Fact check · first aired 1987
Every episode transcribed and checked against what we know today about medicine and biology. Each point shows the episode, the moment it is said, and the exact line from the English dub (or the original French, where no English upload exists).
Watch the episodes on the official Hello Maestro YouTube channel.
These are the major errors: things a viewer could come away believing that are meaningfully wrong. We also found 50 minor slips (a date, a name or a number slightly off, or a likely dubbing error) which are hidden unless you ask for them.
Outdated: matched what was known at the time, but newer research changed the picture. Common belief then: specialists already knew better, but textbooks and popular books of the day still said it. Wrong in its day: a careful writer could have got it right from ordinary references; often a slip in a number, a name or the dubbing. Plain simplifications for children are not counted; they are listed under each episode. How this was made.
The episode tells the story of how the first cells formed in the "primal soup" and shows the main parts of a cell as a factory: the membrane, mitochondria that make energy, ribosome "assembly lines," lysosomes, and a nucleus whose chromosomes send RNA messengers with production orders. A skin injury sets off an urgent order for collagen, and a careless worker nearly sends out the master DNA instead of an RNA copy.
"Approximately 5,000 million years ago, single-celled, the cell developed."
TodayEarth is about 4,540 million years old, so cells cannot be 5,000 million years old. The oldest signs of life are roughly 3,500 to 3,800 million years old. Earth's age had been known since 1956.
"the liquid in which our cells bathe is almost identical to the seawater from which we originally come."
TodayThe fluid around our cells is only about one third as salty as seawater (about 0.9% versus 3.5%), and its mix of minerals is also different. This was an old idea that had already been abandoned by 1987.
Why it was believedArchibald Macallum's 1926 theory that body fluids preserve the saltiness of the ancient ocean was repeated for decades in biology textbooks and popular science as "we carry the sea inside us."
"Take the brain with its three layers. The first layer we inherited from the reptiles. The second, the Paleocortex, from the mammals. And the third, the Neocortex"
TodayThis is Paul MacLean's "triune brain" idea. Brain scientists have rejected it. The brain did not grow by adding new layers on top of old ones. Reptiles and birds have structures that correspond to parts of our cortex, and all brain parts evolved together (comparative neuroanatomy from the 1990s onward, summarized by Cesario et al., 2020).
"And the third, the Neocortex, the most important, developed very rapidly. It only took 500,000 years to form."
TodayAll mammals have a neocortex, and it is well over 100 million years old. It did not appear in human evolution, and it did not form in 500,000 years.
"the human body has 60,000,000 million of them" (later "60,000,000,000", probably a dubbing or Whisper slip)
TodayCareful counts give about 30 to 37 trillion human cells (Bianconi 2013; Sender, Fuchs and Milo 2016). That is about half the old 60 trillion estimate, which is exactly what the episode gives for 1987. ("60,000,000 million" is 60 trillion written in a way that cannot be misread whether "billion" means a thousand million or, in older British and French usage, a million million.)
"The centriole, the command post that controls the unity or the division of the cell."
TodayCentrioles help organize the machinery that pulls chromosomes apart. They do not decide when a cell divides. That decision is made by cell-cycle control proteins (cyclins and CDKs; Nobel Prize 2001). Some cells divide without any centrioles (plants, and fruit flies engineered without them, Basto 2006).
"every day 500,000 million of them vanish and are replaced at the rate of 50 million each second."
TodayThe two numbers contradict each other: 50 million per second adds up to about 4,300 billion per day, not 500 billion. Measurements put turnover at about 330 billion cells a day (Sender and Milo 2021), which is about 4 million per second. The per-second figure is roughly 13 times too high.
Hundreds of millions of sperm set out, and only a few reach the egg. The fertilized egg divides, implants in the womb, and becomes an embryo fed by the placenta. Newly made cells are sent off by type (bone, liver, muscle, eye and so on) to build the body, and the episode tracks the fetus's growth up to a 50 cm, 3.2 kg baby at nine months.
No major errors in this episode. 1 minor slip hidden.
"There are 200 different kinds of you"
Today"About 200 cell types" was the standard textbook number. Since the 2010s, single-cell studies such as the Human Cell Atlas have found several hundred main types and thousands of subtypes. The real number depends on how finely you split them.
