There was a department seminar in radiobiology. The third — year students surrounded the uranium reactor and watched the dark cellular cylinder in its depths respectfully. It gave off a green, calm light in the water, illuminating the wires, the nickel — plated bars, levers, and wheels of the control board above it.

“That beautiful light, the color of young grass, around the body of the reactor,” said Professor Valerno in his rich deep baritone, “is called the Cherenkovsky glow. It is caused by the movement of superfast electrons in the water, which are created, in turn, by the division of nuclei of uranium — 235.”

Krivoshein assisted; that is, he sat around, bored, and waited for the professor to ask him to run the demonstration. Actually, Valerno could have easily done the experiment himself, or asked a student to do it, but his scholarly rank rated a qualified assistant. “So just sit there,” Krivoshein thought gloomily. Then he got the idea that he hadn't tried out radiation sickness on himself. He sat up and started planning how to go about it. “Take a flask of water from the reactor and for starters give myself a slight radiation burn. This was serious stuff!”

“The presence of intense Cherenkovsky glow in the water is evidence of intense radiation in the body of the reactor,” Valerno droned on, “which is not surprising. It's a chain reaction. The growth in the brightness of the light is evidence of the growth of the intensity of the radiation, and a dimming — of the opposite. Here, please look.” He turned the wheel on the panel to the left and the right. The green light in the tank blinked.

“And if you turn it all the way to the right, there'll be an explosion?” a red — haired, freckled boy in glasses demanded.

“No,” replied the professor, barely suppressing a yawn (that question came up every time). “There's a governor on it. And besides, the reactor can be automatically blocked. As soon as the intensity of the chain reaction exceeds certain limits, the automatic device throws additional graphite rods into the reactor — those, see? They consume the neutrons and quench the reaction. And now let's familiarize ourselves with the action of radioactivity on a living organism. Valentin Vasilyevich, could you join us?”

Krivoshein rolled a cart with a fish tank over to the reactor; the tank contained a half — dead eel, with fins and sharp teeth.

“This is a freshwater eel, Anguilliformes,” Valerno announced, without even looking, “the most hardy of river fish. When Valentin Vasilyevich dumps it into the pool, the eel, heeding its instincts, will immediately go to the bottom… hmm… something that I wouldn't do in its place, since even the luckiest ones come floating belly up from there in two minutes. Well, see for yourselves. Mark the time, please. Valentin Vasilyevich, you're on.”

Krivoshein tipped the fish tank over the pool and started the stopwatch. The students leaned over the edge. A streak of black lightning sped to the gray — tiled bottom of the pool, made a circle, another, crossed the green light over the cylinder. Apparently blinded by that, the eel bumped into the opposite wall and reeled back.

Suddenly the light in the pool got brighter — and in the green light Krivoshein saw something that made his skin crawl: the eel got trapped in the wires that held the graphite rods, the regulators of the reactor, and was struggling among them! One rod fell out of its case and flew off like a green stick into the water. The light got even brighter.

“Everyone back!” Quickly appraising the situation, the pale Valerno barked a command. His baritone was flat. “Please leave at once!” He pulled the emergency alarm. The contacts of the automatic blocking device clicked. The light in the water blinked, as though they were doing arc welding in the pool, and got even brighter. The students, covering their faces, raced from the exits. There was a crush at the door.

“Please stay calm, comrades!” Valerno shouted in a real falsetto. “The concentration of uranium — 235 in the heat — generating elements is not enough for an atomic explosion! There will only be a heat explosion, like in a steam engine!” “Oh, God!” some exclaimed.

The doors cracked. A girl screamed. Someone cursed. The freckled four — eyes, not losing his head, grabbed a very heavy Sl — 8 synchronoscope from the table, and threw it through the window, following it rapidly…. The room was empty in a few seconds.

In the first moment of panic Krivoshein followed the rest, but stopped himself and went over to the reactor. Rapid, large bubbles rose from the cylinder and the water churned. Instead of the quiet glow there was a green bonfire in the water. The eel was quiet, but the graphite rods that it had knocked out were crisscrossed and wedged against one another.

“When the water splashes up, there'll be a cloud of radioactive steam all over,” Krivoshein thought feverishly. “That's as bad as an atomic blast. Can I do it? I'm scared. Well! What good are all my experiments, if I'm scared? And what if I end up like the eel? The hell with it!”

(Even now Krivoshein couldn't believe it. How could he have done it? Had he decided that he was invincible? Or was it the thinking of a motorcyclist who has to pass between two oncoming trucks — the important thing is don't think, just go forward! The intoxicating instant of danger, the roar of the trucks, and with a beating heart you tear out into the asphalt expanse! But this wasn't an instant — and it was quite possible he could end up along with the dead eel on the pool bottom.)

The motorcyclist's daring hit him. Tearing off his buttons, he undressed, put his leg over the edge, and — “Stop, Val! Think!” — went to the counter, and put on rubber gloves and goggles (“Wish I had an Aqua — lung!”). He filled his lungs with air and plunged into the pool.

Even at a distance from the reactor the water was warm. “A thousand one, a thousand two….” Krivoshein, instinctively turning his face away, walked across the slippery tiles to the middle of the pool. His rubber gloves were in contact with something, and he had to look: the eel, hanging in a loop between the wires, was there. “A thousand ten, a thousand eleven,” and carefully, so as not to disturb the rods, he pulled at the dead fish. “Thousand sixteen….” His hands got hot, and he instinctively wanted to pull away, but he controlled the impulse and slowly extracted the eel from the jumble. The goggles weren't so hermetic, and streams of radioactive water seeped into his eyes. He squinted. “Thousand twenty, a thousand twenty — one” — he got it out! The green glow flickered, and the rods silently slipped back into the cylinder. It got dark in the pool.

“A thousand twenty — five!” With a sharp push Krivoshein came up to the wall, jumped out of the water, grabbed the edge, and climbed over. “A thousand thirty….”

He had the presence of mind to hop around to get the excess water off his body; he even rolled around on the floor. He wiped his face and eyes dry with his pants. “Just don't let me get blind before I get there.” He dressed haphazardly and ran out of the room.

The radiation counter howled harshly as he went by. An automatic barrier blocked his path. He jumped over it and ran across the freshly dug lawn to his dorm.

“A thousand seventy; a thousand seventy — one,” his brain continued to count. It was twilight and he avoided meeting acquaintances; but someone called after him near zone B: “Hey, Val, where's the fire? He thought it was Nechinorov, a graduate student. “A thousand eighty, a thousand eighty — one….” His skin ached and itched and then it was pierced by a million needles. That was his nervous system, honed in previous experiments, telling him that the protons and gamma — quanta from the decayed nuclei were shooting the molecules of protein in the cells of the epithelium, in the nerve endings of the skin, breaking through the walls of the blood vessels, and wounding the red and white corpuscles. “A thousand hundred. thousand hundred five….” Now the prickling had moved to his muscles, stomach, and under his skull. His lungs were congested as though he had taken a deep draw on the crudest homegrown tobacco in the world. That was the blood carrying the exploded atoms and fractured proteins all over his body.