My name is Rose George, and I'm an author and journalist
and I'm fascinated by blood, and here's why.
We are stardust and seawater.
The iron in our blood comes from the death of supernovas -
like all iron on our planet -
and it contains salt and water, like the oceans we came from.
The circulatory system of veins, arteries, and capillaries
is about 100,000 kilometres long - twice the circumference of the Earth.
Most of that is the capillaries - tiny blood vessels and hollow ways
that reach nearly every cell in the body.
You may know that your blood is...
but there are other types you might not have heard of -
including
and the epically named...
Animals have blood types too, dogs have eight,
cats have three.
When humans first tried to transfer blood between bodies,
they used the blood of a lamb and a calf.
Now, we stick to carefully chosen human blood.
Blood transfusion is so common, every three seconds worldwide
someone receives a stranger's blood.
We don't have the same supply sloshing around our veins
all our lives.
Our blood is in a constant state of decay and renewal.
Red blood cells live in our body for about 143 days.
Decanted into a blood bag,
they have a shelf life of between 35 and 49 days.
Blood lasts longer than milk, but not as long as cheese.
In a resting human, the heart pumps a litre of blood every 10 seconds,
and it beats on average 75 times a minute.
A blue whale's heart, the size of a small car,
beats five times a minute, and less on deep dives.
A shrew's, a thousand times a minute.
The average human contains eight to twelve pints of blood,
but can usually survive losing up to 40%.
After that point, the organs begin to shut down
because they are not being fed oxygen by blood.
Blood has always been thought powerful.
The mythical figure of Medusa
symbolised human fear and awe of blood.
Blood from the right side of her body was fatal,
while that from the left side could restore life.
We may not believe in Greek myths anymore,
but the force of blood remains in language.
Blood is essential for human life,
but there is plenty we don't know about this exceptional substance.
Scientists can now grow red blood cells in the lab,
but they are extremely expensive.
For now, the only way to get this life-saving, life-enhancing liquid
is out of the goodness of someone's heart,
and the veins in their arm.