You Explain The Process to Fran

"It's all right," you assure Fran. "We're theorizing that the disease is caused by one of the four usual suspects: either a virus, a bacterium, a fungus, or a chemical agent. Zack and I have performed a series of tests to characterize the pathogen."

"Really," Fran says. "What characteristics are you testing for?"

"Size," you say, pointing to cages F100A, F100B, F5A, F5B, F0A and F0B. "'A' is the so-called 'evil' milk; 'B' is normal milk."

"We burned some samples in the whatchamacallit," adds Zack. Fran frowns. "The flame photometer," you explain. "We were looking for an unusual chemical agent."

"Find any?" Fran asks.

"The A and B results were identical," you say.

"What about these?" Fran asks, pointing to the MA, MB and MC cages. "The control groups," you say. "MA's been inoculated with the disease-causing milk, and so we expect it to get sick. MB was inoculated with the normal milk, so we expect it to stay healthy."

"And MC got no inoculation at all," Zack cuts in. "Like, the control group thing."

Fran shoots Zack a look. "You made any cultures?"

"Yeah," Zack says. He takes the petri dishes out of the incubator, looks closely at them. "There's stuff growing in 'em, too."

"Let me see that," Fran snaps, and slides the dishes one at a time into an optical reader. "You're right," she says, peering into the reader. "Man, this stuff grows fast. I see colonies of a yellowish growth on PDA -- plus a much larger white growth. On PDB I see only the yellowish growth."

Continue with the mystery

An Access Excellence Science Mystery sponsored by Genentech, Inc.