Owing to the peculiar position of the United States and its distance from the actual battle-front, about 95 per cent of its postal-censorship work was negative in character and only 5 per cent positive, these terms, “negative” and “positive,” being used in the same sense as they applied to other activities of Military Intelligence. By far the greater part of the mail that required censorship was of a nature which might have caused social unrest, labor troubles, or even rebellion in this country. Only a comparatively small number of letters were intercepted which brought positive information concerning the plans of the enemy or of neutrals. In studying this positive information it was necessary for the censors to keep constantly in mind the fact that the enemy intentionally permitted false information to be sent out, which, were it taken at its face value, might lead us to alter our plans or to relax our efforts. For periods of two or three months, perhaps longer, immediately preceding each of the great German offensives, there trickled into the offices of the censor scores of letters depicting in heartrending terms the social unrest and the appalling food conditions in the Fatherland. Early in 1918 the United States, following the example of France and England, established large chemical laboratories in New York and Washington, where thousands of letters were subjected to tests for invisible ink. The usual letter-paper which is used for communications in invisible ink can be given minor tests without altering its appearance. These preliminary tests are for the purpose of ascertaining whether the paper has been moistened or subjected to other treatment preparatory to the use of invisible ink. In case the minor tests show the paper has received some unusual treatment, a major test is given which results in developing any invisible writing, though it at the same time affects the texture and color of the stationery so that it is impossible to restore it to its original appearance. Practically all mail to or from persons on the suspect lists kept by England, France, and the United States was subjected to such examination.