Secret inks were our stock in trade and all were anxious to obtain some which came from a natural source of supply.

I shall never forget [Captain Cumming’s] delight when the Chief Censor [Frank] Worthington came one day with the announcement that one of his staff had found out that semen would not respond to iodine vapour and told the man that he had had to remove the discoverer from the office immediately as his colleagues were making life intolerable by accusations of masturbation.

[O]ur man in Copenhagen, Major [Richard] Holme, evidently stocked it in a bottle, for his letters stank to high heaven and we had to tell him that a fresh operation was necessary for each letter.

Captain Cumming? Seriously?

Photo via the September 1935 issue of Popular Mechanics.
By Michael Smith via Six: The Real James Bonds 1909-1939.