Has the discovery 
of microbes 
aided health? 
36 WORLD OF INVISIBLE LIFE 
saving of countless human lives. We have 
found out that dirty streets, swamps, and refuse 
heaps caused sickness and the spreading of dis¬ 
ease. And at the same time that clean cities 
are healthful cities. And now we can have 
our great present-day cities, with wide, clean 
streets and pleasant living districts. Diseases, 
such as the Black Plague of the Middle Ages, 
can no longer cause the death of thousands of 
people in one city. Before we found out some 
of the causes of these diseases, the care of a city’s 
health was left largely to chance. As late as 
1832 pigs were the only way of cleaning the 
streets in New York. The old town pump 
found in so many towns was another way in 
which sickness was spread rapidly. But today, 
every city cares about the people’s health. A 
group of men called the Sanitary Board see that 
the streets are cleaned, that the garbage is taken 
away, and that the drinking water is fresh and 
pure. You are taught the value of hygiene in 
school. And there is “clean up” week to remind 
people of the value of cleanliness. 
