For their first two nights in this godforsaken territory, Humboldt’s party rode only after dark, to avoid the blistering daytime sun. Late on the third afternoon, they arrived at a little farm called Hato del Caimán (Alligator Ranch), a house surrounded by a few rude huts constructed from reeds and animal skins. There were no corrals at Alligator Ranch, and the cattle, oxen, horses, and mules wandered at will, herded when necessary by half-naked men on horseback. Some of these peones llaneros were slaves and others were free, but all had been hardened by the unforgiving land. Living in the saddle, they subsisted on dried, salted meat, which they sometimes even fed to their horses.
Stepping wearily from their mounts, Humboldt and Bonpland let the mules lead them to a muddy yellow pool, the sole source of water, which an old slave suggested they drink through a handkerchief to minimize the grit and odor. Having slaked their thirst as best they could, the travelers, hot, dusty, and wind burned, stripped naked and dived into the fetid pool. But they had barely begun to savor their bath when they heard a splash on the opposite bank—an alligator slithering into the murky water. The men made a precipitous retreat, grabbing their clothes as they ran.
Dusk was approaching, and the pair headed back toward the farmhouse where they were staying. But after walking for more than an hour, they were forced to admit that they had lost their way. By now the sun had set, and in the dark they were unable even to retrace their steps to the water hole. We may find it ironic that the greatest scientific explorers in South American history could lose their way less than a mile from camp, but in deadly fact, the Llanos were no place to go wandering, whether by day or night. The two meandered across the savannah for a long time before finally taking shelter under a palm, where they kept watch for snakes, jaguars—and bandits, who reportedly made a practice of stripping unlucky travelers and tying them to the trunks of trees.
Eventually, hoofbeats sounded across the steppes, and with some trepidation, the two strained through the dark to see who was approaching. A rider appeared, lance in hand—a llanero, making his nightly rounds among the cattle. Relieved, Humboldt and Bonpland explained their predicament. But the sight of two strange white men claiming to be lost only heightened the horseman’s suspicions, and it was some time before he deigned to let them chase his trotting horse back to the farmhouse.
The party set off again at two o’clock that morning, hoping to reach the small trading town of Calabozo before the worst of the afternoon heat. Incongruous though it seemed, the dark Llanos reminded Humboldt of his days back on the Pizarro. “The solemn spectacle of the starry vault, seen in its immense expanse;—the cool breeze which blows over the plain during the night;—the waving motion of the grass, wherever it has attained any height; everything recalled . . . the surface of the ocean.” (Indeed, an oft-heard observation was Los Llanos son como un mar de yerbas, “The Llanos are like a sea of grass.”) As the sun rose, so did the eerie mirages, making a herd of oxen appear to be floating above the earth, or causing phantom towers and burial mounds to shimmer in the distance, then abruptly vanish. A hot, dust-laden wind kicked up, and as they continued on, the men filled their hats with leaves as insulation against the vicious sun.
Calabozo, situated between the Guárico and the Uritucu rivers in the center of the Llanos, was a prosperous town of five thousand people and twenty-five thousand cattle. The muddy hollows in the surrounding countryside were infested with tembladores, or electric eels (actually not eels at all but a type of fish, Electrophorus electricus, related to carp). The animals had been described by other Europeans but never scientifically examined, and Humboldt, long fascinated by Luigi Galvani’s concept of “animal electricity,” was impatient to find some of the creatures.
Around 1750, Benjamin Franklin had proved, via his famous (and perilous) experiment with the kite, that lightning was a form of electrical discharge. But by the late eighteenth century, the predominant researchers on the topic were two Italians, Luigi Galvani and Alessandro Volta. Galvani, who had trained as a physician, discovered that a frog’s muscles would contract when connected in a simple circuit with two different metals, such as brass and steel or copper and zinc. Publishing his results in 1791, he suggested that this “animal electricity” was produced by the frog’s nerves and transmitted through the metal to the muscle.
Volta, however, had trained as a physicist and saw the phenomenon in starkly different terms. The nerves didn’t produce the electricity, he argued; it was an interaction between the two metals that created the current, with the animal’s tissues simply acting as a conductor. To prove his point, Volta substituted a chemical solution for the frog and was able to produce an electric current without the use of any animal tissue at all.
Not to be outdone, Galvani repeated his experiments without the metal electrodes and managed to create a contraction in the frog’s muscle just by contact with the nerve. What to make of these seemingly contradictory results? It was a classic case of two branches of science being blinded by their own prejudices. For Galvani and Volta were actually studying two different aspects of the same phenomenon: The former, a physician, had stumbled upon electrical conduction through the nerves, while the latter, a physicist, had discovered a more general type of electrical phenomenon independent of living cells. But at the time, neither researcher nor any of their contemporaries could see the distinction.
Back in Germany, Humboldt had refined Galvani’s laboratory techniques and performed thousands of experiments with animal electricity. In the end, he concluded that the nerves produced a substance that caused the muscles to contract, and that, although the metal electrodes increased this effect, they clearly didn’t produce it. But by focusing his efforts on Galvani’s side of the problem and never really turning his attention to Volta’s more general phenomenon, Humboldt, too, never adequately distinguished between the physiological and purely physical manifestations of electricity. Although Humboldt was tantalizingly close to the solution, it was Volta who ultimately discovered the electrical storage device that would be named the voltaic pile in his honor—the electricity-generating configuration of fluids and metal plates that was the forerunner of today’s ubiquitous batteries.
