We know that the heart stops beating, the lungs stop respirating, and the brain shuts down. But sometimes when these events occur, if you hook the body up to a roomful of machines and keep it functioning that way for awhile, the person will eventually wake up.

So what exactly is "death"? What is "life", for that matter, and at what points does it definitely begin and end?

In the interest of NOT being picketed by cyber-protesters on all sides of that fence, I'm not going to voice my personal opinion of these issues. That would open up a dandy can of worms, and since I just had worms for lunch, I don't even want to get into it.

"death: (1) a permanent cessation of all vital functions : the end of life" -- Webster's

Oh, good. That's helpful. Keyword: "permanent". There.

In normal circumstances (wherein the body stays more-or-less intact for the whole procedure), the process of physical death doesn't happen in just an instant. It goes in stages, and can take a good, long time.

Let's say some guy chokes to death, alone in the woods, and no one ever finds him. I don't know; he was trying to hike and chew gum at the same time. This is what happens inside his body:

Somatic Death
First, the brain, heart and lungs shut down. The brain can only live for three to seven minutes without oxygen. The regulation of the heartbeat and respiration are controlled by electrical impulses in a part of the brain called the medulla, so once that goes, none of the other major life functions are going to work. Our friend is now officially dead, but surprisingly, quite a lot of his body is still alive.

The individual cells in the tissues will remain active for a few minutes longer, and some, like skin cells, can even be revived in a laboratory 24 hours later.

At the time of death, all the muscles in the body relax (this is called "primary flaccidity"...isn't that sad?). They'll start to stiffen up again, once rigor mortis sets in.

YES, I hear you giggling in the back there.
YES, this is the point at which the body "lets go" of everything it had been holding in the nether regions.
YES, ha ha, this is very funny.
NO, I don't want to talk about it.

Algor Mortis
Then the body will begin to cool down, and will reach room temperature within three hours.

In the initial stages of decomposition, the body doesn't stay at room temperature for long. It actually begins to heat back up! Have you ever opened the lid of a sealed cafeteria garbage can full of food scraps? Remember the hot air that came out of it? Bacteria are eating the food in the garbage can, and the chemical reactions of their digestive processes cause the rise in temperature. When the bacteria in the body begin to devour the tissues, the same thermal reaction occurs.

Decomposition
Even in full health, the body is teeming with micro-organisms. In most cases, this is a good thing -- they help you digest your food and keep your insides from filling up with dead cells. (The body's individual tissue cells are dying off and being replaced all the time. This is ok; they're supposed to do that.) When the main host body dies, these little guys really get down to business. The unregulated enzymes in the digestive system even start to digest the body itself! This is called autolysis, or self-digestion.

The rate of decomposition varies greatly, depending on the body itself, where it's been placed, and the climate. The bacteria are less active in colder, dryer temperatures (this is why you refridgerate your food), and more active in hot, humid climes.

(Hint: for prime zombie material, you'll want to catch 'em before this process gets too far.)

There are five stages of decomposition:

Stage 1: Initial Decay (The "Fresh Stage")
The blood "pools" in the low spots, causing the skin in those areas to look like a big purple bruise (livor mortis, or hypostasis). The rest of the skin, deprived of fresh blood, takes on that attractive deathly pallor.

Rigor mortis begins. The cells in the muscle tissues are still active (obviously not moving around, but still doing the chemical reaction thang), and when they're deprived of oxygen, lactic acid is produced as the glycogen within them breaks down. The excess lactic acid has a gell-like consistency and causes the body to become rigid.

(Insert appropriate "stiffy" joke here.)

Rigor mortis starts in the thin facial muscles, and will extend throughout the whole body in four to six hours. It lasts anywhere from 24 to 72 hours, then the muscles (or what's left of them) once again relax, as more chemical reactions break down the lactic acid.

Stage 2: Putrefaction (The "Bloat Stage"...nice, eh?)
All of these chemical reactions and hungry bacteria are going to produce more than just heat, bruises and crampy muscles. They're going to produce gas. And, as anyone who's spent a Saturday afternoon in front of the TV with some of my housemates knows, gas produces smells.

Two of the primary gases involved in decomposition are hydrogen sulphide and methane, both of which stink to high heaven. For example, you're probably already familiar with that "rotten egg" smell -- it also comes from water with a high sulpher content, or anyone who's eaten one of Vince's homemade wet burritos.

(Other gases involved in decomposition are "putrescine" and "cadaverine". Who thinks these up?)

To add to the corpse's rainbow effect, the gas and bacteria cause a greenish discoloration of the skin, starting in the abdomen and gradually tinting the rest of the body.

The gas builds up in the body, and hence we get the term "Bloat Stage". The abdomen becomes distended, the eyes may bug out, the tongue may protrude, and as the cells break down further and the pressure grows, the fluids within the body will begin to seep from its openings.

Stage 3: Black Putrefaction (The "Advanced Decay" Stage)
They couldn't have come up with some graphic secondary description for this stage? What happened to the person who came up with "Bloat Stage" for the previous section? Huh. Well, I'll make something up:

Stage 3: Black Putrefaction (The "Eww, ICK!!!" Stage):

I may be a walking corpse myself, and I may be a scientist who studies death and decomposition, but you know what? I don't wear my nice clothes around these guys.

They smell bad. Really bad. They leak all over the place. The soft tissues have been liquified by bacterial digestion. The skin is gooey. The body cavities have collapsed and the skin is not only gooey, but loose -- so loose that if you grab it too hard, the upper epidermis comes off in sheets. (This is known as "skin slip". All together now: "Eww, ICK!!") If the corpse has been exposed to insects, it's now writhing with maggots. The gases are pushing what's left of the internal organs out along with all the fluids. The hair is loose, and if you jiggle the nails and teeth, they come out pretty easily, too.

Don't try reanimating at this stage, unless everyone's wearing their golashes.

Stage 4: Butyric Stage ("The Fermentation Stage")
This stage is chiefly characterized by the fact that the body smells like cheese (caused by the presence of butyric acid), which would explain why I always like to have a little wine while I'm performing dissections.

At least things are, for the most part, dried out now. Mold has formed where the body is in contact with the ground or other surface areas. Fermentation has begun: "an enzymatically controlled anaerobic change with effervescence" (Webster again). Ok, Webster, but we're not talking about grapes here. Fermentation, for our purposes, means that the complex molecules of the body are being broken down, through chemical reactions, into simpler substances. It's a nice way to say "rotting", and not quite as smelly as before, unless you really, really hate cheese.

And, it's effervescent! Tiiii-ny bubbles...

Stage 5: Dry Decay ("The Skeletal Stage")
This should be fairly obvious. Any skin left on the corpse hangs in brittle tatters, and there's not much there except the bones. Depending on the conditions, bones can take years -- or centuries -- to decompose.

(Insert appropriate "boner" joke here)

Bones will either break down into their constituent molecular components and erode away as dust, or, in the right environment, fossilize (the process by which organic material becomes mineral).

---

There. Now all you've got is a skeleton (maybe), and a Zombie trying to write a scienctficic paper while growing more...effervescent by the minute. This was the natural decomposition process of a normal corpse, in a typically temperate outdoor environment. I didn't really get into the roles that insects play or the effects of differing temperatures or humidity levels. We haven't yet got into burial procedures, grave wax, mummification, ghouls, zombification or even the scientific justification for the effects of wine on the Undead, but you bet I'm gonna go there.