WHAT HAPPENS TO A BODY AFTER DEATH
Nature is very efficient at breaking down human corpses. When you die your heart stops pumping blood around your body, thus depriving your cells of oxygen, which rapidly begin to die. Decomposing starts almost immediately, with the skin going through several changes in colour as the blood stops circulating leaving the body an ashen color. However different cells die at different rates. For example, brain cells die within a few minutes, whilst skin cells can survive over 24 hours after death. Soon after death rigor mortis occurs, which is caused by a complex chemical reaction (involving lactic acid and myosin), which forms a gel like substance which creates the body's stiffness. Rigor mortis lasts approximately 24 hours (depending upon ambient temperature).
Upon death blood also starts to settle in the those parts of the body that are closest to the ground, turning the top part grayish white and waxy looking, whilst darkening the underside. This results in a deep red-brown stain. For example if a person was to die and keel over head-first then the blood would settle in their head, which would result in a bruised-like stain to the face and neck. Body extremities will naturally turn blue within 8-12 hours without intervention (eg embalming).
Funeral directors (Undertakers) tend to lift the head of a corpse in the coffin in order to prevent discolouring of the face. They also make sure that the body is properly groomed. The hair will be washed and combed, while the face is skillfully made-up using cosmetics that match as close as possible the person's natural skin colour as when they were alive. Undertakers also use glue to shut the eyes and lips as these naturally draw back and the eyes will sink. It is a myth that fingernails and hair continue to grow after death. What happens is that the skin dries outs and pulls away from the nails and hair which makes them stand out more prominent, giving the illusion of growth.
The intestines are packed with millions of micro-organisms that don't die with the person. Therefore these organisms start the job of decomposition immediately by breaking down the dead cells of the intestines. As the bacteria starts to eat through the gut the first sign is usually a greenish patch on the lower right belly which also blisters. Then special bacteria called clostridia and coliforms start to invade other parts of the body and putrefaction spreads across the stomach before travelling down the thighs and across the chest. This rotting produces foul-smelling matter which include the gases hydrogen sulphide (the smell produced by rotting eggs) and methane. These internal gases push the intestines out through the rectum, the tongue may protrude and fluid from the lungs oozes out of the mouth and nostrils. A hollow needle can be inserted into a corpse to release the gases and this may cause the body to lunge forward. (Not a job for the faint-hearted) At the same time as the bacteria gets to work, our own body mechanisms start the intrinsic breakdown under the action of enzymes and other chemicals which have been released by our dead cells. Some of the last cells to be broken down in the cadaver are those which are more resistant to decomposition, such as tendons and ligaments.
STAGES OF DECAY
Initial decay (Known as 'autolysis') - externally the corpse looks okay, but internally the organs are breaking down.
Putrefaction - after approximately two-three days bacteria are active and the body is swollen with gases and accompanying odours.
Black Putrefaction - Skin starts to turn black and the corpse collapses as gases escape.
Fermentation - Very strong odours with some surface mould but the body has begun to dry out.
Dry Decay - The cadaver has for the most part dried out and the rate of decay has slowed considerably.
Embalming is the practice of preserving human (or animal) remains. However although embalming slows decomposition it does not stop it indefinitely. Embalmers try to pay particular attention to those parts of the body seen by mourners, for example the face and hands. The chemicals used in embalming repel most insects, and slow down bacterial putrefaction by stopping the action of cellular proteins, which means that they cannot act as a nutrient for bacteria, and end up either killing or slowing most of them down. If placed in a dry enviroment or special fluid some embalmed bodies may end up mummified and it is not uncommon for these bodies to remain well-preserved. Three examples are Evita Peron, Ho Chi Minh and Lenin. Other substances can act as a natural embalming agent such as a peat bog and natron salt.
Decomposition is well under way by the time burial or cremation occurs. However, the exact rate of decomposition depends to some extent on environmental conditions.
Decomposition in the air is twice as fast as when the body is under water and four times as fast as underground. A corpse left above ground is rapidly broken down by insects and animals, including bluebottles and carrion fly maggots, beetles, ants and wasps. A corpse can become a moving mass of maggots within days, even hours in hot climates. Approximately 150,000 maggots can be found on an exposed corpse. Left above ground the the main body cavities burst open and the tissues become liquefied after about a month or so.
When buried six feet down, without a coffin, in ordinary soil, an unembalmed adult normally takes eight to twelve years to decompose to a skeleton. However if placed in a coffin the body can take many years longer, depending on type of wood used. For example a solid oak coffin will hughly slow down the process. I believe there was a case where a body was exhumed in an oak coffin and it was found to still be in a state of decomposition some 50 years later. Of course a lot also depends on how deep the coffin is buried, the state of the soil and the local water table.
If cremation is the choice of disposal then the 'ashes' of an average size man weigh approximately 7.4 pounds, whilst those of a woman, about 5.8 pounds. In England and Japan cremation is the most common form of disposition and the second most common in the United States. During the actual cremation process the coffin is placed in a chamber (furnace) which is heated to an extremely high temperature. After several hours all that is left are small bone fragments. These are then reduced to 'ashes' by grinding, which are then placed into an urn and returned to the family. So the ashes you receive are actually mostly bone fragments and not ashes as most people think of - such as those left after burning wood or coal.
In extremely dry or cold conditions, the normal process of decomposition can be halted, either by a lack of moisture or temperature, which controls the bacterial and enzymatic action - effectively turning them off. When this happened the body is preserved as a mummy. If frozen mummies are thawed then the decomposition process will restart, and the same will happened to the ones preserved in sand, such as Egyptian mummies, if exposed to moisture.
It can takes decades for a body to decay, as there are many factors that affect the rate of decomposition, such as how well the person was embalmed, what type of casket and vault they were placed in, humidity, heat, cold, soil type, water level, depth of burial, the availability of oxygen, accessible by insects or scavengers, body size and weight, clothing, the surface on which a body rests - all determine how fast a fresh body will skeletonize or mummify. Aa basic guide for the effect of environment on decomposition is given as 'Casper's Law' which determined that where there is free access of air a body decomposes twice as fast than if immersed in water and eight times faster than if buried in earth. People who have been dead for decades could still look fine whilst others of the same era are completely decomposed. There are just too many factors that affect the rate of decomposition to give a definitive answer.