Here’s a cool science photo from the lab:

What we’re looking at is whole blood that is separating into its various components.

Blood is made up of red blood cells (RBCs), white blood cells (WBCs) and plasma. If fresh, whole blood is left sitting in a tube, the denser RBCs will slowly fall to the bottom, leaving the less dense, pale, yellowish plasma on the top. The WBCs cannot usually be seen unless separated from the red cells by centrifugation.

This particular tube was filled with Ficoll Paque, a chemical that looks and moves like water. It is used to help separate blood into its different components. Ficoll is less dense than RBCs, but more dense than plasma and some of the WBCs. Blood was very slowly and carefully pipetted on top of the Ficoll. You can see where the whole blood was layered and the Ficoll starts – it’s the place where the RBCs begin to “shower down” through the clear layer, making it look speckled. This tube was left sitting on the bench for about 15 minutes and the RBCs are collecting on the bottom of the tube:

Neat stuff, huh? Here’s what it looks like after centrifugation:

The bottom layer is RBCs, followed by a thin layer of granulocytes (the name for WBCs that have granules in their cytoplasm. The granules make them denser than the Ficoll). Above that is a wide band of the Ficoll, then a thin, translucent layer of white blood cells called mononuclear cells (the name for WBCs that have a single-lobed nucleus. MNCs don’t have granules in their cytoplasm). And at the top of the tube is plasma.

And all we have to do at this point is carefully pipet the different layers that we want separated:

From left to right: the first tube contains plasma, the second tube is comprised of three layers: Ficoll, granulocytes and RBCs, and the third tube holds our prize: the mononuclear cells.

And because I think it’s pretty, here’s one more photo of RBCs drifting down through Ficoll. These three tubes were layered one after the other. The one that was layered first has had the most time to separate, the one that was layered last has had the least: