London: British spy agency MI6 mulled using bodily fluids like semen as an invisible ink to write top-secret documents, says a new book.
According to the book, `MI6: The History of the Secret Intelligence Service 1909-1949`, a diary entry belonging to a senior member of the Secret Intelligence Service has revealed that during First World War, it was discovered that the bodily fluid could act as an effective invisible ink.
In June 1915, Walter Kirke, deputy head of military intelligence at the general headquarters in France, wrote in his diary that Mansfield Cumming, the first chief of SIS was "making enquiries for invisible inks at London University", says the book.
In October, he noted that he "heard from C that the best invisible ink is semen", which did not react to the main methods of detection.
Furthermore it had the advantage of being readily available, `The Daily Telegraph` reported.
A member of staff close to "C", Frank Stagg, said that he would never forget his bosses` delight when the Deputy Chief Censor said one day that one of his staff had found out that "semen would not react to iodine vapour".
Stagg noted "we thought we`d solved a great problem". However, the discovery also led to some further problems, with the agent who had identified the novel use having to be moved from his department after becoming the butt of jokes, according to the book.
In addition, at least one agent had to be reminded to use only fresh supplies of the `ink` when correspondents began noticing an unusual smell.
The book has been penned by Prof Keith Jeffery of Queen`s University, who was given access to all of MI6 files between those years.