When you have a pustule under the skin the white blood cells had to get there either locally or be carried in from somewhere else. Where is the first place you would consider? The blood, of course!
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.
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.
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.
Help for Bodily Defenses