MEDICAL ASPECTS OF PLAGUE.] 111
Mr. Hankin has investigated the relation of insects to the dissemination of the disease.
He has found the microbe in bugs from the Infectious Diseases Hospital. He has also found
it in auts that had recently been eating rats dead of plague. A long series of experiments
showed that ants do not retain the plague infection long, and further that no trace of
infection is present in ants from localities in which rats have not been dying recently.
Hence these insects cannot be regarded as important agents for the spread of the disease.
Experiments were carried out on different kinds of grain and other articles of export.
They were infected with plague-microbes under many different conditions. At stated inter-
vals extracts of specimens of the infected grain were prepared and injected into mice. By
this means it was found that the infection usually died out within 4 to 6 days. The possibility
was indicated that it might in exceptional cases survive for so long as 13 days, but of this no
definite proof was obtained. Mr. Hankin points out that grain, when it becomes rotten,
usually acquires a well-marked acid reaction owing to the production of various fatty
acids from the decomposition of carbohydrates. He has found that such fatty acids act as
disinfectants for the bubonic microbe. Hence it is difficult to believe that the microbe can
exist in rotten grain, as has been frequently assumed. The matter was put to an experimental
test by Dr. Srinivasa Rao while working in Mr. Hankin's laboratory. It was found that the
microbe always dies out in rotten grain within 2 to 24 hours.
The microbe, though usually dying out, when placed in sterilised water, within three
days, appears to be able to survive in sterilised cowdung for several days. The observation
appears to have some bearing on the question of the persistence of the infection in houses hav-
ing cowdung and mud floors. Through lack of time these experiments could not be continued
sufficiently for any conclusion to be arrived at as to whether any particular kind of filth is
more suitable than another to sustain the life of the microbe. But the general trend of Mr.
Hankin's observations is to indicate that the chief source of infection is not likely to be in a
saprophytie form of the microbe in the outside world, but more probably in the recently passed
excreta of men or animals suffering from the disease.
[Special emphasis has been laid on the last sentence of Dr. Childe's Report, in order to draw attention to a
conjecture. which. though founded on lender evidence, appears nevertheless to belong to that order of conjectures
which ultimately prove of the highest importance.-J. K. C.]