Tag Archives: medicine

“O, Excellent Air Bag”: Humphry Davy and Nitrous Oxide | The Public Domain Review

“O, Excellent Air Bag”: Humphry Davy and Nitrous Oxide | The Public Domain Review.

Detail from a satirical print from 1830 depicting Humphry Davy administering a dose of Laughing Gas to a woman while Count Rumford looks on (cropped out of the picture above), above the caption “Prescription for Scolding Wives” 

On Boxing Day of 1799 the twenty-year-old chemist Humphry Davy – later to become Sir Humphry, inventor of the miners’ lamp, President of the Royal Society and domineering genius of British science – stripped to the waist, placed a thermometer under his armpit and stepped into a sealed box specially designed by the engineer James Watt for the inhalation of gases, into which he requested the physician Dr. Robert Kinglake to release twenty quarts of nitrous oxide every five minutes for as long as he could retain consciousness.

The experiment was taking place in the lamp-lit laboratory of the Pneumatic Institution, an ambitious and controversial medical project where the young Davy had been taken on as laboratory assistant.

[…]

While seated in the box breathing deeply, Davy had felt the effects that had become familiar from his many previous experiments since he had first inhaled the gas earlier that year. The first signature was its curiously benign sweet taste, followed by a gentle pressure in the head as he continued to inhale. Within thirty seconds the sensation of soft, probing pressure had extended to his chest, and the tips of his fingers and toes. This was accompanied by a vibrant burst of pleasure, and a gradual change in the world around him. Objects became brighter and clearer, and the space in the cramped box seemed to expand and take on unfamiliar dimensions.

Now, under the influence of the largest dose of nitrous oxide anyone had ever taken, these effects were intensified to levels he could not have imagined. His hearing became fantastically acute, allowing him to distinguish every sound in the room and seemingly from far beyond: a vast and distant hum, perhaps the vibration of the universe itself. In his field of vision, the objects around him were teasing themselves apart into shining packets of light and energy. He was rising effortlessly into new worlds whose existence he had never suspected. Somehow, the whole experience was irresistibly funny: he had ‘a great disposition to laugh’, as all his senses competed to exercise their new-found freedom to its limit.

Now the gas took Davy to a dimension he had not previously visited. Objects became dazzling in their intensity, sounds were amplified into a cacophony that echoed through infinite space, the thrillings in his limbs seemed to effervesce and overflow; and then, suddenly, he ‘lost all connection with external things’, and entered a self-enveloping realm of the senses. Words, images and ideas jumbled together ‘in such a manner, as to produce perceptions totally novel’: he was no longer in the laboratory, but ‘in a world of newly connected and modified ideas’, where he could theorise without limits and make new discoveries at will.

After an eternity he was brought back to earth by the sensation of Dr. Kinglake removing the breathing-tube from his mouth; the outside world seeped back into his ‘semi-delirious trance’ and, as the energy returned to his limbs, he began to pace around the room. Yet a part of him was still present in the dimension of mind that had swallowed him whole, and he struggled for the words to capture it. He ‘stalked majestically’ towards Kinglake ‘with the most intense and prophetic manner’, and attempted to shape the insight that had possessed him. ‘Nothing exists but thoughts!’, he blurted. ‘The world is composed of impressions, ideas, pleasures and pains!’

[…]

Davy’s Boxing Day experiment was the culmination of a freewheeling programme of consciousness expansion into which he had co-opted some of the most remarkable figures of his day. Within days of his first self-experiment in April he had offered the gas to his friend Robert Southey, the future Poet Laureate, whose reaction was as effusive as Davy’s own: ‘the atmosphere of the highest of all possible heavens must be composed of this gas’. Southey’s ecstatic report to his brother Tom set the tone for the explorations that were to follow:

O, Tom! Such a gas has Davy discovered, the gasoeus oxyd! O, Tom! I have had some; it made me laugh and tingle in every toe and finger-tip. Davy has actually invented a new pleasure for which language has no name. O, Tom! I am going for more this evening; it makes one strong and so happy, so gloriously happy! O, excellent air-bag!

In the early summer of 1799 the nitrous oxide trials began in earnest. In the evenings, after the Pneumatic Institution had closed, the nitrate of ammoniac reaction would begin to bubble in its upstairs drawing room as Davy and Beddoes’ circle – doctors and patients, chemists, playwrights, surgeons and poets – experimented on themselves and each other. Davy was master of ceremonies and also, by his own account, inhaling the gas himself three or four times a day. The laboratory became a philosophical theatre in which the boundaries between experimenter and subject, spectator and performer were blurred to fascinating effect, and the experiment took on a life of its own.

