“What about hunting? A deer or bear could get that big.”
“Did you find any hairs?”
I shook my head.
“Decaying animals leave behind tons of hair. And bones, of course.”
When an organism dies, scavengers, insects, and microbes take an immediate interest, some munching from the outside, others from within, until the body is reduced to bone. This is known as decomposition.
Ruby would talk in terms of dust to dust, but the process is much more complicated than that.
Muscle, comprising 40 to 50 percent of the weight of a human body, is composed of protein, which is composed of amino acids. At death, the fermentation of fat and protein yields volatile fatty acids, or VFAs, through bacterial action. Inside the gut, other microbes do their part. As putrefaction advances, liquids ooze from the body, carrying with them the VFAs. Death investigators call the mixture soup.
Laslo's research focused at the microbial level, analyzing organic components contained in the dirt under and around a body. Years of work had demonstrated a correlation between the decay process and VFA production.
I watched him filter soil through a stainless-steel sieve.
“Exactly what do you look for in the dirt?”
“I don't use soil, I use soil solution.”
I must have looked blank.
“The liquid component between soil particles. But first I have to clean it.”
He weighed the sample.
“As body fluids flow through, the organic matter becomes bound to the soil. I can't use chemical extractants for separation, because that would partially dissolve the volatile fatty acids from the decomposing body.”
“And alter their measurements.”
“Exactly.”
He placed the soil in a centrifuge tube and added water.
“I use deionized water in a ratio of two to one.”
The tube went onto a vortex for one minute to mix the solution. Then he transferred it to a centrifuge and closed the lid.
“The temperature inside is held at five degrees. I'll centrifuge for forty minutes, then filter the sample to remove any remaining microorganisms. After that it's simple. I'll check the pH, acidify with a formic acid solution, and pop the thing into the gas chromatograph.”
“How about a crash course.”
Laslo finished adjusting settings, then gestured to a desk and we both sat.
“O.K. As you know, I'm looking at the products of muscle and fat breakdown called volatile fatty acids. Are you familiar with the four stages of decomposition?”
Anthropologists and death investigators think of corpses as being in one of four broad stages: fresh, bloated, decayed, or skeletal.
I nodded.
“There's little change in VFAs in a fresh corpse. In the second stage, a body bloats due to anaerobic fermentation, primarily in the gut. This causes skin breakage and the leakage of fermentation byproducts rich in butyric acids.”
“Butyric acids?”
“Volatile fatty acids include forty-one different organic compounds, of which butyric acid is one. Butyric, formic, acetic, propionic, valeric, caproic, and heptanoic are detectable in soil solution because they're soluble in water. Two of them, formic and acetic, are too abundant in nature to be of much use.”
“Formic is the one that causes pain from ant bites, right?”
“That's the one. Caproic and heptanoic are only found in significant amounts during the colder months. Propionic, butyric, and valeric are my boys. They're released from a decomposing corpse and deposited in soil solutions in specific ratios.”
I felt like I was back in Biochem 101.
“Since butyric and propionic acids are formed by anaerobic bacteria in the gut, the levels are high during the bloat stage.”
I nodded.
“Later, during decay, aerobic bacteria join the act.”
“So at stage three there's a surge in all VFA formation.”
“Yes. Then there's a rapid fall-off at the onset of stage four.”
“No flesh, no bacteria.”
“The soup kitchen closes.”
Behind us the centrifuge hummed softly.
