bio

Haematocrit

The percentage of blood volume taken up by red cells — in other words, how thick the blood is in terms of the thing that carries oxygen. A typical adult human sits near 42%. The number is a tight trade-off: more red cells means more oxygen per beat, but also thicker blood and a heart working harder to push it. Which is what makes storing red cells in the spleen and releasing them only on a dive so elegant: the animal gets dense blood exactly when it needs it, and pays the viscosity cost for none of the rest of its life.