Thursday, June 29, 2023

 Could a plant ever eat a person?

Link to Science News Explores article

Monster and horror movies have their own versions of plant or plant-like creatures that devour people. In the 1960 movie The Little Shop of Horrors, a flower the size of a man was grown from seeds from a "Japanese gardener over on Central Avenue". It preferred human blood over regular plant food, for some reason. In the 1986 version Little Shop of Horrors, the plant came "from a Chinese flower shop during a solar eclipse". In 1963, a British movie came out (The Day of the Triffids) in which plant spores from space landed via a meteor shower, and they grew and regenerated and moved in order to eat people. A gigantic plant called a sarlacc grew naturally on the desert planet Tattooine in the Star Wars movie  Return of the Jedi. It feasted on people, although it apparently digested them over a thousand years. But how possible are any of these concepts of plants devouring people?

Movies with man-eating plants

First, consider the 600 + species of carnivorous plants that exist today. They are categorized into 5 major taxonomic groups, so they are not very closely related genetically. The International Carnivorous Plant Society (ICPS) gives three characteristics of plants that are labeled as carnivorous:

  1. They capture and kill prey.
  2. They have a mechanism to facilitate digestion of the prey.
  3. They derive a significant benefit (not a little) from nutrients assimilated from the prey.
People often consider only insects as their prey, but the ICPS says they also consume spiders, crustaceans and other small soil and water-living invertebrates and protozoans, lizards, mice, rats, and other small vertebrates. Most of these plants grow on land (damp heaths, bogs, swamps, and muddy or sandy shores), but some are water-dwellers. Usually, the land-dwellers are in areas that are low in nitrogen, so supplementing their meager intake has evolved into draining the nitrogen from animal life's proteins and nucleic acids.

Three methods are used by plants to capture prey:
  • Active traps are triggered by some motion or touch of the prey, and the plant closes something around it. 
  • Passive traps don't rely on any prey motion. 
  • A third method uses a combination of active and passive trapping.
Traps have (1) leaves folded into pitfall chambers, (2) flypaper or sticky surfaces which wrap around trapped prey, (3) snap types that close around the prey after it brushes against tiny hairs, (4) sacs (bladders) on the stem under negative pressure to suck in prey, or (5) openings in twisted tube-like leaves roughly resembling lobster claws that trap prey with no route out.

Examples of various carnivorous trapping methods (herbspeak.com)

Here is a short YouTube video showing all of these methods in action.

Trapped creatures die from exhaustion, or being smothered, or starvation. They are digested by enzymes that the plant (or bacteria inside it) makes, just like an animal stomach makes acid. At least fifteen types of enzymes have been found so far and specifically digest fats, proteins, DNA/RNA, chitin/sugars, etc. Some carnivorous plants merely collect an animal's feces and eat that instead of the animal.

What would it take to trap and digest a human being? The Science News Explores article goes into that with some scientific, not science fiction, background.

Such carnivores would obviously have to be large enough to trap someone. The largest in nature is a pitcher plant 16.1 inches (41 centimeters) tall with a capacity to hold about 9 gallons (3.5 liters). The most likely plants to evolve large enough would be the pitfall, sticky, or snap variety. The pitfall would need to be enormous, though, and its slippery interior would initially prevent escape. If it filled with rain water, that might drown the victim first, but it would also dilute digestive enzymes.

Pitcher plant Nepenthes rajah (Wikipedia)

The article says a "giant flytrap would need massive amounts of energy to move electrical signals across its hefty leaves and also produce enough enzymes to digest a human". Until a person blunders into the plant, it would also have to exist without our body's nutrition, too, and that means an alternative source of energy. 

Venus flytrap consuming an insect (Wikipedia)

Professor Barry Rice of the University of California - Davis figures that in order to conserve energy, a man-eating plant wouldn’t move but instead would stay in one place unlike the movie character triffids. But digestion of something as large as us would probably take so much time that bacteria would probably rot the body faster (and that might mean from the inside as well as outside). Rotting flesh could damage the plant that has trapped it.

Professor Adam Cross from Curtin University in Bentley, Australia thinks we would be strong enough to fight our way out of snap traps and pitfall traps. His ideal killer plant would be the plain sticky variety like a sundew with many tentacle leaves covered in glue-like material which would continue to latch onto a person as they struggle to escape. Eventually, one would just tire a person out.

Sundew tentacle leaf folding to trap an insect (Wikipedia)

But what attracts insects and other small animals in the first place to a carnivorous plant, and what would be needed for a human? Currently, some carnivorous plants produce attractive scents or display fake flowery colors to bring their prey in. Some are camouflaged with their surroundings. Others like the bladderwort rely on creatures to float nearby naturally until they stimulate the hair triggers that open the pore to suck them in. Humans would have to be fooled by camouflage for an accidental trapping. Or as Prof. Cross suggested, the plant would have to provide a delectable fruit or source of water that a person felt was needed, and then get trapped. So survival training would be necessary in order to identify the danger and avoid being eaten.


