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Louis Pasteur’s Relentless Hunt for Germs Floating in the Air

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Louis Pasteur’s Relentless Hunt for Germs Floating in the Air

Louis Pasteur was at his most comfortable when working in his Paris laboratory. It was there that he had some of his greatest scientific triumphs, including experiments that helped confirm germs can cause disease. “Everything gets complicated away from the laboratory,” he once complained to a friend.

But in 1860, years before he became famous for developing vaccines and heating milk to kill pathogens, Pasteur ventured to the top of a glacier, on a remarkable quest for invisible life.

He and a guide began at the base of Mont Blanc in the Alps, hiking through dark stands of pines. Behind them, a mule carried baskets of long‑necked glass chambers that sloshed with broth. They ascended a steep trail until they reached Mer de Glace, the sea of ice.

The wind blew briskly over the glacier, and the vale echoed with the sound of frozen boulders crashing down the slopes. Pasteur struggled to make out the path in the glare of sunlight bouncing off the ice.

When the scientist reached an altitude of 2,000 meters, he finally stopped. He removed one of the glass chambers from the mule’s pack and raised it over his head. With his free hand, he grabbed a pair of tongs and used them to snap off the end of the neck. The cold air rushed inside the container.

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The sight of Pasteur holding a globe of broth over his head would have baffled other travelers visiting Mer de Glace that day. If they had asked him what he was doing, his answer might have seemed mad. Pasteur was on a hunt, he later wrote, for “the floating germs of the air.”

Now, 165 years later, scientists around the world hunt for floating germs. Some study how coronaviruses wafting through buses and restaurants spread Covid. Spores of fungi can travel thousands of miles, infecting people and plants. Oceans deliver microbes into the air with every crashing wave. Even clouds, scientists now recognize, are alive with microbes.

The sky’s ecosystem is known as the aerobiome. In Pasteur’s day, it had no name. The very idea of living things drifting through the air was too strange to imagine.

But Pasteur began to wonder about the possibility of airborne life when he was a little-known chemist teaching at the University of Lille in France. There, the father of one his students approached him for help. The man owned a distillery where he used yeast to turn beet juice into alcohol. But the juice had inexplicably turned rancid.

Inspecting the liquid under a microscope, Pasteur discovered dark rods — bacteria rather than yeast — in the sour vats. The discovery helped him work out a theory of fermentation: Microorganisms absorbed nutrients and then produced new compounds. Depending on the species, they could turn butter rancid or grape juice into wine.

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The discovery won Pasteur a prestigious new post in Paris. In his account of the discovery, Pasteur suggested in passing that the bacteria might have floated through the air and settled into the vats. That notion earned him an angry letter from Félix‑Archimède Pouchet, one of France’s leading naturalists.

Pouchet informed Pasteur that the microorganisms Pasteur discovered had not dropped into the vats from the air. Instead, the beet juice had spontaneously generated them. “Spontaneous generation is the production of a new organized being that lacks parents and all of whose primordial elements have been drawn from ambient matter,” Pouchet had written earlier.

Pasteur coolly replied that Pouchet’s spontaneous generation experiments were fatally flawed. The conflict between Pasteur and Pouchet prompted the French Academy of Sciences to announce a contest for the best study addressing whether spontaneous generation was real or not. What started as a private spat had turned into a public spectacle. Pasteur and Pouchet both signed up to compete for the prize of 2,500 francs.

The public eagerly followed the competition, struggling to imagine either view of life. Spontaneous generation had the whiff of blasphemy: If life could spring into existence, it did not require divine intervention. But Pasteur’s claim that the atmosphere teemed with germs also strained the 19th‑century mind. A French journalist informed Pasteur that he was going to lose the contest. “The world into which you wish to take us is really too fantastic,” he said.

To prove that his world was real, Pasteur set out to pluck germs from the air. Working with glassblowers, he created flasks with narrow openings that stretched for several inches. He filled them with sterile broth and waited to see if anything would grow inside. If the necks were pointed straight up, the broth often turned cloudy with microorganisms. But if he sloped the necks so that the openings pointed down, the broth stayed clear. Pasteur argued that germs in the air could drift down into the flasks, but could not propel themselves up a rising path.

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When Pouchet heard about Pasteur’s experiments, he sneered. Did Pasteur really believe that every germ in decaying organic matter came from the air? If that were true, every cubic millimeter of air would have been packed with more germs than all the people on Earth. “The air in which we live would almost have the density of iron,” Pouchet said.

Pasteur responded by changing his hypothesis. Germs were not everywhere, he said. Instead, they drifted in clouds that were more common in some places than others.

