Astounding Stories of Super-Science, August 1930

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.