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that an increase or decrease in the number of organisms in fresh air is followed by a concomitant
increase or decrease in the number of organisms in sewer air. These facts furnish presumptive evidence
that the source of the organisms in sewer air is the fresh air gaining access by ventilation, and not the
sewage and sewer walls. Inasmuch as the danger of sewer air is not governed simply by the number of the
micro-organisms present, but also by the question of their harmfulness or otherwise, it was necessary
to make a careful and systematic study of all the various organisms met with during the progress of my
investigations.
This has involved an immense amount of labour, which has this year been considerably increased
by the excessive heat experienced; large numbers of my pure cultivations on gelatine were rendered
nugatory by the high temperature prevailing in August and part of September.
In the process adopted for determining the number of micro-organisms, a known quantity of air
was aspirated through a sterile tube containing two sterile plugs composed of powdered sugar and glass
wool. These plugs, which filter the air, were after the completion of the experiment transferred to two
circular cultivating plates containing nutrient gelatine in a liquid state; after careful admixture the
gelatine was solidified by cooling, each organism thereby becomes fixed and, if capable of growing and
multiplying in that medium, forms a colony which after the lapse of four to six days is evident to the
naked eye. In almost every instance this colony consists of a pure growth of one species only ; these
colonies were examined microscopically, and re-sown in sterile cultivating tubes containing nutrient
gelatine or agar-agar for further study. In order to identify and name the various species, it is
necessary to carefully observe their manner and rapidity of growth, their effect upon the nutrient
gelatine, and whether they form any pigment or induce any special chemical change. The following
lists give the names of the various organisms isolated by me from sewer air and fresh air, and classified
under the different headings of micrococci, bacilli, moulds, toruke, and cladothrices. The order in which
the names are arranged under each separate heading indicates the relative frequency with which the
various species have occurred.
Micro-organisms in fresh air.
Micrococci.
Sarcina Lutea
Micrococcus Aurantiacus
Micrococcus Candicans
Diplococcus Citreus Conglomeratus
Diplococcus Roseus
Sarcina Rosea
Pediococcus Acidi Lactici
Micrococcus Acidi Lactici
Micrococcus Flavus Desidens
Diplococcus Flavus Liquefaciens Tardus
Bacilli.
Bacillus Subtilis
Bacillus Fluorescens Liquefaciens
Bacillus Ochraceus
Bacillus Mesentericus Fuscus
Bacillus Arborescens
Moulds.
Penicillium Glaucum
Aspergillus Glaucus
Aspergillus Albus
Aspergillus Repens
Aspergillus Nigrescens
Aspergillus Nidulans
Brown Mould
Torula.
Pink Torula
Black Torula
White Torula
Cladothrices.
Cladothrix Dichotoma
Cladothrix Rubra
Micro-organisms in sewer air.
Micrococci.
Sarcina Lutea
Sarcina Aurantiaca
Micrococcus Candicans
Diplococcus Citreus Conglomeratus
Pediococcus Cerevesise
Staphylococcus Cereus Albus
Micrococcus Cremoides
Staphylococcus Cereus Flavus
Bacilli.
Bacillus Subtilis
Bacillus Aureus
Bacillus Arborescens
Bacillus Acidi Lactici
Bacillus Helvolus
Bacillus Nigrescens
Moulds.
Penicillium Glaucum
Aspergillus Glaucus
Aspergillus Albus
Aspergillus Repens
Aspergillus Nigrescens
Aspergillus Nidulans
Brown Mould
Torula.
None
Cladothrices.
Cladothrix Dichotoma
As I have stated in my previous report, the organisms of fresh air and sewer air consist chiefly of
moulds and micrococci, whereas the organisms of sewage so far as my limited observations go consist
essentially of moulds and bacilli. I have found the ratio of micrococci to bacilli in fresh air and sewer