Within recent years the recognition of interstitial plasma-cell pneumonia has increased in America. The problem of its etiology is still unfolding, for now it is recognized here in the United States and in Europe that the majority of instances of interstitial plasma-cell pneumonia are really Pneumocystis carinii infections. This latter condition, like interstitial plasma-cell pneumonia, has been reported often from many European countries but has only recently been observed in the United States.1 Perhaps this circumstance may be due to the fact that it was not looked for in the material in the United States.
Pneumocystis carinii is an organism whose taxonomic classification remains controversial. By some it has been stated to be a protozoan, and by others it is called a fungus.2 Chagas first discovered the organism but erroneously believed it was a stage of development of Trypanosoma cruzi.3 After observations by several investigators5-13 it