SEVEN PEOPLE are now dead in the horrifying Chicago cyanide killings. One man in California has been hospitalized with convulsions brought on by strychnine. Each had taken a simple over-the-counter painkiller -- the most widely used drug in the United States -- and swallowed deadly poison instead. We don't yet know how cyanide and strychnine came to be substituted for the analgesic in Tylenol capsules. Without an apparent motive or any connection among the victims, it is reasonable to surmise that at least two madmen have been killing at random. What kind of human being could conceive such a scheme, carefully open the capsules and pour in powder, then see to it that the product was placed among rows of similar medicine on the shelves of drugstores? What other products could be easily contaminated by a deranged person and confidently swallowed by any one of us? For everyone, the thought terrifies.

If seven people had been killed in an automobile crash or a family shoot-out, it would have been a one-day story. Statistically, chances of being killed on a highway or in a fire are far greater than the chance of being murdered by an unknown maniac, yet the latter prospect frightens us far more. It is easy to dissociate ourselves from the more common forms of death. "I wouldn't be driving at 3 in the morning," we say, or, "I'd escape from the burning house because I have a smoke detector." But precautions are impossible when neither the manner of the killing nor its motive can be anticipated. This is especially true when opportunities for spectacular harm are so plentiful.

Modern life, especially urban American life, depends on communal support systems. We rely on others to grow, process and package our food, to manufacture drugs and cosmetics, to purify and pump water. Specialization and the division of labor are efficient, but in exchange we give control of life- sustaining necessities to others. We are, as well, famously a serve-yourself, shelf-top, supermarket society. All of us prefer not to dwell on the potential for injury because of others' carelessness or depravity, but it is there. Toothpaste and apple sauce can be poisoned, scotch whiskey and eye drops, too. We take a chance every time we buy something in a package or eat a piece of fruit we have not grown ourselves. But we have to take these chances in order to live.

Certain steps can be taken. Manufacturing and processing can be carefully monitored. Packaging can be improved and store security upgraded. But in the end, there is no absolute safety from the unpredictable, no sure-fire way to guard against insane schemes and mindless terrorism or from the risks that are real and immutable in any society.