parasitism eve

Chapter 11

Yoshizumi admitted that he couldn't do anything about Mariko, as the current Mariko is not the same person she was two years ago.

However, even Anzai himself didn't know why Mariko had shut herself off.

Anqi remembered clearly that things weren't like this during the last transplant. From the beginning, Mariko had been very cooperative, and after the surgery, she chattered incessantly to Yoshizumi and the nurses. The elevator doors opened in front of him. Anqi instinctively stepped inside, pressed the button for the first floor, and the elevator doors closed again. Anqi felt the slow descent. The ventilation fan above his head made a low hum.

"Chronic kidney failure."

When Anzai first heard this word, he didn't quite understand it. It was winter when Mariko was in fourth grade. The attending physician asked Mariko to wait outside and told Anzai in a regretful tone. Anzai still remembers that there was a small electric stove next to the doctor's desk.

“To be precise, it’s chronic glomerulonephritis,” the doctor said. “The type of nephritis your daughter has develops slowly and lasts for many years. It’s caused by a blockage in the glomeruli that filter urine, preventing the kidneys from working properly and producing urine. Look at these numbers. The glomerular filtration rate (GFR) and blood urea nitrogen (BUN) are basic indicators of kidney failure. Because excess water cannot be excreted from the body, patients like your daughter experience symptoms such as edema, shortness of breath, and restlessness.”

An ominous premonition gripped his heart, and Anqi asked weakly, "...Can it be cured?"

"It's a pity."

Section 28

The doctor immediately denied it. This statement was a huge blow to Anqi.

"Currently, there is no effective treatment for chronic kidney failure. Because the glomeruli lose their function as a whole, neither medication nor surgery can cure this disease."

"...Then, what should I do about my daughter?"

"Dialysis. Actually, many people suffer from kidney failure and are undergoing dialysis treatment. Dialysis is a process where a machine replaces the kidneys, connected to the patient's body, to remove uremic toxins and excess water accumulated in the body. Let me recommend a good hospital to you. It has the best dialysis equipment in the county, and many kidney failure patients go there for dialysis."

Before he knew it, the elevator had reached the first floor. Anqi stepped out and into the lobby. The heat from outside hit him, offsetting the cool breeze from the air conditioner. Anqi wiped the sweat from his neck with a handkerchief and headed towards Yoshizumi's clinic in another building.

Anqi suddenly realized how little he had interacted with Mariko over the years. All his energy had been focused on selling word processors, his mind always on work. He was turning fifty this year; if he didn't keep working, he wouldn't be able to. He couldn't let his performance fall behind others! Actually, this wasn't a new thought. Anqi smiled bitterly. It had been like this ever since he joined the company. His mind was always preoccupied with work—even his wife wasn't someone he pursued. He had never actively approached any woman. At thirty-three, a department head had arranged a blind date, and after that, he readily agreed to the marriage. Whether during their honeymoon or after Mariko's birth, he never thought about going home early, and he often worked overtime on Sundays, rarely having time to enjoy family time with his wife and Mariko. Shortly after buying the house, his frail and sickly wife passed away. The empty two-story house was filled with loneliness and solitude, and Mariko lived in this environment.

When he got home, Mariko was already in bed. He woke her up in the morning and then rushed to the bus stop, repeating the same routine every day. How could he possibly have known that Mariko had contracted nephritis!

