DECOMPOSITION It involves two processes: (1) Autolysis and (2) Putrefaction. Autolysis: Autolysis is self-digestion of tissues Putrefaction: The disintegration of body tissues after death is known as decomposition. The terms decomposition and putrefaction are used as synonyms. Putrefaction usually follows the disappearance of rigor mois. During hot season, it may commence before rigor mois has completely disappeared from the lower extremities. Mechanism: Organisms enter the tissues sholy after death, mainly from the alimentary canal, and less often through the respiratory tract or through an external skin wound. Multiplication of bacteria begins within 4 hours and peak is reached within 24-30 hours. The fall in the oxygen concentration in the tissues and rise in hydrogen ion concentration after death our bacterial growth and spread throughout the body. Because the protective agencies of the body are absent, the bacteria spread through the blood vessels using the proteins and carbohydrates of the blood as culture media. The chief destructive bacterial agent is Cl. welchii, which causes marked haemolysis, liquefaction of postmoem clots and of fresh thrombi and emboli, disintegration of tissue and gas formation in blood vessels and tissue spaces. Bacteria produce a large variety of enzymes and these breakdown the various tissues of the body. Lecithinase produced by Cl. welchii is most impoant. This hydrolyses the lecithin which is present in all cell membranes including blood cells*, and is responsible for the postmoem haemolysis of blood. Features: The characteristic features of putrefaction are: (1) changes in the colour of the tissues, (2) the evolution of gases in the tissues, and (3) the liquefaction of tissues. The first external sign of putrefaction in a body lying in air is usually a greenish discolouration of the skin over the region of the caecum, which lies fairly superficially, and where the contents of the bowel are more fluid and full of bacteria. Internally, this is seen on the undersurface of the liver, anterior peritoneal surface of right lobe of liver and adipose tissue around gallbladder, where that organ is in contact with the hepatic flexure and transverse colon. The colour results from the conversion of haemoglobin of blood into sulphmethaemoglobin by the hydrogen sulphide formed in the large intestine and escaping into the surrounding tissues. The colour appears in 12 to 18 hours in summer and in one to two days in winter. Ref:- k s narayan reddy; pg num:-164,165