Doctors can probably keep a person alive by giving them lots of blood, especially if the person is in a hospital, so there is blood close by.

Where would you get all the blood to keep the badly injured person alive?

Blood comes from blood donors who give a pint of blood at one time. An average person has 10 pints of blood = 5 quarts of blood. A newborn baby has only a half pint!

We also have differences in our blood, so blood from you would probably be bad for me, and vice versa. We have blood types A, AB, B, and O, and we have, or don't have, something called the Rh factor, so we're all either Rh Positive or Rh Negative. My blood is A+, so B blood or AB blood would be bad for me.

Donated blood is stored in a blood bank, and it's used for all the people who need blood.

This website tells about how much blood a person can lose: