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REPORT
on the
RESULT OF INVESTIGATIONS ON THE MICROORGANISMS
OF SEWAGE.
To the Main Drainage Committee of the London County Council.
In previous reports made to the London County Council by one of us, it was shown that the
micro-organisms contained in sewer air were not only less in number than the micro-organisms in
fresh air in the vicinity at the same time, but that they were also apparently related to and derived
from those of fresh air rather than from the sewage, and further that no evidence was forthcoming
that sewage was able to give off micro-organisms to the air in contact with it. Inasmuch as these
conclusions are not in harmony with generally accepted views, it became of great importance to gain
corroborative evidence upon this point by a study of the organisms existing in sewage, and to this end
we were instructed by your committee to invest'igate the matter. This was the more essential because
practically no exact study of the subject had been previously made, at least in this country. By far
the most important work on the micro-organisms of sewage which has yet been done is that of Mr. E. O.
Jordan, published in the Reports of the State Board of Health of Massachusetts (1888-90, Part II.).
Mr. Jordan reports on and carefully describes twelve species of bacilli, most of them previously
unknown, isolated at the experimental sewage station at Lawrence, Mass., and further adds an
important report on nitrification and the organism concerned in the process. In the main the
results which we have attained are in accord with those of Mr. Jordan, and such differences as we have
found may be explained by the probable differences which exist between the floras of English and
American waters, and the sewages of London and Lawrence. The work of Roscoe and Lund* does not
cover the same ground as that which we have attempted to explore. Their work deals more especially
with the chemical properties of a few species of bacteria, chiefly bacilli, isolated from Acton sewage.
PART I.
the micro-organisms of sewage.
Methods adopted.—1. A mode of collection of the sewage was adopted which should give a fair
average sample. It is obvious that, especially in small sewers, the rapid variation in the composition
of the sewage may render a given amount taken at a particular moment a very unfair sample of the
whole bulk. We therefore took repeated small quantities during a period of fifteen to twenty minutes,
thereby gaining a fair sample of the sewage in question. These were mixed in a large sterilised bottle
(a "Winchester quart"), and subsequently the whole was well incorporated by vigorous shaking for
twenty or thirty minutes, in order to break down as far as possible any solid matter. In every case
cultivations were made as soon as possible after collection, since, if three or four hours are allowed to
elapse, especially in warm weather, the rapid multiplication of the micro-organisms present necessarily
vitiates the results.
2. The mode of dilution employed, which was designed to secure an equable admixture of the
sewage with the large amount of diluent required, was as follows—Ten cubic centimetres of the mixed
and shaken sewage were diluted to 100 c.c. with recently boiled distilled water in a sterilised and
accurately stoppered flask, and thoroughly shaken. Of this first dilution 10 c.c. were taken and
further diluted to 1,000 c.c. with sterilized distilled water in a second sterile flask and again well
shaken. From this second dilution (which represents 1 in 1,000) two further dilutions were made in
similar manner—one by taking 10 c.c. and diluting to 100 c.c. (giving a dilution of 1 in 10,000), and
another by taking 10 c.c. and diluting to 1,000 c.c. (giving a dilution of 1 in 100,000). These extreme
degrees of dilution were of course rendered necessary by the enormous numbers of micro-organisms
present in even fresh sewage. A subsequent experiment indicated the possibility that a certain
number of bacteria may have been killed off by the distilled water. A better diluent would probably
have been sewage sterilised by filtration through a Chamberland or Berkefeld filter. The possible
fallacy thus introduced will, however, only be that our results in point of numbers may be somewhat
too low. The reason for employing two dilutions (of 1 in 10,000 and 1 in 100,000 respectively) was
that our plate cultures were incubated at two different temperatures, some at the temperature of the
body (37°C.), and some at a temperature of 22°C., and, inasmuch as many sewage bacteria do not grow
at the higher temperature, a lesser degree of dilution could be employed.
* Transactions of the Royal Society, 1892.