Checkup excitement began within the farm dome as soon as the main fluorescents were turned on. There was a wild noise and a mad scurry. Sand-cars were brought out in rows, each farmboy tending his own.

Makiari was here and there, never too long at any one point. Hennes, in his flat, efficient voice, assigned the parties and set the routes across the farm's vast expanse. He looked up as he passed David and stopped.

"Williams," he said, "are you still of a mind to be on the checkup?"

"I wouldn't miss it."

"All right then. Since you haven't any car of your own, I'll assign you one out of general stock. Once it's assigned, it's yours to take care of and keep in working condition. Any repairs or damage which we consider avoidable will come out of your pay. Understood?"

"Fair enough."

"I'll put you on Griswold's team. I know that you and he don't get along, but he's our best man in the fields and you're an Earthie without experience. I wouldn't care to load you onto a lesser man. Can you drive a sand-car?"

"I think I can handle any moving vehicle with a little practice."

"You can, eh? We'll give you your chance to make good on that." He was about to step away when his eyes caught something. He barked, "And where do you think you're going?"

Bigman had just stepped into the assembly room. He was in a new outfit and his boots had been polished to mirror-shine. His hair was slicked down and his face was scrubbed and pink. He drawled, "On the checkup, Hennes-Mister Hennes. I'm not on detention and I still have my rating as licensed farmboy even though you have put me on chow detail. That means I can go on checkup. It also means I have a right to my old car and my old squad."

Hennes shrugged. "You read the rule books a lot, and that's what they say, I suppose. But one more week, Bigman, one more week. After that, if you ever show your nose anywhere on Makian territory I'll have a real man step on you and squash you."

Bigman made a threatening gesture at Hennes's retreating back and then turned to David. "Ever used a nosepiece, Earthman?"

"Never actually. I've heard about them, of course."

"Hearing isn't using. I've checked an extra one out for you. Look, let me show you how to get it on. No, no, get your thumbs out of there. Now watch how I hold my hands. That's right. Now over the head and make sure the straps aren't twisted in the back of the neck, or you'll end with a headache. Now can you see through them?"

The upper part of David's face was transformed into a plastic-encased monstrosity, and the double hose leading from the oxygen cylinders up each side of his chin subtracted further from any appearance of humanity.

"Do you have trouble breathing?" asked Bigman.

David was struggling, fighting to suck in air. He yanked the nosepiece off. "How do you turn it on? There's no gauge."

Bigman was laughing. "That's the return for the scare you gave me last night. You don't need a gauge. The cylinders automatically feed oxygen as soon as the warmth and pressure of your face trip a contact; and it automatically closes off when you take it off."

"Then there's something wrong with it. I- "

"Nothing wrong with it. It feeds at a gas pressure of one fifth normal to match the pressure of the Mars atmosphere, and you can't suck it in out here when you're fighting the pressure of a normal Earth atmosphere. Out there in the desert it will be fine. And it will be enough, too, because even though it's one fifth normal, it's all oxygen. You'll have as much oxygen as you always had. Just remember one thing: breathe in through your nose but breathe out through your mouth. If you breathe out through your nose, you'll fog up your eyepieces, and that won't be good."

He strutted about David's tall, straight body and shook his head. "Don't know what to do about your boots. Black and white! You look like a garbage detail or something." He glanced down at his own chartreuse-and-vermilion creations with more than a little complacency.

David said, "I'll manage. You'd better get to your car. It looks as though they're getting ready to move."

"You're right. Well, take it easy. Watch out for the gravity change. That's hard to take if you're not used to it. And, Earthman.... "

"Well."

"Keep your eyes open. You know what I mean."

"Thanks. I shall."

The sand-cars were lining up now in squares of nine. There were more than a hundred all told, each with its farmboy peering over its tires and controls. Each vehicle had its handmade signs intended as humor. The sand-car trundled out for David was speckled with such signs from half-a-dozen previous owners, beginning with a "Watch Out, Girls" circling the bullet-like prow of the car and ending with a "This Ain't No Dust Storm, This Is Me," on the rear bumper.

David climbed in and closed the door. It fit tightly. Not even a seam showed. Immediately above his head there was the filtered and refiltered vent that allowed equalization of air pressure within and without the car. The glass was not quite clear. It had a faint misting that was proof of dozens of dust storms met and weathered. David found the controls familiar enough. They were standard for ground cars, for the most part. The few unfamiliar buttons explained themselves upon manipulation.

Griswold came past, gesturing at him furiously. He opened his door.

Griswold yelled, "Get your front flaps down, you jerk. We're not heading into any storm."

David searched for the proper button and found it on the steering-wheel shaft. The windshields, which looked as though they were welded to metal, disengaged themselves and sank down into sockets. Visibility improved. Of course, he thought. Mars's atmosphere would scarcely, raise wind enough to disturb them, and this was Martian summer. It would not be too cold.

