"The world was full of people. The census of 2010 gave eight billions for the whole world—eight crab-shells, yes, eight billions. It was not like to-day. Mankind knew a great deal more about getting food. And the more food there was, the more people there were. ... Eight crab-shells there, yes, eight billion people were alive on the earth when the Scarlet Death began."
Thre were 7.1 billion people who lived on the planet in 2010 according to United Nations.
London, J., (1912) The Scarlet Plague, London, London Magazine