86 
WORLD OF INVISIBLE LIFE 
What was 
“bleeding”? 
beating of tom-toms, or by pounding on the 
body of the sick man until the spirit was so 
uncomfortable that it had to leave. It is easily 
understood why nearly everyone who got sick 
died, when this sort of thing was the only 
treatment. 
As men began to understand a little more 
about their bodies, another idea sprang up con¬ 
cerning the cause of illness. This idea, which 
lasted all through the Middle Ages, when 
terrible plagues often swept over Europe and 
killed millions of people, was that the body 
contained four substances—blood, phlegm, 
yellow bile, and black bile. Health depended 
on the proper mixture of these four substances, 
and if anything upset their proper mixture, 
illness followed. The efforts of doctors were 
spent in keeping this mixture correct, which 
is why they so often took blood out of sick 
people to cure them, for they thought there was 
too much blood in the body, and that this was 
what was making them sick. In the seven¬ 
teenth and eighteenth centuries people had 