A voice called, "Hey, Earthman!" He looked up. Bigman was waving at him. He was in Griswold's group of nine also. David waved back.

A section of the dome lifted up. Nine cars trundled in, moving sluggishly. The section closed behind them. Minutes passed, then it opened, empty, and nine more moved in.

Griswold's voice sounded suddenly and loudly next to David's ear. David turned and saw the small receiver in the car top just behind his head. The small grilled opening at the head of the steering-wheel shaft was a mouthpiece.

"Squad eight, ready?"

The voices sounded consecutively: "Number one, ready." "Number two, ready." "Number three, ready." There was a pause after number six. Just a few seconds. David then called, "Number seven, ready." There followed "Number eight, ready." Big-man's reedy tones came last. "Number nine, ready."

The dome section was raising again and the cars ahead of David began moving. David slowly stepped on the resistor, cutting the coils, allowing electricity to pour into the motor. His sand-car leaped ahead, all but crashing into the rear of the one in front. He let out the resistor with a jerk and felt the car tremble beneath him. Gently he babied it along. The section enclosed them like a small tunnel, shutting off behind.

He became conscious of the hiss of air being pumped out of the section back into the dome proper. He felt his heart begin to pound, but his hands were steady upon the wheel.

His clothing bellied away from him and the air was seeping out along the cylindrical line where boots met thigh. There was a tingling in his hands and chin, a feeling of puffiness, of distention. He swallowed repeatedly, to relieve the gathering pain in his ears. After five minutes he found himself panting in an effort to gather enough oxygen for his needs.

The others were slipping on their nosepieces. He did the same, and this time oxygen slid smoothly up Ms nostrils. He breathed deeply, puffing it out through his mouth. His arms and feet still tingled, but the feeling was beginning to die away.

And now the section was opening ahead of them, and the flat, ruddy sands of Mars glittered in the sun's feeble light. There was a yell in unison from eight farmboy throats as the section lifted.

"Sand awa-a-a-ay!" and the first cars in line began to move.

It was the traditional farmboy cry, made thin and almost soprano in the thin air of Mars.

David let in the resistor and crawled across the line that marked the boundary between dome metal and Martian soil.

And it hit him!

The sudden gravity change was like a sharp fall of a thousand feet. One hundred and twenty pounds of Ms two hundred disappeared as he crossed the line, and it left him by way of the pit of his stomach. He clutched at the wheel as the sensation of fall, fall, fall persisted. The sand-car veered wildly.

There was the sound of Griswold's voice, which maintained its hoarseness even in the incongruous hollowness forced upon it by the thin air which carried sound waves so poorly. "Number seven! Back in line!"

David fought with the wheel, fought with his own sensations, fought to make himself see clearly. He dragged at the oxygen through his nosepiece and slowly the worst passed.

He could see Bigman looking anxiously in Ms direction. He took one hand away from the wheel momentarily to wave, then concentrated on the road.

The Martian desert was almost flat, flat and bare. Not even a scrub of vegetation existed here. This particular area had been dead and deserted for who knew how many thousands or millions of years. The thought suddenly struck him that perhaps he was wrong. Perhaps the desert sands had been coated with blue-green microorganisms until Earthmen had come and burned them away to make room for their farms.

The cars ahead trailed faint dust that rose slowly, as if it were part of a motion-picture film that had been slowed down. It settled as slowly.

David's car was trailing badly. He added speed and still more speed, and found that something was going wrong. The others, ahead of him, were hugging the ground but he, himself, was bounding like a jackrabbit. At every trifling imperfection in the ground surface, at every projecting line of rock, his car took off. It drifted lazily up into the air, inches high, its wheels whining against nothing. It came down as gently, then lurched forward with a jerk as the straining wheels caught hold.

It caused him to lose ground, and when he poured the juice in to gain again, the jumping grew worse. It was the low gravity that did it, of course, but the others managed to compensate for it. He wondered how.

It was getting cold. Even at Martian summer, he guessed the temperature to be barely above freezing. He could look directly at the sun in the sky. It was a dwarfed sun in a purple sky in which he could make out three or four stars. The air was too thin to blank them out or to scatter light in such a manner as to form the sky-blue of Earth.

Griswold's voice was sounding again: "Cars one, four, and seven to the left. Cars two, five, and eight to the center. Cars three, six, and nine to the right Cars two and three will be in charge of their subsections."

Griswold's car, number, one, was beginning to curl to the left, and David, following it with his eyes, noticed the dark line on the leftward horizon. Number four was following one, and David turned his wheel sharply left to match the angle of veer.

What followed caught him by surprise. His car went into a rapid skid, scarcely allowing him time to realize it. He yanked desperately at the wheel, spinning it in the direction of skid. He shut off all power and felt the wheels rasp as the car whirled onward. The desert circled before him, so that only its redness could make any impression.

