In the mid and late 1850s, immigrants from Ireland and Germany streamed into the city, swelling the population of Philadelphia and its suburbs. In Philadelphia, as the rich moved west of 7th Street, the poor moved into the upper class' former homes, which were converted into tenements and boarding houses. Many small row houses crowded alleyways and small streets, and these areas were filthy, filled with garbage and the smell of manure from animal pens. During the 1840s and 1850s, hundreds died each year in Philadelphia and the surrounding districts from diseases such as malaria, smallpox, tuberculosis, and cholera, related to poor sanitation; the poor suffered the most fatalities. Small rowhouses and tenement housing were constructed south of South Street.