Vampires are popular right now. There have been more vampire books, movies and TV series than you could shake a cross at in the past few years.

Vampires, of course, have a number of unfortunate personality quirks–invisible in mirrors, can’t abide crosses, don’t like the sun–but we’d be willing to overlook all that if not for their dietary preferences.

Drinking blood may sound distasteful to us (at least it does to me–if it doesn’t to you, I’d just as soon not know about it), but when you take a closer look at blood, you have to think maybe the vampires have a point.

The main constituent of blood is a yellowish fluid called plasma. It’s primarily water, but also within it are proteins, sodium, potassium, calcium chloride, carbonate, bicarbonate, sugar, hormones, enzymes, fats, amino acids and waste products such as urea. Sounds almost tasty, doesn’t it? (Especially when you consider that one of the most common proteins in blood is albumin, the same protein you find in egg whites.)

Suspended within plasma are millions of cells. In fact, a cubic millimetre of human blood contains five million red blood cells, which give blood its colour. Red blood cells, tiny disks that are concave on both sides, contain a substance called hemoglobin. Ordinarily blue-red in color, hemoglobin combines with oxygen as it passes through the lungs, and turns bright red. Once the oxygen is delivered to other parts of the body, the hemoglobin turns blue-red again, and returns to the lungs for a new load.

Red blood cells are formed in the bone marrow and have an average life span of 120 days, after which time, much damaged, they’re broken down and removed from the blood by the spleen.

Besides red blood cells, there are also white ones. Their main goal in life is to protect you from infection. Some types eat bacteria; some stimulate inflammation; some become active only in response to certain infections and allergies. They’re much larger and much less common than the red cells: that cubic millimetre of blood I mentioned would contain “only” about 5,000 to 10,000 white blood cells.

Finally, after you’d counted all the red and white blood cells in that cubic millimetre of blood, you’d find that you were left with 200,000 to 300,000 “platelets,” each only about a third as large as a red blood cell. Platelets stick to the walls of blood cells wherever there’s been an injury and thus plug the hole. As they disintegrate, they release substances which, in conjunction with many other factors, cause one of the proteins present in plasma, called fibrinogen, to form a new substance, fibrin–which, as its name implies, forms millions of tiny threads. Red blood cells get caught in this mesh of fibers, and the result is a clot or (on the surface) a scab.

Although all blood is pretty much the same in its constituents, you can’t mix and match blood freely. Instead, everyone has a specific “type” of blood. The cell wall of red blood cells contain what are called “antigenic” proteins. Among these proteins are those labeled (somewhat unimaginatively) “A” and “B”. People with antigen A in their blood cells have type A blood, people with antigen B in their blood cells have type B blood, people with both have type AB blood, and people with neither have type O blood. People with type A blood will reject a transfusion of type B blood, and vice versa; people with AB blood can give and receive either type of blood, and people with type O blood can give blood to anyone, but must receive O blood in any transfusion they have to take–which would lead one to believe that vampires must all be type AB, since they can take blood from anyone.

Actually, there are many other types of antigens present in blood, as well (Rh, for example). In fact, there are so many that the specific makeup of a person’s blood is almost as distinctive as a fingerprint, without even getting into DNA.

One would think, given all this diversity in blood from individual to individual, that vampires would have become as picky as vinophiles, selecting only the best “vintages” to enjoy. Alas, it doesn’t appear to be the case. Despite their tendency to dress in formal evening dress and speak with cultured accents, vampires are willing to drink anyone’s blood indiscriminately.

That given, I have to say I think their current popularity is vastly overblown. As far as I’m concerned, vampires are nothing but a pain in the neck.

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