The Life Cycle After Death

Most of us would rather not think about what happens to our bodies after death. But that breakdown gives birth to new life in unexpected ways, writes Moheb Costandi.

"It might take a little bit of force to break this up," says mortician Holly Williams, lifting John's arm and gently bending it at the fingers, elbow, and wrist. "Usually, the fresher a body is, the easier it is for me to work on."

Williams speaks softly and has a happy-go-lucky demeanor that belies the nature of her work. Raised and now employed at a family-run funeral home in north Texas, she has seen and handled dead bodies on an almost daily basis since childhood. Now 28 years old, she estimates that she has worked on something like 1,000 bodies.

Her work involves collecting recently deceased bodies from the Dallas-Fort Worth area and preparing them for their funeral. "Most of the people we pick up die in nursing homes," says Williams, "but sometimes we get people who died of gunshot wounds or in a car wreck. We might get a call to pick up someone who died alone and wasn't found for days or weeks, and they'll already be decomposing, which makes my work much harder."

John had been dead about four hours before his body was brought into the funeral home. He had been relatively healthy for most of his life. He had worked his whole life on the Texas oil fields, a job that kept him physically active and in pretty good shape. He had stopped smoking decades earlier and drank alcohol moderately. Then, one cold January morning, he suffered a massive heart attack at home (apparently triggered by other, unknown, complications), fell to the floor, and died almost immediately. He was just 57 years old.

Now, John lay on Williams' metal table, his body wrapped in a white linen sheet, cold and stiff to the touch, his skin purplish-grey - telltale signs that the early stages of decomposition were well underway.

Self-digestion

Far from being 'dead', a rotting corpse is teeming with life. A growing number of scientists view a rotting corpse as the cornerstone of a vast and complex ecosystem, which emerges soon after death and flourishes and evolves as decomposition proceeds.

Decomposition begins several minutes after death with a process called autolysis, or self-digestion. Soon after the heart stops beating, cells become deprived of oxygen, and their acidity increases as the toxic by-products of chemical reactions begin to accumulate inside them. Enzymes start to digest cell membranes and then leak out as the cells break down. This usually begins in the liver, which is rich in enzymes, and in the brain, which has a high water content. Eventually, though, all other tissues and organs begin to break down in this way. Damaged blood cells begin to spill out of broken vessels and, aided by gravity, settle in the capillaries and small veins, discoloring the skin.

Body temperature also begins to drop, until it has acclimatized to its surroundings. Then, rigor mortis - "the stiffness of death" - sets in, starting in the eyelids, jaw, and neck muscles, before working its way into the trunk and then the limbs. In life, muscle cells contract and relax due to the actions of two filamentous proteins (actin and myosin), which slide along each other. After death, the cells are depleted of their energy source and the protein filaments become locked in place. This causes the muscles to become rigid and locks the joints.

During these early stages, the cadaveric ecosystem consists mostly of the bacteria that live in and on the living human body. Our bodies host huge numbers of bacteria; every one of the body's surfaces and corners provides a habitat for a specialized microbial community. By far the largest of these communities resides in the gut, which is home to trillions of bacteria of hundreds or perhaps thousands of different species.

The gut microbiome is one of the hottest research topics in biology; it's been linked to roles in human health and a plethora of conditions and diseases, from autism and depression to irritable bowel syndrome and obesity, mental disorder, and premature death.

Most internal organs are devoid of microbes when we are alive. Soon after death, however, the immune system stops working, leaving them to spread throughout the body freely. This usually begins in the gut, at the junction between the small and large intestines. Left unchecked, our gut bacteria begin to digest the intestines - and then the surrounding tissues - from the inside out, using the chemical cocktail that leaks out of damaged cells as a food source. Then they invade the capillaries of the digestive system and lymph nodes, spreading first to the liver and spleen, then into the heart and brain.

Samples were taken of liver, spleen, brain, heart, and blood from 11 cadavers, at between 20 and 240 hours after death. They used two different state-of-the-art DNA sequencing technologies, combined with bioinformatics, to analyze and compare the bacterial content of each sample.

