The correct answer to this open question is the following.
According to "How the Other Half Lives," wastewater in sinks filled the building with a terrible smell.
In a time when nobody paid attention to the terrible conditions in which immigrants and poor people lived in large cities, photographer Jacob Riis (1849-1914) documented the life of these people in his book "How the Other Half Lives," taking many photographs of crowded living spaces in New York City. The result of his work was that it generated a kind of consciousness on this terrible issue focused on social reformations.
