I found whole areas of the cellars of both hoes were full of nightsoil to the depth of three feet, which had been permitted for years to accumulate from the overflow of the cesspools…. Upon passing through the passage of the first hose I found the yard covered in night soil, from the overflowing of the privy to the depth of nearly six inches and bricks were placed to enable the inmates to get across dryshod.”
-- Henry Mayhew (Monday, August 28: The Night Soil Men paragraph 17)

Importance: Human excrement was called nightsoil in 1850s London. When landlords failed to remove the night soil because of the expense to do so, the results were as described above making for a very unhealthy environment.

With houses looking on, one every side, save where a reeking little tunnel of a court gives access to the iron gate – with every villainy of life in action close on death, and every poisonous element of death in...
-- Charles Dickens (Monday, August 28: The Night Soil Men paragraph 41)