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show that bacillus coli communis was present in them. It should be noted that this
organism was present in all the samples, surface, middle and bottom consequently
they must have been very numerous. By December 13th (that is to say, one week
afterwards) no coli communis could be found in the lake at all. The surface samples
showed no fœcal organisms in 50 cc., the bottom sample as usual showed a great
preponderance of cloacæ, and the middle the usual lactis æmrogenes, with some bacillus.
grunthal.
The other instance when coli communis was found, was in the sample taken from
the bottom on October 31st, none were found when the next sample was taken on
November 11th.
As regards the other organisms commonly found - in the water it will be observed
that these are mostly lactis æerogenes, coscoroba, grunthal, acidi lactici and the usual
fœcal bacilli, which may be described, as of medium resistibility to the action of sun-
light. It cannot be claimed, as in some of the other works, that bacillus grunthal shows
any tendency to survive other organisms.
The position of B. lactis ærogenes in these analyses is of interest. It will
be noticed that this micro-organism is only found in small numbers when there is
decided evidence of recent pollution, as shown by the great mixture of organisms and.
the presence of coli communis. But when purification has fairly started the numbers
increase particularly in the middle layers. This would indicate that the bacillus is
possessed of fair powers of resistance to sunlight; and conversely, when lactis ænrogenes
is plentiful, a certain amount of purification has been accomplished.
In a general way these results certainly confirm those obtained by Houston
Unfortunately we are not in a position to make any definite statement as to the
percentage of purification obtained, because the water in the Red Hills lake is a
polluted surface water and not polluted river water, whose bacteriological contents
can be examined from time to time. Our experiments however and the results
obtained from them go into much greater detail than those of Dr. Houston.
The following conclusions appear to be justifiable:
—
(1) That the action of the sun is powerful in destroying the fœcal organisms
and that the surface layers of any large volume of water are in consequence purer
than the deeper ones.
(2) A practical point, following on this statement, is that the outlet from a
reservoir should be arranged as near the surface as is possible.
(3) That these analyses show that, in the Red Hills lake, bacillus cloacæ is by
far the commonest fœcal organism isolated from the bottom.
(4) That coli communis even in large numbers, in a huge volume of water,
disappear with great rapidity. In the results obtained from the Red Hills lake the-
organisms never survived longer than six days.
(5) There is some evidence in these results, though as yet it cannot be taken
as thoroughly established, that, under certain conditions, the middle layers of a lake
of over 12 feet deep, contain more water organisms and more fœcal bacilli than the
bottom or the suface.
(6) That, when taking samples of lakes, ponds, etc., the depth from which,
the sample is taken should be carefully stated.
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