The round objects are red bloods cells, the larger blobby cell is the neutrophil (white blood cell) and the tiny circles are bacteria (Staphyloccocus aureus). Although they appear to be actively evading the neutrophil, the bacteria are really bouncing around randomly. They emit a chemical attractant that causes the neutrophil to chase them.
This video was taken in the 1950's by David Rogers at Vanderbilt University. More recently, it was set to music by Youtubian whyimwonderwoman.
Hat tip: Respectful Insolence.