Earth had, however, investigated the Venusian plagues with a view to their use in biological warfare. And out of the investigation, as an accident, as a by-product, had come lobodin. A vaccine, not a serum. No good for Graff right now, for he was almost two full hours into the yellow death. * * * * * He worked his left arm around slowly, wincing with each turn, his eyes on the terry above him circling southward in the damp murky sky. At the same time he tried to plant the broad soles of his boots on mud that wasn't quicksand, on rotten twigs that wouldn't crack too loudly. He knew his blood was now completely infiltrated with the obscene little yellow specks. Pubina was probably trying to force Dr. Bergenson to inject the vaccine into him, ridiculing the old man's protests that all the bottle held was a starter culture, just enough so that with weeks of careful tending they might have sufficient vaccine to immunize the children. It had been so expensive and difficult for the little colony to send Dr. Bergenson and Greta to Earth where his reputation and connections had enabled him to wheedle a spoonful of the precious stuff out of a government laboratory! Pubina hadn't been able to get it, for all of his bribes and underworld contacts. But the bribes and underworld contacts had served another purpose: Pubina had discovered when the Bergensons were due to return--and that was all he really needed. Graff noticed abruptly that the terry was falling rapidly back at him. Could he be trying to warn-- A shriek gave him the answer. Less than a quarter-mile away, a brontosaurus squatted its tremendous bulk in a shallow pool and regarded him from the end of an undulating snake-like neck. The animal screamed again and Graff froze. He watched the incredibly heavy reptile scramble to its feet and desperately tried to think. It wasn't a brontosaurus charge you had to be afraid of, but what usually traveled in its wake. A brontosaurus was herbivorous and, for all its size, extremely timid. It was ridiculous, possibly, but the mountain of living flesh was probably screaming in terror at the sight of him. You only had to control yourself and think while the great beast charged. Because a brontosaurus meets danger by running into it. It is so massive that it is virtually unstoppable once in motion. You can blast its stupid little head off and it will keep running for another twenty minutes, powered by the bundle of nerve cells just under the spine. You just have to stand still and remember that it is much more frightened than you and is trying to trample you to death before you can bite it. Graff stood his ground, bending his knees slowly, until the behemoth was only twenty-five feet away. Then he straightened suddenly and leaped off to the right, then again, further, and again, still further to the right. * * * * *