I've been on a journey of late to learn more about where my family comes from. My Catholic grandfather's dad came over on a boat from Italy. But of my three Jewish grandparents, all of whom were born in the United States, only one is alive, and she doesn't know where her parents emigrated from. Germany and Poland are safe guesses, but that barely narrows the field.

This led my wife to note last weekend that we should both learn more about our family histories before there is no one left to learn from. Today, The New York Times profiles an 81-year-old substitute teacher who is ensuring his students don't suffer from a broken oral history.

He is no beleaguered sub from Central Casting. He has never had to call security. He does not even have to write his name on the blackboard. Everyone knows Mr. Blume.

In a school where the average age of the teachers is under 40, and the students’ grandparents include many of the baby-boomer cohort, Mr. Blume has emerged as a sort of older person in residence, an on-call doctor of memory.

He is the only person in the building, for instance, who remembers the shantytown Hooverville that once blanketed Riverside Park at 72nd Street. He talked about it the other day in Miss Mostrande’s eighth-grade social studies class.

He is the only one who had ever heard of, much less laid eyes on, a sign that said “No Jews, No Negroes, No Dogs Allowed.”

The Jewish history was passed down from an oral tradition, and, in two weeks, Jews will observe Yom Hashoah, or Holocaust Remembrance Day. It's been 62 years since World War II ended and Hitler's plan to exterminate the Jews failed, though not without taking 6 million Jews and millions of Gypsies, Slavs, gays and the disabled. The Holocaust seems so long ago, even child survivors are now approaching and surpassing old age.

One of the lessons I've learned from writing a few Yom Hashoah stories over the years is that some survivors want to keep telling their story so the Holocaust deniers will never be able to gain a foothold in shaky future historic texts.