The samples taken from different organs in the same cadaver were very similar to each other but very different from those taken from the same organs in the other bodies. This may be due partly to differences in the composition of the microbiome of each cadaver, or it might be caused by differences in the time elapsed since death. An earlier study of decomposing mice revealed that although the microbiome changes dramatically after death, it does so in a consistent and measurable way. The researchers were able to estimate time of death to within three days of a nearly two-month period.

The study suggests that this 'microbial clock' may be ticking within the decomposing human body, too. It showed that the bacteria reached the liver about 20 hours after death and that it took them at least 58 hours to spread to all the organs from which samples were taken. Thus, after we die, our bacteria may spread through the body in a systematic way, and the timing with which they infiltrate first one internal organ and then another may provide a new way of estimating the amount of time that has elapsed since death.

"Degree of decomposition varies not only from individual to individual but also differs in different body organs," says Javan, "Spleen, intestine, stomach, and pregnant uterus are earlier to decay, but on the other hand, kidney, heart, and bones are later in the process." One thing that does seem clear, however, is that a different composition of bacteria is associated with different stages of decomposition.

Putrefaction

Scattered among the pine trees in Huntsville, Texas, lie around half a dozen human cadavers in various stages of decay. The two most recently placed bodies are spread-eagled near the center of the small enclosure with much of their loose, grey-blue mottled skin still intact, their ribcages and pelvic bones visible between slowly putrefying flesh. A few meters away lies another, fully skeletonized, with its black, hardened skin clinging to the bones, as if it were wearing a shiny latex suit and skullcap. Further still, beyond other skeletal remains scattered by vultures, lies a third body within a wood and wire cage. It is nearing the end of the death cycle, partly mummified. Several large, brown mushrooms grow from where an abdomen once was.

Once self-digestion is underway and bacteria have started to escape from the gastrointestinal tract, putrefaction begins. This is molecular death - the breakdown of soft tissues even further, into gases, liquids, and salts. It is already underway at the earlier stages of decomposition but really gets going when anaerobic bacteria get in on the act.

Putrefaction is associated with a marked shift from aerobic bacterial species, which require oxygen to grow, to anaerobic ones, which do not. These then feed on the body's tissues, fermenting the sugars in them to produce gaseous by-products such as methane, hydrogen sulfide, and ammonia, which accumulate within the body, inflating (or 'bloating') the abdomen and sometimes other body parts.

This causes further discoloration of the body. As damaged blood cells continue to leak from disintegrating vessels, anaerobic bacteria convert hemoglobin molecules, which once carried oxygen around the body, into sulfhemoglobin. The presence of this molecule in settled blood gives skin the marbled, greenish-black appearance characteristic of a body undergoing active decomposition.

Bloating is often used as a marker for the transition between early and later stages of decomposition, and another recent study shows that this transition is characterized by a distinct shift in the composition of cadaveric bacteria.

Colonization

When a decomposing body starts to purge, it becomes fully exposed to its surroundings. At this stage, the cadaveric ecosystem really comes into its own: a 'hub' for microbes, insects, and scavengers.

Two species closely linked with decomposition are blowflies and flesh flies (and their larvae). Cadavers give off a foul, sickly-sweet odor, made up of a complex cocktail of volatile compounds that changes as decomposition progresses. Blowflies detect the smell using specialized receptors on their antennae, then land on the cadaver and lay their eggs in orifices and open wounds.

Each fly deposits around 250 eggs that hatch within 24 hours, giving rise to small first-stage maggots. These feed on the rotting flesh and then molt into larger maggots, which feed for several hours before molting again. After feeding some more, these yet larger, and now fattened, maggots wriggle away from the body. They then pupate and transform into adult flies, and the cycle repeats until there's nothing left for them to feed on.