[…]

Although the trials commenced within a medical framework, they came to focus increasingly on questions of metaphysics and, in particular, language. Davy was struck by the poverty of the ‘language of feeling’ available to his subjects, and the awkwardness of their attempts to put their experiences into words. The standard medical question ‘how do you feel?’ took on imponderable, existential dimensions. The subjects were not mentally impaired by the gas, but overstimulated beyond the reach of words themselves: as Davy himself put it, ‘I have sometimes experienced from nitrous oxide, sensations similar to no others, and they have consequently been indescribable’. James Thompson, one of the volunteers, captured the magnitude of the task precisely: ‘We must either invent new terms to express these new and peculiar sensations, or attach new ideas to old ones, before we can communicate intelligibly with each other on the operation of this extraordinary gas.’

Davy instituted a loose reporting protocol, asking every volunteer to produce a short written description of their experience. Some subjects produced answers that were oblique but highly imaginative: one of the clinic patients answered ‘how do you feel?’ with ‘I feel like the sound of a harp’. Musical analogies emerged repeatedly, attempting to catch the aural effect of ringing harmonics that often accompanies the rush of nitrous oxide intoxication. Beddoes, emerging from a deep immersion, once shouted out the single word ‘Tones!’. This resonated with images that were emerging in the poetic writings of Southey and his friend Coleridge: the Aeolian wind-harp, for example, which draws its harmonies directly from Nature herself.

Davy also took enthusiastically to experimenting on his own. On full moon nights in particular, he would wander down the Avon Gorge with a bulging green silk air-bag and notebook, inhaling the gas under the stars and scribbling snatches of poetry and philosophical insight. One one occasion he made himself conspicuous by passing out and, on recovery, was obliged to ‘make a bystander acquainted with the pleasure I experienced by laughing and stomping’. He noted an element of compulsion in his use, confessing that ‘the desire to breathe the gas is awakened in me by the sight of a person breathing, or even by that of an air-bag or air-holder’. He began to push his experiments into more dangerous territory. He tried the gas in combination with different stimulants, drinking a bottle of wine methodically in eight minutes flat and then inhaling so much gas he passed out for two hours. He also experimented with nitric oxide, which turned to nitric acid in his mouth, burning his tongue and palate, and with ‘hydrocarbonate’ – hydrogen and carbon dioxide – which left him comatose, the air-bag fortunately falling from his lips. On recovering, he ‘faintly articulated: ‘I do not think I shall die’’.

By the end of the summer, the energy of the trials was dissipating: for most of the volunteers, the novelty of the experience wore off after a few sessions. Davy’s experiments became increasingly solitary, partially focused on resolving technical questions such as how much gas was absorbed into the bloodstream and whether it should be classified as a stimulant or a sedative, but also searching for a framework – scientific, poetic or philosophical – to account for its effects. In this he was assisted by the arrival of Samuel Taylor Coleridge, who returned to Bristol in October from an extended visit to Germany.

Coleridge and Davy’s friendship would evolve and endure through the many phases of their future careers; but it began with a green silk bag of nitrous oxide. As Coleridge inhaled and felt its warmth diffusing through his body, he did not reach for extravagant metaphors but stated precisely that the sensation resembled ‘that which I remember once to have experienced after returning from the snow into a warm room’. In a subsequent trial he ‘was more violently acted upon’ and confessed that ‘towards the last I could not avoid, nor felt any wish to avoid, beating the ground with my feet; and after the mouthpiece was removed, I remained for a few seconds motionless, in great ecstacy.’

Coleridge was captivated by the young chemist: ‘Every subject in Davy’s mind’, he wrote, ‘has the principle of vitality. Living thoughts spring up like turf under his feet.’. Davy was equally swept up in his new friend’s expansive vision, which he felt had the power to transform science as well as poetry. Coleridge had returned from Germany in thrall to the new idealistic turn in its philosophy: the theories of Immanuel Kant and the emerging ‘Naturphilosophie’, according to which the human mind was the ultimate source of our reality, and the material world only an illusion projected by it. The dissociative effects of nitrous oxide, in which consciousness seemed to escape and transcend the physical body, made compelling sense of this insight; and Davy’s climactic revelation that ‘nothing exists but thoughts’ would echo it through the century to come.

