When I Was A Scientist
We all have a particular anxiety dream that we return to over and again. Mine is about being unable to get together the various things required to maintain the clone I looked after, on and off, for twenty years. It's a natural clone of a simple freshwater animal, green hydra, distant relative of corals, sea anemones, and jellyfish. That's it in the photo above - some of you may remember it from university or school biology classes. It's about a half a centimetre long, and has a simple body plan: a tube constructed from an outer ectoderm and inner gastroderm, both mostly one cell thick and separated by an acellular mesoglea (the jelly in jellyfish). At one end is a mouth ringed by tentacles that contain four different kinds of nematoblasts, cells with capsules that explode when triggered, enjecting prey with poison and wrapping barbed coils around them. At the other is a foot by which it adheres to a suitable substrate. Green hydra are an example of a mutualistic symbiosis. They contain, in gastrodermal digestive cells, populations of single-celled Chlorella algae. The algae supply the animal with nutrition; the animal provides the algae with shelter, and nutrients they need to grow.
Hydra can reproduce asexually by budding, which is what the specimen in the photo is doing; eventually that bud at its waist will develop tentacles and a mouth and pinch off from its parent and take up an independent existence. And that means you can clone up from a single specimen a population of genetically identical individuals, ideal for use in experiments. I used to grow thousands of them for my research, which investigated how the intimate relationship between these two very different organisms was regulated.
Hydra aren't difficult to grow. You keep them in artificial pond water made up with simple chemicals, supply them with light and a constant temperature between 15 and 20 degrees Centigrade, feed them with freshly-hatched brine shrimp, and keep the Pyrex trays in which they grow nice and clean. My dream, the one I return to (or which returns to me) is that I can't quite manage this routine. I've forgotten to hatch the brine shrimp, or forgotten to clean the trays after feeding, or I don't have any artificial pond water and the chemicals to make it are missing, or there's something wrong with the incubator cabinets that keep the trays of hydra at the right temperature . . . And I wake up in that state of unresolved anxiety we all have, from time to time.
Other people dream of missing planes or trains, or being unable to find their way out of or into a building, or of arriving at a concert of business meeting without a stitch of clothing. I used to dream about exams, although not in the way that most people do - of having to take an exam without knowing anything about the subject. No, I used to dream about invigilating exams, another part of my former job. That went away after a while, but I still dream about culturing hydra, even though I quit science more than thirteen years ago. Funny, isn't it, what sticks in the mind?