Terror struck during the night when my right foot encountered a warm, lumpy object in my bed. It turned out to be my left foot, which had fallen asleep.

It was our first night aboard the "Delfin," a rebuilt cargo boat carrying its first load of tourists up the Amazon River. Unfortunately, the bunks were designed for Peruvians, who are short people. The lower bunk was set at a right angle to the upper with 10 inches of space between them, so the effect was that of lying in a casket 3 inches too short for the corpse.The toilets on board didn't work most of the time, either. At one time or another during our two weeks in the Peruvian Amazon, we also coped with mud, mosquitoes, ants, sunburn and never-ending dampness. And, of course, there was the fellow who got bitten by a snake.

But that's getting ahead of the story.

Our trip began in Iquitos, a dilapidated city perched precariously on the bank of the Amazon River, into which large chunks of the waterfront occasionally fall. The town is a good starting point for scientists, bird watchers and ordinary tourists bound for the lowland rain forests of the upper Amazon.

Our first destination was Amazon Camp, up the nearby Momon River, whose waters flow into the Amazon. Built mainly of fishtail palm, the thatched roof lodge offers spartan accommodations - primitive double rooms with toilet and sink, running water (don't drink it), communal showers and a dining room where the buffet consists of fresh vegetables and fruit, a little beef, chicken or fish, and rice. Lots of rice. There is no electricity but lanterns cast a pretty if minimal glow after sundown.

From a pleasant veranda we could watch Indian families in dugouts, taking loads of charcoal or stalks of bananas to market in Iquitos. The lodge's pet black saki monkey, whose hair looks blow-dried, and a tiny white-bearded marmoset with a fierce face and a sweet disposition curl up in the nearest lap for a nap.

The veranda also has a tiny bar where a pisco sour went for about 80 cents when we arrived, a price that fell rapidly along with the value of the Peruvian inti. (Valued at 65,000 to $1 on our arrival, the inti tumbled to more than 100,000 to $1 within two weeks.)

Two popular excursions from Amazon Camp involve hiking through the jungle to the villages of the Yaguas and the Boros, two of the many Indian tribes living in the Peruvian jungle. For tourists, they don their old-time grass or bark cloth clothing, paint their faces and trade handmade blowguns and seed necklaces for the T-shirts, shorts and sneakers that are now their everyday wear. The going rate is two necklaces for a T-shirt. One orange number I got at Fort Lauderdale's Thunderbird Swap Shop (six shirts for $10) was a real smash. Accompanying us on these hikes was another tame saki, a red monkey who hitched a ride on someone's head whenever he got tired. His name, Scarface, was the result of an encounter with the camp macaw.

Scarface must have had a premonition on the only day he stayed at camp. He missed a long, hot and grueling afternoon walk to a village on another river - a hike over rough, root-strewn paths, slippery, moss-covered logs and narrow pole "bridges" spanning creeks and mud wallows.

In the equatorial jungle, darkness drops like a curtain at 6 p.m. What with bird watching and dickering in the village for pottery, we dawdled too long. It suddenly became clear that if we were going to walk back to Amazon Camp it would be through dark forest. This was not a happy thought, particularly since neither our leader nor the Indian guides had brought a flashlight.

The guides, however, managed to scrounge a wood dugout built for, at most, eight passengers. In we piled - 13 in all, including guides and the boat owner. Only an inch or two of the leaky boat remained above water, with not a life jacket anywhere.

Not that there was a shore to swim to, if we had swamped. The river bank and edges of the canals that serve as shortcuts across bends in the river were flooded jungle, with not a foot of dry land in sight. We were relieved when the lanterns of Amazon Camp finally flickered up ahead an hour later.

Some of us thought all this was quite primitive enough, but a day or two later we set off up the Momon to what our leader described as a "primitive camp." The "camp" consisted of a rounded clearing atop a steep, muddy creek bank, and a couple of open-sided thatched huts surrounded by jungle. The "bathroom" was a short path hacked into the jungle; for washing up there was the murky creek.

Our Indian helpers were as resourceful as their ancestors were. With machetes, they cut poles and tied them horizontally to the posts of the larger hut. For cord, they stripped tough, flexible fiber from a palm tree and bit it to the lengths they needed, then tied our mosquito nets to the poles.

The area was alive with tropical birds, and the bird watchers in our group were beside themselves with excitement. A half-dozen blue and gold macaws flew over camp, and a young roadside hawk, apparently terrified of flying, took up residence in a small tree in the clearing.

