(a) : Cholera is an acute infection of the small intestine by the bacterium Vibrio cholerae, which causes severe vomiting and diarrhoea (known as ricewater stools) leading to dehydration. The disease is contracted from food or drinking water contaminated by faeces from a patient. The resulting dehydration and the imbalance in the concentration of body fluids can cause death within 24 hours. since, a large quantity of fluid and salts are rapidly lost through stools and vomit, therefore, the most important treatment is to replace the lost fluid and salts equally rapidly. Rapid replacement of fluid and elecrolytes is needed by oral rehydration-therapy. The electrolytes consists of Na+ ions that prevents water loss from the body.