YouTube video of a sticky plant (Sundew) enveloping its prey.

YouTube video of a bladderwort (Utricularia) sucking in its prey under water.

YouTube video of Genlisea with Y-shaped lobster-claw leaves.

Saturday, June 24, 2023

Sally Ride: Astronaut, Scientist, Educator

It was June 18, 1983. Ronald Reagan was the U.S. President. The Disney channel had been running a few months. The third Star Wars film, Return of the Jedi, was a month old. Michael Jackson had just released Billie Jean and introduced the world to his moonwalk dance step. Since April, 1981, the Space Shuttle program (officially called the Space Transportation System, or STS) had sent only six crewed missions into space (5 aboard Columbia and 1 aboard Challenger). It was 20 years since the Russians had sent up two female cosmonauts, the first women into space, and America was now sending up its first woman, Dr. Sally Ride. History was in the making.

Photo from thoughtco.com

Sally Ride was born on May 25, 1951 and graduated from prestigious Stanford University in 1973 with a Bachelor of Science degree in physics and a Bachelor of Arts degree in English literature, and then two years later with a Master of Science degree in physics, and soon afterward with a Doctor of Philosophy in physics in 1978. She became interested in both sports and science at an early age. For example, she enjoyed working on brain teasers in Scientific American magazine, and she was inspired in junior high school by Dr. Elizabeth Mommaerts, who had a doctorate in human physiology and had chosen to work at Ride's school.

While she was studying for her PhD, she responded to an announcement by NASA, who was looking for women to join the new space shuttle program. Out of 8,079 applications for mission specialists, after six rounds of testing and interviews, she found herself as one of six women out of 35 accepted candidates.

NASA's first 6 female astronauts.
L/R: Shannon Lucid, Margaret Seddon, Kathryn Sullivan, Judith Resnick, Anna Fisher, Sally Ride
(from Women in Space Who Changed the World)

As a mission specialist, she and others were not expected to fly the shuttle, but it was wise to train on aircraft in even of an emergency. So, Ride learned how to fly a T-38 Talon jet aircraft and even took private lessons.

Photo courtesy of NASA

Her training included such things as basic science and math (no problem for the straight-A student who had taken a class in advanced math during the summer break in college), meteorology, guidance, navigation, and computer. Before her own first flight, she was assigned as part of the ground-support crew for the second and third shuttle flights (1981, 1982). One of those duties was as the first female capsule communicator ("CapCom") to relay information and instructions to the shuttle crew during flight. 

Ride at capsule communicator console, at Johnson Space Center mission control
during the STS-2 mission in July 1981 (NASA)

The 50-ft (15-m) robotic arm of the space shuttle was a spinoff of a Canadian design and was given the typical NASA abbreviation SRMS for Shuttle Remote Manipulator System. This familiar crane was used to release, repair, and retrieve various shuttle cargo (payloads). Ride was in charge of the training for its use and designing it prior to its initial use by astronauts Joe Engle and Richard Truly in 1981 aboard the second Columbia flight. Training involved practice in a DC-9 cabin and was considered extremely difficult. Ride was considered among the top two most proficient operators with the SRMS in training, and that played a role in selecting her for her first mission where it was necessary to use it.

SRMS being deployed on Columbia (Wikipedia)

Sally Ride became America's first female astronaut and the youngest at the time (32) when the Challenger lifted off on June 18, 1983 for its six-day mission. She was one of three mission specialists on board. Using the SRMS, Ride deployed two communications satellites. In addition, she also operated the robotic arm to deploy and retrieve a special pallet satellite which tested the effects of microgravity on metal alloys. During that part of the mission, she also used the SRMS to take the first pictures of the shuttle while it was in space. 

Challenger crew, June 1983 (Wikipedia)

Being a mission specialist meant using her academic training in physics, too. (After all, her PhD dissertation was "The interaction of X-rays with the interstellar medium".) Ride conducted an experiment aboard the shuttle to see how charged particles move through an electrified gel in microgravity, and another experiment to test how well the chemical reactions to form certain kinds of latex in space. She had the opportunity to fly on a second shuttle in 1984, where she used the robotic arm to deploy the Earth Radiation Budget satellite. At that time, she also studied the Earth's atmosphere and conducted some Earth science observations. All in all, she spent 343 hours doing science in space.

She wanted to be taken seriously as a scientist and mission specialist, not as a woman. For example, she and fellow astronaut Anna Fisher bought khaki pants so they would blend in with the men and not stand out in skirts. She was flooded with questions about how she as a woman would handle herself aboard the first shuttle flight. Many inappropriate questions were asked by the press. Are 100 tampons the right number for one week? How are you going to feel when your hair is weightless? Will you cry if something goes wrong on the shuttle? Will the flight affect your reproductive organs? Ride brushed them aside and tried to steer conversations toward the shuttle mission instead.

