16
We do not suppose that two such skilful workers as Drs. Houston and Savage would
have overlooked the great increase in the number of organisms that gave acid and
gas in lactose broth without some inquiry. for the futility of giving an opinion without
inspection has been frequently insisted on by both, but less skilled analysts, who
accepted their statement of what indicated dangerous excretal pollution, might have
been misled ; at any rate this case demonstrates that the generalization concerning the
interpretation of so-called "true coli" not infrequently misses the mark.
Therefore we think it will be conceded that it is not satisfactory to arrange differ-
ent organisms into groups under one name, and that it is still More dangerous to
make statements relative to the significance of the group as a whole, because these
statements may prove incorrect for the individual members.
The division of organisms into groups according to fermentation reactions is a
necessary part of laboratory routine; but it should not be forgotten, that this method of
classification tells us very little of the many characteristics of the organisms. Thus
taking the group of lactose fermenters as a whole, they may be split up into sub-groups
innumerable, but it is none the less necessary to separate species and to study their
natural characteristics. The danger in generalizing, with the fermentation method as.
a basis of classification, applies to all groups of organisms, including those suggested
by MacConkey and mentioned in Chapter I.
From these criticisms of European standard methods two queries will naturally
arise in the mind of any one reading this report:—Firstly, supposing these objections to
be true what alternative is offered? And, secondly, how does it come about that
English methods have given such satisfactory results, as to have led to their general
adoption? The reply to the first of these queries will be found further on in this
work, and, without wishing to anticipate, it may be stated, that, for the purpose of water
analysis we propose to classify all lactose fermenting organisms according to their
ability to resist the action of sunlight. It will be demonstrated that this arrangement
possesses many advantages over all grouping of organisms that is based on fermentation
reactions, and that it is of great service to water analysts in tropical countries. It is
not however claimed that it will be equally satisfactory in all parts of the world.
As regards the second of these queries, we wish it to be clearly understood that the
primary object of this report is to set water analysis in India on a proper footing, and
not to attempt to criticize the work of others, who may be situated in surroundings
very different from our own. There can be no reasonable doubt that the actual results
obtained by the methods used in England have given satisfactory results, though
everybody is prepared to admit that there is considerable room for improvement. Now
the reason why these results have been so satisfactory is extremely simple.
Firstly, the majority of the contamination in surface and river waters is due to
human excrement in the form of sewage from towns.
Secondly, the guiding principles that assist a water analyst in arriving at a
conclusion are based on the study of organisms present in sewage, that are human in
origin. Thus, the reason Houston gives for saying that saccharose fermenters do
not represent so objectionable a form of pollution as the non-saccharose fermenters, is,
because the non-saccharose fermenters greatly preponderate in sewage. It should be
noted that this kind of reasoning would obviously lead us into serious error in India,
where much of our pollution is due to animals.
Thirdly, there is very little doubt that coli communis of Eseherich (dulcit +,
saccharose, adonit, inulin, Voges and Proskauer—) is probably the commonest organ-
ism found in human forces, and in rivers polluted with town sewage. The work of
MacConkey supports this view.
Fourt hl y, B. col i c communi s of Escheri chi s
a v e r y s u s c e p t i b l e o r g a n i s m t o t h e
forces of nature, that are inimical to bacilli generally, and its presence therefore
does actually represent a recent and dangerous contamination. Evidence in support
of this statement can be found in Houston's annual reports, where the ratio between
his "true colic," "confirmatory" and "presumptive" tests varies with the time of
the year. Thus ir summer the actual number of "true coli" is much less than in
winter, due undoubtedly to the action of the sunlight in killing off these susceptible
organisms.