You conduct the following serial dilution: step 1: in tube 1, you add 100 ul of plasma to 900 ul of distilled water. step 2: in tube 2, you then take 100 ul from tube 1 and add 900 ul of distilled water. step 3: in tube 3, you then take 100 ul from tube 2 and add 900 ul of distilled water.