As cities grew and put more space between cows and people's homes, the longer Journey time allowed bacteria to grow in the milk, causing millions of people to get sick with tuberculosis, scarlet fever and typhoid fever.
He saw death and suffering up close, he was forced into cattle cars, forced to march, contracted typhoid fever, and was separated from his most beloved family members.
Since typhoid fever is one of those olde-timey diseases that isn't talked about much in the modern, industrialized world, this conversation deserves a short foreword on what exactly the disease is.
There's no real evidence that suggests Mallon ever truly believed that she was the cause of all these instances of typhoid fever at the time that she was first arrested and diagnosed.
The final part of our mystery – how it was possible for Mary to give others typhoid fever without herself getting sick from the disease – was not solved until many years later.
Its excursions have been curtailed in rich countries but the disease that it causes typhoid fever is still common in places where modernity has not fully made.