f the microbe of typhoid
fever into the human food to which he has free access after his
previous visits to open latrines. The house-fly is himself a product
of dirt and neglect. The eggs are laid in old manure heaps and kitchen
middens, and the maggots, which eventually are transformed into flies,
nourish themselves in those accumulations. When this refuse is rapidly
and regularly removed by the care of the sanitary officials of a town,
the flies diminish in number, as they have diminished in London within
the last thirty years. We no longer are overrun by flies in London in
the summer months. The man selling sheets of sticky paper is no longer
heard in our streets calling "Catch 'em alive, oh!" But in country
places, where a neglected stable-yard is near the dining room of the
inn, house-flies are as great a nuisance and danger as ever. There is
no difficulty, if the simplest rules of cleanliness are observed, in
abolishing them altogether from human association, but combined and
simultaneous action against them is an essential condition of success.

CHAPTER XXII

IMMUNITY AND CURATIVE INOCULATIONS

During the last twenty years the whole attitude of the study and
investigation of disease-causing microbes has advanced from the
preliminary step of merely identifying certain microbes as the causes
of certain diseases to a further step, viz. that of attempting to
defend the animal and the human body against their attacks in the
manner already so finely started by Pasteur. For many years disease
after disease was examined and found to be caused by special bacteria
or other microbes. Even non-infectious diseases or diseases only
communicable under very special conditions were found to be due to
microbes, so that it is probable that all disease that is not due to
congenital malformation or to mechanical injury, or to poison
fabricated in the weapons of larger animals and plants, or by man
himself, is due to microbes. "Life," says Lord Justice Moulton, "is
one ceaseless war against these enemies, and the periods of our
too-transient successes are known as health." One of the last diseases
traced to microbes is that sad condition known as "infantile
paralysis," by which so many of the brightest and best members of the
community have been crippled, from childhood onwards, through life.

Of late we have been making rapid strides in arriving at a knowledge
as to how Nature herself protects higher creatures from the ex