The hospital the doctor recommended did indeed have comprehensive dialysis equipment. When Anzai and Mariko were first led into the ward, they were stunned. A large room contained nearly fifty makeshift beds, most of which were crammed full of patients. The dialysis machines next to each bed made the space feel even more cramped. Patients lay listlessly on their beds, each with a tube pulled from their arm. Some were reading magazines or comics, others were chatting with their neighbors to pass the time, while nurses bustled about. It was said that nearly three hundred dialysis patients regularly visited this hospital. The patients were of varying ages. Some children looked younger than Mariko, while others were wrinkled, nearly seventy-year-olds. There were also middle-aged men, around Anzai's age. Perhaps due to the lighting, the patients all appeared pale. Although the equipment was advanced, the patients' faces seemed perpetually weary. Mariko wouldn't be able to start dialysis immediately. The doctors at the hospital said that a surgery was necessary beforehand to create a fistula in her arm. This was because a tube connecting to a blood vessel needed to be inserted into her arm for dialysis. It was said that to protect the veins, the artery was connected to the vein, allowing the blood vessel to dilate and blood flow to be smooth. This is what's known as an "arteriovenous fistula." Although this surgery is challenging on children, it has the advantages of low infection risk and easy long-term preservation. Two weeks after the surgery, Mariko began dialysis. Three times a week, she went to the hospital immediately after school. Each dialysis session required her to lie in bed for four or five hours. By the time she got home on the last bus, it was already past 10 p.m. This dialysis routine lasted for six months. During this time, Anzai visited Mariko in the hospital very rarely. Mariko was always lying alone in bed, staring blankly out the window. What was Mariko thinking during dialysis? I've heard that during dialysis, patients sometimes experience spasms due to changes in osmotic pressure. It must be very uncomfortable. Although it's too late to do anything now, Anzai still feels heartbroken whenever he thinks of his daughter lying in the hospital bed. How would Mariko feel watching the dark red blood flow into the bedside monitor, through the slowly rotating blood pump and the slender dialyzer, and then back into her arm? At the time, Anzai hadn't even considered these questions.

"Dialysis can only be considered a temporary, conservative treatment," the doctor said. "Children with kidney failure who undergo dialysis long-term are bound to develop a series of complications. First, their height will stop increasing. Because the kidneys play a role in promoting growth, kidney failure can lead to developmental delays in children. Growing taller is of great importance to children. If Mariko continues on dialysis like this, she will probably worry about her height in the future. Dialysis can also cause bone diseases, and the development of her reproductive organs may also be affected."

"So, you mean there are other, better ways..."

"For children like this, transplantation is the best option. Please consider it."

The doctor enthusiastically recommended the transplant to Anqi. However, Anqi was not mentally prepared at this time.

To give his kidney to Mariko? To lie on the operating table and have the doctor cut open his abdomen with a scalpel to remove his organ?

He couldn't make up his mind right away. It was really quite frightening. "Will everything be alright? Will my body be harmed?" Anqi asked the doctor several questions in a row.

"I heard your daughter has kidney problems?"

While drinking with his boss, this topic suddenly came up. Anqi gave a vague reply, trying to change the subject.

But the drunken boss refused to let Anqi go. At that time, newspapers were reporting extensively on living donor liver transplants.

"Donating your liver to your son, what a great act of family love! Don't you think?" the drunken boss said in a slurred voice. "I heard that in other countries they take organs from the dead and transplant them to patients, that's so barbaric! It seems the Japanese approach is more humane. Anqi, just give your kidney to your daughter! A person has two kidneys. Even if you lose one, it's not a big deal. Can you really bear to let your daughter suffer? Didn't your husband pass away early? Your daughter can only rely on you now! You're a parent, you should learn from others, they've reported it, that's what family love is all about."

An Qi smiled broadly, appearing to agree, but in reality, he was full of resentment.

This opinion is nothing but empty talk from someone who doesn't care. Anqi thought, "My boss's child doesn't have kidney failure! So, does that mean parents who aren't willing to donate their organs to their children are morally corrupt? For their children, parents have to sacrifice their own bodies? If their children have any problems with their liver or kidneys, are parents obligated to unconditionally donate their organs? Who wants to have surgery when they're not sick? If there's a way to manage without surgery, I definitely wouldn't choose to have it. Does this kind of thinking really go against the bond between father and daughter?" Anqi gripped her glass of sake tightly, listening silently to her boss speak…

Anqi snapped out of his daze and realized he was already in Yoshizumi's consultation room. He shook his head to cool down his racing mind before knocking on Yoshizumi's door.

"Parasite Eve"

Chapter Ten

The water in the thermostat began to boil with a gurgling sound. Sachiko Asakura placed the test tube containing the sample into the tank and set the timer. The day's experiments were finally nearing their end. Asakura sighed and looked around the room. This place was on the second floor of the radioisotope laboratory building, quite far from the pharmacy department. Asakura's room was specifically for handling low-level radioactive materials. She was probably the only one left in the entire building; it was eerily quiet. Looking at the wall clock, it was already 10:30. Summer vacation was exactly halfway over. Asakura smiled wryly. There probably wouldn't be anyone else there; only she would be doing experiments so late at this hour.

