I was listening to some Sherlock Holmes stories last night, and it occurred to me that Holmes and Watson never once call each other by their first (Christian) names, despite the length (depth?) of their friendship. I know that men usually called their male friends and associates by their surnames (the only exception in Victorian literature that I can think of off the top of my head is Pip and Herbert in Great Expectations, when the two characters specifically give each other permission to use Christian names), and that the custom dates to well before Victorian times; but when did it die out? After WWI, when so many other social customs changed? As a side note, in all of the modern "re-interpretations" of the Sherlock Holmes characters/series, the characters refer to each other as John and Sherlock (with the notable exception of The Abominable Bride, when the writers preserved historical accuracy in that regard).