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III.—SUMMARY OF WORK CARRIED ON BY ME. HANKIN.
Mr. Hankin has carried out a long series of researches on the action of dis-
infectants on the microbe of bubonic plague. He finds that it is somewhat
resistant to the action of carbolic acid. Both phenyle, lysol and izal appear to
have a more energetic action. Phenyle and lysol, however, were found not to
exert a marked bactericidal action on a cowdung floor. Naphthaline was found
to have no action on the plague microbe. The plague microbe was found to be
comparatively resistant to the action of alkalies, and especially sensitive to the
action of acids. Even weak organic acids appear to destroy it readily. It is
however usually able to exist for some hours in acid urine. Milk, so soon as
it has acquired an acid reaction, appears to have acquired the power of destroy-
ing the microbe. Inorganic acids are naturally still more active, and Mr. Han-
kin thinks that sulphuric acid might be used as a cheap disinfectant against
the plague infection. The microbe was found to be resistant to the action of
reducing agents, and sensitive to the action of oxidising agents, such as per-
manganate of potash or chloride of lime. A solution of one part of perman-
ganate of potash in 50,000 parts of water appears to be capable of destroying
the plague microbe in five minutes under the conditions of Mr. Hankin's ex-
periments, 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, &c. 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 recom-
mended 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. Han-
kin 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 courtyards, 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 dis-
infectants. 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 numbers 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 Professor Yersin in
Hong Kong, 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