When the shuttle Challenger exploded on liftoff in 1986, she immediately joined the team to investigate. Information she had discreetly relayed to General Donald Kutyna was passed to Nobel laureate Richard Feynman, leading him to announce the cause of the disaster. Later, in 2003 when the Columbia shuttle broke up upon its return, she became part of that accident investigation board, too, and co-wrote the summary report. She was the only astronaut and only person to serve on both investigatory panels.

Ride attending the Challenger investigation (Associated Press)

Ride left NASA in 1987 to join the Stanford University Center for International Security and Arms Control (CISAC), where she researched how to count nuclear warheads from space. When that 2-year scholarship ended, she was accepted as a professor of physics at the University of California, San Diego (UCSD), and director of the California Space Institute (Cal Space). She retired as professor emeritus in 2007.

Not losing complete attachment to NASA, Ride co-founded its educational outreach program EarthKAM (Earth Knowledge Acquired by Middle school students). Her design of installing cameras aboard the International Space Station allowed students to submit requests to take pictures of specific locations on Earth. Her science education company Sally Ride Science (founded 2001) made science programs and publications for upper elementary and middle school students, focusing on girls. It created the GRAIL MoonKAM (Moon Knowledge Acquired by Middle school students) program in 2011 to take photos of lunar features such as craters, highlands, and plains and learn about past and future landing sites. She also took over the space news website Space.com in 1999 for a few years. 

To show how much of an educator Sally Ride was, she also left behind a legacy of five books on science for children:

She has had a research ship the R/V Sally Ride named after her (the first for a female), a postage stamp made in her name, and many other science-related things such as spacecraft, satellites, an asteroid, and a moon probe crash site.
R/V Sally Ride (from Scripps Institute of Oceanography)

Ride was appointed to the President's Committee of Advisors on Science and Technology (PCAST) by President Clinton assess the risk of fissile materials (uranium-233, uranium-235, plutonium-239, and plutonium-241) being stolen in Russia and used by terrorists. She was a member of several organizations on education, as well, such as the Math and Science Initiative. President Obama awarded her the Presidential Medal of Freedom a year after her death.

Sally's life partner Tam O'Shaughnessy accepting Ride's Presidential Medal of Freedom (Alamy)

Despite accolades and achievements and a serious dedication to providing science education to children, Ride was a very private person, sometimes even to her family. She was married briefly to fellow astronaut Steven Hawley, but she eventually became a life partner with tennis player and her children's book co-author Tam O'Shauhnessy, which was not made public until her death due to pancreatic cancer in 2012. Perhaps one statement she made sums up her view of being in science: "Scientific careers are not geeky."


Wikipedia does an excellent job of describing her achievements.

Read this LA Times cover story for an in-depth biography of Sally Ride, including many personal aspects of her life.

Monday, June 19, 2023

Nontoxic powder uses sunlight to quickly disinfect contaminated drinking water

Link to article

Have you ever been camping or survived a natural disaster and needed to sterilize water for drinking? There are filtration methods, or you can use chemicals like iodine or bleach. If all else fails, boiling the water for a sufficient time will kill the bacteria in it. All of these methods have their disadvantages, though. What if you could just sprinkle some powder into the water and wait a very short time? Now, that's possible thanks to scientists at Stanford University.

The Centers for Disease Control in Atlanta, Georgia, USA describe several ways that people can sterilize drinking water.

  • You can boil it for a minute (longer at elevations above 6,500 feet). Being able to make a fire is the key point, though.
  • You can add a few drops of household chlorine bleach. How much you add depends on the concentration of the bleach and the volume of water. But, you'll have to wait half an hour for it to take effect. And, it may leave an odor that you don't like.
  • You can add tablets of chlorine dioxide or iodine. Chlorine may leave a taste or smell, and iodine will not kill parasites. Iodine is also not recommended for pregnant women.
  • Filters with pumps can remove parasites, but most don't remove bacteria and viruses. They are bulky and need cleaning for reuse. You also have to add iodine, chlorine, or chlorine dioxide to the filtered water to kill bacteria.
Methods to kill bacteria in water: boiling, filtering, tablets, iodine drops

About 2 billion people in the world do not have access to clean water on a regular basis, and 80% of them live in rural areas, so this problem is not limited to campers or emergency situations. Contaminated water is responsible for killing millions of people from various illnesses, so it is critical to find ways to clean it up, and the easier and cheaper, the better.

People have introduced cooking methods to Africa that eliminate the need for firewood, just by providing basic materials to make solar ovens. Why not give similar populations a magnet and a bottle of some powder to clean up their drinking water, too? That's all that the Stanford U researchers say may be needed.

It all works on a simple disinfection principle that uses hydrogen peroxide, the stuff in some household cleaners. The chemical formula for water is the familiar H2O, but hydrogen peroxide is a bit unstable because it has an extra oxygen on it to make H2O2. Its instability causes it to react with bacterial cell membranes and DNA to kill the bugs rapidly on surfaces. The instability also gives it a short lifespan of activity when mixed with water, but if the concentration is high enough, that will not matter. The main point is that it leaves behind nothing toxic but oxygen and water.

