This image depicts a Centers for Disease Control and Prevention (CDC) scientist, who was quantitatively measuring the polio antibodies present in someone’s blood. Each of these purple colored plates tests four serum samples, for antibodies against a single poliovirus serotype. This scientist was using a robotic plate stacker to collect data from the stained serology plates. This test allows one to determine how many antibodies are present, by using the color purple. A purple well means the antibodies in the serum sample prevented poliovirus from infecting and killing cells within the cell culture. If the well shows up as colorless, this means that antibodies did not block the virus from infecting and killing the cells. The presence of antibodies in a serum sample, capable of blocking poliovirus from infecting cells, means that the person, from whom the sample was extracted, is protected from developing paralysis after exposure to poliovirus.