fabrics soiled by crushing
infected fleas and bugs on them, or by the faeces of these insects
the plague microbes can under favorable conditions remain alive and
virulent during more than five months.

"(16) Chemical disinfectants do not in the ordinary course of
application kill plague microbes in infected fleas and bugs.

"(17) The rat flea _Typhlopsylla musculi_ does not bite human
beings.

"(18) Human fleas do bite rats.

"(19) Fleas found on dogs and cats bite both human beings and rats.

"(20) Human fleas and fleas found on cats and dogs can live on rats
as casual parasites, and therefore can under certain conditions
play a part in the transmission of plague from rats to human
beings, and vice versa."

RESULTS OF VARIOUS INVESTIGATIONS

Various other plague commissions from other countries as well as many
individuals have investigated the same subject, and the results all
point conclusively to the fact that the rats and the fleas are at least
the most important factors in the spread of the disease. The evidence
from many sources and from many experiments may be briefly summed up as
follows: The disease is caused by the presence in the system of minute
bacteria, _Bacillus pestis_. It is probable that plague is primarily a
disease of rats and only secondarily and accidentally, as it were, a
disease of man.

Rats are subject to the plague and are often killed by it in great
numbers. An outbreak of plague among men is often preceded by a very
noticeable outbreak among rats.

Rats dying of the plague have their blood filled with the plague
bacillus. Fleas or other suctorial insects feeding on such rats take
myriads of these bacilli into their stomach and get many on their
proboscis.

The fleas usually leave a rat as soon as it dies and of course seek some
other source of food. When such infected fleas are permitted to bite
other rats or guinea-pigs these animals often develop the disease.
Several of the species of fleas that infest rats will bite man also, and
in the cases of many plague patients it can be definitely shown that
they had recently been bitten by fleas.

STRUCTURE AND HABITS OF FLEAS

A study of the structure and habits of fleas shows that in many respects
they are particularly adapted for spreading such a disease as bubonic
plague. The piercing proboscis consists of three long needle-like
organs, the epipharynx and mandi