Stanford scientists found a way to make nano-sized flakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide linked together into a powder. 

Aluminum oxide (left) and molybdenum sulfide (right) nano particles

The aluminum component absorbs sunlight. The molybdenum component takes the sunlight energy from the aluminum to generate hydrogen peroxide in the water. And, the iron oxide component is magnetic, so after the powder has cleaned the water, the entire powder made of these 3 chemicals can be separated with a magnet and reused at least 30 times. 

Top left: add powder to contaminated water
Top right: allow light to activate the powder into H2O2
Bottom right: after disinfection, remove power with a magnet
Bottom left: recovered powder is put into a new beaker with contaminated water for reuse
Diagram from phys.org

They tested this powder with a million E. coli per 20 drops in a container with nearly a cup of water. (Drinking water standards prohibit any E. coli at all, and just 10 cells of some highly infectious strains can cause illness.) In just one minute of exposure to sunlight, it killed 99.999% of the bacteria. See the jagged cell membranes as a result in the pictures below.

Healthy E. coli (left), peroxide-damaged E. coli (right, red circles), from nanotechnologyworld.org

Not only is E. coli a bacteria commonly used in the lab, but certain types can cause severe diarrhea at a drastic level. It is one of four types of bacteria responsible for this life-threatening situation, along with Shigella, Campylobacter, and Salmonella (typhoid fever). But various parasites and viruses can also cause that disease, so the Stanford researchers will test their powder on them in the near future, too.

They also speculated on how this technology might be used in the developed countries by replacing UV light in wastewater treatment plants to disinfect water before it is released into the environment. Since the starting materials for the powder are cheap and commonly found, and the chemical reaction doesn't create any smelly or toxic chemicals, this is a promising step to helping people around the world. 


Here are some tips for using hydrogen peroxide for cleaning surfaces in your home.

Saturday, June 17, 2023

Psyche, exploring a metal world

Link to article

In our solar system, we have 8 bodies revolving around the sun which are currently called planets. They are grouped into 3 categories. The four closest to the sun -- Mercury, Venus, Earth, and Mars -- are rocky planets. The next two further out --Jupiter and Saturn -- are called gas giants. They have a super dense solid core surrounded by a thick layer of helium and hydrogen in gas form. The furthest two from the sun --Uranus and Neptune-- are called ice giants. They have helium and hydrogen in their atmosphere, too but also ammonia, water, and methane which freeze into solid "ice". Between Mars and Jupiter is the asteroid belt made up of rocks from 33 feet (10 m) wide to 329 miles (530 kilometers) in diameter.

One of these asteroids is called Psyche (pronounced "sigh-key"), and NASA has its eye on sending a probe to it this year to arrive by 2029. It's 210 km (130 miles) wide (about the length of Massachusetts), and it is either all metal or a combination of metal and rocks. Why is any of that that so interesting?

To begin, Italian astronomer Annibale de Gasparis discovered the asteroid on March 17, 1852 and named it after the Greek goddess of the soul who was born mortal and married Eros, the god of Love. He also discovered 8 other asteroids and wrote his first research paper in 1845 on the largest asteroid Vesta. which was discovered in 1807 by Heinrich Olbers.

We know its general shape already, something like an oblong potato (most asteroids seem to have that shape), but radar images have also shown some of its topography. Red color below represents peaks, and blue represents depressions  and craters.

Radar images from all sides of Psyche

Psyche rotates every 4 hours for a short day cycle, and it travels around the sun every 5 years. It also rotates on its side, that is, perpendicular to its route around the sun similar to an airplane propeller spinning sideways to the direction the plane flies, which is unlike most objects in the solar system. Again, what makes Psyche so special that NASA is building a specific explorer to send there? From measurements scientists have made so far, they think it could be different from other asteroids. They think it might actually be the core of a planet that formed when the other planets did, about the size of Mars, but that may have been hit by something which ripped away the outer layers. See the animation video below for a demonstration.

Clips from psych.asu.edu website video

After the outer layer was removed, the remaining core cooled and hardened, forming a thinner layer that had been hit by other smaller asteroids over time to leave craters. But, most of Psyche is its original core, which is very different than its thicker original crust but similar to what we know about Earth's core. Scientists want to study Psyche because they can't drill deep enough into the Earth to get samples of its own core (too far, too much pressure, too hot). Learning more about Psyche might give us more information about our own planet's layers.

By watching how Psyche affects the movement of other objects, scientists have estimated its mass and density. Right now, they have calculated it is one of the densest asteroids studied so far, twice as dense as most, about 3,400-4,100 kg per cubic meter. By measuring the type of light coming from Psyche, scientists have also estimated it is composed of an iron-nickel metal, maybe kamacite, not just rocks like iron silicates. Kamacite is an alloy of 90-95% iron and 5-10% nickel, only in meteorites, so it is reasonable to think that Psyche may have the same composition. Data gathered about its surface show metallic material in part of the craters, so scientists think this may mean a thin layer of the original crust was hit by other asteroids deep enough to cause eruptions of metallic lava to rise to the surface before the hot core cooled.

