58 
As regards the other organisms commonly found in the 
water it will be observed that these are mostly lactis zro- 
genes, coscoroba, Grunthal, acidi lactici and the usual fecal 
bacilli, which may be described, as of medium resistibility 
to the action of sunlight. It cannot be claimed, as in some of 
the other work, that bacillus Grunthal shows any tendency to 
survive other organisms. 
The position of B. lactis aerogenes in these analyses is 
of interest. It will be noticed that this micro-organism is 
only found in small numbers when there is decided evi- 
dence of recent pollution, as shown by the great mixture of 
organisms and the presence of colicommunis. But when puri- 
fication 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 in all 
probability multiplies during a certain stage of the purifying 
process ; and conversely, when lactis erogenes is plentiful, a 
certain amount of purification has been accomplished. 
The following conclusions appear to be justifiable :— 
(1) That the action of the sun is powerful in destroying 
the fecal organisms, and that the surface layers of any large 
volume of water are in consequence purer than the deeper 
ones. A practical point, following on this statement, is that 
the outlet from a reservoir should be arranged as near the sur- 
face as is possible. 
(2) That these analyses show that, in the Red Hills Lake, 
bacillus cloace is by far the commonest fecal organism 
isolated from the bottom. 
(3) That coli communis, even in large numbers, ina huge 
volume of water, disappear with great rapidity, In the results 
obtained from the Red Hills Lake the organisms never sur- 
vived longer than 6 days. 
Two years after the work above described, a short series 
of analyses were conducted on the same lake in order fur- 
ther to investigate the clearing up process. These results have 
already been referred to in Chapter VI, in connection with the 
acid and gas line in glucose and lactose media. Separa- 
tion of the various lactose fermenters was carried out and a 
