110
[CHAP. II.
the plague-microbe in five minutes under the o onditions of Mr. Hankin's experiments,
but this substance is not recommended as a disinfectant except in cases in which there may
be reason for thinking that water has been infected by the washing of infected clothes, etc.
It was shown that the activity of potassium permanganate in destroying microbes may be
greatly increased by the addition of a small quantity of sulphuric acid, but the mixture
is not reconnu ended except under special conditions. Mr. Hankin discusses the bearing
of his observation of the sensitiveness of the microbe to oxidising agents on the
generally advocated plan of combating the infection by means of ventilation, which, he
shows, is probably a means of producing oxidation under the influence of air and light.
A series of observations was made in houses undergoing disinfection. Results were obtained
throwing doubt on the utility of sulphur fumigation and whitewashing as a means of
destroying the microbe. Mr. Hankin comes to the conclusion that the only substance
capable of satisfactorily disinfecting a cowdung floor is sublimate in an acid solution.
Sublimate in a neutral solution was found to be without action on the microbes present. As
an after-treatment and as a means of treating court-yards, passages, and drains, Mr. Hankin
recommends sulphuric acid in a strength of 1 in 250, which solution he shows to be far
cheaper than that of other disinfectants in common use. It is likely that this will make the
treated places for some time unfitted to act as a nidus for the microbe, for the latter is
shown to be destroyed within 5 minutes by a solution of the strength of 1 in 1429. Another
method of disinfecting floors investigated by Mr. Hankin is by covering them with a layer
of combustible material at least two inches thick, which is then set on fire. It was shown
that this treatment is far more efficacious than the use of ordinary disinfectants. Though
it is pointed out the risk of fire may prevent the wide application of the method in towns,
it may find application in the treatment of public latrines that may be supposed to be
infected, and which are commonly built of incombustible materials.
Mr. Hankin has also carried out a series of experiments on the asserted possibility of
finding the bubonic microbe in the earth of infected houses. He has examined large num-
bers of specimens brought from places in which many people had recently succumbed to
the infection without finding the microbe in any case, with one probable exception. The
search has been carried out by several methods, including one communicated to him by
Professor Calmette, which method appears to have been the one employed by Yersin in
Hongkong, and which led him to positive results. In Mr. Hankin's hands no such results
were obtained, thus throwing doubt on the statement that the microbe can be readily found
in the soil of infected houses, at any rate by existing methods.
The only case in which a microbe probably identical with that of plague was met with
was in some salt-water in a field near Siwri, at the time that the epidemic was present in
the place. Some of this water was injected into a mouse. On its death a microbe was
isolated from its organs, which resembled that of plague in most respects, but which diffe-
ed from it in the rapidity with which it formed involution forms on agar-agar. Mr. Hankin
found that the plague-microbe could be changed into a microbe having these aberrant
characters by cultivation on agar-agar containing three or four per cent. of salt, and that
further the microbe from Siwri was pathogenic to a rabbit that had not been protected by
Haffkine's plague vaccine, but had no effect on a rabbit that had been so protected. Conse-
quently it was supposed that this microbe was the plague-microbe altered by its sojourn in
salt-water. This observation had led to the discovery of a rapid method of identifying the
plague-microbe by its cultivation on agar-agar containing a certain percentage of salts.
It has been further worked out by Surgeon-Captains James and Thomson under Mr. Hankin's
supervision.