Kamacite meteorite from China

So, what is the NASA Psyche mission? Despite earlier delays, the mission to Psyche is now expected to launch in October, 2023 with a spacecraft explorer of the same name, and arrive in August of 2029. It will not land on the asteroid, but it will spend about 2 years orbiting and recording various data. What data?

The Psyche spacecraft will carry several instruments. One will create high-resolution images using special filters to distinguish between metallic and silicate (rocky) material. Another two will analyze the elements on the asteroid's surface. Others will measure and map out the magnetic field and gravity field to learn more about its center.

Psyche spacecraft under construction (NASA)

The spacecraft will also use a unique type of propulsion system called SPT (stationary plasma thruster). Energy from the sun will be collected by the solar panels and converted into electricity. That will be fed into a supply of xenon gas to make electrically charged ions (plasma) that shoot out the back to propel it. Gas is lighter than the usual chemical liquids used in other spacecraft, and the SPT system is expected to take less time for the spacecraft to reach the asteroid.

SPT thruster in use, from psyche.asu.edu

For some explanations of what we know about Psyche's surface and how we learned it, check out this article from MIT

For another blogger's excellent recap of what Psyche it, go to vissiniti.com.

For an hour-long scientific description of the asteroid and project, checkout this YouTube video lecture by Dr. Lindy Elkins-Tanton of the National Academy of Science.

Tuesday, June 13, 2023

Petri dish, and Richard Julius Petri the scientist

At some point, you may have heard about a Petri dish and have the image that it is some sort of lab tool to grow things, usually bacteria. If you haven't, that's about the simplest description that can be given. By "dish", the term actually means a flat circular container that has a cover which rests on it to keep out airborne contaminants.

The man credited with its design, Richard Julius Petri, was born in Germany on May 31, 1852. Both his father and grandfather were professors of various subjects. After high school, he studied at Kaiser Wilhelm Academy for Military Physicians from 1871 to 1875, did some work as a military physician, then finished his doctoral degree in 1876 in Berlin. The title of his dissertation was "The Chemistry of Protein Urine Tests". At some point in his life, he joined the Freemasons.

He continued his military physician work until 1882. During 1877-1879, Petri was assigned to a research facility called the Kaiserliches Gesundheitsamt (Imperial Health Office) in Berlin, where he became a laboratory assistant to the famous bacteriologist and physician Robert Koch. Koch's research team was producing great results in developing revolutionary laboratory methods to study the causes of infectious diseases and find their causes.

Petri and an example of his self-named dish with a bacterial culture on it

As an example of their research, they studied such things as tuberculosis, anthrax, and cholera, all devastating diseases at the time. To grow samples from humans, animals, or the environment in order to detect bacteria in them or to measure their growth properties, researchers like Koch's team would put them in rich nutrient solutions like beef broth. It had been only 17 years earlier when Louis Pasteur created the first actual broth recipe to grow bacteria, using a mixture of yeast, ash, sugar, and ammonium salts in 1860. Other recipes were soon developed to grow bacteria or to identify them based on color changes or production of gas as the germs grew.

These broths were commonly sterilized by boiling then put into glass test tubes with cotton plugs after they had been inoculated with test samples. If certain dyes were in the broth, bacteria that made acid would change the pH and color of the broth. If they also made gas as they ate nutrients, the tiny bubbles could be trapped inside a Durham tube flipped upside down in the tube.

Color changes and gas production in bacterial broth tubes (from asm.org)

Some bacteria need oxygen in different concentrations or not at all. Growing bacteria in a tube of broth was sometimes convenient to identify this property and add to the list of characteristics of what a scientist was examining. A non-inoculated tube would be clear, but based on the location of bacteria growing in it, the scientist could tell if the bacteria required atmospheric levels of oxygen (growth only at the top), a little oxygen (near the top), or no oxygen at all (growth only at the bottom). Some bacteria were able to grow with or without oxygen, so a tube would show cloudiness through its length.

Pigments made by the bacteria were also an important tool to distinguish between some bacteria grown on solid or semi-solid surfaces. Before looking at them under a microscope, if a scientist could see their color in large colonies growing on potato slices, bread, coagulated egg whites, etc., it would help identify them more quickly. For example, Bartolomeo Bizio studied "blood spots" on communion wafers in 1832, and the distinctive red was one trademark of the bacteria Serratia marcescens, later grown in the lab on bread chunks. Molds have also been commonly seen in prominent colors from snow white to blue-green to jet black.

"bloody bread" with bacteria; moldy bread

But using foods was not always convenient for lab work, nor did it show colorless bacteria very well. Some bacteria didn't even grow on food surfaces. Robert Koch's lab developed many carefully designed nutrient recipe broths mixed with gelatin which hardened into a semi-solid jelly that could be smeared on glass slides and inoculated with test samples then examined under microscopes. But this presented a few problems.
  • Incubating them at body temperature melted the gelatin and made it fall off the slides.
  • Some bacteria digested gelatin, and the result was changing it to a cloudy liquid that ran off slides.
In 1881, Koch made a "moist chamber" with a glass container that contained a thin layer of gelatin containing the bacteria smeared onto a microscope slide resting on wet filter paper. (Today's incubators provide humidified air for all cultures, so the filter paper is no longer necessary.)


