aberdeen
Proving Ground. On each ambulance was a hastily awakened and partially
clothed medical officer. For three miles they tore along the curving
road at high speed. Without warning the leading machine slowed down.
The driver of the second ambulance shoved home his brake just in time
to keep from ramming the leading vehicle.

"What's the matter?" he shouted.

As he spoke he gave a muttered curse and switched on his amber
fog-light. From the marshes on either side of the road a deep blanket
of fog rolled up and enveloped the vehicle, almost shutting off the
road from sight. The forward ambulance began to grope its way slowly
forward. The senior medical officer sniffed the fog critically and
shouted to his driver.

"Stop!" he cried. "There's something funny about this fog. Every one
put on gas masks."

He coughed slightly as he adjusted his mask. His orders were shouted
to the ambulance in the rear but before the masks could be adjusted,
every member of the crew was vying with the rest in the frequency and
violence of the coughs which he could emit. The masks did not seem to
shut out the poisonous fog which crept in between the masks and the
men's faces and seemed to take bodily possession of their lungs.

"I don't believe we'll ever make the last mile to Michaelville through
this, Major," cried the driver between intervals of coughing. "Hadn't
we better turn back while we can?"

"Drive on!" cried the medical officer. "We'll keep going as long as we
can. Imagine what those poor devils on the range are going through
without masks of any sort."

* * * * *

On through the rapidly thickening fog, the two ambulances groped their
way. The road seemed interminable, but at length the flood lights of
the Michaelville end of the range came dimly into view. As the
vehicles stopped the two surgeons jumped to the ground and groped
their way forward, stretcher bearers following them closely. Presently
Major Martin stumbled over a body which lay at full length on the
concrete runway between the two main buildings. He stooped and
examined the man with the aid of a pocket flashlight.

"He's alive," he announced in muffled tones through his mask. "Take
him to the ambulance and fit a mask on him."

Three more unconscious men were carried to the am