To prove his claim, Pasteur took his straight-necked flasks out of his lab and began collecting germs. In the courtyard of the Paris Observatory, all 11 of his flasks turned cloudy with multiplying germs. But when he traveled to the countryside and ran his experiment again, more of his flasks stayed sterile. The farther Pasteur got from human settlements, the sparser airborne life became. To put that idea to an extreme test, Pasteur decided to climb Mer de Glace.

His first foray to the glacier ended in failure. After holding up a flask, he tried using the flame from a lamp to seal its neck shut, but the glare of the sun made the flame invisible. As Pasteur fumbled with the lamp, he worried that he might be contaminating the broth with germs he carried on his skin or his tools. He gave up and trudged to a tiny mountain lodge for the night.

He left his flasks open as he slept. In the morning they were rife with microorganisms. Pasteur concluded that the lodge was packed with airborne germs that travelers had brought from around the world.

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Later that day, Pasteur modified his lamp so that the flame would burn bright enough for him to see it under the glacier-reflected sun. When he climbed back up Mer de Glace, the experiment worked flawlessly. Only one of the flasks turned cloudy with germs. The other 19 remained sterile.

In November 1860, Pasteur arrived at the Academy of Sciences in Paris with the 73 flasks he had used on his travels. He entered the domed auditorium, walked up to the table where the prize committee sat, and laid out the flasks. The judges peered at the broth as Pasteur described his evidence, saying it gave “indubitable proof” of floating germs in inhabited places.

Pouchet refused to accept the evidence, but nevertheless withdrew from the contest. Pasteur was awarded the prize.

Still, the two continued to spar. The rivalry remained so intense that the Academy set up a new commission to evaluate their latest experiments. Pouchet dragged out the proceedings, demanding more time for his research.

Pasteur decided to seize public opinion and put on a spectacle. On the evening of April 7, 1864, in an amphitheater filled with Parisian elites, Pasteur stood surrounded by lab equipment and a lamp to project images on a screen. He told the audience it would not leave the soiree without recognizing that the air was rife with invisible germs. “We can’t see them now, for the same reason that, in broad daylight, we can’t see the stars,” he said.

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At Pasteur’s command, the lights went out, save for a cone of light that revealed floating motes of dust. Pasteur asked the audience to picture a rain of dust falling on every surface in the amphitheater. That dust, he said, was alive.

Pasteur then used a pump to drive air through a sterile piece of cotton. After soaking the cotton in water, he put a drop under a microscope. He projected its image on a screen for the audience to see. Alongside soot and bits of plaster, they could make out squirming corpuscles. “These, gentlemen, are the germs of microscopic beings,” Pasteur said.

Germs were everywhere in the air, he said — kicked up in dust, taking flights of unknown distances and then settling back to the ground, where they worked their magic of fermentation. Germs broke down “everything on the surface of this globe which once had life, in the general economy of creation,” Pasteur said.

“This role is immense, marvelous, positively moving,” he added.

The lecture ended with a standing ovation. Pasteur’s hunt for floating germs elevated him to the highest ranks of French science.

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By the time he died 31 years later, Pasteur had made so many world-changing discoveries that his many eulogies and obituaries did not mention his trip to Mer de Glace.

But scientists today recognize that Pasteur got the first glimpse of a world that they are only starting to understand. They now know that life infuses the atmosphere far more than he had imagined, all the way to the stratosphere. Our thriving aerobiome has led some scientists to argue that alien aerobiomes may float in the clouds of other planets. Ours is not the only world that seems too fantastic to believe.

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What to plant (and what to remove) in California’s new ‘Zone Zero’ fire-safety proposal

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What to plant (and what to remove) in California’s new ‘Zone Zero’ fire-safety proposal

After years of heated debates among fire officials, scientists and local advocates, California’s Board of Forestry and Fire Protection released new proposed landscaping rules for fire-prone areas Friday that outline what residents can and can’t do within the first 5 feet of their homes.

Many of these proposed rules — designed to reduce the risk of a home burning down amid a wildfire — have wide support (or at least acceptance); however, the most contentious by far has been whether the state would allow healthy plants in the zone.

Many fire officials and safety advocates have essentially argued anything that can burn, will burn and have supported removing virtually anything capable of combustion from this zone within 5 feet of houses, dubbed “Zone Zero.” They point to the string of devastating urban wildfires in recent years as reason to move quickly.

Yet, researchers who study the array of benefits shade and extra foliage can bring to neighborhoods — and local advocates who are worried about the money and labor needed to comply with the regulations — have argued that this approach goes beyond what current science shows is effective. They have, instead, generally been in favor of allowing green, healthy plants within the zone.