While working in Koch's lab, Richard Petri noticed the problems people had with growing bacteria in these moist chambers or in stacks of glass plates under heavy glass bell jars. 

Bell jar and one glass tray to go inside stacked on others

So, he suggested pouring the agar nutrient mixture recently devised by Fanny and Walther Hesse (also in Koch's lab) into the glass dishes to make a layer covering the entire bottom, and then covering them to prevent airborne contamination. The agar was harder than gelatin, would not melt as easily, and was not eaten by bacteria. The dish with bacteria growing on it had an additional benefit; it could be comfortably put on microscopes for closer examination or counting. Petri modestly published this in a 300-word paper in 1887, "A minor modification of the plating technique of Koch".

Similar work with covered dishes had been done at nearly the same time by other people. In 1885, William Nicati and Maximilien Rietsch grew the bacteria Vibrio cholerae in what they called godets (“jars”) with nutrient gelatin. They described these as similar to parts of a pill-box, but they were much smaller than Koch's moist chamber, and they didn't publish any pictures of them. Researchers like Percy Frankland and Walther Hesse were interested in studying bacterial contaminants of the air. In 1886, Frankland published a paper where he showed a deep glass dish that had a thin layer of gelatin (not agar) coating its bottom. This was exposed to air in various locations to collect bacteria, then the cover was placed on it before incubation. 

Frankland's dish, 1886

Romanian Victor Babes and Frenchman Victor Cornil collaborated on studies in bacteriology and wrote a definitive book on the topic. In their 1890 edition, they claimed to have invented the culture dish before Petri, but they had never mentioned it in their 1885 or 1886 editions, so this passed unnoticed. Moreover, their 1890 drawing showed a different design than Petri's with a slanted body to the dish, plus the need to use rubber bands to hold the cover in place. So, the credit has gone to Richard Petri simply because he took the time to write a short article to describe his idea.

A year after Petri's publication, Isidor Soyka and Frantisek Král described another type of dish with a cover which they used to grow potato slices and then seal up the cover with wax to prevent it from drying out.

Soyka and Král dish for potato slices, 1888

Today, Petri dishes are used for a variety of laboratory experiments. They may still be glass, but the majority are plastic. They may be built in several diameters, and some even contain sections in them for various media use at the same time. Not only are bacteria and mold grown in them, but they may be used to test antibiotic resistance. Some Petri dishes even have grids on them to aid in counting. Some are used as dissection containers. 

Petri dishes today

From 1882 to 1885, Petri oversaw the Brehmerschen Göbersdorf tuberculosis sanatorium in what is now Poland. He was considered quite strict to everyone around him, perhaps as a result of working for an equally strict Koch or his own military training. He enjoyed wearing his military uniform of chief army doctor whenever he could, including a sash that accentuated his large belly in later years.

For a short time, he was director of a Berlin museum of hygiene, and then he returned to the Imperial Health Office until he retired in 1900. During his lifetime, Petri published 150 papers. One of the most interesting titles (and topics?) was "The microscope from its beginnings up to the present perfection for all lovers of this instrument", published in 1896. Petri was married twice and died on December 20, 1921.

Saturday, June 10, 2023

Scientists document how space travel messes with the human brain

Link to article


Many people are excited when they hear about the accomplishments of astronauts. Some envy their short-term missions aboard the space shuttle or the long-term missions aboard the International Space Station (ISS). But it's not all fun and excitement. Living in an environment of reduced gravity (microgravity) conditions can put a strain on the human body, including the brain. A recent study by NASA showed that fluid inside the brain expands during long missions, and that can be a problem.

The brain is an organ weighing about 3 pounds (1.3-1.4 kg) in adults. It is protected by the skull bones, but it is also cushioned by liquid inside and outside. This fluid also travels down the spinal cord, so it is known as cerebrospinal fluid. You can see it in blue in the picture below.

Cross-section images of brain with cerebrospinal fluid

Like blood, this fluid actually moves (see the black arrows on the left image above) from the center of the brain, where it is made, to a lining around the brain, down the spinal cord, and back again. There is no pump like the heart. Cells in the center cavity have little hair outside them that paddle the liquid. The cavities in the center of the brain that have the greatest volume are called ventricles (just like the 2 ventricles in the heart). There's about half to two-thirds of a cup (125-150 mL) in your body at any moment, and it gets absorbed by the body, so the brain makes about 2 cups (500 mL) per day.

You can see the beating pulses of the fluid in this MRI. 
Video courtesy of © Nevit Dilmen, CC BY-SA 3.0
https://commons.wikimedia.org/w/index.php?curid=9388427

One of the main functions of this fluid is to be a cushion against the brain shaking inside the skull. There is also a barrier layer of cells (membrane) between the fluid and blood flow that protects the brain from infection.