Young white blood cells go to "school" in the thymus. There they learn to tell enemies (viruses and bacteria) from friends (red cells, platelets, helpful gut bacteria), and to check the HLA "identity card" that marks the body's own cells. The episode introduces B cells that release antibodies, killer T cells, phagocytes, macrophages, basophils and interferon. It ends with a T-cell patrol fighting off a virus in the lung.
"every day 15,000 million white corpuscles come into the world"
TodayThe bone marrow makes about 50 to 100 billion neutrophils a day, plus the other white cells. That is several times more than 15 billion, and estimates from the 1970s already showed this.
"Thymus, the school for white cells."
TodayOnly T lymphocytes are trained in the thymus. B cells mature in the bone marrow, and neutrophils (the "polynuclears") and macrophages never go to the thymus. The episode shows all these cell types as pupils in the same school.
"These are bacteria. ... They cause chickenpox, diphtheria, meningitis, and many other illnesses."
TodayA virus (varicella-zoster) causes chickenpox, not a bacterium. This was known well before 1987. Diphtheria is bacterial. Meningitis can be caused by either bacteria or viruses.
"Those are basophiles. They fight allergies."
TodayBasophils cause allergic symptoms rather than fight them. They release histamine, which drives allergic reactions.
The bone marrow is shown as a factory that turns a "master cell" (stem cell) into red cells, white cells and platelets every day. A programming error in the chromosomes produces too many rogue white cells, and a girl is diagnosed with leukemia. She is treated by destroying her blood-forming cells and then receiving a bone marrow transplant from her HLA-matched brother, whose cells find their own way to her marrow.
"Every day, 200 billion red blood corpuscles, 15 billion white blood corpuscles, and 500 billion platelets are produced."
Today200 billion red cells a day is correct. Platelet production is about 100 to 150 billion a day, so 500 billion is several times too high. (Episode 6's "half a billion" is the same figure in the older British long scale, where a billion is a million million, so the two episodes agree.) White cell production is about 50 to 100 billion a day or more, not 15 billion.
"Triction enzymes, ligase enzymes to work immediately. We've got to repair this at once" (Whisper: "Triction" = "Restriction"), and later "Calling restriction enzymes. It's absolutely essential to reduce production."
TodayRestriction enzymes are bacterial defense tools that people use in the lab. Human cells do not use them to repair DNA or to control how many blood cells are made. Ligase does take part in DNA repair, so that part is correct.
"The white blood cells attack the population of their own organism. ... Leukemia. The white cells are unbalanced. They've become attackers, not protectors."
TodayLeukemia is a cancer of blood-forming cells, not white cells attacking the body. Abnormal, immature cells multiply out of control and crowd out normal blood production in the marrow. That crowding is what causes the anemia and low platelets. White cells attacking the body's own tissue is autoimmune disease, which is a different illness. This was well understood in 1987.
"right ventricle pushes them into the pulmonary aorta"
TodayThe right ventricle pumps into the pulmonary artery, also called the pulmonary trunk. The aorta leaves the left ventricle. This is a small naming error. (likely a translation/dubbing slip)
The episode follows red blood cells carrying oxygen and carbon dioxide through the blood vessels, with white "police" cells clearing out bacteria such as streptococci. It covers how long red cells live, how they are replaced, how cells release stored sugar during a shortage, and an antibody-led fight against a flu virus.
No major errors in this episode. 3 minor slips hidden.
"blood vessels of the human body. Their surface area is 700,000 square meters."
TodayThe inner surface of all the blood vessels (mostly capillaries) is usually estimated at a few hundred to about 1,000 square meters. 700,000 is roughly 1,000 times too large.
"One cubic millimeter of liquid blood plasma contains five million red corpuscles and 700,000 phagocytes, or white."
TodayNormal blood has about 4,000 to 11,000 white cells per cubic millimeter, so 700,000 is about 100 times too high. (The red cell figure is right, though the cells are in whole blood, not plasma.) This could be a dubbing slip for 7,000, but the figure as spoken is wrong. (likely a translation/dubbing slip)
"a signal goes out to the part of the cell where sugar is stored. The Golgai bodies. When the signal is received, sugar is released through the walls of the cell."
