(F) the size of Io’s molten lakes
(G) the disappearance of impact sites on Europa
(H) the discovery of volcanic activity on Io
(J) the evidence of asteroid bombardment on all four moons
(K) the accuracy of Galileo’s original observationsFor thousands of years, smallpox was one of the
world’s most dreaded diseases. An acutely infectious
disease spread by a virus, smallpox was the scourge of
medieval Europe, where it was known by its
( 5 ) symptoms of extreme fever and disfiguring rash as
“the invisible fire.” In many outbreaks, mortality rates
were higher than 25 percent. Ancient Chinese medical
texts show that the disease was known as long ago as
1122 BCE. But as recently as 1967, more than 2
( 10 )million people died of smallpox in one year.
The first method developed to combat smallpox
was an attempt to immunize healthy patients. In a
procedure called variolation, known since the ninth
century CE, a healthy patient’s skin was deliberately
( 15 )scratched with infectious material from a person with
a mild case of smallpox. If the treatment was
successful, the patient suffered a mild smallpox
infection and then became immune to the disease. By
the 18th century, when smallpox epidemics were
( 20 )regular occurrences, variolation was a common
practice among the wealthy and aristocratic.
Unfortunately, variolation sometimes led to severe,
even fatal, infections. Moreover, even if it was
successful, the patient could spread smallpox to
( 25 )others.
A safer method of conferring immunity was
discovered in 1796 by an English doctor named
Edward Jenner. Jenner, who had himself undergone
the variolation process as a child, was fascinated by
( 30 )the fact that people who caught cowpox, a harmless
disease spread by cattle, became immune to smallpox.
To test whether this immunity could be replicated,
Jenner inoculated a young boy with infectious matter