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number of micro-organisms found in the sewer air was
particularly low.
5. Micro-organisms found in sewer air appear to come from
the fresh air outside (passing into the sewers by ventilation),
and not from the sewage or sewer walls, and are
chit fly moulds and micrococci (as found in fresh air)
and not bacilli and moulds (as found in sewage), the
ratio of micrococci to bacilli being, in the case of fewer
air and fresh air, about five to one. Further, the bacillus
coli communis and micrococcus ureœ are absent from
sewer air, as are also, with very few exceptions, organisms
capable of very rapidly liquefying gelatine, though all
these organisms are found in immense quantities in
sewage.
6. It is impossible to ignore the evidence, though it is on
circumstantial, that sewer air in some instances has had
some causal relation to zymotic disease—the danger of
sewer air causing disease being, perhaps (though at
present no evidence is forthcoming), an indirect one,
e.g., the sewer air containing some highly poisonous
chemical substance, possibly of an alkaloidal nature,
which, though present in but minute quantities, may,
nevertheless, produce, in conjunction with the large
excess of carbonic acid, a profound effect upon the
general vitality.
(c.) Results of a detailed examination and cultivation
of the various micro-organisms of sewage.
Conclusions.
1. The study of the sewage bacteria fully confirms the
conclusion given in the two previous Reports, viz., that
there is no relationship between the organisms of sewer
air and sewage.
It is possible that some of the ill-effects which have
been erroncously ascribed to sewer air may be due to