TodayCells store sugar as glycogen, in small grains in the cell's fluid (cytoplasm), not in the Golgi. Only the liver (and to a small extent the kidney) can release that sugar back into the blood. Muscle keeps its glycogen for its own use. The Golgi packages proteins.
Young platelets learn their job of patching damaged blood vessel walls, and fibrin "ropes" (made from fibrinogen by thrombin) bind them into clots. An old platelet tells the story of a disease in which antibodies attacked the body's own platelets. When Peter cuts his thumb with a dirty knife, platelets and clotting factors stop the bleeding while white cells fight a staphylococcus infection, and the pus is shown to be dead white cells.
No major errors in this episode. 3 minor slips hidden.
"This is the bone marrow, where nearly half a billion blood platelets are produced every day." (repeated at the end: "Your body produces nearly half a billion platelets every day")
TodayThe dub most likely uses the older British long-scale "billion" (a million million, like the French billion), so "half a billion" means about 500,000 million, the same figure episode 4 gives as "500 billion." That is still about 3 to 5 times too high: the body makes about 100 to 150 thousand million platelets a day, a rate already measured with isotope-labelled platelets in the late 1960s (Harker and Finch, 1969). Platelets live 7 to 10 days and there are about a million million in circulation.
"He injected the bloodstream with Trojan horse platelets. They were full of medicine that killed any antibody that touched them."
TodayThe disease is immune thrombocytopenia (ITP). The experimental "Trojan horse" treatment (platelets loaded with the drug vinblastine, 1970s to 80s) was aimed at the macrophages that eat antibody-coated platelets, not at the antibodies, and it never became standard. Today ITP is treated with steroids, immunoglobulin infusions (IVIG), rituximab, and drugs that boost platelet production (romiplostim and eltrombopag, approved in 2008).
"I'm calling in the Prostaglandin squad immediately. ... Only Prostaglandin can remove the blockage."
TodayClots are dissolved by the fibrinolytic system: plasmin, activated by tPA (approved as a clot-busting drug in 1987). Some prostaglandins, such as prostacyclin, stop platelets from clumping, while others, such as thromboxane, make them clump more. None of them dissolves an existing blockage.
The episode opens with the history of how blood circulation was discovered, then follows red blood cells through the heart's four chambers, the tricuspid valve, the short loop through the lungs and the long loop through the body. A flashback shows a smoker with a fatty diet who gets chest pain, is told to change his lifestyle, ignores it, and has a coronary thrombosis.
"Before that, the Belgian anatomist, Andreas Vassale, first dared to speak of it in 1543. The result? He was condemned to be burnt at the stake. He was saved from the Inquisition in the nick of time by a powerful friend, Philip II of Spain."
TodayVesalius's 1543 anatomy book did not describe blood circulation. The story that he was sentenced to death by the Inquisition and saved by Philip II is a legend with no reliable evidence behind it.
Why it was believedThe tale of a death sentence commuted by Philip II goes back to late-16th-century rumours and was retold as fact in popular histories of medicine, which cast Vesalius as a martyr of anatomy.
"Ten years later, Michel Servette, a Spaniard, dared to speak of the circulatory system. But he had no king to protect him, so he died at the stake."
TodayServetus did describe blood passing through the lungs (in 1553), and he was burned at the stake in Geneva that year. He was executed for his religious views (he denied the Trinity), not for his ideas about blood. Ibn al-Nafis had described the same lung circulation around 1242.
Why it was believedPopular histories of science told Servetus's execution as martyrdom for scientific truth, because his account of blood passing through the lungs appeared in the same theological book (Christianismi Restitutio, 1553) for which he was burned.
"You must cut out all tobacco, all alcohol, all salt, all fats, everything. A very strict diet"
TodayStopping smoking is still the top priority. But guidelines no longer tell heart patients to cut out all fat. They advise replacing saturated fat with healthy unsaturated fats such as olive oil, nuts and fish (the PREDIMED trial in 2013; the US dietary guidelines dropped their limit on total fat in 2015). Salt should be reduced, not eliminated.
"Obviously, when the fats built up, the passageways became completely blocked. ... That's what a thrombosis is."
