
pleuropneumonia-like organisms
despite their small size, the pplo carry
the full complement of the chemical com-
pounds and enzymes contained in larger
bacteria and in cells.  they contain both
dna and rna, and in their independent
metabolism they are essentially like other free
living cells in contrast to the viruses which
have no independent metabolism outside the
living host cell.  several strains of pplo have
been cultivated from the mucous membranes
of apparently normal human subjects, espe-
cially from the respiratory and urinary tracts.
until recently, however, definite evidence of
the association between the pplo and clear-
ly defined clinical disease in the human sub-
ject was lacking.  in 1962 it became evident
that the so-called eaton "virus," originally
isolated by eaton and his associates in 1944
from patients with primary atypical pneu-
monia, was in reality a pleuropneumonia-like
organism.  typical pplo colonies are pro-
duced on a cell-free agar medium which is
enriched by the addition of blood serum or
yeast.  a number of strains of pplo has now
been identified, and in recognition of their
unique characteristics, they have been classi-
fied in a separate order, the mycoplasmatales,
genus mycoplasma.
