Imagine living in darkness. You’re in a room the size of a closet. With your entire family.



You can't see a thing, but you can hear and smell everything. Every breath, sneeze, cough that hits your face.



This is life in a 19th century city.



There's a story of 19th century American history, which is about progress, the rise of America to becoming a great economic power.



But there's a pretty grim underbelly to that story and that is a really shocking rate of death to infectious diseases.



America in the 1700s is to a large extent a country of hamlets and villages and small towns with a few cities which are slowly growing.



Come the 1800s, cities like Boston and New York are doubling and doubling again.



Technological innovation was thriving.



Titans of business like Rockefeller and Carnegie were growing industries at unprecedented rates.



Railroads were transporting people and things faster.



Machines were making things more efficiently than humans ever had in history. This was quite literally a revolution.



Tons of new jobs were created. Millions of people poured into the cities to work.



Tons of new jobs were created. Millions of people poured into the cities to work.



But here’s the thing. The cities weren’t ready for all those people.



So, places like New York City ended up packing these newcomers into cheap apartments, or “tenements”. They were small and rarely had windows, so there was no light or ventilation.



What this means is that people are living in very, very close proximity to lots of other people. Houses are overcrowded, they're working in factories, they're breathing on one another, they're contaminating one another with their germs and also with feces.



That’s right. Feces.



That’s because there weren’t proper sanitation or sewer systems or clean water supplies.



So, very rapidly people are starting to drink water which contains feces from their neighbors.



Really it got to the point in which these cities are so big, so crowded, so dirty and unhealthy where everybody's life is in jeopardy.



There were a number of diseases that claimed a lot of lives. The most serious were respiratory illnesses and the biggest killer of all was tuberculosis.



Tuberculosis killed 1 in 7 in the United States and Europe.



At this point, people came to suspect that their living conditions influenced their health.



They began to argue really forcefully that if you want to combat diseases you've simply got to clean up the slum areas. They start making efforts to do so. In fact, in New York in the 1830s, they have people sweep the streets, and this really has barely been done for decades and they're amazed to find that underneath all of the muck and the filth and the decomposing animal bodies, they're actually cobblestones.



They're all doing this because they believe in what were called miasmas.



It's these gases that rise up from decomposing matter, which they believed somehow caused sickness.



But the effort to clean cities got a major push in the late-19th century, when doctors and scientists were able to prove that diseases were not caused by miasmas but by germs.



One of those doctors was Robert Koch.



Robert Koch was a German general practitioner who devoted endless hours to investigating disease under the microscope.



He discovered that specific germs caused specific diseases. But he’s probably best known for his work in tuberculosis.



He discovered the germ responsible, and found that it’s transmitted through the air.



Now that people realized what causes infectious disease, they have every incentive in making sure that people have clean water and they have sewage pipes to take away the effluence. What this leads to is large scale civil engineering projects across America.



Due to the improved access to clean water in the first few decades of the 20th century, U.S. cities saw an estimated 50% drop in mortalities.



Laws were also passed to reform housing in the cities to ensure residents had sufficient light and proper ventilation in their homes.



In less than 20 years, the death rate from tuberculosis plummeted from 1 out of every 7 to more like 1 in 1,000 in the U.S.



Robert Koch even got a Nobel Prize for the impact of his tuberculosis research.



Life generally was getting better and better for Americans and that was reflected in their improved health. But knowing that germs cause disease was a significant component of that.