PUTREFACTION OR DECOMPOSITION 139 fig. 36.—Skin from hand after three to four days' immersion in water. Fig. 37.—Skin from foot after "three to four days' immersion in water. Water.—Dead bodies float in the shallow and stagnant water of a pond sooner than in the deep water of a running stream, as the water of a pond, being warmer from the action of the sun's rays, favours putrefaction. Bodies float more readily in sea water than in fresh water, the specific graviy of the former being higher. Circumstances modifying Putrefaction.—These may be divided into external^ and internal. External Circumstances.—These are warmth, moisture, air, and manner of burial. Warmth.—Putrefaction commences at a temperature above 500F., and is most favoured between TO^EL^and 100 °K, and even upto 115°F. The rapidity of the change considerably lessens as the temperature advances above 100°F. It is altogether arrested below 32°F. and above 212°F. A higher temperature accompanied by dry ah* generally retards putrefaction. Moisture.—This is very essential for the occurrence of putrefaction, as the micro-organisms, which are the causative agents of decomposition, thrive well in both heat and moisture. Hence the organs which contain water decompose more rapidly than dry ones. Air.—The presence of air promotes, and its absence retards, putrefaction. Closely fitting clothes on the body retard decomposition by excluding the air. Similarly, bodies placed in air-tight lead or zinc cofSns resist putrefac- tive processes for a long period. Moist air favours putrefaction by diminish- ing evaporation, while dry air retards it. In the same way still air helps putrefaction, and air in motion retards it. Putrefaction is also delayed in bodies completely submerged in water to the entire exclusion of air, and it has been ascertained that at the same temperature the putrefactive changes observed in a body exposed to the air for one week will almost cor- respond to those in a body submerged in water for two weeks, or buried in a deep grave for eight weeks.28 28. Casper, Forens. Med.s Balfour's Eng. Transl., Vol. I, p. 37.