28 Description of Plague: [ CHAP. II.
lime, contained virulent bacilli after 30 minutes, and had become sterile
in an hour. The plague bacilli were found to be extremely sensitive
to mineral acids; for the plague bacilli contained in the mixture were
killed in less than 5 minutes by pure sulphuric acid diluted to 1 : 2,000.
Bacilli dried in thin layers on splinters of glass and exposed to
direct sunlight died within an hour."
Experiments of
Mr. Hankin.
Mr. Hankin's researches on the action of disinfecting agents were
to the following effect:-
"A. Phenols and their allies.-The bubonic microbe was found to
be somewhat resistant to the action of carbolic acid, a one per cent.
solution not being always sufficient to kill it under the condition of
the experiment. Phenyle, lysol, and izal were found in all cases to
destroy the microbe when in a quarter per cent. solution. The limit of
dilution of the solutions of these substances necessary to destroy the
microbe was not however found. Naphthaline, both pure and impure,
and a patent preparation ' naphtho-sublimate ' were found to exert no
disinfectant action although tested in solutions containing an undis-
solved excess of these substances.
"B. Corrosive sublimate and copper sublimate.-Corrosive sub-
limate was found to destroy the microbe in a strength of one in five
thousand, but the lower limit of its action was not investigated.
Copper sulphate was found to be efficient in a strength of one in a
thousand. A five per cent. solution of this substance was used by the
French Government in 1892 in combating cholera. It is easily
obtainable in India, and might under certain conditions be used
against the plague as shown by the above result.
"C. Alkalies.-The microbe appears to be relatively resistant to
the action of alkalies including ammonia, caustic potash, and freshly
slaked lime. Under the conditions under which lime washing must
be carried out in India, it must not be regarded as a disinfectant for
the infection of bubonic plague.
"D. Acids.-The microbe is extremely sensitive to the action of
acids. The sensitiveness is greater in the case of inorganic acids,
but certain organic acids were also found to destroy the microbe
rapidly. The following results were obtained:-
With inorganic acids.
Under the conditions of the experiments the microbe was de-
stroyed in five minutes by-
Nitric acid of a strength of 1 in 133.
Hydrochloric acid of a strength of 1 in 500.
Sulphuric acid of a strength of 1 in 1,429.