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floors for any length of time. It was found that the longest period
that floors remained infective after gross contamination was 24
hours.
In short, all experimental evidence, which need not be again
detailed, proves that there can be no question of a continued exis -
tence of the bacillus in the soil.
All the epidemiological facts accumulated by the Commission
point to there being no such thing as soil infection.
2. The existence of the bacillus in man.
We have already pointed out that human plague is dependent
upon plague in the rat, and that the only way man becomes in-
fected is by the bacilli being conveyed to him from the rat by the
rat-flea. There is no evidence that infection is ever carried from man
to rat, although the possibility of this occurring cannot be denied.
Cases of human plague which occur in the off-season must, therefore,
be dependent upon acute plague in rats. This correlation was
shown to be present in Bombay City during the off-plague season.
Again, there is no evidence that man harbours the bacilli after
he has recovered from the disease or while he is not a sufferer.
All the evidence, in fact, is against such a contingency.
These considerations, therefore, would negative the view, that
man was in any way responsible for the bridging over of plague
epidemics.
3. The existence of the bacillus in the rat.
In Bombay City it was found that the period between the
epidemics was bridged over by cases of acute plague amongst the
rats, accompanied by a few cases in man. There was never a
week in which acute rat plague was not present.
In the case of the two Punjab villages no rats were found in the
non-epidemic season suffering from acute plague nor did any
human plague cases occur. While this is so, a considerable number
of rats were caught alive, which, although apparently in good
health, harboured living and virulent plague bacilli in chronic
abscesses. It is to be carefully noted that these chronic plague-
rats inasmuch as the bacilli are shut up in abcesses, where fleas