Despite their chaotic melange of hedonism, heroism, poetry and philosophy, Davy’s report on the trials, when it emerged, made a coherent and powerful case for their scientific worth. After his climactic Boxing Day experiment, he began writing at top speed and by Easter of 1800 had produced a 580-page monograph on the new gas and its effects. Under the businesslike title Researches, Chemical and Philosophical; chiefly concerning Nitrous Oxide, or dephlogisticated nitrous air, and its Respiration, he described the synthesis of the gas, its effect on animals and animal tissue and, in an unprecedented final section, the descriptions of the subjective effects of nitrous oxide intoxication on himself and two dozen further subjects, including Beddoes, Coleridge and Southey.

Davy’s report combined two mutually unintelligible languages – organic chemistry and subjective experience – to create a groundbreaking hybrid, a poetic science that could encompass both the chemical causes of the experience and its philosophical consequences. By the end of 1800 his reputation had spread through Britain’s scientific community and beyond, and he was already preparing to leave Bristol for a post at the Royal Institution, at the centre of the London network of power and privilege through which he rose to prominence with breathtaking speed. His dazzling lectures there would make him the public face of science for the coming generation, and the nitrous oxide experiments would become an emblem of the heroic commitment to discovery that it would demand of its practitioners in the new century.

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What’s Up With That: Why Toothpaste and Pine Nuts Can Make Some Foods Taste Disgusting | Science | WIRED

What’s Up With That: Why Toothpaste and Pine Nuts Can Make Some Foods Taste Disgusting | Science | WIRED.

Miracle fruit.

What’s up with things that alter our sense of taste? Why does orange juice taste revolting if you drink it too soon after brushing your teeth? Or how about sipping white wine after eating artichokes? For some people, that makes the wine taste weirdly sweet. Even more bizarre are the berries of the so-called miracle fruit, Synsepalum dulcificum, which make even sour lemons taste sweet.

[…]

Some scientists are even trying to exploit such taste oddities to make healthier foods that trick the brain into thinking it’s getting something more delicious than it really is. Linda Bartoshuk, an experimental psychologist at the University of Florida, and her team have been investigating naturally occurring volatile compounds in fruit that make foods taste sweeter or saltier by influencing how the sense of smell and the sense of taste interact in the brain. “Those interactions are much more interesting than we ever dreamed, and they may lead to new ways to add sweet and salty taste to foods without actually adding sugar or salt,” Bartoshuk said.

[…]

Miracle fruit

In tropical West Africa, berries of the shrub Synsepalum dulcificum (photo above) were traditionally used to sweeten palm wine and make stale bread more palatable. More recently they’ve been used in Queens at “flavor tripping parties” where people do vinegar shots and say things like “Doughnut glaze, hot doughnut glaze!” after someone puts Tabasco sauce on their tongue.

The secret to this freaky fruit is a chemical called miraculin. It’s a protein with sugars attached to it. Normally these sugars don’t activate the sweet receptors on the tongue; they are like a key that doesn’t quite fit the lock. That’s why miracle berries on their own don’t taste particularly sweet. But in the presence of vinegar, lemon juice, or other acids, the molecule changes shape in a way that allows it to fit the sweet receptors and trigger the perception of sweetness. (It’s also possible the receptors themselves change shape—scientists haven’t yet worked out all the details). “It adds an intense sweet taste and in turn suppresses the perception of sour in the brain,” Bartoshuk says. The effect can last an hour or two—plenty of time to eat enough strange things to give yourself a serious bellyache.

[…]

Artichokes

Artichokes are notoriously hard to pair with wine. You’d think they’d go well with whites, but for many people they make wine (or other beverages) taste unusually sweet. Whether that’s good or bad depends on your perspective.

[…]

In a 1972 paper in Science, Bartoshuk identified the compound responsible for this effect. It’s called cynarin, and unlike miraculin, it doesn’t require acid to work its magic. It makes even water taste sweet. Again, the cellular-molecular details are a bit murky, but Bartoshuk says what seems to happen is that cynarin temporarily inhibits sweet receptors. Then, when you wash off the cynarin by taking a drink, the receptors bounce back and fire, sending a signal to the brain that they’ve detected something sweet.

[…]

Orange juice and toothpaste

Scrubbing your teeth before breakfast is a bad idea for lots of reasons, but if your breakfast includes orange juice it’s even worse. The normally delicious sweet-tart juice will taste bitter and awful.