Asakura was conducting protein transport experiments on the mitochondria of "Eve1". Although she had arrived at school early in the morning to do the experiment, she hadn't expected that adjusting the division of the mitochondria using density tilt centrifugation would take so much time. By the time the isotopically labeled enzymes reacted, it was already dark. These kinds of experiments are always hectic once they begin. Even a little free time like this, waiting for the samples in the test tubes to boil, is precious to Asakura right now.

“Eve1” is truly an incredible cell. Asakura stared blankly at the bubbling tank, lost in thought. In the two and a half years since attending this lecture, Asakura had seen many cells from Toshiaki, including cancer cells and primary cultured cells, but none as remarkable as “Eve1.” “Eve1” has not stopped proliferating. Toshiaki added antacids conjugated with bovine serum albumin to the culture medium, and its division rate seemed to surpass that of ordinary cancer cells.

Li Ming said that "Eve1" is a cell taken from a human liver and cultured in primary culture, but this does not explain why it has such a vigorous proliferative capacity.

Asakura had asked Toshiaki several times where "Eve1" came from. There was no doubt that what was in the refrigerator that night was an uncloned "Eve1" cell. However, each time he was asked, Toshiaki cleverly evaded the question.

Asakura secretly reviewed the cell's background information, but the list didn't include anything about "Eve"—even searching various literature sources yielded no results. It seemed to be a cell line that hadn't been publicly reported before. In other words, "Eve1" wasn't a cell line transferred from another lab, but rather one that Toshiaki himself established and named. So, where did Toshiaki get these cells from?

I heard from others that Li Ming has been taking care of his wife all along, so he probably doesn't have time to contact other universities.

If you think about it this way, then there's only one answer.

The thought that wouldn't leave his mind sent a chill down Asakura's spine. Suddenly, the classification of "Eve1" mitochondria that he was currently working on became terrifying.

I never expected Mr. Nagashima to do something like this.

Section 29

Asakura was always grateful to Toshiaki. For the past two and a half years, thanks to Toshiaki, she had been able to complete her experiments so smoothly. When Asakura entered her fourth year, her choice of the Physiology and Pharmacy Lecture as her aspiration wasn't entirely driven by a specific purpose. Looking back now, it's almost impossible for third-year undergraduates to truly grasp the research content. When deciding which lectures to join, students mostly chose based on utilitarian reasons: for example, whether it would be easy to find a job afterward, or whether the experiments would be simpler. Asakura didn't have a strong desire to attend any particular lecture either. Therefore, it wasn't until her third year, when she casually participated in a student internship, that she first experienced the joy of experimentation during an internship at the Physiology and Pharmacy Lecture. That experiment involved extracting plasmid DNA from E. coli and then inserting another type of DNA. Before that, Asakura had always thought of DNA as something mysterious and sublime. However, the process of extracting plasmid DNA was surprisingly simple; Asakura couldn't even believe that she could carefully cut and bind DNA herself.

Asakura inadvertently told the teacher next to him about his surprise.

The teacher smiled calmly and replied, "The purpose of the internship is to help you understand this."

That teacher was none other than Toshiaki Nagashima.

The internship summary was held in the seminar room of the Physiological and Pharmacological Lecture, and Asakura's seat happened to be next to Riming's. Through her conversation with Riming, Asakura learned that this lecture used mitochondria, a fascinating organism, as the subject of experiments. At that moment, Asakura decided to join the lecture, because she felt that she could do more interesting experiments there and do all sorts of things.

This wish was soon fulfilled. Coincidentally, Asakura was again assigned to conduct experiments under Toshiaki's guidance. For some reason, Asakura felt very excited when she heard the decision; in fact, being able to learn experiments from Toshiaki was a stroke of luck for her. Toshiaki was the type with a wide range of interests; he mastered various experimental techniques, and Asakura learned a great deal of experimental experience from him. She learned almost all the basic methods in the field of biochemistry from Toshiaki. Experimenting was a joyful experience, and it was even more joyful if the desired results pleased Toshiaki. Toshiaki's insightful observations of the data always amazed Asakura. Whenever interesting results appeared, Toshiaki would propose a series of hypotheses. He would quickly consider how to prove these hypotheses and how to arrange the experimental combinations. However, Toshiaki wouldn't conduct these experiments without certainty; he usually decided on the next step only after repeated deliberation, and Asakura often discussed these matters with him. At these times, Toshiaki's expression was particularly energetic. Although Asakura was impressed by Toshiaki, she also conducted numerous experiments and read many papers to close the gap with him. The reason Asakura chose to spend another two years in lectures after graduating from university instead of seeking employment was purely because she enjoyed doing experiments with Toshiaki. Asakura never imagined she would pursue a master's degree. While she did enjoy science in junior high and high school, she never imagined she would end up wearing a white lab coat and working with isotopes until late at night.

