We have learned that pestilences will only take up their abode among
those who have prepared unswept and ungarnished residences for them.
Their cities must have narrow, unwatered streets, foul with accumulated
garbage. Their houses must be ill-drained, ill-lighted, ill-ventilated.
Their subjects must be ill-washed, ill-fed, ill-clothed. The London of
1665 was such a city. The cities of the East, where plague has an
enduring dwelling, are such cities. We, in later times, have learned
somewhat of Nature, and partly obey her. Because of this partial
improvement of our natural knowledge and of that fractional obedience,
we have no plague; because that knowledge is still very imperfect and
that obedience yet incomplete, typhus is our companion and cholera our
visitor. But it is not presumptuous to express the belief that, when our
knowledge is more complete and our obedience the expression of our
knowledge, London will count her centuries of freedom from typhus and
cholera, as she now gratefully reckons her two hundred years of
ignorance of that plague which swooped upon her thrice in the first half
of the seventeenth century.

Surely, there is nothing in these explanations which is not fully borne
out by the facts? Surely, the principles involved in them are now
admitted among the fixed beliefs of all thinking men? Surely, it is true
that our countrymen are less subject to fire, famine, pestilence, and
all the evils which result from a want of command over and due
anticipation of the course of Nature, than were the countrymen of
Milton; and health, wealth, and well-being are more abundant with us
than with them? But no less certainly is the difference due to the
improvement of our knowledge of Nature, and the extent to which that
improved knowledge has been incorporated with the household words of
men, and has supplied the springs of their daily actions.