Paris in 1806 still had nearly the same sewers numerically as stated in 1663; five thousand three hundred fathoms. After Bruneseau, on the 1st of January, 1832, it had forty thousand three hundred metres. Between 1806 and 1831, there had been built, on an average, seven hundred and fifty metres annually, afterwards eight and even ten thousand metres of galleries were constructed every year, in masonry, of small stones, with hydraulic mortar which hardens under water, on a cement foundation. At two hundred francs the metre, the sixty leagues of Paris’ sewers of the present day represent forty-eight millions.

In addition to the economic progress which we have indicated at the beginning, grave problems of public hygiene are connected with that immense question: the sewers of Paris.