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the sewage. Knowing that the typhoid bacillus grows well at 37° C. and that it can grow
in the presence of .05 per cent. of carbolic acid, we made six agar-agar plates, with 1 c.c.
of a dilution of 1 in 5,000; and after the addition of .05 per cent. of carbolic acid to each plate they
were incubated at 37° C. In this way, as we have shown earlier in this report, some 90 per cent. of
the organisms present in sewage are prevented from growing, and so the task of searching for one
particular organism capable of growing under these conditions is proportionately lightened. Bacillus
coli communis and other allies of the typhoid bacillus can, however, also grow in such plates, and it
was from these that we now had to differentiate any possible typhoid colonies. The chemical tests
which have been mentioned above as distinguishing B. coli communis from B. typhosus suggested the
following mode of procedure. From every colony which resembled the typhoid bacillus a sub-culture
was at once made in sterilized milk and incubated at 37°. Those milk tubes which coagulated were
rejected as being certainly not typhoid. From the ones which did not coagulate, streak cultures were
made on gelatine; some of these liquefied and were hence rejected as certainly not typhoid. Those
which did not liquefy were each tested by shake cultures in gelatine, as to their power of gas
production, and by cultures in broth to which the indol test with nitrous acid was applied. Some gave
rise to both gas formation and the indol reaction, many others to one of the two reactions; all such
could be rejected, and at the end we were left with two colonies only which resembled B. typhosus in
their morphological and cultural characters, which failed to produce coagulation in milk and which
gave rise to no gas bubbles in gelatine and produced no indol in broth. These two colonies we hence
regard as colonies of the typhoid bacillus, or at least as absolutely indistinguishable from that organism.
Inasmuch as animals are not susceptible to typhoid fever in the strict sense of the term (i.e. since the
typical lesions of human typhoid have not so far been reproduced experimentally in animals), it was useless
to attempt any further verification of our results by inoculation experiments on animals, or we should
have done so. We must be content to have shown that in the drain from the typhoid block of a
fever hospital, when the stools have not been disinfected for two days a bacillus can be found which,
so far as demonstration can go, is identical with that believed to be the actual cause of typhoid fever.
So far as we are aware this important fact has never previously been demonstrated.
A week or two later we examined in the same way sewage taken from a drain in Bridge-street,
Homerton, about a quarter of a mile from the hospital, which received the hospital sewage as well as
that from the surrounding district. Exactly the same method of procedure was adopted, and the
results proved entirely negative; no single colony could be referred to B. typhosus. This may have
been due in part to the great dilution of the hospital sewage with that from the surrounding district,
or in part to the fact that the typhoid stools were then being disinfected as usual.
experiments on the vitality of the typhoid bacillus in sewage.
We have shown above that the number of typhoid bacilli which gain access to our sewers, when compared
with non-pathogenic microbes, is relatively very small, inasmuch as the amount of typhoid excreta
forms but a minute proportion of the whole, and much even of this is in a measure disinfected. The
same is true of the diphtheria bacillus and, during the prevalence of cholera, of the cholera vibrio. It
is hence evident that it is a matter of the greatest importance to determine the duration of vitality of
these pathogenic organisms under conditions which may be considered normal to their dissemination.
The points to be determined are (1) whether normal sewage is a favourable or unfavourable soil for
their life and growth, and (2) what influence, if any, the various non-pathogenic organisms present in such
overwhelming numbers exert upon their pathogenic companions. It will be evident that the question
is one of much complexity, demanding for its solution much detailed and laborious experiment. In
order to gain some definite knowledge on these points, we have carried out a series of preliminary
experiments with the bacillus of typhoid fever, and the results, though far from complete, appear to us
of sufficient value to merit record.
The duration of vitality of the typhoid bacillus in sewage.—It was necessary in the first place to
prepare sterile sewage in which to sow the typhoid bacilli. In the earlier experiments we did this by
boiling sewage for a short period on two or three consecutive days, after it had undergone a preliminary
filtration through ordinary filter paper. It became clear to us, however, that this was not a
good method, since the process must of necessity affect the composition of the sewage and so render it
abnormal. Not only will volatile organic matters be driven off by boiling, but the carbonates of lime
and magnesia will be thrown out of solution together with certain soluble organic matters. We,
therefore, adopted a method suggested to us by Dr. Klein, and employed the Berkefeld filter, which
has sufficiently fine pores to prevent the passage of micro-organisms through it. The sewage was
twice filtered through the Berkefeld filter and then heated to 60° C. in a sterile flask for 20 minutes
on two consecutive days. In this way complete sterility was obtained, with the smallest possible
departure from the normal as regards chemical composition. The sewage employed was from Barking
or Crossness.
We first compared the typhoid bacillus with the colon bacillus as to their respective powers of
vitality and multiplication in sewage which had been sterilised by heat.
Experiment I.—Two tubes of sterilised sewage were inoculated with B. typhosus and two with
B. coli communis, and incubated at 37° C. After the lapse of 24 hours the tubes inoculated with
B. coli communis showed abundant growth, while those inoculated with the typhoid bacillus showed
no growth at all. After four days' incubation one typhoid tube showed very slight development, the
other none, even when tested by sub-culture on gelatine.
Experiment II.—Three tubes of sewage sterilised by heat were inoculated respectively with a
culture of B. typhosus obtained from the spleen of a fatal case of typhoid fever, with a culture of B.
coli communis derived from the human intestine, and with one of B. coli communis obtained from the
fresh sewage of St. Bartholomew's Hospital. All three cultures had been previously tested and gave
typical reactions. The sewage tubes were incubated at 37° C. After two days the two B. coli tubes