Short answers, pulled from the story.
Blood is composed of blood cells suspended in plasma. Plasma constitutes about 55% of blood and is mostly water, 92% by volume, while the cells are mainly red blood cells, white blood cells, and, in mammals, platelets. By volume, red blood cells make up about 45% of whole blood and white cells about 0.7%.
The average adult has a blood volume of roughly 5 liters, or 1.3 gallons. Blood accounts for 7% of human body weight and has an average density around 1060 kilograms per cubic meter, very close to pure water.
Hemoglobin is the principal determinant of the color of blood. Blood is bright red when its hemoglobin is oxygenated and a darker shade of red when it is deoxygenated, because the spectrum of light absorbed by hemoglobin differs between the two states.
Karl Landsteiner discovered the ABO blood group system in 1900. Jan Jansky is credited with the first classification of blood into the four types A, B, AB, and O in 1907, and the Rhesus factor was discovered in 1937.
About 98.5% of the oxygen in arterial blood is chemically combined with hemoglobin, while about 1.5% is physically dissolved in the blood's other liquids. Hemoglobin increases the total blood oxygen capacity seventyfold compared with relying on oxygen's solubility alone.
Blood is given particular emphasis in the Islamic, Jewish, and Christian religions because Leviticus 17:11 says the life of a creature is in the blood. This grounds dietary laws forbidding the consumption of blood, and in some Christian churches the consecrated Eucharistic wine is taught to become the blood of Jesus.