72 THOMPSON YATES LABORATORIES REPORT 
in stagnant water, sulphide of iron is formed, and the fungus assumes a black colour 
and undergoes putrefactive decomposition. 
Microscopic examination shows that it consists of long branching filaments, 
which are constricted at regular intervals ; the branches bud off below the con- 
strictions, and each segment has a very characteristic refractile nucleus. Zoospores are 
formed in the terminal segments. 
Sph^erotilus natans 
This organism may be readily confounded with the preceding. It forms quite 
as long wavy masses in the drains and streams as does Leptomitus. It is, however, 
usually white and cotton wool-like when seen in the water. It is much more 
gelatinous than Leptomitus. On stones in shallow streams, or coating the sides of 
drain pipes, it forms low velvety or feather-like growths. Like Leptomitus, it 
requires oxygen, and grows best in shallow water-courses and where there is plenty of 
movement. Its presence indicates much greater pollution than does the former 
organism, and therefore it is of importance to be able to distinguish the two forms. 
In two cases where bacterial analyses were made of the water in which both forms of 
'fungus' were found, that in which Leptomitus occurred contained at least less than 
100 Bacillus coli per c.c, whilst that in which Sphaerotilus was found contained over 
19,000 Bacillus coli per c.c. With the introduction of the bacterial bed method of 
treatment, this organism has also made its appearance. In one case, where in the 
method of treatment the bacterial filter is warmed, I found that the Sphaerotilus had 
made its appearance in large quantity, the food materials — circulation, aeration, and 
warmth — being the conditions most favourable to its development. It is, therefore, an 
organism which may cause blocking of aerobic contact beds. 
Sphaerotilus has been long confounded with Beggiatoa. It is allied to the 
Leptothrix forms. As the microscopic preparations show, it occurs in chains of short 
bacilli, or as long undivided filaments. It is, therefore, very much more minute than 
Leptomitus ; this is readily seen from the photomicrographs, which are equally 
magnified. The filaments and rods are surrounded with a gelatinous capsule. 
In crude, undiluted sewage, a skin-like growth may form at the sides of the 
conduit in contact with the air, or at those points where crude sewage passes over a 
'lip.' The growth, which has a coarse velvety appearance, consists of club-shaped 
zooglea masses of bacilli, and it seems probable that this bacterium, if not identical 
with Sphasrotilus, is closely allied to it. 
Sphaerotilus may also be confounded with Carchesium. I have found 
Carchesium Lachmanni coating the surface of the stones in a polluted stream and 
producing the white cotton wool-like appearance of the fungus ; in fact, on the farm 
in question, it was always regarded as the 'sewage fungus' ; microscopic examination, 
Plate VL, Fig. 6, showed, however, a striking difference. 
