Blood is a liquid that circulates in the body to distribute oxygen as well as the nutritive elements that are necessary for a person to stay alive.

It also permits the organism to get rid of some wastes like carbon dioxide, and diffuses hormones in it. Vertebra have a red tainted blood. Blood gets load with oxygen in the lungs where it turns into a light red, and then travels through arteries to transmit it. Its color gets dark when it loses oxygen in favor of the tissues.

When looking closely to veins, we can notice that it's blue, and when you cut yourself, the blood coming out of your wound is very red: oxygen taints the blood. The heart pumps the blood and makes it circulate through the body.

Blood, because it flows everywhere in the body, is a very precious thing: if it gets infected, it can cause death.
You can get AIDS for instance, if your blood has been mixed up with a drop of blood of somebody who was infected. In France the scandal of the “infected blood” that took place in some hospitals in the 80's is a good illustration of this.

There are 4 blood groups. You can “exchange”, “replace” or “remove” the blood of someone by an other blood sample of the same group. That is why during wars or human catastrophes, it's important for health services to have a massive stock of blood to save those who lost a too great quantity of it.

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