This is where the snake entered the picture. A lovely green with a turquoise, wedged-shaped head, it came crawling near the huts. Bob, our leader, picked it up.

"Are you sure that thing is harmless?" someone asked.

"I think so," he said.

Wrong. When Manny, another in our group, attempted to handle the snake, the creature understandably became annoyed and fastened its fangs between Manny's right thumb and forefinger. It hung on until Bob pried its jaws open with a ball-point pen.

Manny went to lie down. Bob went to look at another bird. I went down the path into the jungle. This was no place to come down with turista.

When Manny's hand began to puff up like a baseball mitt, his wife commandeered our extra aluminum motorboat and an Indian to run it. Toting the snake in a drawstring bag - a doctor would need to know what kind of snakebite he was dealing with - they headed down river.

As we were packing up to leave the next day, a huge tarantula plopped from the thatched roof onto the floor of the hut. On the way back to Amazon Camp, a squall came up, churning up the river and sending vast amounts of rainwater into our open boat. I'd had enough of Primitive by this time, and it seemed sensible, once back on the veranda, to ask the bartender to pour a double rum immediately.

As for Manny, he spent a couple of days in the hospital in Iquitos being pumped full of anti-venin and antibiotics. Then one afternoon, he came up the river in the camp boat and climbed ashore at Amazon Camp, his hand dark and swollen but still clutching the bag with the snake. He kept insisting it was "toxic," not "poisonous," a distinction some of us failed to grasp.

That evening, Manny paddled across the river where there was only uninhabited jungle. He got out of the boat, opened the bag and spilled the still live snake on the ground. He watched it until it disappeared into the undergrowth, then paddled back to camp. We applauded what we considered his selfless respect for wildlife, but the Indians thought he'd gone off the deep end.

One night at Amazon Camp, we were joined by about 20 Taiwanese bankers in neckties who spent their time playing mah-jongg and drinking vast amounts of brandy. With them was a young Chinese tour leader from San Francisco, who glued himself to our dinner table to explain the intricacies of mah-jongg. Even when our eyes glazed with boredom he wouldn't go back to his bankers. "I can't take anymore," he whimpered.

The next day the bankers went for a jungle hike to the Indian village. They were still wearing their neckties.

The best times at Amazon Camp were the evenings when the guides and camp staff sang, accompanying themselves on guitars and drums.

Our second week in Peru took us about 125 miles up the Amazon from Iquitos to the junction of the Ucayali and Maranon rivers. If someone could have made the communal toilets work and done away with the hot, minuscule cabins, the week on the "Delfin" would have been marvelous.

My favorite spot was at the bow, on a little bench just in front of the pilot house. The captain had no maps or charts as he zigzagged from one bank to the other to stay in deep water. We shared the river with dugouts, rafts and thatch-covered boats called collectivos, or river taxis, the only form of public transportation in these parts. On the shores, riberenos, or river people, live in open-sided huts surrounded by patches of bananas, yuca, rice, beans, sugar cane, corn and, inevitably, a breadfruit tree.

We watched the river dolphins and fished for piranha, whose ferocity - this variety's, at least - didn't live up to its reputation. We swam and shampooed our hair in the same waters where we fished for them, and only once was someone nipped - when he tried to remove one from his fishhook.

The "Delphin" lacked an anchor, so when we stopped for the night we simply tied up to an available tree, usually close to a village. Invariably, the inhabitants were both curious and gregarious, and soon the boat would swarm with people, including zillions of beautiful, big-eyed children.

There were also the usual entrepreneurs with seed jewelry, food and live animals to sell. We turned down two live curassows, an owl-eyed monkey and a side-necked turtle, but when a fellow paddled up with a dozen large oscars - the same fish that may inhabit your aquarium - we handed over a couple of dollars and ate them for dinner.

For a visitor who can overlook minor discomforts and forget more familiar standards of sanitation, the Amazon is a wonderful adventure. The sweeping miles of brown river are awesome during the day, sunrises and sunsets are glorious, if brief, and at night the blazing Southern Cross and perhaps even a meteor shower light the sky.

And unlike the tourist-oriented Indian villages close to the city, nothing this far from civilization is contrived.

Images linger in the mind. Pink dolphins playing where a tributary meets the big river. An Indian casting his fishing net for supper while his wife paddles their tiny water-logged dugout. The dark-haired, teen-age mother joyously hugging and kissing her fat, laughing baby. And the two canoes with three enormous logs lashed behind them, the sinewy men in the boats steering their fragile shells into the rough, downstream current and then disappearing at last into the rain-laden dusk.