Infectious mononucleosis has been known under different names since 1889, when it was described by E. Pfeiffer1 as glandular fever. Thirty-four years later, Tidy and Daniel2 and Downey and McKinlay3 described the characteristic blood changes and inaugurated the hematologic diagnosis of infectious mononucleosis. The blood changes are very helpful in the recognition of the disease, but they are not pathognomonic. Similar changes are found in several clinically unrelated diseases, particularly acute infections of the pharynx. Furthermore, in the early stages of infectious mononucleosis the characteristic elevation of the mononuclear cells may be absent and the blood picture may show merely a slight to moderate increase of the total number of white cells with a normal differential count.
A second phase in the diagnosis of infectious mononucleosis was initiated in 1932 by Paul and Bunnell,4 when they found that the blood serum of the patients is able,