"Why can't we survive the intense cold of space? The answer is a simple one. The protoplasm of all forms of living things that we know of, including the Space Men themselves, is a colloidal jelly the principal portion of which is, and must be, a liquid. Cells must be bathed and nourished, and impurities washed away. Without liquids there seems to be no likelihood that there would be any life, unless in some manner a gas could perform this fluid function. Solids would remain forever dead and motionless. "If anything happens to chill even slightly the protoplasm of any of the higher forms of planetary life, the body fluid becomes sluggish and death may result. No mammals or birds that we know of can live actively with their body temperatures at all approaching the freezing point of water. However, in the polar seas of both planets there are creatures whose systems function quite normally with their blood temperatures just above this point. But beyond this deadline, zero degrees Centigrade, or a little lower or higher, depending on the actual congealing point of the water in their bodies, even they cannot go, for there, the cold limit of Terrestro-Martian life has been reached. "Why couldn't these polar fish survive the cold of space? Simply because the protoplasm of their tissues, based on water, would instantly become solid, and in solids as I have said, there can be no real life except perhaps in the form of suspended animation. "The Space Men face no such danger, for first, their bodies are protected by this heat-resisting outer covering; and second, the liquid in their veins freezes only at absolute zero, and since it is radio-active--producing heat from within itself--it cannot get that cold even in the void. And that, friends, is the whole stupendous, simple explanation." "And how do the Space Men's vehicles move?" asked Jan. Hekki shook his head. "Except that a strange propulsive ray is involved, I know very little about it. I have not yet discovered how the Space Men manage to produce the ray. The works of Nature ever surpass the works of man. "And that is all I have time for now, my friends. Breakfast is ready aboard ship. Enjoy my hospitality to the fullest!" Hekki's mask of smiling sardonic cruelty had dropped again. He waved something to Sega. * * * * * Janice, sensing that she was about to be separated from her lover, threw herself into his arms. The series of things she had gone through in the past twenty-four hours had frayed her nerves almost to the breaking point. "Don't let them take me away from you, Austin. Don't let them! Oh, Hekki, please!" Hekalu's face reddened, and then Sega tore the two apart. Shelby struggled but it was useless. Sega's huge muscles were quite equal to the task of mastering a dozen of the best fighting men of Earth.