S e c o n d e d I t I o n 1 Reading for the Real World 1

willow
bark called 
salicin
. When a person eats salicin, the 
chemical is changed inside his or her body into salicylic acid. It turns out that 
salicylic acid is good for stopping pain, including headache pain, but it is bad for 
a person’s stomach. In the 1800s, a chemist in Germany changed the acid’s form 
a little to make it easier for people to take. This new form of the chemical was 
called acetylsalicylic acid, commonly known as aspirin today.
Aspirin was used throughout most of the 1900s to treat headaches, but 
doctors had little idea about what really caused headaches. When doctors know 
the cause of a disease, they can find better ways to treat it. Therefore, as medical 
technology developed, doctors began to use the technology to learn more about 
the human brain and about headaches. 
Currently, doctors classify headaches into two general types: primary and 
secondary. A primary headache is a condition suffered as only the headache itself. 
4
severe --- strong; very bad
5
estimate --- a guess; approximate calculation
9
Hippocrates --- a Greek doctor who started the study of medicine
14
willow --- a kind of tree, having narrow leaves
14
salicin --- C
13
H
18
O
7
; a glucoside related to the sugar family
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On the other hand, a secondary headache is one caused by another condition. 
For example, someone who catches the flu may suffer from headaches along with 
other 
symptoms
of the illness. Flu headaches are thus secondary headaches. 
For primary headaches, doctors have determined three possible causes. One 
kind of primary headache is caused by stress. Doctors usually call headaches of 
this kind