ABSTRACT
The second three examples of ‘classic plagues’ have
two paradoxical things in common. First, they are
among our very oldest diseases. How old remains a
matter of informed speculation, but such evidence as
exists points to a very considerable antiquity going
back to the dawn of agricultural civilizations. Second,
and unlike the classic bacterial diseases considered in
Chapter 2, all three are caused by viruses. Since
viruses are too small to be seen by the light micro-
scope (recall Figure 1.26), they could only be dis-
cerned after the invention of the electron microscope
in the 1920s. Thus smallpox, measles and rabies share
the paradox of their great antiquity but having causal
mechanisms that could only be recognized within the
last 70 years.
