Ryenel James leaned over the laboratory dish yesterday to cough out some bacteria for D.C. Mayor Marion Barry. There were TV cameras and lights around him. The other ninth graders were waiting. James was appropriately nervous. He coughed weakly.

"Cough on it," Barry urged. This time, James let out three big ones. "Don't cough on me," the mayor laughed.

James' mission -- to grow some bacteria -- was accomplished, and the mayor proceeded with his. It was part educational experience for the 18 students in Irene Randolph's biology class at Fletcher-Johnson Educational Center, and part publicity stunt to highlight American Education Week.

Although it was not the biology class that the 18 students are used to, they came away with some knowledge they could use about free dental exams and after-school jobs in a lesson that ranged from coccus, bacillus and spirillum -- bacteria's three shapes -- to personal hygiene, drugs, crime, go-gos and jobs.

If the class were given a name, "Biology you can use" would be appropriate.

Reading from a list of questions for which the students had studied, Barry led the students in a quiz on the basics of bacteria. Then he moved on to what it means in everyday living. He asked for some examples of harmful bacteria.

"Tooth decay," said James Leach, 16.

"That means you should brush every day," Barry said. "Anybody here ever have a cavity?" Hands shot up. "What happened?"

"They pulled it out," LaRaine Boyd, 15, said. She told the mayor she hadn't been to the dentist in two years. Why? he asked.

"I don't know. It costs too much," she said.

"There's a dental clinic right downstairs that's free. Free," the mayor said. He told the girl he'd be checking with Principal George Rutherford to make sure she had a dental exam.

Barry told the students that they could make it if they studied hard, saved parenthood for later, stayed out of trouble and away from drugs.

Then the mayor threw out a trial balloon about go-go clubs and the hours they should keep. About half the students said they don't go to go-go clubs. Barry asked them what they thought about the go-go's closing at 11:30 p.m. during the week and 1 a.m. on weekends.

"They shouldn't close down so early because they just start getting good at those times," said Martinus Thomas, 16.

"What would you do if you had a job on Saturdays?" Barry asked. "I'm going to get you a job. Out of this class, how many of you are 15? That's eight of you." Barry turned to questions about drugs.

"Most people now smoke crack," Thomas said. "Do I know anybody? A whole lot of people."

"You know, we got a serious drug problem," Barry said. "What does PCP do to your brain? The brain cells are the only cells in the body that don't reproduce themselves. And so when PCP eats those cells up then they can never grow back."