Humboldt had made some original discoveries concerning the interplay of nerves and muscles, but after Volta’s breakthrough, both his and Galvani’s work was brushed aside. Humboldt was mortified to have been on the verge of the same discovery but never to have made the critical leap. As he despaired to a friend, “I have observed a great many things, as I am not without ability, but I have achieved nothing.” Had he thought to substitute nonorganic material for organic in some of his thousands of experiments, today we might be measuring electric potential not in units called volts but rather in humboldts.
Humboldt was eager to continue his research on animal electricity in a natural environment, and immediately after his arrival in Calabozo he set about trying to procure some electric eels, without success. He inquired again, promises were made, but still no eels materialized. He offered cash, but even that did no good. As Humboldt discovered, “Money loses its value as you withdraw from the coast; and how is the imperturbable apathy of the ignorant people to be vanquished, when they are not excited by the desire of gain?”
Meanwhile, he was astonished to meet in Calabozo a self-taught electrical experimenter named Carlos del Pozo. Del Pozo had never even heard the names Galvani and Volta. But he had pored over books on the subject, including Benjamin Franklin’s memoirs, and, with that slight introduction, had managed to assemble two capacitors (devices for storing electricity)—a Leyden jar and a more sophisticated apparatus fashioned from two large metal plates he’d had shipped from Philadelphia. He’d also constructed electrophori for charging the capacitors and electrometers for measuring their potential, with the result that his one-man laboratory, hidden in these remote plains of South America, was virtually as complete as anything to be found in the great European centers of learning.
The Leyden jar, developed about fi
fty years before by Pieter van Musschenbroek at the University of Leyden (or Leiden) in the Netherlands, consisted of a glass bottle partly covered on both its outer and inner surfaces with metal foil; a conducting rod passed through an insulating material in the neck of the jar and contacted the foil on the inside. With the outside grounded, a charge was given to the inside surface (as by rubbing a glass rod over a piece of fur and touching it to the conductor in the jar’s neck), which gave the outside surface an equal but opposite charge. When the inside and outside surfaces were joined by a conductor, the stored electricity would be released and a spark would be produced. Del Pozo’s more sophisticated capacitor used the large metal plates, separated by a nonconducting material such as glass or wax, to produce an even more impressive (and potentially hazardous) jolt of electricity.
Until the unexpected appearance of these European visitors, del Pozo had had no audience for his demonstrations except his neighbors, who, though impressed, didn’t have the scientific training to fully appreciate his accomplishment. Accordingly, he was delighted to display his apparatus to the distinguished naturalists and in turn to examine the Leyden jar and the electrometers they carried. Humboldt was pleased to encounter a kindred spirit in this out-of-the-way place. And for his part, “Senor del Pozo could not contain his joy on seeing for the first time instruments which he had not made, yet which appeared to be copied from his own.”
Humboldt hadn’t given up his quest for the electric eels. But he’d concluded that if he were to procure some of the tembladores, he would have to find them himself. Early on the morning of March 19, he and Bonpland hiked to the village of Rastro, where a group of Indians led them to a muddy basin in which eels were known to congregate. Because the creatures buried themselves in the mud, nets were useless for their capture. The roots of certain trees were sometimes used to poison them, but this method permanently enfeebled the fish, so that their powers couldn’t be demonstrated adequately. The only other alternative was the method called embarbascar con caballos, “to excite [the eels] with horses.”
Rounding up about thirty wild horses from the savannah, the Indians drove the animals into the pond. Their hooves aroused the tembladores, who wriggled to the surface and initiated a cruel and extraordinary contest. Shocked repeatedly around their bellies, the terrified horses strove to escape, but were blocked by Indians standing on the banks, crying and brandishing reeds. Stunned into unconsciousness, two horses disappeared beneath the surface, and at first it appeared that the others would share their fate. But the ferocity of the eels’ shocks diminished in time, and the surviving horses were finally allowed to stumble out of the water and throw themselves, exhausted, in the sand. Meanwhile, the eels, having discharged their stored electricity, were easily taken by the Indians, using small poles fitted with long cords.
The tembladores were about five feet long, with olive-green, scaleless skin, yellowish-red heads, and two rows of yellow spots along the back. Even in an enfeebled state, their two- or three-second charge produced a painful numbness, similar to the shocks that Humboldt had administered to himself during his physiology experiments. After four hours of handling the enfeebled animals, the naturalists experienced muscle weakness, joint pain, and a general lethargy that lingered till the next day. And once the eels had a chance to recharge themselves, they delivered a severe shock—up to six hundred volts—whose “pain and numbness,” Humboldt discovered when he imprudently stepped on one, “are so violent that [they are] impossible to describe. . . .” No wonder the locals had been so reluctant to search out the creatures.