TodayA thrombosis is a blood clot, not a fatty blockage. Most heart attacks happen when a fatty plaque in the artery wall cracks and a clot forms on it suddenly (shown in the early 1980s by Falk and by Davies and Thomas). It is not usually fat slowly filling the artery until it closes.
Why it was believedThe "clogged pipe" picture, with fatty deposits slowly narrowing an artery until it closes, was how 1980s textbooks and health campaigns explained heart attacks; the role of plaque rupture and clotting was only being established in specialist journals in the early 1980s.
The episode introduces the alveoli, where blood gives off carbon dioxide and picks up oxygen. A gang of bacteria and viruses tries to get in through the mouth. The defenders in the tonsils wipe out most of them, and the survivors try the lungs, where infected cells send interferon alarms and order antibodies. It also shows dust and pollution building up in the lungs.
"That's where oxygen is transformed into carbon dioxide."
TodayThe oxygen we breathe ends up as water. The carbon dioxide we breathe out is made from the carbon in food (sugars and fats), which is broken down in the mitochondria of cells all over the body. This was shown with isotope tracer experiments decades before 1987. (The line also seems to place this "real breathing" in the lungs, which is wrong too, though the transcript is unclear there.)
Why it was believedSchool textbooks summed up respiration as "glucose + oxygen gives carbon dioxide + water" and "we breathe in oxygen and breathe out carbon dioxide," which reads naturally as oxygen turning into CO2; that inhaled oxygen ends up in water was known mainly from isotope tracer studies.
The episode presents the brain as three evolutionary layers: a reptilian brain, a primitive mammalian brain and a modern neocortex. It explains the brain's large need for oxygen and sugar, how neurons pass messages through synapses, and how the medulla, hypothalamus and cerebellum handle automatic jobs such as breathing, thirst and balance. It also explains memory as storing sensory information (a rose's color and thorns), and the body map in the brain where more sensitive parts get larger areas.
"Others say it probably has more than a hundred billion." / "Brain contains a hundred thousand million cells."
TodayThe human brain has about 86 billion neurons (Azevedo and Herculano-Houzel, 2009), plus a similar number of support cells (glia). The old "100 billion neurons" figure was an estimate that had never been measured. The episode also says "the brain has 10 billion nerve cells," which is too low.
"Approximately a hundred thousand years ago, the neocortex developed."
TodayAll mammals have a neocortex, so it is well over 100 million years old. Only its large expansion in humans is recent, and even that took millions of years.
"The reptilian brain, the paleocortex or primitive mammalian brain, and the neocortex or modern man's brain. Unfortunately, communication between them is not always perfect." (and "the most primitive part always tries to dominate")
TodayThe "triune brain" model has been abandoned by neuroscientists. Brains did not evolve by stacking new layers on top of old ones, and there is no separate "reptile brain" fighting the "thinking brain" (see for example Cesario et al., 2020).
"It uses 2,000 liters of blood a day ... This is 20% of the body's oxygen requirements."
TodayThe 20% share of the body's oxygen is right. But blood flow to the brain is about 750 ml a minute, which is about 1,000 to 1,100 liters a day, so 2,000 is roughly double.
"Nerve cell has 100,000 synaptic connections."
TodayA typical neuron has a few thousand to about 10,000 synapses. Only special cells, such as the Purkinje cells of the cerebellum, reach about 100,000 or more.
The episode shows nerve cells as busy offices that receive thousands of messages, "vote" on a response and send runners along nerves. It walks through a cough reflex during a run, the sympathetic nerves speeding up the heart, and ends by saying that thought and personality come from brain chemistry.
No major errors in this episode. 2 minor slips hidden.
"they're the cells in the human body that are never renewed"
TodayMost neurons do last a lifetime, but adults do grow some new neurons, at least in the hippocampus (a memory area). This was first shown in humans in 1998 (Eriksson and colleagues) and backed up by later work, including a 2025 study in Science. How much it happens is still debated.
"Coughing is a reflex, so you're entitled to go straight to the command centres bypassing the brain ... Shortcut along reflex road, and straight to the spinal column."