The chief culprit is probably sodium lauryl sulfate, a detergent added to many toothpastes to increase foaming and make your mouth feel clean. “The detergent tends to reduce your ability to taste sweet, and whenever you encounter any type of acid, there’s a bitter taste that’s very unpleasant,” Bartoshuk said. The most likely explanation at the molecular level is that the detergent alters the responsiveness of taste receptors by disrupting the fatty membranes that enclose each cell (much as dish detergent would break up the oily layer atop a sink filled with dirty dishwater).

Pine nuts

What do you do when one of your favorite ingredients suddenly turns against you? For some people, that’s what happened with the emergence of “pine mouth,” a mysterious syndrome in which eating pine nuts causes an unpleasant bitter or metallic taste that starts a day or two later and can last for a week or more.

[…]

One species in particular, Pinus armandii, a white pine from China, has been linked to “pine mouth.” According to one report, a poor pine nut harvest in 2010 resulted in Chinese imports accounting for up to 80 percent of pine nuts sold in the U.S. that year, coinciding with an uptick in reports of pine mouth.

[…]

The culprit could also be a contaminant or something used to process the nuts, Pelchat adds.

[…]

So far, scientists can only guess at the mechanism, and some of those guesses are kind of creepy. One idea, suggested by Bartoshuk, is that the metallic taste is a phantom caused by nerve damage, essentially a taste equivalent of the phantom limb experience of some amputees. The nerves that carry taste signals to the brain inhibit one another, she explains. Damaging one nerve releases inhibition on the others and can cause phantom taste sensations. Indeed, she notes, a metallic taste is a common side effect of damage to the chorda tympani nerve. This nerve passes through the middle ear on its way from the tongue to the brain, and it can be damaged by surgery or infections of the middle ear. So far, though, no neurotoxic agent has been identified in pine nuts.

Another idea, proposed by Gregory Möller, a Professor of Environmental Chemistry and Toxicology at the University of Idaho, is that the metallic taste arises, at least in part, not in people’s mouths, but in their guts. The small intestines have bitter receptors similar to those on the taste buds, and some pine nuts may contain compounds that either stimulate those receptors directly or by prompting the production of bile,

[…]

We smell things in the air around us by sniffing with the nose. But when we eat, there’s an additional pathway involved. “When you put food in your mouth and chew it up, the aroma from the food is forced up behind your palate and into your nasal cavity from the back,” Bartoshuk explains. “That’s called retronasal olfaction.” She thinks retronasal olfaction has a bigger impact on our perception of taste than the regular old route through the nose.

Her group has been studying this effect in tomatoes and strawberries. They’ve found, for example, that people perceive tomatoes of one variety, Matina, as twice as sweet as another, Yellow Jelly Bean, even though the sugar content of Matinas is actually lower. The reason, Bartoshuk says, is the mix of volatile compounds in each strain. She says her group has identified more than 80 volatile compounds that alter the perception of sweetness and saltiness via retronasal olfaction. Most have only modest effects on their own, but they have much stronger effects when combined. Bartoshuk thinks it should be possible to exploit those effects to create healthy foods that taste better.

Our brains evolved to crave sweet, salty and fatty foods because our ancestors needed to gobble up energy and nutrient-rich foods when they found them, Bartoshuk says. That’s why it’s so hard to change people’s behavior with education alone. ‘If we want people to get healthier, we can either keep trying to educate them, or we can find ways to make food taste the way evolution makes us want it to taste,” she said.

 

What’s Up With That: Why Does Sleeping In Just Make Me More Tired? | Science | WIRED

What’s Up With That: Why Does Sleeping In Just Make Me More Tired? | Science | WIRED.

Oversleeping feels so much like a hangover that scientists call it sleep drunkenness. But, unlike the brute force neurological damage caused by alcohol, your misguided attempt to stock up on rest makes you feel sluggish by confusing the part of your brain that controls your body’s daily cycle.

Your internal rhythms are set by your circadian pacemaker, a group of cells clustered in the hypothalamus, a primitive little part of the brain that also controls hunger, thirst, and sweat. Primarily triggered by light signals from your eye, the pacemaker figures out when it’s morning and sends out chemical messages keeping the rest of the cells in your body on the same clock.

Scientists believe that the pacemaker evolved to tell the cells in our bodies how to regulate their energy on a daily basis. When you sleep too much, you’re throwing off that biological clock, and it starts telling the cells a different story than what they’re actually experiencing, inducing a sense of fatigue. You might be crawling out of bed at 11am, but your cells started using their energy cycle at seven. This is similar to how jet lag works.

