84
this indicates that the lake is very low and conditions are suitable for the spread
of cholera.
River Waters.
Good river water should not contain more than 100 colonies (on agar at 37°C.) .
Fœcal organisms should not exceed 1 in 10 cc.
No organisms of class 1 should be present in 50 cc.
Fœcal organisms present should belong to either class III to the more resistant
group of class II .
Fair or usable river water should not contain more than 300 colonies (on agar
at 37° C.).
Should not contain more fœcal organisms than 1 in a cc., and no organisms of
class 1 in less than 20 cc.
The fœ cal organisms present should consist mainly of mixtures of class III and
class II, and there should be a tendency for one organism to preponderate.
River waters should he condemned if total colonies are more than 800 (on agar at
37° C.).
If lactose fermenters present in number of 10—100 per cc.
If organisms belonging to class I exceed 1 in 5 cc.
Or if the fœc al organisms isolated (class 1 being absent) are rich in varieties
such as occur in an emulsion of f œc es.
Well and Spring Waters.
A good water should contain no fœ cal bacilli in 20 cc.
No class 1 in 100 cc.
Total colonies under 50 per cc.
We are for the present unable to give any other standards than this.
All filtered waters should conform to the standards of a good water, when this
is not the case, the filters and pipes should be examined.
Before closing this chapter, we wish to point out the enormous superiority of
MacConkey's method of separating out all lactose fermenters over the usual plan of
remaining content with the single determination, viz., as to whether " true coli " are
present or absent. As long ago as 1905, MacConkey recommended that all f œ tal bacilli
in a water sample should be separated and studied, and that by doing so, we should
probably greatly increase our knowledge of the true significance of the presence
of these micro-organisms.
We consider that we have amply proved the truth of these contentions, and
the utility of his method.
Laying aside for the time being all the debatable part of our work—such as the
difference in powers of resistance of various bacilli—as not yet proven, who ever heard
it even suggested, that by the old method, it would be possible for an analyst to say
from his results if a water was taken from a lake nearly empty, or from a well after
long drought ? Who ever reported that such-and-such a mixture of f œ cal organisms
was highly suggestive of fresh fœ ces, or that such another mixture suggested that
some alteration from natural conditions had occurred ? Was it ever seriously put
forward that bacillus cloacæ , lactis æ rogenes and oxytocus perniciosus might be as
valuable in indicating a certain definite stage of pollution as " true coli " itself ?
Would it have been possible, working with the " true coli " method, to discover
the many interesting problems connected with animal and human fœces mentioned in
this work ?
An honest answer to these queries should convince any unbiased mind, that in
adhering rigidly to the presence of " coli " as an indication of pollution, and being
content therewith, we are deliberately shutting our eyes to a very fruitful field of
knowledge, which is of great value in the study of fœcal pollution generally.
Truly, we believe, that such terms as " true coli " and the statement that all
soli " equally indicate dangerous excretal contamination " will require considerable
modification in the future.