On Earth, gravity pulls down on the body and everything inside. In orbit or beyond, the reduced gravity no longer does that, so your blood and other fluids are more evenly distributed. That makes a weightless astronaut's face look puffy. A similar thing happens to the mucous membranes in the nose, and it makes the astronaut sound like they have a head cold. Both of these tend to go away after a few weeks as the body adjusts to microgravity conditions.

Puffy face on right while in space (photo from SpaceRef.com)

 So, in a similar way, the brain's ventricles are no longer under gravity pressure, so they swell up, at least for the first 6 months of being in space. The graph below for one of the brain's ventricles shows the difference between a 2-week flight and flights of 6 months or a year. The actual amount of swelling is small (0.15 mL or 0.03 teaspoon in the third ventricle, 0.75 mL or 0.15 teaspoon in the right lateral ventricle). But these were still statistically confirmed. They amount to a 10-13% increase.

Swelling in 2 brain ventricles depending on the length of the flight (from Nature.com)

Also, the more missions the astronauts went on had an influence on this expansion. If they went on fewer missions, the expansion was less (see graph below).

Data from Nature.com

If astronauts went back into space within 3 years, the expansion was minimal. After a 3-year delay, though, the body doesn't remember how to compensate, so they expand again by about 10-20%. 

A key point in this research is that scientists have not determined whether this expansion is a problem to brain functions during space flight. Earlier studies in 2011 and 2019 , though, have shown that 29% of astronauts on short-term flights and 60% of the on long-term missions suffered vision problems which might be related to pressure increases in the brain. 

For more information on other changes to the human body in space, see this Space.com article.

Wednesday, June 7, 2023

 Plants sound off when they’re in trouble

Link to Science News Explores article

People often talk, sing, or play music to their plants. They feel such things help them grow. But do plants actually make noise to tell us anything about their condition? Researchers at Tel Aviv University in Israel have just discovered that the answer is yes! Audible not to the human ear, but the sounds are there.

Normally, sound is energy vibrating through solid, liquid, or gas materials. Our voices make sounds by vibrating vocal cords as we breathe and speak. But what about plants? They have no vocal cords.

Water moves up a plant in three ways beginning at the roots and then through special tubes. First, the water is pushed up by pressure near the roots. Water also clings to itself and the walls of containers, which is why you see a U-shaped curve in a glass or straw. Put the straw in water, and this causes the water to move up the straw a little. This is called capillary action, like the capillaries carrying blood between arteries and veins. A third way is when water is drawn up from the leaves when it evaporates there (called transpiration, as opposed to perspiration or sweating). Sometimes, air gaps form in the tubes, and that slows down the flow of water, and that's the key to sounds.

Movement of water in a plant (explained on byjus.com)

In 1914, Irish professor Henry Dixon filled a narrow glass tube almost full with water and sealed both ends. This was then heated until the tiny air bubble dissolved into the water. As it cooled, the air was released to form a new bubble, and he noted a metallic clicking sound at that moment. He repeated the experiment with sap from a beech tree and got the same clicking. (Similar experiments had been done in 1850 in France, but this was the first time that sound had been noted.)

The formation and popping of gas bubbles in a liquid is called cavitation, where the word "cavity" refers to holes or space. The "father of cavitation research" was British professor John Milburn, who studied the clicking sounds in plants more than anyone, beginning 50 years after Dixon's research. 

John Milburn 

Milburn attached probes initially to the side of a leaf stem, and later inserted probes into the plant stem's tube to record cavitation events he called audible acoustic emissions, AAEs 

Milburn's apparatus with probes outside (left) and inside (right) plants

Here are results of 3 experiments Milburn conducted. On the left, he measured clicks/min as the leaf is allowed to lose its water. At first, there are many clicks as bubbles formed, but then the leaf was just full of air and no way to pop bubbles. In the middle, clicks rose as the plant dried out, but when the leaves were covered in a plastic bag to prevent water loss, the number of clicks decreased because fewer bubbles were formed. Remove the bag, and the counts rose again. On the right, Milburn put a drop of water at the base of a leaf, and as water evaporated from its surface, bubbles formed and click count rose. When the drop was removed 3 times, the leaf content had no water coming in, so no bubbles or clicks were seen.

Milburn's cavitation experiments, 1966

Milburn found that the intensity of the clicks was different depending on which plants he used. Medium-Loud sounds came from castor oil plants, currants, gooseberry, geranium, plantain, fern, sycamore, nasturtium, water lily, and hogweed. Weaker sounds came from coltsfoot (aster), fireweed (primrose), catnip, couch grass, and laurel. No sounds came from small seedlings of mustard, but Milburn suggested that maybe his equipment just wasn't sensitive enough.

Over the years, people injected a dye into the plant to see where the air bubbles has been created, but that meant cutting open the plant. The 2023 report from Israel measured sound at a distance from the plants. Instead of attaching or inserting sensors to the plants directly, they set up a soundproof box with 2 microphones about 10 cm (5 inches) away from the plants. 

