Page "belles_lettres" Paragraph 51

Now we must become vague, for we are approaching one of the nation's most guarded secrets.

The codes in the red box -- there are several of them covering various contingencies -- are contained in a sealed X-ray-proof `` unique device ''.

They are supplied, a batch at a time, by a secret source and are continually changed by Wisman or his staff, at random intervals.