[…]

If you’re oversleeping on the regular, you could be putting yourself at risk for diabetes, heart disease, and obesity. Harvard’s massive Nurses Health Study found that people who slept 9 to 11 hours a night developed memory problems and were more likely to develop heart disease than people who slept a solid eight. (Undersleepers are at an even bigger risk).

[…]

When you go to bed, your body cycles between different sleep stages. Your muscles, bones, and other tissues do their repair work during deep sleep, before you enter REM. However, if your bed or bedroom is uncomfortable—too hot or cold, messy, or lumpy—your body will spend more time in light, superficial sleep. Craving rest, you’ll sleep longer.

Tracks of My Tears: Design Observer

Tracks of My Tears: Design Observer.


Tears of ending and beginning, Rose-Lynn Fisher ©2013


Tears of grief, Rose-Lynn Fisher ©2013


Onion Tears, Rose-Lynn Fisher ©2013


Tears of possibility and hope, Rose-Lynn Fisher ©2013

1.
You can’t be impersonal when it comes to tears. They are by their nature intimate, as unique as the patterns of a snowflake or the swirl of the skin on your thumb. As Rose-Lynn Fisher’s photographs make clear, your tears are yours alone and each one is different.

2.
Fisher used a standard light Zeiss microscope and a digital microscopy camera to make these images. She photographed over one hundred tears in her quest to discover their distinctive formations. She worked like a surveyor mapping the topography of a new land. But rather than surveying the mountains and valleys of an external landscape her explorations are of the proteins, hormones and minerals of an inner world.

[…]

4.
Medieval theologians grouped tears into four different types:

Tears of contrition
Tears of sorrow
Tears of gladness
Tears of grace

Twenty first century scientists have identified three different types of tears:

Basal tears which moisten the eye
Reflex tears caused by an outside irritant, like a stray eyelash or chopping an onion or a smoky wind.
Emotional tears that are triggered by sadness, grief, frustration, ecstasy, mourning, or loss.

5.
Emotional tears are packed full of hormones, up to 25 percent more than reflex tears. In Fisher’s photographs a tear from chopping an onion looks very different than tear of possibility and hope.

Emotional tears contain the Adrenocorticotropic hormone, which signifies high levels of stress, leucine-enkephalin, an endorphin that reduces pain, and prolactin, a hormone that triggers breast milk production (and found in higher levels in woman’s tears).

William Frey, of the St. Paul Ramsey Center in Minnesota, discovered that tears contain thirty times more manganese than blood, and manganese is a mineral that effects mood; it’s linked to depression. All of these elements build up in the body during times of stress, and crying is a way for the body to release them. A good cry slows your heart rate; it helps you to return to an emotional equilibrium.

In other words, you can cry yourself back to mental health.

[…]

7.
Samuel Beckett once said “my words are my tears.” But the opposite is also true: tears are your words. Tears are a language, a means of communication. Overwhelmed by emotion, babies cry out in need, having no other way to express their feelings. A lover, not getting the response that she craves, cries in frustration: tears of distress as a plea for emotional connection. Tears flow when mere words don’t.

8.
Rose-Lynn Fisher writes that “the topography of tears is a momentary landscape.” Isn’t it strange that a tear, which is transitory and fragile, can look just like the topography of an actual landscape: the solid stuff of soil, water, stone and vegetation, and which has been in formation for thousands of years? How is it that the microcosm of the tear mirrors the macrocosm of the earth?

9.
In Lewis Carroll’s Alice in Wonderland, Alice cries when she grows to be nine feet tall, and she can’t get into the garden. She reprimands herself just like a parent scolding a child: “You ought to be ashamed of yourself, a great girl like you to go on crying in this way! Stop it this moment, I tell you!” But she can’t stop and she cries gallons of tears that form a large pool around her that is four inches deep.

And then Alice loses her sense of self. “Who in the world am I?” she asks, like a person experiencing a breakdown. She becomes more and more confused, imagines herself as someone else, and yearns to be told who she is really is (“If I like that person I’ll come up”). She then bursts into tears again when she realizes how lonely she feels.

And then Alice shrinks and she finds herself swimming in the pool of her own tears, the same tears that she shed when she was nine feet tall. She meets a mouse, and later a Duck, a Dodo, a Lory and an Eaglet, and they all fall into the pool as well, and then they all climb ashore, and are saved.