Under the right conditions, an actively decaying body will have large numbers of stage-three maggots feeding on it. This 'maggot mass' generates a lot of heat, raising the inside temperature by more than 10°C. Like penguins cuddling in the South Pole, individual maggots within the mass are constantly on the move. But whereas penguins huddle to keep warm, maggots in the mass move around to stay cool.

The presence of flies attracts predators such as skin beetles, mites, ants, wasps, and spiders, which then feed on or parasitize the flies' eggs and larvae. Vultures and other scavengers, as well as other large meat-eating animals, may also descend upon the body.

In the absence of scavengers, though, the maggots are responsible for the removal of the soft tissues; "three flies could consume a horse cadaver as rapidly as a lion." Third-stage maggots will move away from a cadaver in large numbers, often following the same route. Their activity is so rigorous that their migration paths may be seen after decomposition is finished, as deep furrows in the soil emanating from the cadaver.

Every species that visits a cadaver has a unique repertoire of gut microbes, and different types of soil are likely to harbor distinct bacterial communities - the composition of which is probably determined by factors such as temperature, moisture, and the soil type and texture.

All these microbes mingle and mix within the cadaveric ecosystem. Flies that land on the cadaver will not only deposit their eggs on it but will also take up some of the bacteria they find there and leave some of their own. And the liquefied tissues seeping out of the body allow the exchange of bacteria between the cadaver and the soil beneath.

When a body purges, the gut bacteria start to come out, and we see a greater proportion of them outside the body. Thus, every dead body is likely to have a unique microbiological signature, and this signature may change with time according to the exact conditions of the death scene. A better understanding of the composition of these bacterial communities, the relationships between them, and how they influence each other as decomposition proceeds could one day help forensics teams learn more about where, when, and how a person died.

For instance, detecting DNA sequences known to be unique to a particular organism or soil type in a cadaver could help crime scene investigators link the body of a murder victim to a particular geographical location or narrow down their search for clues even further, perhaps to a specific field within a given area.

Purging

According to one estimate, an average human body consists of 50-75% water, and every kilogram of dry body mass eventually releases 32g of nitrogen, 10g of phosphorous, 4g of potassium, and 1g of magnesium into the soil. Initially, it kills off some of the underlying and surrounding vegetation, possibly because of nitrogen toxicity or because of antibiotics found in the body, which are secreted by insect larvae as they feed on the flesh. Ultimately, though, decomposition is beneficial for the surrounding ecosystem.

The microbial biomass within the cadaver decomposition island is greater than in other nearby areas. Nematode worms, associated with decay and drawn to the seeping nutrients, become more abundant, and plant life becomes more diverse. Further research into how decomposing bodies alter the ecology of their surroundings may provide a new way of finding murder victims whose bodies have been buried in shallow graves.

Grave soil analysis may also provide another possible way of estimating time of death. A 2008 study of the biochemical changes that take place in a cadaver decomposition island showed that the soil concentration of lipid-phosphorous, taken from a cadaver, peaks at around 40 days after death. A 2008 study of the biochemical changes that take place in a cadaver decomposition island showed that the soil concentration of lipid-phosphorous aking from a cadaver peaks at around 40 days after death, whereas those of nitrogen and extractable phosphorous peak at 72 and 100 days, respectively. With a more detailed understanding of these processes, analyses of grave soil biochemistry could one day help forensic researchers to estimate how long ago a body was placed in a hidden grave.

Burial

In the relentless dry heat of a Texan summer, a body left to the elements will mummify rather than decompose fully. The skin will quickly lose all of its moisture, so that it remains clinging to the bones when the process is complete. The speed of the chemical reactions involved doubles with every 10°C rise in temperature, so a cadaver will reach an advanced stage of decomposition after 16 days at an average daily temperature of 25°C. By then, most of the flesh has been removed from the body, and so the mass migration of maggots away from the carcass can begin.

