Every scientist has a “moment”, an event that set them on their path. This is my moment.

Scientists are a pretty disparate bunch. Some come from academic pedigrees, some are lone offshoots of the family tree. All though will have a moment, an experience that changed and fixed their outlook on the natural world. That outlook is often referred to as a childlike sense of wonder, a way of seeing, of continuing to see the world as if for the first time – while for most scientists’ contemporaries the world’s horizons gradually narrow around the prosaic requirements of work, food, shelter, parenting, recreation, and shagging.

I don’t come from an academic family. My father, like so many of the Baby Boomers, yielded his dream of being an artist to paternal insistence that he get a real job. My mother worked in the law. Under different circumstances, I might have done the same. It was a friend of the family who shaped my future, who provided my moment. His name was Ian Gauld.

Ian was a taxonomist who worked in the entomology department of the Natural History Museum in London. He was a friend of my mother’s from their days spent commuting together on the train from Northampton. Ian specialised in the Ichneumonidae, the parasitoid wasps which lay their eggs inside caterpillars and have an exquisite specificity for their prey species. He spent a lot of time in Costa Rica on collecting trips, and his home – a former council house in the village of Spratton, emblematic of his unpretentious style – was decorated with mementoes of these trips that gave it an exoticism unthinkable from its drab, unprepossessing exterior. Here he and his wife and collaborator Pammie entertained, surrounded by native American souvenirs, a stained glass scarab hanging in the window, long shelves stacked with copies of the National Geographic, a profusion of potted plants that gave the whole place an echo of the jungle…even the Portmeirion crockery decorated with botanical patterns and insects was rich with a sense of life.

Ian was a genial giant. Standing well over six feet tall, he possessed a barrel chest that gave him a permanently broad-legged stance in order to balance his well-fed girth. His face, topped with a greying mane of hair, was framed by a full beard and moustache that gave him the air of a latterday Professor Challenger from “The Lost World”. He played the part well, very well.

His travels, general bonhomie, rich baritone voice and commanding presence made him a natural and extraordinary raconteur. A visit to Spratton meant hearing of exotic locations, adventures, and danger – it was only years later that I realised his frankly obese physique would have made all these Indiana Jones escapades physically impossible, as he regaled his wide-eyed young audience with tales of being chased through the jungle, dodging poison-tipped arrows, and all the while carefully safeguarding his precious specimens for the museum. Scientists, I solemnly concluded, were quite clearly the coolest people on the planet. They travelled the world, did unusual and remarkable things, and enjoyed their work. I only had to see my dad counting the years until retirement, a retirement that he ultimately never saw, to see how valuable that enthusiasm was.

One of the upstairs rooms in the Gaulds’ house was the laboratory. The air was always sweet and slightly heady from the alcohol used to preserve the insect specimens that Ian observed and classified. Book-filled shelving lined the walls from floor to ceiling, with long desktops stretching the length of the room on both sides supporting dissecting microscopes and notebooks. The wooden floorboards always squeaked and the light coming from the window overlooking the garden at the far end of the room served to pull a visitor inwards.

I loved that room. Often when we were visiting I would sneak upstairs by myself, marvelling at the preserved insects in their vials, the drawings of their wing veins filling pages and pages of paper, and the intricate craftsmanship of the microscopes. It was a window onto a different world, and it finally offered me a window into an even more extraordinary one.

Ian had picked up on my then-nascent interest in biology and encouraged it. One weekend afternoon when we were visiting, he’d gone a step beyond showing me the wings and stings of wasps, and put a spot of blood on a microscope slide. I knew about blood cells already, so it was fun but not too surprising to see them at first hand, red discs rubbing together like baked beans in a tin. Red blobs. Anucleate. Inanimate.

Whether it was planned or a sudden inspiration I’ll never know, but Ian then took me outside to the water butt collecting the flow from the house’s drainpipe. We took one drop of water as a sample. One drop. One drop that changed my life.

It was clear to the naked eye, with maybe some greenish flecks if one stared very hard, but utterly unremarkable compared to the rich red of the blood we’d seen earlier. Ian placed it under the microscope, grunted approvingly, and beckoned me to look. I put my gaze to the eyepieces, and my world changed, forever.

It was like one of those moments in a science fiction film where your head flips as a different dimension is revealed. The world inside the drop seemed to be bigger than the one outside it. It was a solar system, a cosmos, a universe. Grains of dirt became asteroids, the light of the microscope a distant and unseen sun. And then some of the inhabitants came into view.

Time and memory have confounded my visual recollection, but not my impressions. Sometimes when I relive that moment now the scene is populated by creatures that do exist, but probably weren’t there – my mind embellishing with details learned later on. But two I am sure of. A huge Paramecium cruised by, hungry and pulsating, propelled effortlessly by the beating of hundreds of tiny oars like some kind of intergalactic battlebarge. Bobbling across the field of view shortly afterward came Volvox, like a large transparent golf ball, its green daughter colonies bouncing inside the spherical colonial mass.

We talk about the body politic, the huddled masses, and the cells of multicellular organisms like ourselves generally fit this description. They pack together in tissues, functionalised, de-individualised, and domesticated. They don’t have the unfettered abandon of their unicellular relatives. Unicellular life, whether free-living or parasitic, is a gallery of the weird, the wild, the strange, and the beautiful. While mammalian cells sit placidly like fried eggs, unicellular microbes are as ferocious as the spaceships of the sadistic Reavers in “Firefly”. Whips, flails, harpoons, claws, chains, bristles; strange shapes and esoteric motions. Swimming drunkenly, swimming effortlessly, some simply thrashing as if they can’t breathe. Armour plating, armour-piercing, mouths, eyespots. Large, small, fast, slow, grazers, predators. A universe in every drop of water. A universe in every speck of soil. An unseen universe, all around us.

That drop of water changed everything. It’s easy to read about cells, about microbes, but it’s only when you’re confronted by the profusion of life present within something as banal as a former raindrop that you suddenly sense the teeming urgency of the biological world. Everything I did from then on, the biochemistry and the molecular biology and the cell biology and the parasitology and the eventual arrival in the world of trypanosomes – unicellular parasites of animals – stemmed from that moment. My moment.

What’s yours?