TodayThe cough reflex is run by the brainstem (the medulla), which is part of the brain. It is not a spinal reflex like the knee-jerk. The episode is right that the thinking part of the brain is skipped, but wrong that the signal goes straight to the spinal cord.
Light is shown as photons that bounce off objects into the eye, where the lens focuses them onto the rods and cones of the retina. The signal travels along the optic nerve to the brain, which does the real "seeing" and interprets images (optical illusions, an orange vs. the sun). The episode also covers tears, which clean the eye and contain germ-killing enzymes (lysozyme).
"The left brain deals with the signals from the right eye and vice versa."
TodayEach side of the brain handles the opposite half of what you see, using input from both eyes. About half the fibres from each eye cross over at the optic chiasm. This has been known since the 1800s. A simple crossover like the one described happens in some animals, not in humans.
Sound waves vibrate the eardrum. The three small bones (hammer, anvil, stirrup) pass the vibration to the cochlea, where hair cells turn it into nerve signals, and the brain turns those signals into sound. The episode also covers an ear infection that spreads up the Eustachian tube, noise damage that cannot be undone, and the semicircular canals that help with balance.
No major errors in this episode. 1 minor slip hidden.
"polarize the cell, let the sodium ion messengers in" (hair cells of the cochlea)
TodayThe inner-ear hair cells are activated mainly by potassium (plus some calcium) flowing in from the potassium-rich fluid around them, not by sodium. The unusual potassium-rich fluid had been known since the 1950s, and the potassium-based mechanism was well described by the early 1980s. (Sodium is right for ordinary nerve impulses further along.)
A tour down through the three layers of skin (epidermis, dermis, hypodermis), showing melanocytes, sweat glands, goosebump muscles, fat and the various touch, pressure, heat and cold sensors. A mosquito bite and a scratch infected with streptococci show how the skin's defences respond.
"It also helps the body to breathe"
TodayHuman skin takes in only a tiny amount of oxygen (around 1% or less of what the body needs). Skin "breathing" matters in frogs, not humans. The old idea that covering the whole body in paint suffocates you is a myth.
Why it was believedOlder physiology and school texts listed "respiration" among the skin's functions, and the idea that skin must breathe was spread by the story (popularized by the 1964 film Goldfinger) that painting a body gold suffocates it.
"We protect the skin by turning brown to create a suntan. And we also manufacture vitamin D" (said by melanocytes)
TodayVitamin D is made mostly in keratinocytes, the main skin cells, not in the pigment cells. Melanin (the brown pigment) actually reduces vitamin D production. Both facts were published in the early 1980s.
"Ruffini, the heat sensor" (plus the cold-sensing "Krause" character)
TodayRuffini endings sense skin stretch and steady pressure, not heat. Temperature is sensed by free nerve endings. The idea that each type of corpuscle senses one temperature comes from the late 1800s and had been disproved by the 1960s–70s, though some textbooks still repeated it.
Why it was believedVon Frey's 1890s scheme giving heat to Ruffini endings and cold to Krause end bulbs was still printed in many textbooks and encyclopedias in the 1980s, long after physiologists had shown that free nerve endings do the work.
"Antibodies, who kill them. Or histamine, which destroys them chemically."
TodayHistamine does not destroy germs or poisons. It is a signal that widens blood vessels and causes swelling, redness and itching (it causes the itch of a mosquito bite).
"The skin draws one-third of the blood circulation."
TodayAt rest the skin gets about 5–10% of the blood the heart pumps. It can get much more when the body is shedding heat, but one-third is not a normal figure.
The mouth is the first stage of digestion. Teeth cut, tear and grind, saliva starts digestion and helps keep the mouth clean, and the tongue detects tastes. Sugar-loving bacteria (Streptococcus mutans) turn sugar into acid, dig a cavity through the enamel and threaten to reach the bloodstream until a dentist steps in. The message is to brush your teeth and cut down on sugar.
No major errors in this episode. 1 minor slip hidden.
"the tongue is sensitive to four basic elements of taste: bitter, acidic, sweet and salty"
TodayThere is a widely accepted fifth basic taste, umami (savoury, the taste of glutamate). It was proposed in Japan in 1908 but only became accepted in the West after its taste receptors were found in 2000–2002.
