Flow cytometer © Charité | Arne Sattler (IMAGE) Charité - Universitätsmedizin Berlin Caption An instrument known as a flow cytometer (left) allowed the researchers to demonstrate the presence of immune memory cells. © Charité | Arne Sattler Credit © Charité | Arne Sattler Usage Restrictions Image may be used to cover the accompanying press release, provided that full credit is given. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.