But the writer in me prefers another metaphor, used by the virologist Richard Krause as the title of a book: The Restless Tide. As the subtitle explains, it’s about “the persistent challenge of the microbial world,” the relentless ebb and flow of the sea of microorganisms, friendly and hostile, symbiotic and erosive or even deadly, constantly lapping at the shores of human life.

We humans have been living with pigs for 10,000 years, with birds for at least 5,000; day by day, microorganisms take advantage of those intimate relationships, and sometimes they seem to take unfair advantage, and the restless tide surges ominously through pigs or birds into us. Microbes race to take advantage of lapses in our immune systems, we race to defend ourselves, and so we have an arms race, with our swine and avian friends caught in the middle.

Theoretically, microbes should hold back their virulence. They tend to do a lot better in evolutionary terms if they don’t kill, since the death of the host often puts an end to transmission. But unfortunately for us, they are not always so clever. They spread, kill, and contain themselves, but not before they have done tremendous damage.

Yesterday my wife and I took a step we have talked about for a couple of years. We went to the local farmers’ market and bought a hundred pounds of rice, thirty pounds of beans of various kinds, thirty gallons of water, eight or ten gallons of low-salt chicken and vegetable broth, and some assorted durable spices that my wife, ardent foodie that she is, knows would make those spare staples a lot more bearable. (She also ruled out the gassier pinto and kidney beans—“We’ll be in a confined space after all”—and fava beans, since one of our kids’ significant other is allergic.)

After lugging these things into a cool corner of the basement, I was amazed at how easy it had been—less than two hours from outset to storage—and wondered why we had put it off. We still had to buy a rain-barrel, stores of vitamins and over-the-counter medicines, fire-making equipment, and masks and gloves, but the basic necessities of human life for a small group of adults for at least two weeks took up a surprisingly small amount of space. So I wondered why we hadn’t done it years before.

The answer perhaps was in Ann’s sense of disturbance, her sadness at the conscious thought of what we and our grown children might have to go through. It’s always comforting in a certain way to assume the best-case scenario, rather than the worst. But even our friend who works at the CDC on influenza told us a couple of months ago she had not made preparations—or rather, she had made many preparations for the protection of Americans, but none yet specifically for her family. “I know I should,” she said. “But I haven’t gotten around to it.”

I found it surprisingly comforting finally to do it. I have long lectured on infectious disease in general and the influenza virus in particular. I am not paranoid—I am not even very worried. But I was an Eagle Scout back in the day, and the Scout Motto is “Be Prepared.” Much as we made fun of it, we learned to try to do it.

I don’t know why this new Mexican swine flu tipped the balance for me. I don’t give it more than a one percent chance of becoming the kind of challenge that would drive us into the basement to draw on those stores of long-grain rice and black-eyed peas. But then, I don’t give myself more than a one percent chance of dying within the year, yet my life insurance premium gets paid every month.

Perhaps it was that two of our kids were planning to go to Mexico next week. Listening to the news on Sunday, I heard no travel advisory, but I knew enough to see one coming. I wrote our CDC friend, apologizing briefly but intensely for intruding on what is surely among the hardest weeks of her professional life. I asked for one word of advice and it came back, “Cancel.”

Today, Tuesday, the travel advisories are out, and there are twice as many cases worldwide—and twice as many deaths in Mexico, where the only deaths have been so far—than there were yesterday. There are at least fifty cases in the U.S., and some European advisories warn against travel here. There are confirmed cases in England, Spain, Israel, China, and New Zealand, every one of which is directly or indirectly linked to Mexico. Alas, that “indirectly” means community transmission: people have gotten it at home from people who have been to Mexico.

The World Health Organization today used the phrase “turning point” in announcing that we are on the verge of a pandemic—a spread throughout the population, in this case meaning the population of the species. Now, “pandemic,” like “epidemic,” really just means more cases than expected. But it could mean “a lot more.”

In the influenza pandemic of 1918, which is now thought to have gone from birds to us without passing through pigs, a minimum of 20 million people died worldwide, at least double the death toll of World War I. No country was unaffected. The main victims were not infants and the elderly, as with seasonal flu, but young and healthy adults, now thought to have been victims of a sort of internal storm of their own immune responses. They developed their first symptoms, became gravely ill, and died within hours to days.

The fabric of society tore and then shredded. Caregivers quickly became victims, fear was rampant, services were gone.

The strain of influenza A, H1N1, was the same as the one that has now passed from pigs to us in Mexico. As in 1918, the dead have mainly been healthy young adults. So far, that is the extent of the similarity, and the good news is that so far there have been no deaths outside of Mexico. But the acting head of the CDC predicts more U.S. cases, and he also predicts U.S. deaths.

Another U.S. government official said, “We don’t want anyone to panic at this point.” Does this mean that later they will want us to panic? At times, the abuse of language can be discouraging.

Perhaps we can learn from children’s self-calming, dark wisdom. As bubonic plague devastated Europe, London children invented a chant: Ring around the rosy, pocket full of posies, ashes, ashes, we all fall down! In 1918, a girls’ jump-rope-skipping rhyme went, I had a bird, and his name was Enza, I opened the window, and in flew Enza! Life’s fragile, they seem to know, but they still chant and sing.

Don’t panic, now or ever. Be prepared. Follow the rules. Cough or sneeze into your elbow or shoulder. Wash your hands frequently, longer and harder than you think you really need to. Use hand sanitizer. Go to the doctor if you are ill. Get the treatment you need but protect others from your illness. Watch the news. And put away some water, rice, and beans.