Fig. 4.1 is a transmission electron micrograph of the bacterium that causes cholera, Vibrio cholerae. The flagellum shown in Fig. 4.1 allows movement of the bacterium within the gut and may also function to help it to bind to an intestinal epithelial cell. The organism does not enter the cell but the toxin it releases can enter and cause damage. Large quantities of water, chloride ions and sodium ions are lost from the cell. People with symptoms of cholera have severe watery diarrhoea and as a result can become very dehydrated. [Figure 4.1]