Mysteries of Curare

The conquistadors had no sooner begun cutting their way through the jungles of South America than they found themselves suffering casualties from Indian darts tipped with a potent, paralyzing poison. But a century passed before Sir Walter Raleigh in 1595 carried to Europe the first samples of "urari"--a variant of curare. Years later botanists classified the shrubs from which curare is made,* and the brilliant French physiologist, Claude Bernard, in 1856 made an important discovery: from samples supplied by Brazil's Emperor Pedro II he showed that curare paralyzes its victims by blocking transmission of impulses from nerve to muscle. Beyond that, scientists were as baffled as laymen by the mysteries of curare.

Last week in Rio de Janeiro more than a hundred experts--some top medical men, some ethnologists and botanists--got together for the world's first International Symposium on Curare and Curare-like Agents. For in the meantime, curare has passed from the jungles, where it is an agent of death, to the most aseptic operating theaters, where it is an important aid in many a life-saving operation.

How the Indians Make It. The basic rules for preparing curare vary little over millions of square miles, reported French Ethnologist Jehan Vellard, who has watched the process in Brazil's Mato Grosso, and now works in Peru. The essential components are dissolved out of the roots or stalks with cold or tepid water, and the solution is concentrated by heating. The finished product is a gooey paste. Natives have no fear of inhaling its vapors or of putting their hands in it, and they judge its strength by the bitterness of a drop, which they nonchalantly taste.

Greatest variation is in the accompanying rites. Among some tribes curare is prepared by old women; in a few the witch doctor has a monopoly of the business, but usually all the wise old men get together to brew a batch. A widespread restriction is that the curare-makers shall operate in an isolated part of the forest; often they are required to refrain from sexual intercourse while a batch is being run, and women may be kept at a distance. In some tribes the work must be finished before the sun reaches the zenith (or interrupted then). Many refuse to put new curare into old bottles, insist on new containers (gourds, bamboo sections or earthenware jars).

How Surgery Uses It. Today purified natural forms of curare and also synthetic varieties are available to medicine. Unlike the Indians' brews, they do not vary in strength from batch to batch. Since their effects are precisely measurable and predictable, surgeons use them to relax muscles by blocking the transmission of impulses from nerves, but stopping well short of the Indians' desired end point--where the muscles of breathing are denied signals from the brain's respiratory center, causing death. In surgery curare-like compounds permit the use of lighter anesthetic doses. They are especially valuable in abdominal operations because they cut down the activity of muscles around the gut. They facilitate the passing of a tube through the windpipe for artificial respiration. They are useful in some nervous disorders, in controlling convulsions from shock treatments, and have been tried for paralysis resulting from poliomyelitis.

Dr. Carlos Chagas, of the University of Brazil's Institute of Biophysics, took the conference a long step beyond Pioneer Claude Bernard's work by showing how the curare compounds block the impulses where nerve joins muscle. He learned this by experiments with electric eels (used for observation because of their particularly large nerve ends) and radioactive carbon 14. Normally, a signal for action is transmitted through a nerve, at the end of which is generated a chemical called acetylcholine. This, it had been known, acts on an "endplate" in the muscle. But how? Dr. Chagas explained: in the end-plate he had identified a complex chemical containing eight amino acids and a polysaccharide. Acetylcholine transmits its orders though this amino-polysaccharide. But curare (as shown by its radioactive form injected in the electric eel) attaches itself to this transmitting substance and makes it insensitive to the action of acetylcholine.

Satisfied that in Chagas' work they had a major contribution to neurophysiology, extending in significance well beyond its application to curare, the experts adjourned from Rio to Manaus, 1,000 miles up the Amazon, for sightseeing in a land where Indians and curare both grow plentifully. They were safe from poisoned blowpipe darts. But in the jungle, only a few miles away, the ancient industry was still going full blast.

*In most areas these are of the genus Strychnos. Old World species of Strychnos commonly yield strychnine but not curare; in the New World 59 species may yield curare but no strychnine. In the foothills of the Andes shrubs of the genus Chondodendron replace Strychnos as sources of curare.

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