And then there was Bigman's thin cry through the receiver, "Stamp on the emergency traction. It's just to the right of the resistors."

David probed desperately for the emergency traction, whatever it was, but Ms aching feet found nothing. The dark line on the horizon appeared before him and then vanished. It was much sharper now, and broader. Even in that rapid flash, its nature became appallingly evident. It was one of the fissures of Mars, long and straight. Like the far more numerous ones on Earth's Moon, they were cracks in the planetary surface, made as the world dried through millions of years. They were up to a hundred feet across and no man had plumbed their depth.

"It's a pink, stubby button,". yelled Bigman. "Stamp everywhere."

David did so, and there was a sudden slight yielding beneath his toes. The: swift motion of his sand-car became a rebellious grinding that tore at him. The dust came up in clouds, choking him and obscuring everything.

He bent over the wheel and waited. The car was definitely slowing. And then, finally, it stopped.

He sat back and breathed quietly for a moment Then he withdrew his nosepiece, wiped the inner surfaces while the cold air stung at nose and eyes, and replaced it. His clothes were ruddy gray with dust and his chin was caked with it. He could feel its dry-ness upon his lips, and the interior of his car was filthy with it.

The two other cars of his sub-section had pulled up next to him. Griswold was climbing out of one, his stubbled face made monstrously ugly by the nose-piece. David was suddenly aware of the reason for the popularity of beards and stubble among the farmboys. They were protection against the cold, thin wind of Mars.

Griswold was snarling, showing yellowed and broken teeth. He said, "Earthman, the repairs for this sand-car will come right out of your wages. You had Hennes's warning."

David opened the door and climbed out. From outside, the car was a worse wreck still, if that were possible. The tires were torn and from them projected the huge teeth which were obviously the "emergency traction."

He said, "Not one cent comes out of my wages, Griswold. There was something wrong with the car."

"That's for sure. The driver. A stupid, dumb-lug driver, that's what's wrong with the car."

Another car came squealing up, and Griswold turned to it.

His stubble seemed to bristle. "Get the blast out of here, you cinch-bug. Get on with your job."

Bigman jumped out of his car. "Not till I take a look at the Earthman's car."

Bigman weighed less than fifty pounds on Mars, and in one long, flat leap he was at David's side. He bent for a moment, then straightened. He said, "Where are the weight-rods, Griswold?"

David said, "What are the weight-rods, Bigman?"

The little fellow spoke rapidly. "When you take these sand-cars out into low gravity, you put foot-thick beams over each of the axles. You take them out when you're on high grav. I'm sorry, fella, but I never once thought that this might be what.... "

David stopped him. His lips drew back. It would explain why his car had floated upward at each bump while the others were glued to the soil. He turned to Griswold. "Did you know they were gone?"

Griswold swore. "Each man is responsible for his own car. If you didn't notice they were gone, that's your negligence."

All the cars were now on the scene. A circle of hairy men were forming around the three, quiet, attentive, not interfering.

Bigman stormed. "You big hunk of silica, the man's a tenderfoot. He can't be expected to- "

"Quiet, Bigman," said David. "This is my job. I ask you again, Griswold. Did you know about this in advance?"

"And I told you, Earthie. In the desert a man has to watch himself. I'm not going to mother you."

"All right. In that case I'll watch myself right now." David looked about. They were almost at the edge of the fissure. Another ten feet and he would have been a dead man. "However, you'll have to watch yourself, too, because I'm taking your car. You can drive mine back to the farm dome or you can stay here for all I care."

"By Mars!" Griswold's hand shot to his hip and there was a sudden rough cry from, the circle of watching men.

"Fair fight! Fair fight!"

The code of the Martian deserts was a hard one, but it drew the line at advantages considered unfair. That was understood and enforced. Only by such mutual precautions could any man be protected from an eventual force-knife in the back or blast-gun in the belly.

Griswold looked at the hard faces about him. He said, "We'll have it out back in the dome. On your jobs, men."

David said, "I'll see you in the dome if you wish. Meanwhile, step aside."

He walked forward unhurriedly, and Griswold stepped back. "You stupid greenhorn. We can't have a fist-fight with nosepieces on. Do you have anything but bone inside your skull?"

"Take your nosepiece off, then," said David, "and I'll take mine off. Stop me in fair fight, if you can."

"Fair fight!" came the approving shout from the crowd, and Bigman yelled, "Put up or back down, Griswold." He leaped forward, ripping Griswold's blaster from his hip.

David put his hand to his nosepiece. "Ready?"

Bigman called, "I'll count three."

The men yelled confusedly. They were waiting now, in keen anticipation. Griswold glanced wildly about him.

Bigman was counting, "One.... "

And at the count of "Three" David quietly removed his nosepiece, and tossed it, with the attached cylinders, to one side. He stood there, unprotecteds holding his breath against the unbreathable atmosphere of Mars.