"Asakura is really tall!"

Men often say this. In fifth grade, Asakura suddenly started growing taller and soon became the tallest in her class; at that time, all the boys seemed short in her eyes. By the time she was halfway through junior high, the boys' height had finally caught up, and there were more and more classmates taller than Asakura—but among the girls, Asakura still stood out from the crowd. Because of her height, Asakura joined the girls' volleyball team. The team activities were naturally quite interesting, and Asakura participated in training diligently, feeling incredibly happy when they won against other schools. However, after entering high school, Asakura began to worry about her height.

Although she stopped growing at around 1.75 meters tall, she was still considered tall by everyone around her. Despite her smiling face and the envious glances from her female classmates, Asakura felt a pang of sadness. In high school, she dated a boy in the same grade for about a year, but because she was taller than him, she always felt awkward. She could never find clothes that fit, and even buying shoes became a problem; she often had to give up on clothes she liked. As a result, except when wearing her uniform, Asakura mostly dressed in a shirt and jeans. At school, Asakura was often the target of teasing from her male classmates. Of course, they might just be trying to make a joke, but even such jokes can be hurtful if repeated too often. At her high school's morning assemblies, girls stood in front of boys, arranged by height. Every time they lined up, Asakura consciously leaned forward, afraid of blocking the view behind her. After entering university, Asakura still didn't have a boyfriend. Although she doesn't feel lonely because of it, Asakura sometimes asks herself if she's too concerned about her own standing, which makes her negative towards the opposite sex. Isn't it to desperately deny this fact that she stays in the lab until late every night, trying to distract herself?

The sharp electronic beep of the timer echoed in the room, snapping Asakura out of her reverie; the boiling time for the samples had expired. Asakura lightly tapped her head with her fist as punishment for her earlier distraction. Then, she hurriedly removed the samples and placed them on ice. Asakura placed the polyacrylamide gel on the electrophoresis apparatus, and after the samples cooled, she began to inject the solution into the sample wells at the top of the gel. Asakura carefully used an adjustable pipette. Once all the samples were in place, Asakura turned on the power, turned the dial to set the current to twenty milliamps, and immediately, small, powdery bubbles appeared in the sample wells.

"alright."

Asakura stretched vigorously. The electrophoresis would last for nearly three hours, and there wouldn't be much to do until it was over.

Looking at her watch, it was already past eleven. If she stayed motionless in the lab reading papers, she'd definitely fall asleep; she might as well go home and take a bath. With that thought, Asakura tidied up her belongings. She left the isotope lab building, returned to her research lab in the Physiology and Pharmacology Lecture Hall, took her bag from the cabinet, turned off the lights, went to the corridor, and locked the door.

Asakura thought that it was almost time to prepare for the conference. She was to give a presentation at the Biochemistry Society in early September. Researchers led by Toshiaki and three students, including Asakura, would be presenting their research findings at the conference. The experiments for the conference were mostly complete; now only a couple more supplementary experiments were needed.

How much longer will Liming need to analyze "Eve1"? Asakura felt there must be something going on; otherwise, wouldn't it be better to finish the experiments at the Academy first?

Asakura walked down the corridor. The lights were all off, creating a vaguely eerie atmosphere. A sticky, warm breeze caressed Asakura's cheeks, and her slippers made a creaking sound as they rubbed against the floor. For some reason, Asakura felt that the sound was enveloped by the sticky wind, drifting away into the distance. That feeling was truly strange.

Asakura was constantly thinking about this problem, not only its characteristics, but also the cells themselves seemed to be emitting something.

Deep down, Asakura didn't want to get too close to it. However, she couldn't bring herself to tell Toshiaki about this childlike thought. So, while quietly conducting her experiments, Asakura often found herself caught in a strange feeling. Asakura felt it was her intuition.

