Next, you would need to see if white cells are in the blood stream.  But how could you do that? Just for a moment, think about what happens if you are in a car and the driver turns the corner quickly. You get thrown in a direction opposite to the turn of the car. 

This is the principle behind the "centrifuge," a device that spins biological samples in a horizontal plane at high speeds (see the photo on the right). If you have tubes of fluid that contain large heavy particles or cells, and spin the tubes really fast, the heavier material will get thrown to the end of the tube. The cells, both white and red, spin down to one end. Pour off the liquid, and the cells from the blood are left.  In fact, white cells are lighter than red cells, so they spin down in a separate layer on top of  the red cells. This makes finding the white blood cells easier.

Picture courtesy of Separation Technology Inc.

Culturing White Cells
If you want to study a cluster of white blood cells to examine what they do, you can collect them from blood or flush body cavities. But it is also possible to culture them. (Learn more details about cell cultures.)

If you put bacteria in a culture of white blood cells and look at the cells under a microscope, you will see that one type of white cell actually "eats" the bacteria.  This is accomplished by the membrane folding over the bacterium to seal off the bacterium and pull it into the cell. Once inside the white blood cell, the bacterium is digested and destroyed by enzymes in the white cells.

Outside Help for Bodily Defenses
So what happens when your white blood cells cannot fight an infection? Then it is time to help your immune system with medicines and antibiotics. Sometimes the immune systems can be boosted through vaccines! How do vaccines work?

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