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(2) That taken up by MacConkey, Drs. Bergey and. Deehan, of the Pennsylvania
University, Dr. Orr (in his recent work on the contamination of milk) and. ourselves;,
who apply the name bacillus coli communis to Escherichs organism only, calling all..
bacilli that differ from it in any " permanent " test, different species, to which different
names or numbers are applied.
We in India consider the position maintained by the former authorities is open
to two objections : ( I ) That it is inadvisable to apply the term " coli communis " to
a group of organisms, or even so-called varieties, and. (2) The tests laid down as essen-
tial according to the definitions quoted, do not go far enough ; that the list contains too,
many that are of doubtful significance and utility, and too few that are admittedly
of greater importance in the identification of a bacillus. To discuss this last objection
first : Houston, Savage and all experienced bacteriologists admit, that the tests.
given above are not of equal value in the identification of what they term " coli."
Thus to quote from Savage, " Different characters have not an equal value. Some,
such as the fermentation of sugars, liquefaction of gelatine, and acid production in
milk are of so permanent a type that for an isolated. organism to show divergence from
a typical bacillus coli in any one of these particulars Would be to throw grave doubt on
its being excretal at all, while others, such as the gelatine surface colonies, and the
exhibition of motility, are so subject to variation that comparatively little significance.
can be, attached to their, perhaps temporary, absence or modification." And again in
another place he says : " Organisms that differ from the typical excretal type (bacillus.
coli communis) only in the fact that they show no motility and that their gelatine
colonies are atypical may be regarded as not having their significance diminished on
these grounds. Similarly the loss of Indol-production power 'would not reduce their
significance very markedly. On the other hand the absence of glucose or lactose
fermentation would at once, in the writer's opinion, exclude the organism isolated from
being bacillus coli at all."
The obvious inference 'from these opinions is, why not do away with some of.
these doubtful tests and substitute for them the more important fermentation reactions_
in sugars such as dulcite, adonite and inulin ? These are entirely on a parallel
with the glucose and lactose fermentation referred to as being " of a permanent character."
This is practically the position taken up by MacConkey, in his paper on the Bac-
teriology of Milk (Journal of Hygiene, Vol. IV, No. 3, July 1906), and, following•
his recommendations, by ourselves in the work under report.
But the real objection to calling a group of bacilli, made up of definite and distinct
species, by the single term " coli " becomes more apparent when an attempt is made.
to interpret the results obtained by these methods. It is accepted that as long as a
bacillus fulfils all the tests in the previous quotations it is looked upon as fccal ; but
the difficulty arises when bacilli are isolated which either do not fulfil all the above
conditions, or possess additional characteristics. Thus a fair number of the so-called
" coli group " are non-motile ; some do not produce indol ; others ferment saccharose.
The difficulty is to estimate what is the significance of these aberrant or atypical
varieties, and. it is this point which demonstrates the weakness of the above system.
Thus authorities interpret these facts differently : Houston says that the saccharose
fermenting organisms are not to be looked upon as so " significant of undesirable
pollution " as the non-saccharose fermenters. Savage, on the other hand, says that
they are equally significant of fecal contamination. Here we have two contradictory
opinions on a most vital point. In discussing this difficulty in estimating the value of
these aberrant. types, Savage says : " undoubtedly this question of variation and l o s s
of atributes complicates the subject and detracts from the value of this indicator "
(i.e. " coli " as an indicator of fecal contamination). Again " There is the great
difficulty which attaches io the precise significance given to the bacilli which
deviate from the characters ascribed to the coli communis." Surely, therefore, it
would be better to separate these organisms, by the use of well defined fermentation
reactions in sugars into different species, and to study them separately, endeavouring-
to obtain the relative significmce of each as an indicator of contamination.
Thus, to take an example, supposing by the use of dulcit., inu in and
s accharose (without making use of any of what may be termed
foacal
the more doubtful
tests such as motility, indol-production, etc.), it were possible to sub-divide what
is termed " coli group " into species A, B, C and D, it would be possible to
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