One hundred years ago, in the autumn of 1912, an African-American musician by the name of WC Handy published a song that would take the US by storm - Memphis Blues. It launched the blues as a mass entertainment genre that would transform popular music worldwide.
In 1903 William Christopher Handy was leading a band called the Colored Knights of Pythias based in Clarksdale, in Mississippi's Delta country, when one day he paid a visit to the little town of Tutwiler.
"A lean loose-jointed Negro had commenced plunking a guitar beside me... His face had on it the sadness of the ages," Handy writes in his 1941 autobiography, Father of the Blues.
"As he played, he pressed a knife on the strings of the guitar in a manner popularised by Hawaiian guitarists who used steel bars... The singer repeated the line three times, accompanying himself on the guitar with the weirdest music I had ever heard."
The music was "weird" because it was new.
The blues is not, as some imagine, as old as the hills. According to David Wondrich, author of Stomp and Swerve: American Music Gets Hot, it was "a particular creature of the 1890s".
Handy describes the 12-bar form "with its three-chord basic structure (tonic-subdominant-dominant seventh)" as one widely used "by Negro roustabouts, honky-tonk piano players, wanderers and others of their underprivileged but undaunted clan from Missouri to the Gulf [of Mexico]".
It had become, he says, "a common medium through which any such individual might express his personal feelings in a sort of a musical soliloquy".
Handy himself was from a very different world. A skilled, musically-literate, and well-travelled band leader from northern Alabama, he nonetheless saw the possibilities in this form of music, and when in 1909 he moved to Memphis, Tennessee, he took some of the music he had heard in Mississippi and rearranged it for his band.
"It did the business too," writes Handy. "Folks went wild about it."
In 1912, with the recording industry still in its infancy, Handy published one of his compositions on paper as Memphis Blues. It was a hit.
"Handy's Memphis Blues was hugely significant," says Elijah Wald, author of The Blues: A Very Short Introduction. "It started the blues craze and made the blues a key marketing term."
Memphis Blues became the song of 1912, the song people were asking to hear in dance halls nationwide.
"Memphis Blues was spread by the sale of sheet music and by the fact that every dance band in America was being asked to play it, and was playing it," says Wald.
For Handy, writing in the late 1930s, Memphis Blues "was the first of all the many published 'blues' and it set a new fashion in American popular music and contributed to the rise of jazz, or, if you prefer, swing, and even boogie-woogie".
As originally published, Memphis Blues is an instrumental piece, about three minutes long in the earliest recording.
It contained both 16-bar melodies that the audience was used to, and innovative 12-bar sections, and mixed regular two-four time with the Afro-Cuban habanera dance rhythm.
As for the melody, it uses "what have since become known as 'blue notes'," said Handy, "the transitional flat thirds and sevenths... by which I was attempting to suggest the typical slurs of the Negro voice".
From the moment it emerged into US mass culture, blues was popular music for both blacks and whites.
Black dance styles had already been popular in white society for two decades. Teddy Roosevelt had even led a cakewalk - a former slaves' dance - in the White House during his presidency (1901-1909).
"It was an exaggerated dance and very hard to do. It was like the thing you used to see on Soul Train," says Wondrich.
The cakewalk paved the way for a host of other dances, including the turkey trot, the possum trot, and the grizzly bear. "These all came out of low music halls, dive bars and whorehouses, basically," says Wondrich.
If you had wanted to see such dancing in 1894, you would have had to go to red-light districts. But less than a decade later, these dances had been toned down and were being popularised by people such as the ballroom dancing enthusiasts Irene and Vernon Castle.
Vernon was an Englishman from Norwich, Irene a white New Yorker, and together they became leaders of fashion in New York City. The dance that the Castles promoted was the foxtrot, which was invented in 1914. It was a little more sedate than the earlier animal dances but still had some of their sexy energy.
The Castles had a night club near New York's Times Square and they hired a black band leader, James Reese Europe, to supply the music. Europe's Society Orchestra played the latest black dance music, including by 1914 Handy's Memphis Blues. So the blues and the foxtrot emerged hand in hand.
In 1914, Handy followed up Memphis Blues with his next hit, another 12-bar blues piece with a 16-bar habanera section. The song was called St Louis Blues. It was even more popular and influential than its predecessor and it went on to become a jazz standard played by musicians such as Louis Armstrong, Count Basie and, the queen of 1920s blues, Bessie Smith.
Part of the success of the blues can be attributed to changes in the role of black people and women in US society.
Blacks had fought with distinction in the Spanish-American War and would enlist en masse during World War I. One key difference between Handy's blues and earlier black-inflected popular music, says Chris Kjorness of Longwood University, was that it was no longer played for laughs. It lacked the white mockery of the minstrel show.
Women, meanwhile, were going out to work in ever larger numbers, especially in the big cities, in offices and department stores. They wanted to have fun.
"Before the teens (1910-1920), the idea of going out dancing un-chaperoned didn't exist," says Wald. "But from the mid-teens you start to see dance halls where unmarried young people can go out to dance."
By 1917, records (78 rpm singles) had come of age. The Original Dixieland Jass [sic] Band - a white quintet from New Orleans - released Livery Stable Blues, which is thought to have sold as many as a million copies. Bessie Smith's version of St Louis Blues was even filmed in a kind of predecessor of today's music videos - she acts out the part of a woman knocked to the ground by a two-timing boyfriend, and then moves to a bar to sing the blues.
There has always been more than one school of blues playing - the commercial and the non-commercial, the band and the solo performer - and the various schools have influenced and cross-fertilised each other.
"The style that emerged in the 1910s and '20s was largely created by professional entertainers and greeted by audiences as a modern pop trend," says Wald.
Blind Lemon Jefferson, the star of 1920s country blues, who sang and accompanied himself on the guitar, "devoted the overwhelming majority of his records to material that reflected the commercial blues craze," Wald adds.
A very different kind of musician also acknowledged his debt to Handy.
"In a letter to Handy, George Gershwin thanked him for helping him to write Rhapsody in Blue," says Barbara Broach, director of the W C Handy museum in Florence, Alabama.
The blues went on to have a major influence on jazz, soul, rock and roll, and heavy metal.
Handy did not invent the blues. As a musical style, it had deep roots in African-American culture. But the Memphis Blues did start the commercial blues craze. In Handy's words, the song introduced "the blues form to the general public", and the American public introduced it to the world.
Barbara Broach was speaking to Newshour on the BBC World Service