Since time immemorial, humans have sought to preserve bodies after death. The ancient Egyptians practised mummification, embalming the bodies in order to preserve them. Internal organs were removed and the body cavities filled with a mixture of natural materials including herbs. The body was then bathed in oils and bound tightly in linen. Thousands of years after their deaths, the mummified remains of the early rulers can be seen on display in various museums. Some mummies have been estimated to be 3000 years old.

Bodies may also be accidentally preserved, buried deep in ice or in dry, hot sand, or lava or peat bog. Certain environmental conditions lead to a significantly slowed rate of decomposition. Bodies buried in ground that is cool and dry will show a retardation of decomposition. Again, the presence of large amounts of certain compounds in the soil will bring the bodies' moisture to the skin surface, slowing the rate of decomposition. Bodies with low amounts of muscle and body fat may also resist decomposition for a time. But eventually and certainly once exposed, bodies usually break down and 'return to dust'.

While kept from air and moisture, a varying amount of decay can be avoided. However when discovered, the bodies are generally wrinkled, distorted and discoloured. They appear skeletal, have no elasticity and emit an unpleasant odour. Once exposed to air and moisture, decay is rapid.

Accidental preservation has occurred in comparatively recent times. Much to the consternation of the authorities, many graveyards in Germany are revealing preserved corpses. High subsoil moisture content together with low temperatures and a lack of oxygen has been blamed for the phenomenon.

Cemeteries in Germany are recycled after a period of 15 to 25 years, a period during which human remains can be expected to rot away almost entirely. However cemeteries established in areas with high amounts of clay have been found to be unsuitable for 'recycling. Because of the poor drainage qualities of clay, air is unable to permeate the compact layers and decaying does not take place – or at least takes place much more slowly.

The figures become waxen, the soft tissue transforming not into humus but into a grey-white, pasty mass. Over time, this coagulates to become a hard, durable substance which sounds hollow when knocked. In some instances, burial in a shroud has been forbidden as enshrouded bodies won't decay in damp soil. Many Islamic immigrants now arrange for loved ones' bodies to be shipped home to Turkey or Lebanon because of the ban on shrouds.

As already stated, bodies may be deliberately preserved by being embalmed or treated before burial with the intention of staving off decomposition. Again, if air and moisture are kept from the corpses, they may avoid significant decay. Embalming in older days involved filling the body cavities with specific materials. These might be resin or sawdust soaked in resin. The entire body might be submerged in honey, rum or sand. More modern methods include submerging the body or filling it with resin, alcohol, tar, salt or a combination. However, when examined later, the bodies are found to be discoloured, wrinkled, distorted and odorous. Like accidentally preserved remains, they are skeletal with no elasticity, decaying rapidly once exposed to the air.

There is a third type of preservation and that is incorruptibility. The 'incorruptibles' excite a great deal of cynicism and comment, mainly because there is no rational explanation for their existence. The incorruptibles continue to baffle scientists. They have been found in many different environments, including those which would normally result in decomposition. A few have been exposed as fraudulent.

Regardless of the manner of burial, temperature, moisture, delay in burial, frequent moving or proximity to other decaying corpses, the incorrupt body remains free of decay. There are a number of incorruptibles. Typically they remain moist and pliant. Some have not been subjected to any type of embalming or treatment. Some contain clear, flowing oils and/or blood for many years after death. In some examples, parts of the body remain absolutely free of decomposition while other parts show some decay. In all cases, decomposition eventually makes its mark but sometimes only after hundreds of years.

In almost every case of an incorruptible, the person has been found to be an extremely devout Catholic. For the moment, there are no instances of incorruptibles coming from other faiths. There are many incorrupt bodies on display to the public, mainly in Europe. Most of the discovered incorrupt bodies have been canonised by the Catholic Church. It would seem that some saints have been specifically chosen as incorruptibles to confirm significant events of which they were a part, such as Jacinta Marta.

Some of these incorruptibles have a degree of decay. In some cases, a light coating of wax has been applied to improve their appearance. However such additions could not possibly prevent further decay of the bodies once they are put on display. Most remain incorrupt whether 'enhanced' or not. Incorruptibles also display the 'odour of sanctity', with a sweet odour emanating from the body, frequenting described as like roses. The bodies are generally flexible and soft.

One incorruptible was Padre Pio who was born in 1887 and died in 1968. In March 2008, his body was exhumed and found to be incorrupt. During his life he also displayed the stigmata or wounds of Jesus Christ.

Jacinta Marto was one of three girls who were visited by Mary, at Fatima in Portugal. Jacinta died aged ten. Her body was exhumed in 1935 and again in 1951. In both cases the body was found to be intact. Her tomb is now in the Basilica of Our Lady of Fatima which has been built on the site where the children first saw the vision.

The first United States citizen to be made a saint was Frances Xavier Cabrini, also known as Mother Cabrini. She died in Chicago in 1917 and was exhumed in 1938. Her body was partially incorrupt and it has now been covered in wax and lies enshrined in the chapel of St Francis Cabrini Shrine in New York City.

St BernadetteCredit: Wikimedia

St Bernadette died in 1879 and was exhumed three times. The last time, in 1923, her body was dissected and her organs were found to be still soft and malleable.  St Catherine of Bologna died in 1463. She has been on display in an upright position for over 500 years.

Despite our cleverness and knowledge, there are still some things that defy explanation. Incorruptibility would seem to be one of these.