Pneumocystis pneumonia is a disease which has been recognized only recently in the United States, although it has been observed in Europe since the early part of this century.1 Re-examination of autopsy material at one institution indicates that the disease occurred in North America 30 years ago.2
The presumptive causative organism, Pneumocystis carinii, has been well characterized morphologically3,4 and is present in lungs in two forms. The cystic form of the organism is easily stained with a methenamine silver preparation and is slightly larger and more irregular than an erythrocyte. The vegetative forms are small, about 1μ in diameter, and are most frequently found within the cysts. There may be as many as eight in a single cyst. In addition to those in cysts, the vegetative forms are sometimes found free in the foamy exudate in alveoli and may occasionally be seen within macrophages. These forms are
GILBERT CF, FORDHAM CC, BENSON WR. Death Resulting From Pneumocystis Pneumonia in an Adult. Arch Intern Med. 1963;112(2):158–163. doi:10.1001/archinte.1963.03860020056003
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