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How is Blood Type Determined?

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Last week’s season finale of The Knick saw the cocaine-addicted Dr. John Thackery try to solve the mystery of blood types before another doctor could do it. I won’t spoil what happened for you here, but the episode did make me wonder: How are blood types determined these days?

First, some basics about your blood. There are 4 to 6 liters of it in the average adult body, and all blood is made of the same essential elements: Red blood cells, which, using a protein called hemoglobin, transport oxygen and remove carbon dioxide; white blood cells, which fight infection; platelets, which help blood clot; and plasma, which contains salts and proteins and is the fluid that transports the other components.

But though all blood is made of essentially the same stuff, there are some differences—which caused problems for patients receiving blood transfusions before 1901, when Austrian Karl Landsteiner discovered human blood groups (this earned him the Nobel Prize in 1930). According to the Nobel Prize website, mixing two different blood types “can lead to blood clumping or agglutination. The clumped red cells can crack and cause toxic reactions.” The problem is the immune system. Most blood contains antigens, which are substances that make the body produce antibodies. Usually antibodies are for things like viruses and bacteria, but in a wrong transfusion the immune system sees the new blood as an intruder that must be destroyed. Which can prove fatal.

Two blood group systems are important for transfusions, and Landsteiner was involved in the discovery of both. In the ABO Grouping System, there are four types of blood: Type A, Type B, Type AB, and Type O, which are determined by the presence or absence of certain antigens on the surface of red blood cells. According to the American Red Cross,

Group A – has only the A antigen on red cells (and B antibody in the plasma)
Group B – has only the B antigen on red cells (and A antibody in the plasma)
Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)

Immune systems are adapted to individual blood types. If someone from Group B donated blood to someone from Group A, the B antibodies would recognize the B antigen as a threat and blood clumping would occur. But if someone from Group B donated to someone in Group AB there are no B antibodies, so the immune system doesn’t recognize the intruder.

Additionally, there’s the Rh factor blood grouping system. The Rh antigen is either present (+) or absent (-) in the blood. Typically, Rh negative blood goes to patients without the antigen, and Rh positive blood goes to patients who have the antigen—but an Rh positive patient can receive Rh negative blood without any problems.

So there are eight blood groups you can belong to: A Rh+, A Rh-, B Rh+, B Rh-, AB Rh+, AB Rh-, O Rh+, and O Rh -, although doctors usually leave out the Rh and just say + or -. What blood type a person ends up with is determined by genetics.

To figure out a person’s blood type, doctors can use two methods: ABO Typing or back typing. In ABO typing, doctors take blood and mix it with serums containing the antibodies in Type A and B blood. According to the National Institutes of Health,

If your blood cells stick together when mixed with:

Anti-A serum, you have type A blood
Anti-B serum, you have type B blood
Both anti-A and anti-B serums, you have type AB blood
If your blood cells do not stick together when anti-A and anti-B are added, you have type O blood.

In back testing, known A and B cells are added to samples. If the blood clumps together only when B cells are added, the donor has type A blood. If the blood clumps together when A cells are added, the donor is Type B. And if the blood clumps when either type of cell is added, the donor has Type O blood. No clumping indicates Type AB.

Rh is determined by mixing in anti-Rh serum. If the blood cells stick together when the serum is added, the person is Rh positive; if not, the person is Rh negative.

Fun fact: Everyone knows that people with O Rh- blood are universal donors, but there are also universal receivers—they have the AB Rh+ blood type. The opposite is true for plasma donors. O plasma contains antibodies for both A and B, so it would cause an immune reaction in any other blood type. AB plasma doesn’t have either antibody, so it’s universal.

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Big Questions
Where Should You Place the Apostrophe in President's Day?
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Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


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Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
How Do You Steer a Bobsled?
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Quinn Rooney, Getty Images

Now that the Olympics are well underway, you might have developed a few questions about the games' equipment. For example: How does one steer a bobsled? Let's take a crack at answering this pressing query.

How do you steer a bobsled?

Bobsled teams careen down an icy, curving track at up to 90 miles per hour, so steering is no small concern. Drivers steer their sleds just like you steered your childhood sleds—by manipulating a pair of ropes connected to the sled's steel runners. The driver also gets help from the rest of the crew members, who shift their weight to aid with the steering.

Why do speed skaters wear glasses?

speed-skating

Speed skaters can fly around the ice at upwards of 40 mph, so those sunglasses-type specs they wear aren't merely ornamental. At such high speeds, it's not very pleasant to have wind blowing in your eyes; it's particularly nightmarish if the breeze is drying out your contact lenses. On top of that, there's all sorts of ice and debris flying around on a speed skating track that could send you on a fast trip to the ophthalmologist.

Some skaters also say the glasses help them see the track. American skater Ryan Bedford recently told the Saginaw News that his tinted shades help him focus on the track and filter out distracting lights and camera flashes from the crowd.

What kind of heat are the biathletes packing?

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As you might guess, there are fairly strict rules governing what sort of rifles biathletes carry on the course. They are equipped with guns chambered for .22 LR ammunition. The gun must weigh at least 3.5 kilograms without its magazines and ammunition, and the rifle has to have a bolt action or a straight-pull bolt rather than firing automatically or semi-automatically.

Is a curling stone really made of stone?

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You bet it is, and it's not just any old stone, either. Curling enthusiasts swear by a very specific type of granite called ailsite that is only found on the Scottish island of Ailsa Craig. Ailsite supposedly absorbs less water than other types of stone, so they last longer than their competitors.

Ailsa Craig is now a wildlife sanctuary, so no new ailsite has been quarried since 2002. As a result, curling stones are incredibly expensive. Kays of Scotland, which has made the stones for every Olympics in which curling has been an official event, gets prices upwards of $1,500 per stone.

What about the brooms?

The earliest curling brooms were actual brooms made of wood with straw heads. Modern brooms, though, are a bit more technologically advanced. The handles are usually made of carbon fiber, and the heads can be made of synthetic materials or natural hair from horses or hogs. Synthetic materials tend to be more common now because they pull all of the debris off of the ice and don't drop the occasional stray bristle like a natural hair broom might.

What are the ski jumpers wearing?

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It may look like a ski jumper can pull on any old form-fitting bodysuit and hit the mountain, but things are a bit more complicated than that. Their suits have to be made of a spongy material and can't be thicker than five millimeters. Additionally, the suits must allow a certain amount of air to pass through them; jumpers wearing suits without sufficient air permeability are disqualified. (This rule keeps jumpers from wearing suits that could unfairly act as airfoils.) These rules are seriously enforced, too; Norwegian skier Sigurd Petterson found himself DQed at the 2006 Torino Games due to improper air permeability.

Those aren't the only concerns, though. In 2010, judges disqualified Italian jumper Roberto Dellasega because his suit was too baggy.

What's up with the short track speed skaters' gloves?

Gloves
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If you watch a bit of short track speed skating, the need for gloves quickly becomes apparent. When the skaters go to make passes or careen around a turn, they need the gloves to keep from cutting their hands due to incidental contact with other skaters' blades.

There's more to the gloves than just safety, though. Since the skaters' hands often touch the ice during turns, they need hard fingertip coverings that won't add friction and slow them down. The tips can be made of any material as long as it's hard and smooth, but you've got to give American skater Apolo Ohno some style points for the gold-tipped left glove he broke out in 2010.

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