The new draft regulations attempt to bridge the gap. They outline more stringent requirements to remove all plants in a new “Safety Zone” within a foot of the house and within a bigger buffer around potential vulnerabilities in a home’s wildfire armor, including windows that can shatter in extreme heat and wooden decks that can easily burst into flames. Everywhere else, the rules would allow residents to maintain some plants, although still with significant restrictions.

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The rules generally do not require the removal of healthy trees — instead, they require giving these trees routine haircuts.

Once the state adopts a final version of the rules, homeowners would have three years to get their landscaping in order and up to five years for the bigger asks, including removing all vegetation from the Safety Zone and updating combustible fencing and sheds within 5 feet of the home. New constructions would have to comply immediately.

The rules only apply to areas with notable fire hazard, including urban areas that Cal Fire has determined have “very high” fire hazard and rural wildlands.

Officials with the Board will meet in Calabasas on Thursday from 1 p.m. to 7 p.m. to discuss the new proposal and hear from residents.

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Some L.A. residents are championing a proposed fire-safety rule, referred to as “Zone Zero,” requiring the clearance of flammable material within the first five feet of homes. Others are skeptical of its value.

Where is the Safety Zone?

The proposed Safety Zone with stricter requirements to remove all vegetation would extend 1 foot from the exterior walls of a house.

In a few areas with heightened vulnerabilities to wildfires, it extends further.

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The Safety Zone covers any land under the overhang of roofs. If the overhang extends 3 feet, so does the Safety Zone in that area. It also extends 2 feet out from any windows, doors and vents, as well as 5 feet out from attached decks.

What plants would be allowed in the Safety Zone?

Generally, nothing that can burn can sit in the Safety Zone. This includes mulch, green grass, bushes and flowers.

What plants would be allowed in the rest of Zone Zero?

Homeowners can keep grasses (and other ground-covers, like moss) in this area, as long as it’s trimmed down to no taller than 3 inches.

The rules also allow small plants — from begonias to succulents — up to 18 inches tall as long as they are spaced out in groups. Residents can also keep spaced-out potted plants under this height, as long as they’re easily movable.

What about fences, trees and gates?

Any sheds or other outbuildings would need noncombustible exterior walls and roofs in Zone Zero — Safety Zone or not.

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Residents would have to replace the first five feet of any combustible fencing or gates attached to their house with something made out of a noncombustible material, such as metal.

Trees generally would be allowed in Zone Zero. Homeowners would need to keep any branches one foot away from the walls, five feet above the roof and 10 feet from chimneys.

Residents would also have to remove any branches from the lower third of the tree (or up to 6 feet, whichever is shorter) to prevent fires on the ground from climbing into the canopy.

Some trees with trunks directly up against a house in this 1-foot buffer or under the roof’s overhang might need to go — since keeping branches away from the home could prove difficult (or impossible).

However, the board stressed it wants to avoid the removal of trees whenever feasible and encouraged homeowners to work with their local fire department’s inspectors to find case-by-case solutions.

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What’s new and what’s not

Some of the rules discussed in Zone Zero are not new — they’ve been on the books for years, classified as requirements for Zone One, extending 30 feet from the home with generally less strict rules, and Zone Two, extending 100 feet from the house with the least strict rules.

For example, homeowners are already required to remove any dead or dying grasses, plants and trees. They also have to remove leaves, twigs and needles from gutters, and they already cannot keep exposed firewood in piles next to their house.

Residents are also already required to keep grasses shorter than 4 inches; Zone Zero lowers this by an inch.

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Video: Rescuers Mount a Likely Final Push to Save a Stranded Whale

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Video: Rescuers Mount a Likely Final Push to Save a Stranded Whale

new video loaded: Rescuers Mount a Likely Final Push to Save a Stranded Whale

Rescue crews mounted a likely final push to save a stranded humpback whale off the coast of Northern Germany on Friday. The large mammal, nicknamed “Timmy,” captivated the nation after it was stranded in shallow waters for weeks.

By Jorge Mitssunaga

April 17, 2026

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1,200% jump in kratom-related calls to poison control centers in last decade, analysis shows

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1,200% jump in kratom-related calls to poison control centers in last decade, analysis shows

Over the last decade, poison control centers around the country have received tens of thousands of calls from consumers of kratom products reporting adverse and life-threatening health effects, with researchers saying reports in 2025 reached a new level. California’s poison center is reporting similar findings.

Last month, researchers analyzed information from the National Poison Data System and found that between 2015 and 2025, poison control centers across the nation received 14,449 calls related to kratom. More than 23% of those calls, or 3,434, were made last year, according to a published report in the Centers for Disease Control and Prevention. That represents a more than 1,200% increase from 2015, when only 258 calls were reported.

