Camille Saint-Saens (1835-1921) was an extraordinary talent, from the age of 10 he played in the Salle Pleyel, and as an encore offered to play anyone of Beethoven's 32 piano sonatas from memory. He studied organ and composition at the Conservatoire de Paris and became good friends with Franz Liszt. He published his first symphony at just 16. He played the organ at St Merri and then at La Madeleine where his weekly improvisations stunned the public, causing Liszt to exclaim he was the greatest organist in the world. He taught only briefly at the Ecole Neidermeyer for 4 years, his pupils include Gabriel Fauré and André Messanger. He spent his latter years travelling and was granted a state funeral at La Madeleine.
Of the 7 Improvisations Op. 150 the nr. 7 is the one that is played the most. The theme sounds like a folk song, but I don't know the name of it. It might as well have been invented by Saint-Saens himself. Saint-Saëns frequently visited his student Périlhou at the organ gallery, often also Fauré then joined in. The three friends then improvised each at his turn during the mass to enjoy lunch later afterwards together. Perhaps these improvisation sessions formed the base for these pieces. Saint-Saens wrote the improvisations around New Year 1916-1917 while he had to stay in bed because of illness.