A trickle of sweat slid past Bowren's eyes, loosening a nervous flush along his back that prickled painfully. His throat was tense and his heart pounded loud in the hot dark. A sharp pain ran up his body and exploded in his head. He tried to swallow, but something gagged in his throat. He was afraid of retching. He lay with his mouth open, spittle dribbling over his lips. The pain returned, hammered at his entrails. He fought the pain numbly, like a man grappling in the dark. The wave subsided and he lay there gasping, his fists clenched. "The pain will come in increasingly powerful waves," the Doctor had said. "At a certain point, it will be so great, the analytical mind will completely short-circuit. It will stay that way enroute to Mars, and meanwhile your body will rapidly change into that of a beast. Don't worry about it. A catalytic agent will return you to normal before you reach the planet. If you live, you'll be human again." * * * * * A male human couldn't stand the acceleration. But a woman could. Animals could. They had experimented on human males and animals in the giant centrifuges, and learned what to do. Animals could stand 25 "G" consistently, or centrifugal forces as high as 120 revolutions a minute. About 10 "G" was the limit of female endurance. Less for men. It had never been thoroughly determined why women had been able to stand higher acceleration. But human females had the same physical advantages over men as female rats, rabbits, and cats over males of the same species. A woman's cellular structure was different; her center of gravity was different, the brain waves given off during acceleration were different. It was suspected that the autonomic nervous system in women could function more freely to protect the body during emergency situations. The only certainty about it was that no man had ever been able to get into space and live. But animals could so they had worked on it and finally they decided to change a man into an animal, at least temporarily. Geneticists and biochemists and other specialists had been able to do a lot with hormones and hard radiation treatment. Especially with hormones. You could shoot a man full of some fluid or another, and do almost anything to his organism. You could induce atavism, regression to some lower form of animal life--a highly speeded up regression. When you did that, naturally the analytical mind, the higher thought centers of a more recent evolutionary development, blanked out and the primal mind took over. The body changed too, considerably. Bowren was changing. Then the pain came and he couldn't think. He felt his mind cringing--giving way before the onslaught of the pain. Dimly he could feel the agony in his limbs, the throbbing of his heart, the fading power of reason.