I’ve been showing a newbie how to work with bacteria, and today her transformation plates were sprinkled with dozens of lovely colonies. I described to her how she should inoculate a single colony into antibiotic broth and left her to it.

After lunch, she came to my desk with a worried crease to her brow.

“What it it?” I said.

“The colony,” she said. “Are you sure it’s going to work?”

“It’ll work,” I said.

“But…I couldn’t actually see anything on the tip before I put it into the broth.”

“It’ll work.”

“Are you sure there was anything on the tip?”

“Show me the plate,” I said. She did so, and pointed out the colony she had selected, now smeared into a tiny linear smudge by the action of the sterile plastic yellow tip she had used to collect it.

“It will work,” I said. “It’s all down to the wonders of exponential growth.”

She didn’t look entirely satisfied, but come tomorrow, I’m sure she’ll be convinced by 100 mL of frothy bacterial goodness.