Let’s go back to a dark and stormy night in 1938, when a white-coated man took up a scalpel. Now, this is chilling, but true*: he raised the flashing blade and brought it down on a squirming rat. The deed done, he deftly sliced the brain and liver of the creature, and placed them into a bright yellow liquid. (This post is part 2 of a series uncovering the dark side of scientific methods; part 1 is here).
What was this witchery? The yellow liquid – known in the dark trade as ferricyanide – slowly lost its colour, turning clear! Chanting under his breath, the man poured the broth into another tube of clear liquid, which had been stewing with yellow sticks in it. Bubbles emanated from the foul mixture, and, panting slightly with excitement, he measured the quantity of gas produced.
To deliver the coup de grace, he spun the mixture in a centrifuge to remove the remains of the rat, and performed two checks. For the first, he sprinkled white powder into the mixture. As it turned dark brown, he gave a satisfied grunt. To finish his test, he dropped in more bright yellow solution, and his mixture became a startling blue. Dusting off his hands, the man turned to a typewriter and published his technique for his peers to emulate and build upon. He was one of the first to contribute to what became the FM-TOX test.
He reported that the yellow ferricyanide was a useful way to study the presence and amount of enzymes in different tissues. The finding was based on the ability of the ferricyanide to be converted chemically to ferrocyanide, which is colourless. Importantly, the enzymes studied were parts of the metabolic system of the rat.
Fast forward 70 years. After being lost in the scientific wilderness for decades, the method was resurrected in the 1990’s and rose in stature. Now the subjects of the tests are bacteria, not rats, but the deviousness of the scientists has multiplied.
Imagine you’re a little E. coli bacterium. You’ve been swimming around happily in a nutrient-filled paradise for, oh, 4 hours, with billions of your friends. Wait, what’s this? You’re poured out and put into a machine which whirls you around and around until you’re crammed, along with all your friends, into the tiny end of the tube. You’re put through a washer and spun again. The process stuns you, and you barely notice being sucked into a pipette and dumped in a tiny tube.
The monstrous pipette tip disappears briefly, then returns with a new payload: 3,5-DCP. This pesticide is notorious for breaking down the ability of cells to respire properly, by damaging the protein machinery responsible. As the DCP floods the tube, you feel an initial rush of energy as your body goes into overdrive, then a slump worse than any hangover.
But the trauma’s not done yet. Ferricyanide is then mixed in, turning your world yellow. All the energy sloshing around, freed by the DCP, is quickly used up by the new chemical, and you’re left battered, broken and drained. The reaction is similar to the one pioneering all those years ago on rat tissue.
And finally – as if all that wasn’t enough – the scientists need to take a measurement. An electrode is inserted into the solution, forming what amounts to a miniature electric black hole, dragging the ferrocyanide in and spitting it back out after the signal is read. By doing this, the scientists measure how much the metabolic function of the cells was affected by the DCP, so they get an idea of its toxic effects, without having to inflict harm on animals or humans.
The job completed, the remaining hardy bacteria – you, your family and cousins – are snuffed out by a concentrated alcohol solution and washed down the sink.
More hapless victims of the scientific method.
Quastel JH, & Wheatley AH (1938). Anaerobic oxidations. On ferricyanide as a reagent for the manometric investigation of dehydrogenase systems. The Biochemical journal, 32 (5), 936-43 PMID: 16746707
Catterall, K., Robertson, D., Hudson, S., Teasdale, P., Welsh, D., & John, R. (2010). A sensitive, rapid ferricyanide-mediated toxicity bioassay developed using Escherichia coli Talanta, 82 (2), 751-757 DOI: 10.1016/j.talanta.2010.05.046
*Events are definitely dramatised and more attention would have been paid to ethics.