While filming “The Blues Brothers” in 1979, John Belushi was partying so hard that he was often unable to function.

One night, after yet another Belushi delay, director John Landis knocked on the door of his trailer, fed up.

“Inside, John sat disheveled, eyes vacant. Atop a desk sat a mound of cocaine,” writes Daniel de Visé in his new book, “The Blues Brothers: An Epic Friendship, the Rise of Improv, and the Making of an American Film Classic,” (Atlantic Monthly Press, March 19).

“ ‘John, you’re killing yourself,’ Landis cried. ‘Do not do this to my movie. Don’t do this to me. Don’t do this to [Belushi’s wife] Judy. Don’t do it to yourself.’ ”