Cragie tube
The Cragie tube or Craigie tube is a method used in microbiology for determining bacterial motility. Technique. A hollow tube with some culture medium is placed in semi-solid agar inside a bottle. A sample of the bacterium to be tested is inoculated into the medium in the hollow tube and the setup is incubated at 37 °C overnight. Observation. On examining the areas where bacterial growth has occurred there are several observations to be made: Confirmation may be obtained by subculture and retesting.