Food travels from the oesophagus to the stomach, where acid and enzymes break it down, then on to the small intestine. There bile and pancreatic enzymes finish the job and nutrients are absorbed through the villi (fats go into the lymph). In the large intestine water is taken back and friendly bacteria make vitamins (B, K) and keep harmful germs such as Salmonella in check. The episode warns about overeating and not washing your hands.
No major errors in this episode. 1 minor slip hidden.
"That's the appendix, dear." / "Well, what's it for?" / "Absolutely nothing apart from getting appendicitis."
TodayThe appendix is no longer seen as useless. It contains immune (lymphoid) tissue and may act as a "safe house" from which good gut bacteria can regrow after illness (Bollinger and colleagues, 2007). People without an appendix may be more likely to get repeat C. difficile infections.
The liver is shown as a chemical factory. It stores sugar and vitamins, builds proteins (ribosomes reading RNA instructions), makes bile and cholesterol, makes clotting factors such as fibrinogen, and sends sugar to the brain. In the second half, hepatitis A viruses hijack liver cells, causing jaundice, and the body fights back with interferon and lymphocytes.
No major errors in this episode. 3 minor slips hidden.
"The liver is only 10% of the body's mass" (note: "10%" may be a transcription error)
TodayThe liver is about 2–2.5% of body weight (about 1.5 kg in an adult). The part about it using roughly a quarter of the body's oxygen is broadly right.
"There is a blockage developing in coronary artery number four ... Liver will cease cholesterol production immediately." / "All that cholesterol wasn't manufactured in the liver."
TodayThe link between cholesterol and blocked arteries still holds. But the suggestion that most of the problem comes from cholesterol in food is out of date. The liver makes most of the body's cholesterol, and for most people dietary cholesterol has only a modest effect on blood levels. US dietary guidelines dropped their daily cholesterol limit in 2015. Saturated fat, genetics and overall diet matter more.
"We are hepatitis viruses ... Our very own DNA molecule." ... "The liver has been invaded by type A hepatitis virus."
TodayHepatitis A is an RNA virus, not a DNA virus. This was known by the early 1980s, and its full genome was sequenced in 1987. (Hepatitis B, by contrast, is a DNA virus.)
The liver turns toxic ammonia into urea, which travels in the blood to the kidneys. There about a million filtering units per kidney (glomeruli and Bowman's capsules) filter the blood, and hormones (ADH, aldosterone) help reclaim about 99% of the water, salt and sugar. The waste leaves as urine through the ureters to the bladder.
No major errors in this episode. 1 minor slip hidden.
"the kidney had been severely overloaded by alcohol abuse. And it failed to get rid of all the waste products ... If the kidney stone stays in place..." / "As soon as I gave up drinking"
TodayAlcohol is not considered a major cause of kidney stones. Large studies since the 1990s (Curhan and colleagues, 1996/1998, and later analyses) found that moderate beer and wine drinking goes with a slightly lower stone risk, probably because of the extra fluid. The main risk factors are not drinking enough water, diet (salt, animal protein, oxalate), genetics and metabolic conditions. Heavy drinking is still harmful in other ways.
Lymph is a clear fluid carried in its own vessels. It passes through lymph nodes, which act as checkpoints where immune cells catch germs, and drains into the blood through the thoracic duct, carrying fats absorbed from the gut. An old red blood cell (Professor Globus) dies in the spleen after 120 days. A staph infection from a cat scratch, after a bout of flu, swells a lymph node and needs an antibiotic.
No major errors in this episode. 2 minor slips hidden.
"The spleen stores the metal and uses it to create new red corpuscles."
TodayThe spleen breaks down old red blood cells and recycles their iron, but in adults new red blood cells are made in the bone marrow, not the spleen. The spleen only makes red blood cells before birth.
"[Lymphocytes] originate here in the lymphatic system, which accounts for the derivation of their name."
TodayLymphocytes are made in the bone marrow, and T cells then mature in the thymus. They multiply in lymph nodes and are named after lymph, but that is not where they start. This was known by the 1960s–70s. (The transcript is incomplete here, so the exact wording is uncertain.)
