Maria Lagunas is slapping dough balls into tortillas. I stand watching her near the front door of the original Ninfa's on Navigation. After a short wait, we are seated in the old dining room near a huge enlargement of Mama Ninfa's wedding picture. "She was skinny then," says our waitress, with a laugh. "I think she was 18 or 19 in that picture." A photo of the latter-day Mama Ninfa appears on the menu. She appears well fed. I order her specialty fajitas.

The green and red hot sauces served with the chips at Ninfa's have radically different heat levels. The red is hot, while the green is mild and creamy. "Ninfa's was the first place I ever saw both red and green hot sauces," Houston food lover Jay Francis remembers. "Pretty soon after that, Molina's and other places were offering a variety of table sauces, too. But it was Ninfa's that really got the salsa thing started." The original Ninfa's is also largely responsible for the fajita craze that swept the country late in the last century.

A press release distributed to newspapers a few months ago states, "It is a fact that a true legend of the food business, Mama Ninfa Laurenzo of Houston, Texas, originated the first fajita in the United States in 1973."

The year 1973 was a remarkable one in the Mexican restaurant business; it could be called the year that the paradigm shifted. It was the year the term "Tex-Mex," as a food description, first appeared in print, according to the Oxford English Dictionary.

The Cuisines of Mexico, by Diana Kennedy, was published in 1972; by 1973 it was a national sensation. For the first time ever, an author clearly spelled out the difference between real Mexican food and Americanized Mexican cuisine to stateside diners. Kennedy berated the "mixed plates" that pass for Mexican food in this country and challenged readers to raise their standards. It was no coincidence that Kennedy's cookbook, Mama Ninfa's restaurant and the term "Tex-Mex" all entered the American food scene at the same time.

The term "Tex-Mex" was first coined as the nickname of the Texas Mexican Railway, which was chartered in 1875. The Tex-Mex railroad was built by English engineers and Mexican laborers. They communicated with each other in a half-English, half-Spanish patois that came to be called Tex-Mex Spanish.

The modern definition of Tex-Mex, according to the OED, is "designating the Texan version of something Mexican." The dictionary cites usage of Tex-Mex Spanish as early as 1941. The OED also notes that the first use of the term in relation to food occurred in 1973 in this quote from the Mexico City News, an English-language newspaper for American tourists and expatriates: "It is a mistake to come to Mexico and not try the local cuisine; it is not the Tex-Mex cooking one is used to in the United States."

Americanized Mexican food has long been reviled in Mexico City. In the Diccionario de Mejicanismos, first published in the Mexican capital in 1958, the Texas dish chili con carne is defined as (roughly translated) "a detestable food passing itself off as Mexican in the United States." The English-born Diana Kennedy moved to Mexico City to be with her husband, the late Paul Kennedy, a New York Times correspondent. Her culinary point of view reflected the Mexican capital's anti-American bias.

Disdain from rich Mexicans never bothered Texans much. After all, the members of the Europeanized elite in Mexico City also turned up their noses at native Indian foods, such as chili peppers, corn and squash, and the rustic vaquero cooking of the northern ranch lands. These sophisticates of Spanish descent believed that only such elaborate dishes as chiles en nogada (chilies in walnut sauce), huachinango a la veracruzana (red snapper in a tomato, olive and caper sauce) and mole poblano (chili, chocolate, sesame and raisin sauce) represented the true mestizo spirit of Mexican cuisine.

The Cuisines of Mexico was a breakthrough cookbook, one that could have been written only by a non-Mexican. It unified Mexican cooking by transcending the nation's class divisions and treating the food of the poor with the same respect as the food of the upper classes.

Thanks in large part to the influence of Kennedy's friends at The New York Times, particularly the late food editor Craig Claiborne, The Cuisines of Mexico became the definitive book on Mexican cooking. Its sermons on the inferiority of this country's Mexican food were accepted as gospel by food-savvy Americans who soon started using the derogatory term Tex-Mex to describe it.

To some extent, the Tex-Mex coinage was unfairly arbitrary. Italian-American cooking of that era wasn't authentic, and Chinese-American cooking wasn't either. But nobody coined any new names for these cuisines. The effect that her prejudices were having on Mexican-Americans never occurred to Diana Kennedy. She had never lived in the United States, and didn't know anything about the League of United Latin American Citizens, La Raza Unida or the problems of Mexican-Americans. Fair or not, Kennedy's criticisms triggered a culinary paradigm shift.