Stomach

The stomach is a muscular, hollow, dilated part of the digestion system which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing).
The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines.

Peritonitis

Peritonitis is a bacterial or fungal infection of the peritoneum, a silk-like membrane that lines your inner abdominal wall and covers the organs within your abdomen. Peritonitis can result from any rupture (perforation) in your abdomen, or as a complication of other medical conditions. Peritonitis requires prompt medical attention to fight the infection and, if necessary, to treat any underlying medical conditions. Treatment of peritonitis usually involves antibiotics and, in some cases, surgery. Left untreated, peritonitis can lead to severe, potentially life-threatening infection throughout your body.