This year marks the 150th anniversary of an American classic. In 1855, Walt Whitman published a collection of 12 poems he called Leaves of Grass. He continued to add to that collection for the rest of life, and new editions of Leaves of Grass have been appearing ever since. This year's anniversary has inspired readings, exhibits and conferences across the United States.

When the Folger Shakespeare Library in Washington held a reading to honor Walt Whitman this past May, poet Mark Doty was among those who came to pay tribute to the man he calls a spiritual father. "I think none of us as American poets can get away from Whitman," explains Mr. Doty. "He opens the doors to a sense of American identity. He opens the doors to democratic inclusiveness. He is certainly an inventor of free verse. And as such he stands behind American poetic practice."

With the first poem in Leaves of Grass, called Song of Myself, Walt Whitman established himself as a new kind of American poet -- one who celebrated urban life, working class people, and the sheer joy of being alive, as a physical, sexual creature. He wrote in a lyrical voice that aimed to capture the rhythms of everyday speech.

Manuscript Specialist Barbara Bair helped assemble a Leaves of Grass anniversary exhibit at the U.S. Library of Congress called Revising Himself. The exhibit includes one of the only extant pages of trial lines from Song of Myself:

The pure contralto sings in the organ loft
The carpenter dresses his plank
The tongue of his foreplane whistles its wild descending lisp
The married and unmarried children ride home to their Thanksgiving dinner
The pilot seizes the king-pen
He heaves it down with a strong arm.

"This is a celebration of working class America," says Barbara Bair of those lines, "and of the worth of every human being in every kind of occupation, men and women, black and white."

Walt Whitman was born on Long Island, New York, and later lived in Brooklyn and Manhattan. He reveled in the city's energy and excitement, and longed to write poetry that would capture its bustling spirit. He held jobs as a journalist, teacher and printer before publishing the first volume of Leaves of Grass, at his own expense.

Yale University scholar Harold Bloom wrote the introduction for the 150th anniversary edition of that collection, which he says was a homemade work in every way. "He prints it up himself," Mr. Bloom explains. "He sets the type. He chooses the paper. He himself manufactures and does the binding. It has almost no punctuation. He doesn't title the poems. His name isn't even on the title page. It's just called Leaves of Grass."

Whitman even wrote his own enthusiastic review of the book, notes Barbara Bair of the Library of Congress. "It was published anonymously in the newspapers, and it begins 'An American bard at last.' So he was very aware of that legacy of breaking through into a new kind of literature expressive of American life and particularly of the laboring classes and of democracy with a small 'D.'"

Ms. Bair says the Library of Congress selected the exhibit title Revising Himself, partly as a play on words, recalling Song of Myself. "But we also wanted to bring home to visitors the idea that Leaves of Grass was an evolving work, that the first edition in 1855 was a slim, tall book with 12 poems in it, and by the time of Whitman's death in 1892 the so called 'death bed edition' has 400 poems. Throughout his life, he not only added to Leaves of Grass, he changed the poems themselves. He rewrote. He revised. He changed the way they were clustered together. He was a person who never let well enough alone."

The expanding collection reflected changes in Whitman's personal life and the life of the nation. His experience as a Civil War nurse, his grief at the assassination of President Abraham Lincoln, and the struggles of old age all found their way into his work. But if those poems bear the mark of a 19th century life, poet Mark Doty believes they still speak to readers today.

"Whitman is concerned with how to live,' Mr. Doty says, "and he believes that by paying attention to our own bodies and our own experience, we can find a way toward knowledge. That seems very contemporary. Whitman also represents a certain anxiety about being an American -- how we are to be part of this throbbing, new, confusing nation, which seems as confusing and probably as new now as it did in 1855."

Whitman's language remains fresh and startling as well, says Mark Doty. As an example, he points to the poet's lines claiming that "to die is different from anything one supposed, and luckier."

"Who would think it would be lucky to die? Not a way that we would usually talk about death," Mr. Doty notes. "And there you hear the man of the streets, the man of common speech who is using his ordinary language to relay to us a radical spiritual vision."

Walt Whitman has also had a huge impact in other parts of the world, according to Yale University scholar Harold Bloom. He says that poetry written in languages as varied as Spanish, German, Russian and Hebrew bears the mark of Whitman's influence. "He addresses himself to those divisions in each one of us. He knows that we will one thing and frequently do another. But he wants to teach us to be what you might call a singularity, that cares about itself and others, rather than just an individuality."

Walt Whitman, the man who introduced himself to the reading public with his Song of Myself has emerged a century and a half later as a universal poet, who celebrates the connections among us all.