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(17) Poisons are most suitable for use in the open, particularly when there is little
risk of domestic animals picking up the bait, and in the case of open spare ground, such
as that which is left after the demolition of a building, poisons judiciously laid down
undoubtedly represent the best means of attack.
Inside premises the main objection to poisoning is that where the rat has made a
room its natural home, the rat frequently dies on the premises. In such cases, therefore,
repeated poisoning means a continual increase of dead rats lying in inaccessible
places. To meet this difficulty I note that it is suggested in the Memorandum on
Destruction of Rats and Mice issued by the Ministry of Agriculture—"That there is
always a possibility of a rat dying under floorings or behind wainscoting, either through
poison or otherwise. If a rat from a drain takes poison and cannot regain its habitation,
the carcase will most probably become putrid. If such a rat dies near a fireplace
or a hot-water pipe, the stench will be intensified. Chloride of zinc is a good
deodoriser in such cases, and combines with and neutralises the offensive chemical
products of putrefaction. If necessary a hole should be bored with a bit and brace in
the vicinity of the supposed origin of the odour if possible. Some perfume or pine
wood oil can be added to the zinc chloride, which should be applied through a hole,
A cork will close the orifice and can be withdrawn from time to time to ascertain
whether the nuisance has abated."
It is not always easy to locate with even approximate precision the exact place of
origin of a smell, and deodorisation does not appear to be the remedy. Particularly is
this the case if, as suggested, repeated invasions, as must result in many premises in
the City, are dealt with by poisoning. For these reasons, I prefer to suggest that rats
should be exterminated inside business premises by means which ensure the bodies
being readily recovered.
(18) VIRUSES.—Viruses have been on the market for a long time, and by some
have been assumed to be of special value. Experience hardly supports the suggestion,
and in addition there are certain objections which may justifiably be advanced against
the use of viruses, particularly in places where food is prepared. These viruses have
been investigated in several laboratories and, as a rule, they have been found to be
cultures of Gaertner's bacillus or allied species. With the object of ascertaining what the
present composition of these viruses might be, I sent samples of three purchased in the
open market to Professor Andrewes, City Bacteriologist, who reports as follows :—
"The three viruses sent for examination were specimens of :—
"(a) A living Agar culture.
"(b) A tin of material resembling bread paste.
"(c) A bottle of living culture in a fluid medium.
"(a) Virus proved in every respect identical with Gaertner's B. Enteritidis, giving
"the same fermentation reactions and being agglutinated to full titre by a Gaertner serum.
"(b) Virus. This material yielded on culture a preponderance of colonies resembling
"those of Gaertner's bacillus, together with a number of contaminations. The former
"differed from classical Gaertner's bacillus in being non-motile, and were only very weakly
"agglutinated by a Gaertner serum, and not at all by a Aertrycke serum, or by two
"paratyphoid sera (A and B). They gave weak agglutination by a typhoid serum. The
"nature of the organism was thus doubtful. I therefore fed two mice on the virus. These
"were at first unaffected, but one died in seven days, the other in ten days. The appearances
"were those of Gaertner infection, and the bacillus was readily recovered from the heart's
"blood and enlarged spleen in each case. The bacillus, though now motile was, however,
"still only weakly agglutinated by Gaertner serum and not at all by Aertrycke serum.
"I cannot, therefore, affirm that this virus is Gaertner's bacillus, though 1 conjecture
"that it may be this organism modified by long culture. Other observers have found this
"material formerly sent out as (6) virus to be typical Gaertner.
''In any case the tin of virus received by me was of a low order of virulence.
"(c) Virus proved also to be B. Enteritidis (Gaertner). Subcultures were
"spontaneously agglutinable, so that at first the agglutination test failed, but on testing the
"original fluid culture sent out, it proved well adapted for the test and gave specific
"agglutination with a Gaertner serum. The fermentation reactions were also identical
"with those of Gaertner's bacillus.