Why it was believedLymphocytes multiply in lymph nodes and are named after lymph, and older textbooks and encyclopedias described the lymph nodes as where lymphocytes are made; the bone-marrow and thymus origin, established in the 1960s, reached popular references slowly.
The episode shows how a child's soft cartilage is slowly turned into bone by osteoblasts, helped by calcium, phosphorus and vitamin D, and how osteoclasts break bone down so it can be reshaped. Peter and Claire break their legs skiing, and we watch the fractures heal while bacteria try to infect Peter's open wound. It ends with diet advice: milk, cheese and sunshine.
No major errors in this episode. 1 minor slip hidden.
"does a broken bone ever regain its full strength? ... Heavens, yes. In fact, it's a great deal stronger than before at the site of the fracture"
TodayFor a while after healing, the lump of new bone around a break is thicker. Over months to years the body reshapes it back to roughly normal, so the bone ends up about as strong as before, not "a great deal stronger." The idea that a healed break is the strongest spot is a common myth.
Why it was believedThe callus around a healing fracture is visibly thicker than normal bone, and the saying that a healed break becomes the strongest point of the bone was widely repeated by doctors, coaches and popular books.
The episode explains how nerves tell muscles to contract, and how muscles burn sugar with oxygen for energy, switching to fat reserves when the sugar runs out. It contrasts fit Peter with his overweight friend Jumbo, whose extra fat strains his spine, heart and lungs. It ends with a doctor ordering exercise and a diet.
No major errors in this episode. 1 minor slip hidden.
"The muscle, the most important system in the human body, making up more than half its weight."
TodaySkeletal muscle makes up about 30–40% of body weight in adults (roughly 40% in a fit young man, less in women and older people), not more than half. This was already the textbook figure in the 1980s.
Air pollutants such as smoke particles get past the lungs' defenses and into a cell. The cell's nucleus makes "detoxifying enzymes" from a DNA copy (messenger RNA) to destroy them. A chemical damages a chromosome, the episode explains that such mutations can lead to cancer, and repair enzymes fix the DNA. Lysosomes and the kidneys then clear away the waste.
No major errors in this episode. 1 minor slip hidden.
"But why do we need iron in proteins? / Because the iron gives them energy. / Go and order some from the spleen, the great iron reserves."
TodayThe iron in detox enzymes (the cytochrome P450 family) is part of the machinery that grabs oxygen and drives the chemical reaction. It is not a source of energy. The body's main iron store is the liver, with more held in bone-marrow and spleen cells. The spleen recycles iron from old red blood cells, but it isn't "the great iron reserve."
Why it was believedBecause the spleen breaks down old red cells and recovers their iron, older textbooks and popular references often called it the body's iron store (the line about iron "giving energy" was never standard, but the item is filed here for the spleen claim).
Tetanus bacteria survive in soil as spores and get into the body through a scratch while two boys move a rose bush. In vaccinated Peter, ready-made antibodies destroy the toxin at once. Unvaccinated Jumbo develops a stiff jaw and needs hospital treatment with anti-tetanus serum and antibiotics. The message: get vaccinated and keep up your boosters.
No major errors in this episode. 1 minor slip hidden.
"Those are the antibodies of an antibiotic, a medicine made to fight microbes."
TodayAntibiotics are drugs that kill bacteria or stop them from growing. They contain no antibodies. Antibodies are proteins made by the immune system, and here they came from the anti-tetanus serum. The episode mixes up the two words. (likely a translation/dubbing slip)
The episode introduces the hormone glands and shows the hypothalamus and pituitary acting as the "conductor" of the hormone system. During a long tennis match, adrenaline, thyroid hormone and glucagon are called in to speed up the heart and release stored sugar. When Peter's reserves run out, pneumonia bacteria take advantage and he needs antibiotics.
No major errors in this episode. 2 minor slips hidden.
"Immediate secretion of TSH hormones in order to stimulate the thyroid gland, in order to make the metabolism speed up. The game has just begun"
TodayThe pituitary hormone TSH and thyroid hormones work over hours to days. They don't act within a tennis match to supply quick energy. The fast exercise hormones are adrenaline, noradrenaline and glucagon, which the episode also shows correctly.