Over the course of a typically exhaustive investigation, Humboldt and Bonpland determined that the eels were able to discharge their shock at will. The creatures could also electrocute their prey without contact, and could even aim the shock. Cutting an eel in two, Humboldt discovered that only the front half was capable of producing a discharge. Also, although the eels’ skin was covered with mucus, an electrical conductor, the animals were immune from shocks both from other eels and from themselves. Indeed, the only way to observe the shocks was by the obvious effect on their victim: No sparks were produced during the discharges, even in the dark; the bursts didn’t register on the electrometer; and they produced no magnetic reading. Over the next several days, Humboldt and Bonpland subjected themselves to every imaginable abuse in the name of science. Among their discoveries: By gripping the eel with both hands or by holding the animal in one hand and a piece of metal in the other, they could magnify the charge; also, when two people held hands and one touched the eel, both felt the jolt simultaneously. Conversely, glass, wax, horn, dry wood, and bone served as effective insulators.
The first to scientifically study electric eels, Humboldt greatly increased our understanding of the animal and its peculiar abilities. However, he realized that a great deal more work remained to be done. Accordingly, he called on other scientists to continue the investigations, which he believed could even elucidate the mechanism by which all animals move. “It will perhaps be found,” he presciently suggested, “that, in most animals, every contraction of the muscular fiber is preceded by a discharge from the nerve into the muscle; and that the mere simple contact of heterogeneous substances is a source of movement and of life in all organized beings.” Two centuries later, scientists have built on these observations to develop a thorough knowledge of nerve-muscle interactions.
Their researches concluded, the scientists left Calabozo on the twenty-fourth of March. As they trekked south through the Llanos in the coming days, the ground grew even drier and more lifeless. The palm trees petered out, and the temperature hovered at a sun-scorched ninety-five degrees from eleven in the morning until sunset. If losing their way at the water hole had left any doubt concerning the Llanos’ hazards, the point was driven home to them on their first day out of Calabozo. Around four o’clock in the afternoon, the travelers came upon an Indian girl sprawled in the brittle grass. About thirteen or fourteen years old, the girl was naked, exhausted, disoriented, and dangerously dehydrated. Her eyes, nose, and mouth were caked with earth, her breathing was reduced to a rattle in her throat, and she was unable to speak. A clay pitcher, half filled with sand, lay at her side.
The men managed to rouse her by washing her face and forcing a few drops of wine down her throat. Overcoming her initial alarm, she eventually told them her story. She had been working at a nearby farm, she said, till an illness had reduced her capacity for work. Losing her position, she’d set out for a nearby mission but had run out of water and collapsed in the unrelenting heat. From the position of the sun, she estimated she’d been unconscious for several hours. The travelers tried to convince her to mount one of the mules and accompany them as far as the neighboring town of Uritucu, but she could not be persuaded. All they could do was empty the sand from her pitcher, fill it with water, and watch her straggle off in a plume of dust.
Three scorching but uneventful days later, the party reached the Capuchin mission of San Fernando on the Río Apure, the principal tributary of the Orinoco. Stopping in San Fernando for three days, just long enough to hire a canoe and crew and to take on provisions, Humboldt prepared, at last, to venture into the greatest forest on the planet.
IT has been said that a journey through the South American rain forest is a journey through time as well as space. Over the past hundred million years, while continents have drifted and mountains have risen, the forest has remained essentially unchanged. (The great forests of Europe and North America, by comparison, are just eleven thousand years old, having grown up only after the last ice age.) The most abundant, diverse ecosystem on earth, the Amazon constitutes only two percent of the planet’s landmass but is home to fifteen percent of the world’s plant mass, including an estimated five million botanical and animal species (most still unidentified by science today). Paradoxically, despite this biological profusion, the rain forest is not particularly fertile, since the nutrients have already been absorbed by the abundant plant life. With up to 150
inches of rain per year and relative humidity at a near-constant eighty percent, the forest is one of the wettest places in the world, and the unremitting dampness, combined with the high temperature, has long since leached the nutrients from the soil. Only the tiny fraction of forest regularly flooded by the silt-bearing rivers has soil that could be considered fertile.
Consequently, competition for nutrients in the rain forest is fierce. Since only ten percent of the sun’s energy penetrates to the ground, due to the density of the foliage, most botanical life is found in the canopy, where plants battle for precious sunlight. Throughout the forest, no scrap of food goes wasted, and each species of plant and animal must carve out a highly specialized niche in order to endure. This produces the second paradox of the rain forest: Although there is unparalleled diversity of species, there is extremely low density of any particular species. Because there simply isn’t enough food to support a large number of identical individuals in a given locale, members of each species must fan out through the forest to secure the resources they need. As a result, there are no groves of like trees in the rain forest, as there are in temperate forests, only isolated individuals. Animal and human populations are similarly limited. Though there are more than 1,500 species of fish, for example, compared with about 150 species in all of Europe, they are abundant only during the wet season. Similarly, food-bearing trees such as the Brazil nut are widely scattered, and having discovered one, a band of foragers could travel for days without sighting another. The only human food that could be called relatively abundant in the rain forest is the cassava, cultivated for its roots, which are ground into a flour that is the traditional staple of the region.
Humboldt's Cosmos Page 14