What is that white-vanilla entry that are within the theory test tubes when the technician draws blood from us?

The other day I go to draw blood and I see all of the trial tubes have a white-vanilla piece on the bottom. I have never asked the individual who drew my blood, since that question didn't come to me until very soon.
What is it?
What purpose does it serve?What is that white-vanilla entry that are within the theory test tubes when the technician draws blood from us?
There is different substances in different tubes.
Each substance any stops blood from clotting or causes the blood to clot and so the plasma and red blood cell can be separated easily.
That "vanilla white thing" prevents the blood from coagulating (clotting).
Most theory test tubes have some type of stabilizer, depending on what the test is.
That stuff you saw is a serum separator. The tube is placed within a machine and spun really hasty; then the plasma section of your blood is separated from the blood cells.
IT is blood plasma