"well he overdid things and to cope with the situation the hormones had to release all the reserves when these were all used up and the defense is exhausted the germs invaded the body"
TodayToday's evidence doesn't support the idea that one bout of hard exercise leaves you open to infection, such as getting pneumonia after a long tennis match. A 2018 review (Campbell & Turner) concluded that exercise doesn't suppress immunity this way, and regular exercise improves immune function. The "exhausted defenses" idea was popular in the 1980s–90s, when it was known as the "open window" theory.
The episode traces food chains back to the sun and shows plants using sunlight to make sugar. A prehistoric man with no vitamin C develops scurvy. It ends by warning that modern people eat too much rich food and exercise too little, while an old food-grabbing instinct in the brain overrides the signal that we're full.
No major errors in this episode. 1 minor slip hidden.
"Order from the primitive brain. Nourishment in sight. To be seized." / "Memories and ancient instincts still exist, which the modern brain can't always subdue"
TodayThis is the "triune brain" model, which pictured a "primitive" (reptile-like) brain buried under a newer, rational brain. Brain scientists have since abandoned it. Appetite is controlled by connected circuits in the hypothalamus and reward system, steered by hormones such as leptin (discovered in 1994) and ghrelin (1999). The fact that people overeat is real, but the "two brains fighting" explanation is outdated.
While Peter sleeps, his brain sorts the day's memories and mixes them into dreams, and his cells carry on repairs. A copying mistake in a cell creates harmful proteins, which the body quickly cleans up. The episode explains that young bodies repair themselves fast, while old bodies wear out.
No major errors in this episode. 1 minor slip hidden.
"The RNA instructions for assembling proteins are all scrambled. I want you to get some repair enzymes down there" ... "You've created wild genes, you have."
TodayCells don't repair damaged messenger RNA, the short-lived working copy of a gene. They break it down and make a fresh copy from the DNA. A mistake in an RNA copy can't create new or "wild" genes, because genes live in the DNA. Only changes to the DNA itself (mutations) alter genes.
Grandpa explains ageing: cells are constantly replaced, but they slow down, and in old age the heart, lungs and defenses weaken. He passes on his genes to his grandchildren. The story then follows a newborn baby learning to use its senses and building its own immune defenses, and ends with a science-fiction space voyage in which human chromosomes carry humanity into the future.
No major errors in this episode. 5 minor slips hidden.
"nerve cells die in their thousands each day without ever being replaced"
TodayStudies in the 1990s found that healthy ageing loses far fewer neurons than once thought (Morrison & Hof, 1997). Brain cells mainly lose connections rather than dying off. Researchers also found evidence that adults can grow some new neurons in a memory area of the brain called the hippocampus (Eriksson et al., 1998), though how much this happens is still debated.
"They're here on transfer from the bloodstream of the mother ... seconded to us from the maternal organism" (about the lymphocyte patrol)
TodayA baby's borrowed protection is mostly the mother's antibodies, which cross the placenta before birth and come through breast milk. The mother's immune cells (lymphocytes) don't move in and run the baby's defenses. The thymus as the place where the baby's own T-cells are trained is correct.
"Dose of Alpha Interferon to activate your bodily defenses" (to treat a cold)
TodayInterferon nose sprays were tested against colds in the mid-1980s and dropped. They caused nose irritation and bleeding and weren't practical. Interferon is not used to treat colds.
"even if we could touch the speed of light ... it would take us a quarter of a million years to cross our own galaxy"
TodayThe Milky Way's main disc is about 100,000 light-years across (some newer estimates go higher), so crossing it at light speed takes about 100,000 years. Astronomers used that figure in 1987 too.
"ten times longer to voyage to Andromeda, our nearest galactic neighbor"
TodayThe Large and Small Magellanic Clouds (about 160,000–200,000 light-years away) were known to be much closer long before 1987. The Sagittarius Dwarf Galaxy, discovered in 1994, is closer still. Andromeda is only the nearest large galaxy. Its distance (about 2.5 million light-years) does work out to roughly "ten times" the episode's own galaxy figure.
Why it was believedPopular astronomy books routinely called Andromeda "our nearest neighbour galaxy," meaning the nearest large spiral, and treated the closer Magellanic Clouds as satellites of the Milky Way rather than neighbours.