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Determination of the total number of Fleas per Rat.—The dead rat was
carefully taken from the lethal chamber and placed on a large square of white paper.
The interior of the chamber was then examined for fleas which might have jumped or
fallen from the rat. The rat was then held by the tip of the tail and the fur was
combed with a fine comb in a direction away from the operator or " against the grain."
The whole fur of the rat was thus searched, particular attention being paid to the
inguinal regions, abdomen and neck.
The cadaver was next lifted by the tip of the tail and well beaten all over with a
light rod. This operation was followed by a similar beating of the cadaver held
suspended by the ears. (This procedure may with advantage be repeated two or
three times.) All fleas obtained as a result were collected to await identification and
were labelled under the serial number allotted to the individual rats.
The following particulars of the rat were recorded—
(1) Serial number.
(2) Date of capture.
(3) Locality of capture, and nature of premises.
(4) Species.
(5) Sex ; and in the case of females whether pregnant.
Preparation of Fleas for Identification.—The medium employed for
clarifying fleas for identification was absolute Phenol. The Phenol was warmed to
melting-point, the specimens were immersed therein and subjected to the action
of the Phenol for some ten minutes. Such treatment shows up clearly the necessary
distinguishing features of the specimens, which may be preserved indefinitely in this
medium. Should permanent preparations, mounted in Balsam, be desired, it is
necessary only to pour off the excess of Phenol and drop on the Balsam.
When fleas from many rats had to be identified it was found convenient to employ
a special porcelain tile containing twelve depressions, each depression being numbered
and of about 1 c.c. capacity. By this means fleas from twelve rodents could be
cleared simultaneously.
The identification of the fleas was carried out under the low power of the microscope.
All fleas examined were allotted to their respective genera, were numbered by
sexes, and the results were entered on the card index under the serial numbers of
their respective hosts.
Area investigated.—For the purpose of rat control the Port of London Sanitary
area is divided into six zones, which are as follows:—
A. London Dock, St. Katharine Dock, Regent's Canal Dock and wharves on
the North side of the River Thames.
B. Surrey Commercial Dock and wharves on the South side of the River Thames.
C. Millwall Dock, Poplar Dock and West and South West India Docks.
D. Royal Albert and King George V. Docks.
E. Victoria and East India Docks.
F. Tilbury Dock and lower reaches of the Thames up to and including the
Medway.
During the course of this investigation all rats examined have been trapped in
one or other of these zones.
The area involved in Zone B. is extensive and includes several privately-owned
wharves not within the area of jurisdiction of the Port Sanitary Authority. From
those private wharves, through the courtesy of the proprietors, many rats were
collected and examined.