TheCodeBreakers
period and cemented it there with collodion. Later, one Professor Zapp
simplified the process so that most of these operations could be
performed mechanically in a cabinet the size of a dispatch case. The
microdots, or "pats," as T.O.D. called them, were photographically fixed
but were not developed; consequently, the image on them remained
latent and the film itself clear. In this less obtrusive form they were
pasted onto the gummed surface of envelopes, whose shininess
camouflaged their own. The pats could show such fine detail because the
aniline dye used as an emulsion would resolve images at the molecular
level, whereas the silver compounds ordinarily used in photography
resolve only down to the granular level.
The microdots solved the problem of quantity flow of information for
the Nazis. Professor Zapp's cabinets were shipped to agents in South
America, and soon a flood of material was being sent to Germany
annaabi.ee 
