The sine qua non in plague prophylaxis is the diagnosis. This is not so easy a matter as some are led to believe. The many forms which plague infection may assume, taken together with its insidious character, the inexperience of the medical profession of a given place, may render its recognition extremely difficult, even notwithstanding the fact that accurate methods of examination can, with certainty, be relied on to detect it.
The chief difficulty, however, which confronts one is that it may be so easily diagnosed as one of certain diseases of local origin, which it may so closely resemble, that it is an easy matter to overlook it. If the first cases were of the frank type—the bubonic—the task would be made easy. As a rule, this does not occur, and the ease in recognizing them as advocated by some is more a theory than a condition.