Alice’s tears of distress become her means of salvation.

Why do we have blood types? | Mosaic

Why do we have blood types? | Mosaic.

Blood groups illustration by Elena Boils

Why do 40 per cent of Caucasians have type A blood, while only 27 per cent of Asians do? Where do different blood types come from, and what do they do? To get some answers, I went to the experts – to haematologists, geneticists, evolutionary biologists, virologists and nutrition scientists.

In 1900 the Austrian physician Karl Landsteiner first discovered blood types, winning the Nobel Prize in Physiology or Medicine for his research in 1930. Since then scientists have developed ever more powerful tools for probing the biology of blood types. They’ve found some intriguing clues about them – tracing their deep ancestry, for example, and detecting influences of blood types on our health. And yet I found that in many ways blood types remain strangely mysterious. Scientists have yet to come up with a good explanation for their very existence.

“Isn’t it amazing?” says Ajit Varki, a biologist at the University of California, San Diego. “Almost a hundred years after the Nobel Prize was awarded for this discovery, we still don’t know exactly what they’re for.”

[…]

Renaissance doctors mused about what would happen if they put blood into the veins of their patients. Some thought that it could be a treatment for all manner of ailments, even insanity. Finally, in the 1600s, a few doctors tested out the idea, with disastrous results. A French doctor injected calf’s blood into a madman, who promptly started to sweat and vomit and produce urine the colour of chimney soot. After another transfusion the man died.

Such calamities gave transfusions a bad reputation for 150 years. Even in the 19th century only a few doctors dared try out the procedure. One of them was a British physician named James Blundell. Like other physicians of his day, he watched many of his female patients die from bleeding during childbirth. After the death of one patient in 1817, he found he couldn’t resign himself to the way things were.

[…]

The first clues as to why the transfusions of the early 19th century had failed were clumps of blood. When scientists in the late 1800s mixed blood from different people in test tubes, they noticed that sometimes the red blood cells stuck together. But because the blood generally came from sick patients, scientists dismissed the clumping as some sort of pathology not worth investigating. Nobody bothered to see if the blood of healthy people clumped, until Karl Landsteiner wondered what would happen. Immediately, he could see that mixtures of healthy blood sometimes clumped too.

[…]

Landsteiner found that the clumping occurred only if he mixed certain people’s blood together. By working through all the combinations, he sorted his subjects into three groups. He gave them the entirely arbitrary names of A, B and C. (Later on C was renamed O, and a few years later other researchers discovered the AB group. By the middle of the 20th century the American researcher Philip Levine had discovered another way to categorise blood, based on whether it had the Rh blood factor. A plus or minus sign at the end of Landsteiner’s letters indicates whether a person has the factor or not.)

[…]

The blood from people in group O was different. When Landsteiner mixed either A or B red blood cells with O plasma, the cells clumped. But he could add A or B plasma to O red blood cells without any clumping.

It’s this clumping that makes blood transfusions so potentially dangerous. If a doctor accidentally injected type B blood into my arm, my body would become loaded with tiny clots. They would disrupt my circulation and cause me to start bleeding massively, struggle for breath and potentially die. But if I received either type A or type O blood, I would be fine.

[…]

Each person’s immune system becomes familiar with his or her own blood type. If people receive a transfusion of the wrong type of blood, however, their immune system responds with a furious attack, as if the blood were an invader. The exception to this rule is type O blood. It only has H antigens, which are present in the other blood types too. To a person with type A or type B, it seems familiar. That familiarity makes people with type O blood universal donors, and their blood especially valuable to blood centres.

[…]

The most striking demonstration of our ignorance about the benefit of blood types came to light in Bombay in 1952. Doctors discovered that a handful of patients had no ABO blood type at all – not A, not B, not AB, not O. If A and B are two-storey buildings, and O is a one-storey ranch house, then these Bombay patients had only an empty lot.

Since its discovery this condition – called the Bombay phenotype – has turned up in other people, although it remains exceedingly rare. And as far as scientists can tell, there’s no harm that comes from it. The only known medical risk it presents comes when it’s time for a blood transfusion. Those with the Bombay phenotype can only accept blood from other people with the same condition. Even blood type O, supposedly the universal blood type, can kill them.

The Bombay phenotype proves that there’s no immediate life-or-death advantage to having ABO blood types. Some scientists think that the explanation for blood types may lie in their variation. That’s because different blood types may protect us from different diseases.