"It tastes so old-fashioned," said a friend who came along to lunch recently. "It reminds me of my childhood. The chicken and the soft tortillas with sour cream, it's like chicken and dumplings, comfort food."

Between the 1970s and 1980s, the "American melting pot" was being replaced by the "American mosaic" as the official metaphor for ethnic assimilation. At the same time, America's tastes in food were growing more adventurous. Influenced by Diana Kennedy and other proponents of authentic Mexican cuisine, food lovers sought more assertive flavors. Old-fashioned Mexican food like Felix's began to be referred to, condescendingly, as Tex-Mex.

A crop of restaurants that reflected the new mood, including the original Ninfa's on Navigation, sprang up starting around 1973. Their slogans promised authenticity, just as the Original Mexican Restaurant and Felix had before them. "Our food is so Mexican, don't drink the water here," read the sign for a defunct Mexican restaurant across from Market Square Park. But in fact, the new Mexican restaurants weren't much more authentic than the ones they replaced. The new menus touted fajitas, soft (flour tortilla) tacos, chimichangas, burritos and other dishes of Mexican-American ancestry that were unknown in Mexico City. This new kind of Mexican food featured fresh spicy salsas, charcoal-grilled meats and seafood, and dishes that seemed much more distinctive than the combination plate. Monterrey House, El Chico and the other giants of 1950s-style Tex-Mex declined in popularity or went out of business. A few old Tex-Mex restaurants, like Molina's [5227 Buffalo Speedway, (713)432-1626; 7901 Westheimer, (713)782-0861; 3601 South Highway 6, (281)497-1800], Loma Linda on Telephone Road, the Original Mexican Cafe in Galveston [1401 Market, Galveston, (409)762-6001] and Felix's last restaurant on Westheimer, seem to remain open for reasons of nostalgia. Run by Felix Tijerina Jr., the lone Felix location is frequented mainly by patrons who have been eating there for half a century.

Here are a few of the entries in the guest book that stands in Felix's foyer:

"My husband and I ate here regularly in the '50s. This is a nostalgia trip for me. The food is as delicious as I remember it."

"I have been coming here my whole life. This is my favorite restaurant. I came from New Braunfels four hours away."

"We have been coming here since the early '50s; we remember Mr. Felix."

If Felix's customers all appear to be over 60, across town at Molina's on Buffalo Speedway, most of the tables seem to be occupied by people under 12. I order the Mexico City Dinner ($8.55) because of the irony of the name. The first plate includes a beef taco, a bean tostada, a puffy taco with queso and an order of guacamole. The second plate is made up of cheese enchiladas in chili gravy, a tamale with chili con carne, and rice and beans. Pecan pralines are included in the price of the dinner, just like in the good old days. I can just imagine what the Mexican food snobs would have to say about puffy tacos and chili con carne.

Molina's combination plate is similar to Felix's, but the chili gravy has more bite and better body. It's made with ancho peppers and a lard-and-flour roux. Molina's was founded in 1941 by Raul Molina Sr., who is now in his nineties. His son, Raul Molina Jr., is semiretired as well. The operation is now run by the third generation of Molina family restaurateurs, including Raul the third.

The amazing thing about Molina's is all the kids eating here. Outside in the parking lot, I approach a family leaving the restaurant. Ken and Martha Johnson tell me they are from Bellaire as they secure their daughters, Caroline, eight, and Annabelle, six, in the backseat of a Honda minivan. I ask them why they chose Molina's for dinner.

"The kids like it. They eat their dinners," Martha Johnson tells me.

I ask her if she doesn't prefer other Mexican restaurants with spicier food and more modern dishes. "Yeah, but if we go somewhere where the food is spicy, the kids won't eat. And then when we get home, they say they're hungry and we have to feed them again," she says. She admits there's a nostalgia factor, too. "I grew up eating this kind of classic Tex-Mex. But the truth is, we don't like our food as hot as we used to, either."

From the "genuine Mexican food" of George Caldwell in 1907 to the claims you hear today, Mexican restaurants have always promised authenticity and have always delivered what sells. The real changes that have taken place are in the public's tastes. And understanding the way our tastes have changed can tell us a lot about where we're going and where we've been.