The ancient Egyptians learned inadvertently how the environment affects decomposition. In the predynastic period, before they started building elaborate coffins and tombs, they wrapped their dead in linen and buried them directly in the sand. The heat inhibited the activity of microbes, while burial prevented insects from reaching the bodies, and so they were extremely well-preserved. Later on, they began building elaborate tombs for the dead, in order to provide even better for their afterlife, but this had the opposite of the intended effect - separating the body from the sand actually hastened decomposition. And so they invented embalming and mummification.

Embalming involves treating the body with chemicals that slow down the decomposition process. The ancient Egyptian embalmer would first wash the body of the deceased with palm wine and Nile water, remove most of the internal organs through an incision made down the left-hand side, and pack it with natron (a naturally-occurring salt mixture found throughout the Nile Valley). He would use a long hook to pull the brain out through the nostrils, then cover the entire body with natron and leave it to dry for 40 days. Initially, the dried organs were placed into canopic jars that were buried alongside the body; later, they were wrapped in linen and returned to the body. Finally, the body itself was wrapped in multiple layers of linen, in preparation for burial. Morticians study the ancient Egyptian embalming method to this day.

Back at the funeral home, Holly Williams performs something similar so that family and friends can view their departed loved one at the funeral as they once were, rather than as they now are. For victims of trauma and violent deaths, this can involve extensive facial reconstruction.

Living in a small town, Williams has worked on many people she knew or grew up with - friends who overdosed, committed suicide or died texting at the wheel. When her mother died four years ago, Williams did some work on her, too, adding the final touches by making up her face: "I always did her hair and make-up when she was alive, so I knew how to do it just right."

She transfers John to the prep table, removes his clothes and positions him, then takes several small bottles of embalming fluid from a wall cupboard. The fluid contains a mixture of formaldehyde, methanol, and other solvents; it temporarily preserves the body's tissues by linking cellular proteins to each other and 'fixing' them into place. The fluid kills bacteria and prevents them from breaking down the proteins and using them as a food source.

Williams pours the bottles' contents into the embalming machine. The fluid comes in an array of colors, each matching a different skin tone. Williams wipes his body with a wet sponge and makes a diagonal incision just above his left collarbone. She 'raises' the carotid artery and subclavian vein from the neck, ties them off with pieces of string, then pushes a cannula (thin tube) into the artery and small tweezers into the vein to open up the vessels.

Next, she switches the machine on, pumping embalming fluid into the carotid artery and around John's body. As the fluid goes in, blood pours out of the incision, flowing down along the guttered edges of the sloped metal table and into a large sink. Meanwhile, she picks up one of his limbs to massage it gently. "It takes about an hour to remove all the blood from an average-sized person and replace it with embalming fluid," Williams says. "Blood clots can slow it down, so massaging breaks them up and helps the flow of the embalming fluid."

Once all the blood has been replaced, she pushes an aspirator into John's abdomen and sucks the fluids out of the body cavity, together with any urine and feces that might still be in there. Finally, she sews up the incisions, wipes the body down a second time, sets the facial features, and re-dresses it. John is now ready for his funeral.

Embalmed bodies do eventually decompose. Exactly when, and how long it takes, depends largely on how the embalming was done, the type of casket in which the body is placed, and how it is buried. Bodies are, after all, merely forms of energy, trapped in lumps of matter waiting to be released into the wider universe.

What is a "natural" burial?

According to the laws of thermodynamics, energy cannot be created or destroyed, only converted from one form to another. In other words: things fall apart, converting their mass to energy while doing so. Decomposition is one final, morbid reminder that all matter in the universe must follow these fundamental laws. It breaks us down, equilibrating our bodily matter with its surroundings, and recycling it so that other living things can put it to use. Ashes to ashes, dust to dust.

The Universal Law of Full Circle:

The Human Physical Body Form grew from the process of Mitosis, cell division; energy converted from one form to another, and shall be intended to be used with incoming Soul to learn lessons. This form of vehicle (body) was agreed to at the planning stage to last a certain duration; and the life span of it will return back to the source whether through decomposition (ground burial), food chain (sky burial), or return to ether (cremation). This is also the universe's way of balancing In Exchange with Out Exchange.

Tags: death