Israeli acoustic box setup, 2023

But even in a soundproof box, regular microphones are not going to detect bubbles popping (cavitating) inside plants. You need the type that measures ultrasonic noise, whether it's coming from cavitation or the vibration of nearby fibers in the plants. Milburn pioneered the ultrasonic emissions from plants in 1988. The Israeli researchers tested tomatoes and tobacco plants. Like Milburn with probes directly attached, the Israeli group with microphones not touching the plants monitored how clicks rose after plants were watered and bubbles formed, then fell off as they dried out and bubbles presumably stopped forming.

Measuring clicks from tomato plants

Why is all of this important? Well, the Israeli researchers speculated that animals may be attracted to certain sounds, so this research would potentially tell us more about how that works related to pollination. The results might also be important for farmers if recorders were sensitive enough to measure crop clicking in the fields and filter out background noise. Farmers would know when to water the plants, or set up an automatic system to do it.

Here's a YouTube video showing how a new device called PlantWave can be used to change the sounds from plants into music.


Saturday, June 3, 2023

‘Puzzling’ rings from ancient humans posed mystery for a century — until now

Link to Yahoo article

Archaeologists dig up many types of artefacts in their studies. Sometimes it reminds me of going to an auction at a farm where you might see old farming or kitchen tools no longer in use today. You often have to guess what they are used for and how they operate. At least with semi-modern things like that, there are people to ask or the internet to search by posting a picture of the object. Archaeologists have less at their disposal, usually just someone else's findings to relate to, or their own reasoning power.

For the past century or more, people have found some curious U-shaped objects of shell, stone, or bone, often with elaborate decorations carved into them. They sit in museums with speculations that they might be simple decorations, or clothing fasteners, or even hair ties. Nobody has been quite sure. Some of these recently showed up in France.

Ring ornaments from French studies

Similar things were found in Central or South America over the years, but the French report was the first time they'd been found in Europe. In 1962, Gordon Ekholm described the ones in the Americas as finger loops for an atlatl. (There's a word for your Scrabble game! It means a holder for arrows or short spears, something you use instead of a bow to throw them at high speeds.)

Ekholm's drawings of spear holders (5 cm = 2 inches)

An atlatl is a tube with a groove in it, plus a blunt end where the feathered part of the arrow sits. You grip the atlatl with the loaded spear or arrow and make a throwing motion, but keep the atlatl in your hand a little like casting a fishing rod.

How to use an atlatl to launch a spear (pic from Wikipedia)

Knowledge of atlatls has been around for many years by their users. In 1896,  Frank Hamilton Cushing published one of the first papers "Exploration of Ancient Key Dwellers' Remains on the Gulf Coast of Florida" in which he described many things he'd dug up related to these dart throwers. Actually, other people accidentally found them in garden muck and shell banks of their coastal homes, in canals, and in burial mounds, and he took advantage of the situation to explore further when they were brought to a local museum. Among the artefacts, he discovered two throwing weapons with one or two holes carved into them for finger grips. When he compared these to other items found in Central and South America, he figured he knew what they were.

Throwing tools from Cushing's 1896 study

In a 2023 paper, rather than calling the French rings decorations or clothing adornments, Justin Garnett and Frederic Sellet from the University of Kansas took a page from spearthrower technology to determine that the French finds might be handles that are attached to atlatls. Instead of drilling the finger holes into the atlatl body like in Cushing's discovery, the hunter or warrior could perhaps strap these pieces of bone, stone, or shell onto it and give them a strong grip. Garnett and Sellet made their own models, and the photos below show how a one- or two-finger type could be held, with the weapon between the index finger, middle finger, and thumb. The ones in France were all made of antler from a deer species. 


Garnett and Sellet's models (from their 2023 paper)

The two Kansas researchers made several types of models based on research and speculation. See the types they devised below.

Models made by Garnett and Sellet

Archaeologists like Garnett and Sellett felt there were several reasons these objects were part of atlatls, aside from their similarity to ones found in the Americas.

  • They were the correct size for human fingers.
  • They were found among spear-throwing materials.
  • They were worn down in a way that suggested how they were held.

You might call this Stone Age technology, and you wouldn't be far off. The Paleolithic period, also called the Old Stone Age, runs from about 3 million years ago to 50,000 years ago. It was closer to the 50,000 year-old period that scientists started finding tools for fishing, projectile points, engraving tools, sharp knife blades, and drilling and piercing tools. Although the U-rings from France have not been carbon-dated, bones in the area were, and they showed ages ranging from 16,000 to 25,000 years ago. They also found bone flute fragments that suggested the hunters there even used whistles to call animals that they were stalking.

Watch a demonstration of an atlatl on this short YouTube clip.

Here's another video showing the actual primitive tech used to make the dart and atlatl (without finger grips) and to practice throwing at a target.

For a description of atlatls from Aztec ruins on display in the British Museum, read this paper with some cool photos.