From the past to the present, his intuition has often come in handy. Things like predicting a stomachache tomorrow, or the volleyball game will be lost—though they're all trivial matters, they're always surprisingly accurate. Whenever this happens, Asakura feels as if the hair around his neck is standing on end, and he experiences a complex sensation on the back of his head that's both painful and itchy. And this feeling is now growing stronger every day.

Asakura intuitively judged that it was due to that type of cell.

—An ominous feeling. I don't usually pay much attention to it, but when I'm doing experiments at night with no one around, this feeling comes to me unexpectedly. In the lab, I can turn on the radio to distract myself, but the isotope lab building is not a place to play music. Perhaps that's why I've become so sensitive today. I really hope Liming can leave those cells soon, but at the moment, that possibility seems too slim.

Riki's obsession with "Eve1" had gone beyond the norm, a fact Asakura could discern. Since the interesting results of the "Eve1" experiments, Riki's demeanor had become much more cheerful; compared to the period after the accident, he seemed to have returned to his former self. However, this only applied when he wasn't conducting "Eve1" experiments. Once Riki began operating "Eve1," he became completely mesmerized, even his gaze shifting. At these times, Riki would emanate an unusual heat, making Asakura hesitant to speak to him. Moreover, "Eve1" seemed to be working in concert with Riki. In fact, the progeny produced by Riki himself had a higher proliferation rate than those produced by Asakura, as if…

Asakura hugged his shoulders with both arms.

It's as if the cells are very happy.

"Stop overthinking!"

Asakura reluctantly dismissed the thought and started walking down the stairs to the first floor. But her pace quickened unconsciously. "It's okay, I was just overthinking it," she kept muttering to herself. But all she could think about was getting home as soon as possible, and she rushed down the stairs.

"Parasite Eve"

Chapter Eleven

"Our bodies are home to a large number of parasites."

This was the professor's very first and foremost statement.

A note hung in front of the podium, which read in calligraphy, "Lecture on Physiological Function and Pharmacy by Mr. Rikuo Ishihara." Judging from his gray hair, he was probably in his fifties, but his voice was very loud.

Saint-Mei sat on a hard chair in the large classroom, thinking to herself, "This person is probably younger than my father."

It was called a large classroom, but it was actually just a rectangular room with a little over 150 seats. Compared to the literature department's classrooms, which could accommodate over 300 students, it was dwarfed. However, the pharmacy department didn't have many students in each year, so this size was sufficient. Seimei sat a little further back, in a higher position, from where she could look down at the podium. There were only about fifty people in the classroom. Because she could only see their backs, she couldn't make out the exact number, but it seemed that half of them were young students. Some might be from other departments like Seimei, but most were likely from pharmacy. They might very well be students attending this lecture on physiological pharmacology. The majority of the audience were in their fifties and sixties; there were hardly any teenagers. A gentle breeze caressed her cheeks, and a soft breeze drifted in through the slightly open classroom windows. The rustling of the leaves came and went, like ripples on water. Looking out the glass window, the lush greenery swayed in the wind, reflecting the soft light into my eyes.

Section 30

Saint-Mei is now a third-year university student.

Two years passed in the blink of an eye: attending classes diligently, taking notes, sharing notes with friends to prepare for exams, participating in instrumental club activities, school garden parties, regular concerts, and the department's summer camping and ski trips.

"It'll be time to look for a job next year," a friend remarked casually. Only then did Shengmei realize she had no way out. Entering university had temporarily banished that feeling of uncertainty about the future, as she thought these issues could be addressed later. However, she now suddenly realized that university life was coming to an end, and she had no mature ideas whatsoever.

Although it was mid-June, the weather remained consistently hot. A hot wind swayed the branches of roadside trees and ruffled the collars of white shirts. The sky, which had been overcast throughout autumn and winter, now shone brightly with a clear blue sky. The direct sunlight illuminated the streets and skyscrapers. At this time, Shengmei was invited by a friend from the Literature Department to attend a public lecture by the Pharmacy Department.

To promote pharmaceutical knowledge, the pharmacy department at Shengmei's university holds free educational lectures for the general public every year on the second Sunday of June. This year, several professors, led by the department head, will introduce their respective research topics in an easy-to-understand manner. In addition, there seems to be time dedicated to explaining basic knowledge of medicinal plants, drug side effects, and recent hot topics such as HIV. The large medicinal plant garden behind the university is also open to the public at the same time, resembling a picnic. Although Shengmei knew this event was always popular, she had never participated before. Hearing from a friend that there would be free samples of Korean ginseng tea and houttuynia cordata tea, Shengmei finally couldn't resist the temptation.

