Barium can be used together with x-rays to study the mucosal lining (inner surface) of the digestive tract. It is a contrast medium that coats the mucosal surface and render the x-ray less penetrable thus appears as a white lining on the x-ray of the digestive tract. Irregularities on the surface such as ulcers, tumors and polyps, as well as, narrowing of the caliber of the digestive tract can be made out. Air, which is introduced either as an effervescent tablet or pumped in through a tube, allows a better visualization of the surface. Patients need to fast for the upper digestive tract examinations, and laxatives have to be given to cleanse the colon before the lower tract examination. The major disadvantages of barium studies when compared with endoscopy are those of accuracy, the inability to obtain a biopsy (a tissue sample) from the abnormal area, if found during examination, and its inability to afford immediate treatment e.g. removal of a polyp or to treat a bleeding ulcer. The barium swallow is used to examine the pharynx and oesophagus. Liquid barium is swallowed down, and x-rays are taken while the barium outlines the oesophagus. This test is often used for symptoms of dysphagia - food getting stuck during swallowing. It is also used when there is pain thought to arise from the oesophagus, or to look for a foreign body e.g. fish bone, that may have embedded itself in the oesophagus. Abnormally large veins in the oesophagus called varices may also be seen during the barium swallow. When the problem is thought to reside in the stomach, a barium meal may be the x-ray test ordered. The mucosal surface of the stomach being outlined by the layer of barium coating is shown on the x-ray, especially when it is distended by gas. Ulcers, tumors, and narrowed openings can be detected. If significant amounts of barium reflux back into the oesophagus, the patient could be suffering from esophageal reflux. Should part of the stomach sit up inside the chest, a hiatus hernia could be seen on the barium meal. Normally, the barium meal test ends after the barium reaches the second to third part of the duodenum. A small bowel series (also known as the follow through) is the continuation of the barium meal, with a view to studying the small intestines. While the barium flows through the small intestines and reaches the colon, the abdomen may be massaged and the patient repositioned several times, so that the mucosal pattern and caliber of the small intestine is examined in detail. Polyps, ulcers, strictures, diverticuli and tumors are looked for. The time taken for the barium to complete this journey is also indicative of the motility of the intestines. Occasionally another test called enteroclysis (small bowel enema), which is a variation of the small bowel series may be used. The barium is pumped into the jejunum via a tube placed through the nose, stomach and duodenum. It is more uncomfortable, but better x-ray pictures may be obtained. In the case of the colon, barium and air is introduced by pumping it through a tube via the anus. This is called the barium enema. The patient has x-rays taken while tilted in many directions, as this enables the barium to flow backwards to outline the entire length of the colon. Lesions (abnormalities) similar to the ones above can be detected. In view of the difficulty associated with keeping the barium inside the colon and the difficult positions needed during the tilting, this test is usually not suitable in the elderly.