79
though not often, entirely absent. At certain times of the year it is by far the com-
monest organism in water, particularly in lakes, wells and. springs. It has a very
decided preference for the bottom of a lake—vide Chapters IX and X. It is an
extremely resistant organism, and it is doubtful whether, under perfectly natural
conditions, it is not the most resistant of the whole list. In the experiments
given in Chapter VIII it appears to be second to that of bacillus grunthal in
its powers of resisting the action of sunlight. It has also been found to live
in the ground for many months and even for two or three years. It was by far
the commonest organism isolated in the old trenches in our work on polluted earth
—vide Chapter VI. It also seems to have a decided preference for the sands of
fi l t er beds and of ri vers; t hi s i s, however, probabl y due t o i t s l ongevi t y i n soi l .
Bacillus No. 106.—This has twice been isolated by us, once from the fœces of
goats, and once from the fœces of cows. It is one of the inulin fermenters found in
October, and the same remarks apply to this as to bacillus No. 10.
Bacillus No. 110 (vide remarks concerning bacillus No. 10).
This completes the list of organisms, with their natural characteristics and their
position in nature, as observed by us.
The following is a list of these organisms arranged in three classes as regards
their power to resist the action of sunlight :—In class II, considerable differences of
power exist between the individuals. We consider that, as more experience is accumu-
lated, this class will probably be divided into two. We have, however, arranged
the organisms in this class in the order of their powers of resistance, as far as our
experience goes at present, so that it will be understood that the ones high up in
this list are considered to be less resistant than those at the bottom :—
Class I.
Class II.
Class III.
Oxytocus perniciosus
...
No. 33
...
No. 73.
No. 10
...
No. 38
...
...
No. 75.
* No. 39
...
... Pneumonia ... Grunthal or No. 7 or 8.
* No. 69
...
... No. 9 ... Cloacæ.
* No. 70
Neapolitanus.
* Nos. 97 and 98 ...
Lactisærogenes.
Coli communis
Coscoroba.
Acidi lactici.
No. 35 ...
No. 36 ...
...
No. 6.
No. 100.
No. 101.
* About all these there is a certain amount of doubt.
If a reference be made to the conclusions arrived at in Chapters VIII, IX and X,
it will be observed how remarkably these agree with one another. Even if those
arrived at as a result of the sunlight experiments be deducted, for, we feel that possibly
others may not be so convinced as to their value, as we ourselves are, there can be no
getting away from the following three facts as demonstrated in Chapters IX and X :—
(i) That delicate organisms exist in nature, such as coli communis.
(ii) That resistant organisms also are present in natural surroundings—vide
.
(iii) That organisms standing intermediate between these two positions also
exist, such
as cloacæ. slaetis ærogenes.
Now, considering that the conclusions deduced from the sunlight experiments
corroborate these facts in every way, this is additional proof of their reliability.
Hence we consider that the classification given above is based on satisfactory
foundations, and is in accordance with nature.
The discussion of the application of these classes to water analyses will be dealt
with in the next chapter.