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They stumbled toward the riverbanks, some crying out, "Mizu, mizu!" (Water, water); the temperature and their injuries had left them severely dehydrated. Because light colors reflect heat and dark ones absorb it, some bomb victims had the images of their clothing tattooed on their flesh: the pattern of a kimono on a woman's back, the unburned swath left by a sash around the waist of an otherwise charred man. "Big black flies appeared and tried to lay eggs on human flesh," says survivor Michiko Watanabe, now 65. "The injured were so weak that they couldn't brush away the flies that nestled in their hands and necks. Some were black from a blanket of flies that covered them."
The heat from Little Boy singed more than 4 sq mi. of Hiroshima reddish-brown. In the process, it left a bizarre photographic negative of the instant of destruction. Objects, human or inanimate, that came between the blast and other objects cast their shadows as unburned patterns on the protected space: a spiral ladder was imprinted on the surface of a storage plant behind it. Survivors foraging for food in vegetable gardens later that day dug up potatoes and found that they had been baked in the ground.
Nature itself seemed deranged by the violence. Whirlwinds tore through the city. Fires jumped rivers with ease. Dark, marble-size drops of water--later called black rain--condensed off the explosion's towering smoke and fell to earth.
After the thermal heat came the blast, spreading out from the explosion center at an initial speed of 2 m.p.s. and then subsiding toward the speed of sound. Shock waves were the principal threat of conventional bombs, but Little Boy achieved a new order of destructive power. Unleashing the equivalent of 12,500 tons of TNT, it essentially flattened Hiroshima in one blow: only 6,000 of the city's 76,000 buildings were undamaged; 48,000 of them were entirely destroyed. Practically every window and mirror in the city splintered, hurling shards of glass into the bodies of anyone nearby. The explosion started more fires outside the central ring of devastation, as flammable houses collapsed onto cooking fires or sputtering electric wires. People pinned under rubble inside burning buildings cried out for help; few heard them, and even fewer were in any condition to save them from burning alive. An estimated 100,000 died that first day, and the death toll climbed to 140,000 by the end of the year.
Assistance of any kind vanished that morning in Hiroshima. All the usual functions of municipal government simply stopped when the bomb exploded. Hospitals and medical centers, to which the tens of thousands of grievously wounded people swarmed, were part of the general ruin. Of the city's 150 doctors, 65 had died in the blast and most of the rest had been seriously hurt. More than 90% of the nurses were either dead or incapacitated.
Those physicians able to function did so heroically. They could not know that they would be the first medical experts to observe a new disease, the third effect, after heat and blast, of Little Boy. On Tuesday an official of the Red Cross Hospital in Hiroshima discovered that the X-ray plates stored in a basement vault that had survived the blast and a fire had all been exposed. The atomic bomb had spread radiation throughout central Hiroshima, with lingering, lethal effects on its survivors that would not be fully understood for years.