rder. Slowly, reluctantly, one of the green men moved
toward them. Quickly they removed a metal disk fastened to his arm,
exposing a small orifice like an unhealed wound. Onto this they
fastened a suckerlike object from which a transparent tube led back
through the mechanism. The machine hummed and at once a red stream
pulsed through the tube and back through the mechanism. The man to
whom it was attached was growing rapidly pale!

Norman, sick with horror, clutched his companion. "Hackett--these
frog-men are sucking his blood from him!"

"Good God! And look--they're doing it with another!"

"All of these men--kept prisoners to furnish them with blood. It must
be the damned creatures' food! And we here with the others--"

A common horror shook the two. It did not seem to affect the green men
in the room, though, who advanced to the mechanism one by one with a
reluctant air as of cows unwilling to be milked. Each was attached to
the mechanism by the sucking disk on his arm, and out of each the
blood poured through the tube. The metal disk was replaced on his arm
then and he went back to the others. Norman saw that the frog-men took
only from each an amount of blood that they could lose and yet live,
since, though each came back pale and weak from the mechanism, they
were able to walk.

"It must be their food--human blood!" Norman repeated. "They may have
thousands on thousands of humans penned up like this, like so many
herds of cows, and perhaps they live entirely on the life-blood they
milk from them. Human cows--God!"

"Norman--look--they're calling to us!"

* * * * *

The two stiffened. All the others in the room had taken their turn at
the blood-sucking mechanism and now the frog-men croaked their order
to the two fliers. They had forgotten their own predicament in the
horror of the scene, but now it became real to them. They backed
against the room's wall, quivering, dangerous.

The frog-guards came forward to drag them to the machine. A webbed paw
was outstretched but Hackett with a wild blow drove the frog-man back
and downward. The frog-guards leaped, and Norman and Hackett struck
them back with all the greater strength the lesser gravitation gave
them. The room was in an uproar, the green men shouting hoarsely and
seeming on the point of rushing to their aid.

But the menacing force-pistols of the other frog-guards held back the
shouting men and in moments the two flie