21
conveying plague-infection. Clothing and bedding from plague-
infected houses may contain infected rat-fleas : the chanco, however, of
such finding a susceptible rat as a host, without which they cannot give
rise to an epidemic, is sufficiently remote to explain the fact that
merchandise is a more potent source of plague-infection.
When articles from a plague-infected source are of such a nature
as to render them likely to harbour fleas they can be rendered innocuous
by exposure to the direct rays of the sun. The ground used for the
purpose should be so chosen that the sun is able to shine on it for the
whole of each day. It should be flat, devoid of grass, stones, or any-
thing which might afford shelter to fleas. Preferably it should be
covered with a smooth layer of fine sand three inches deep. The surface
temperature of the sand should be at least 120° F. to ensure the
destruction of all fleas. One hour's exposure in such conditions is
sufficient for the purposes of disinfection. Thick coats and rezáis should
be turned once or twice during the process. No articles should be
placed within three feet of the edge of this sand.
III.—EAT DESTRUCTION.*
Careful attention to detail a,nd a knowledge of all that has been
said above regarding the habits and customs of rats are essential to
success in any rat-destruction campaign. Not infrequently rat destruc-
tion as a plague measure has been stigmatized as useless on the results
of attempts at rat-tra'pping with traps into which entry is difficult, and
from which escape is absurdly easy, or of attempts at poisoning with
substances which possess taste or smell, or both, which is positively
repulsive to rats.
1. Eat poisons.—Poison if intelligently used can accomplish much
by means of a ' poison campaign, ' a rapid reduction in the rat
population can be effected. The chief disadvantage of the method is
the nuisance caused by the decomposing bodies of dead rats, a
nuisance which is small however when compared with the dangers of
plague that rat infestation denotes. The selection oí.' a suitable poison
is the most important consideration. Most of the rat poisons on the
market will kill rats if the rats can be induced to swallow sufficient,
but most oC them are distasteful or positively repulsive to rats. All
phosphorus poisons possess this disadvantage ; their inflammable
nature also makes them objectionable. .The most satisfactory of all
pqisons, and happily the cheapest, is bad um carbonate. Barium
carbonate t occurs in nature, unfortunately not in any quantity in
India, and is a heavy white tasteless inodouiiess powder that is almost
insoluble in water. As a rat poison it is certain in its action and
safe to handle. When mixed with flour and water it in no way makes
the mixture less palatable to rats who seem quite unable to detect its
* All that is new in the following paragraphs, relating to the use of poison baits, ia
the outcome of numerous well-designed and carefully controlled experiments that have
been carried out in Poona by Dr. Chitre in the course of an inquiry that was planned
and commenced by Major J. C. Q. Kunhardt, I.M.S., under Ihe auspices of the Indian
Research Fund Association.
t The carbonate is the only salt of barium that should be used. Barium sulphate
or barytes, the most common barium salt, is valueless as a rat poison.