Officers gather illegally grown kratom plants in 2019 in Phang Nha province, Thailand. The country decriminalized the possession and sale of kratom in 2021.

(Associated Press)

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Kratom is derived from the leaves of Mitragyna speciosa, a tree native to Southeast Asia. It has a long history of being used for chronic pain or to boost energy and in the U.S., research points to Americans also using it to alleviate anxiety. In low doses, kratom appears to act as a stimulant but in high doses, it can have effects more like opioids.

But in the last few years, a synthetic form of kratom refined for its psychoactive compound, 7-hydroxymitragynine or 7-OH, has entered the market that is highly concentrated and not clearly labeled, leading to confusion and problems for consumers. The synthetic form gaining momentum in the market is sparking concern among public health officials because of its ability to bind to opioid receptors in the body, causing it to have a higher potential for abuse.

Los Angeles County leaders, meanwhile, have grappled with differentiating the two and regulating the products that come in the form of powder, capsules and drinks and have been linked to six county deaths. Sales of kratom and 7-OH products were banned in the county in November.

In reviewing the data, which did not differentiate whether callers had consumed natural or synthetic kratom, researchers set out to understand the effect of what they believe is a “rapidly evolving kratom market,” and highlight the role poison centers can play as an early warning surveillance system to detect new trends.

National Poison Data System findings

The data showed that over the last 10 years, 62% of the kratom-related calls to poison control centers were from people who said they consumed the drug by itself, and the other 38% were from people who combined it with another substance or substances.

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Those who consumed kratom with another substance combined it most frequently with one or a combination of the following: alcohol, opioids, benzodiazepines (like Xanax or Valium), cannabis and cannabinoids, stimulants and antidepressants.

The data also broke down hospitalizations related to kratom — adults who took it alone or in combination and experienced “adverse” health effects; and adults who took it alone or in combination and experienced more serious “moderate” or “major” health effects, including death.

Kratom powder products are displayed at a smoke shop.

Kratom powder products are displayed in a smoke shop in Los Angeles in 2024.

(Michael Blackshire/Los Angeles Times)

Hospitalizations for adults who had consumed kratom alone and experienced adverse effects increased from 43 in 2015 to 538 in 2025. For those who took it in combination and were hospitalized with an adverse health effect, the total jumped from 40 in 2015 to 549 last year.

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The numbers were even higher for hospitalizations where the health effects were more serious or fatal.

In 2015, there were 76 reports of people being hospitalized after taking kratom alone and experiencing a serious health effect or dying. By last year, that number had climbed to 919. The reports of serious health effects, including death, for those who took kratom in combination with another substance grew from 51 in 2015 to 725 last year.

The research does not break down kratom-related deaths by year but states that there were 233 deaths over the 10-year study period, or just over 3% of all 7,287 serious medical outcomes. Of the total number of kratom-related deaths, 184 cases involved the consumption of multiple substances.

What California’s poison control system found in its state data

The California Poison Control System is currently reviewing its data concerning kratom-related calls but an initial analysis shows parallels to the national report, said Rais Vohra, medical director of the state poison control system.

“We have about 10% of the national population and about 10% of the national call volume with poison control,” Vohra said. “And so, not surprisingly, we were able to identify over 900 cases of calls related to kratom in that same period.”

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Local researchers are still deciphering the state data but they too have found that kratom-related calls are climbing.

“It’s accelerating, which I think is one of the main points of the [published] report,” Vohra said.

A majority of calls received by poison control come from healthcare facilities where “presumably someone has a problem … severe enough to warrant calling 911 or going to the emergency room, and that’s when our agency gets involved,” Vohra said.

Kait Brown, clinical managing director for America’s Poison Control Centers, said the fact that kratom and 7-OH are federally unregulated products sold online, in gas stations and smoke shops gives people across the country easy access.

And while kratom enthusiasts maintain that it has been used in its natural form for hundreds of years, “there are new formulations that are a little bit different than how people have used it, at least historically,” said William Eggleston, a pharmacist and the assistant clinical director of the Upstate New York Poison Center in Syracuse.

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People are no longer consuming kratom only as a powder or capsule but also in the form of an energy shot or extract; it’s similar for synthetic, more concentrated 7-OH products.

When regional poison centers compare their findings and experiences with the analysis of calls in the National Poison Data System, Eggleston said, “undeniably there is an increase in calls related to kratom.”

“But when you put it in the bigger perspective of all the calls … this is still a very small percentage of what we’re dealing with on a day to day basis,” he said.

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