s a whole, no single feature will stand out with
greater distinctness than the fulfilment of the prophecy of Descartes
that we could be freed from an infinity of maladies both of body and
mind if we had sufficient knowledge of their causes and of all the
remedies with which nature has provided us. Sanitation takes its place
among the great modern revolutions--political, social and intellectual.
Great Britain deserves the credit for the first practical recognition of
the maxim salus populi suprema lex. In the middle and latter part of
the century a remarkable group of men, Southwood Smith, Chadwick, Budd,
Murchison, Simon, Acland, Buchanan, J.W. Russell and Benjamin Ward
Richardson, put practical sanitation on a scientific basis. Even
before the full demonstration of the germ theory, they had grasped the
conception that the battle had to be fought against a living contagion
which found in poverty, filth and wretched homes the conditions for its
existence. One terrible disease was practically wiped out in twenty-five
years of hard work. It is difficult to realize that within the memory of
men now living, typhus fever was one of the great scourges of our large
cities, and broke out in terrible epidemics--the most fatal of all to
the medical profession. In the severe epidemic in Ireland in the forties
of the last century, one fifth of all the doctors in the island died
of typhus. A better idea of the new crusade, made possible by new
knowledge, is to be had from a consideration of certain diseases against
which the fight is in active progress.

Nothing illustrates more clearly the interdependence of the sciences
than the reciprocal impulse given to new researches in pathology
and entomology by the discovery of the part played by insects in the
transmission of disease. The flea, the louse, the bedbug, the house fly,
the mosquito, the tick, have all within a few years taken their places
as important transmitters of disease. The fly population may be taken
as the sanitary index of a place. The discovery, too, that insects are
porters of disease has led to a great extension of our knowledge of
their life history. Early in the nineties, when Dr. Thayer and I were
busy with the study of malaria in Baltimore, we began experiments on
the possible transmission of the parasites, and a tramp, who had been
a medical student, offered himself as a subject. Before we began, Dr.
Thayer sought information as to the varieties of mosquitoes kn