"What is the optimum temperature for bacteria?" inquires Henry Ziegler, scanning his 25 students for a raised hand, a fluttering jaw, or some other sign of life. But the class is in a distinctly nonparticinatory frame of mind, so Ziegler winds up answering his own question. "Ninety-eight degrees." he said. "And what's the temperature of us?"

This time, there is a volunteer, "Ninety-eight point six."

Ziegler beams triumphantly. The Socratic method is working. "Now you see why bacterial love us the way they do!" he declares.

It is Day One of the five-day course that all restaurant and carry-out supervisors in the District of Columbia must, by law, take and pass. And if the initial level of enthusiasm seems restrained, that could be because a number of the students got here because a D.C. health inspector dropped by their establishments and, among other possible violations, was unable to locate a certified food-service supervisor on the premises.

Henry Ziegler is a former food-service supervisor himself, a graduate of the Gold Nugget bar at 14th and Chapin Streets NW, then Hot Shoppes, and most recntly Holly Farms fried chicken. In 1975, he and several colleagues formed Culinary Service Associates, the Herndon, Va., firm which now has a contract with the D.C. Government, at $25 per student, to teach the sanitary approach to handling food.

This particular week, Ziegler's class includes representatives from Drug Fair, Emerson's Ltd., Amtrak, Fiddler's Marjack (they make the pop-corn served in many local movie theaters), and MacDonald's.

"How many of you people have been out to a restaurant or had a meal at home and a couple of hours later you wake up and feel nauseious?" begins Ziegler, to scattered affirmative mumbling and a raised hand or two. "Okay, when that happens, what do you say? You say, 'It must have been something I ate.'"

"Well," he says, "as a food service supervisor, it's going to cost you money. These people aren't going to come back."

Personal hygiene - the first day's curriculum - includes the following basic cautions:

Keep your fingernails trimmed;

No nail polish;

No chewing gum;

And, never touch "the business end of the silverware."

After an hour of lecture, Ziegler sets up his slide projector at the back of the room, and shows a picture on the wall of the haughty French chef tossing salad with his hands. Not the preferred practice, says Ziegler. Then a waiter bearing a basketful of uneaten rolls into the kitchen.

"What should you do with those rolls when they come back from the dining room?" asks Ziegler.

"Cover them!" says one student confidently.

Ziegler shakes his head in disappointment. "Throw them out," he admonishes.

Next, a shot of a sleazy dining room watched over by two indifferent waitresses "standing in a corner holding up a post," as Zeigler describes the scene. Both are wearing dirty uniforms. One is scratching her nose. "That reflecs right back on the kitchen," says Ziegler. "It all goes back to the kitchen."

On the following day another slide show features "Jack the Germ," a small, swarthy fellow who travels about perched on waiters' shoulders or clutching a lock of waitress's hair. Bacteria are dangerous, says Ziegler - "in a four-hour period you can have better than 4,000 bacteria from only one."

"We need four things to make bacteria grow, and you are going to have to remember these four things," says Ziegler, giving his students ample time to locate their pens and raise them to the ready position. "Food . . . moisture . . . temperature . . . and time."

The third day is consumed with a discussion of botulism and salmonella and staphylococci and amoebic dysentery and trichinosis - things to be avoided if at all possible. Day four deals with insects and vermin, and their lamentable tendency to associate with our old friend Jack the Germ.

And now at last the time has arrived for the final review and the final exam.The passing score will be 70, says Ziegler and he proceeds to do everything but recite the questions and answers in order. "Below 45 degrees," he reminds us, "what happens? We retard the growth of bacteria. Above 140 degrees, what do we do? Again, we retard growth. The temperature in between 45 degrees and 140 degrees is what?" After a weighty pause: "The DANGER ZONE,"

Lest anyone forget the answers in the five minutes that remain before the exam itself, Ziegler adds this caution: "Out of all the true and false questions, 80 per cent are true. So if you don't know the answer, what do you put?"

Then the proctor arrives with the exam in hand, and hurriedly passes it around before leaving, as he explains, to move an unlawfully parked car. When Ziegler, too, steps out of the room, one of the students immediately starts copying another's answer sheet.

Among the question:

True or False? Unclean hands play an important role in the rtransmission of disease;

Hands should be washed (a) after smoking, (b) after going to the toilet, (c) after handling raw meat or poultry, (d) after sneezing, or (e) all of the above; and

True or False? Water boils at 212 degrees Fahrenheit.