Josh Bonanno peered into the 400-power microscope at the Buck Institute for Research on Aging, a world-class science facility in Novato.
His fifth-grade classmates from Sequoia School in Rincon Valley let out oohs and aahs as they saw on an adjacent monitor the throng of bacteria grown from a swab Josh took last week at school.
"There was like seven big brown blobs," Josh said. "The rest was all yellowish."
Julie Mangada, the K-12 education coordinator at the Buck Institute, said she could tell just from holding up the clear plastic petri dish that Josh had corralled a bacterial bonanza.
"There's so much stuff in this one," said Mangada, a Santa Rosa resident who has a doctoral degree in molecular medicine.
"Jackpot, Josh," Sequoia teacher Rhiannon King said approvingly.
Where did he find so many germs? "Inside the toilet," Josh said.
Sequoia's entire fifth-grade class, about 60 students, on Tuesday made the first school field trip to Buck's brand new $500,000 Learning Center, a training and demonstration space for visitors of all ages, or "K to gray," as Mangada put it.
Last year, more than 1,700 students visited the institute, housed in a white limestone-clad building overlooking Highway 101 at the north end of Novato. It's where about 200 scientists work on solutions to age-related conditions, such as Alzheimer's and Parkinson's diseases, cancer, diabetes and stroke.
The number of student visitors will grow now that the Learning Center is open, with a DNA double-helix design embedded in the floor and work tables soon to be lining the walls.
Tuesday's lesson was about bacteria, the mostly benign organisms -- ten-thousandth of a centimeter long -- that live almost everywhere on Earth and thrive on the skin and in the gut of humans.
The students, under Sequoia science teacher Wendy Schwartz's direction, came well prepared.
"Do we have bacteria on us?" Mangada asked.
"Yes," the students chorused.
"Is that normal?" she asked.
"Yes," they said.
"Do you guys know any types of bacteria?"
"Good and bad," student Amber Balogh replied.
Right, Mangada said, explaining that Escherichia coli inhabit the lower intestine and help people digest food.
"We all have our own E. coli," she said. But if you pick up someone else's E. coli, perhaps from contact with a restroom fixture, "that can make you sick."
Last week at school, Schwartz's students swabbed various surfaces -- including trash cans, a toilet flushing handle and a model skeleton -- then wiped the swabs in petri dishes primed with nutrient.
Under the microscope at the Learning Center, a swab from the school's bridge handrail produced two types of bacteria, including staphylococcus, and a fungus.
"That's a pretty dirty place," Mangada said.
A comparatively huge mite, an invertebrate, turned up amid the germs Orion Tiscornia harvested from a classroom pencil box.
"Wow," he said, peering into the microscope. "It looks dead, that's for sure."
"It's not happy," Mangada said, explaining that the mite would have been eating dead skin cells in the pencil box.
Dustin Ward and Ameen Adel scored a Pseudomonas aeruginosa, a colonial bacteria with a shiny crust that favors damp, dark places.
They swabbed the top of a toilet seat.
Students also toured the hillside Buck facility, including a visit to the rumbling boiler room, a place off-limits to most visitors.