The day of the lecture was a beautiful day with clear blue skies and a gentle breeze.

At 9:30 a.m., Shengmei and her friend took a bus to the Pharmacy Department. Shengmei's school had a typical "octopus-shaped" layout. The science departments, in particular, were scattered throughout the city. The Medical Department and its affiliated hospital were located on the north side of the street, the Agricultural Department was behind the bus stop, and the Engineering Department was at the foot of the hill. The Pharmacy Department was situated on a hill. The bus went up a small road next to the Literature Department, a five-minute walk. When they got off at the stop, the street scene below was spread out before them. Perhaps it was just psychological, but standing there, Shengmei felt the breeze brushing against her cheek was cooler than near the Literature Department.

Each lecture lasts about an hour and a half, with one in the morning and three in the afternoon. Participants are free to visit the botanical garden in between. The morning lectures begin at 10:00 AM. The lecture titles are posted in the hall displaying Chinese medicinal herbs, and Shengmei begins to browse through them one by one.

The morning's lecture was titled "Pharmaceutical Manufacturing - Chemistry and Pharmacy," seemingly related to the development of pharmaceutical products. While worried she might not understand much, Shengmei slowly shifted her gaze downwards. Below were the afternoon's lecture titles: "Traditional Chinese Medicine for Your Health," "What is Gene Therapy," and so on. The last lecture title caught her eye: "Symbiosis with Mitochondria - The Evolution of Cellular Society."

At that moment, Saint-Mei's heart unexpectedly pounded.

Saint-Mei frantically pressed her hand to her chest. This wasn't a normal heartbeat; it was a sudden, uncontrollable pounding. Saint-Mei felt short of breath, and her blood seemed to rush. The tremors were palpable in her palms. Saint-Mei pressed even harder against her chest. She heard her ribs crack, her chest relaxed, and waves of pain washed over her. But no matter how hard she pressed, she couldn't stop her heart from pounding. Saint-Mei stood still, trying to figure out what was happening inside her body. A bead of sweat trickled down her temple. Saint-Mei felt she couldn't tear her gaze away from the poster. ...Her breathing became intermittent. Saint-Mei gritted her teeth and let out a long sigh.

Finally, the strange vibrations gradually faded away. Then, a soft "thump-thump" of heartbeat returned to her chest, just like usual, and her blood flowed normally again. However, Shengmei was unable to move for the time being, and another bead of sweat rolled down her temple, following the path of the previous bead.

"What's wrong, Shengmei?" her friend asked, looking at Shengmei with concern.

Saint-Mei shook her head and replied, "It's nothing." Saint-Mei looked up, intending to smile politely, but her expression froze, and she could only manage a slight twitch of her lips. "Really, it's nothing. Let's go to the venue."

After speaking, Shengmei started walking. Her friend still looked somewhat uneasy, but reluctantly agreed.

Just as she was about to leave the hall, Shengmei looked back at the poster one last time. What was wrong? Shengmei was completely baffled. The moment she saw the last topic of the lecture, a strange heartbeat started, a vibration distinctly different from a normal heartbeat. This must be what they call an irregular pulse, Shengmei thought, her heart trembling slightly. "Symbiosis with Mitochondria"... Why was her body reacting to that strange topic?

She didn't understand. However, Shengmei was already captivated by the lecture. Visiting the botanical garden and having tea could be done when the lecture on traditional Chinese medicine and gene therapy came up; Shengmei decided she absolutely had to attend the lecture. The lecture was about to begin.

Saint-Mei's friend went home just before the lecture started, saying she had a tutoring session at five o'clock. However, Saint-Mei would never miss this lecture.

Behind the podium was a screen, with a backdrop displaying the title of the lecture in large print: "Symbiosis with Mitochondria." Those words had unsettled Seimei that morning, but now they no longer disturbed her heartbeat. However, it was undeniable that Seimei's heart had reacted to this earlier. She wanted to know why, what had happened during that episode. She felt the answer lay in today's lecture. Professor Ishihara, after listing several parasites such as roundworms, began explaining the concept of "symbiosis" using intestinal bacteria as an example.