1 88 1.] 
with reference to Polluted Waters. 
x 39 
crease and the subsequent increase of oxygen dissolved in 
the water. To these charges I must beg to call attention. 
Above Rheims various kinds of fish were found in the 
Vesle, whilst aquatic vegetation of a fairly high type, i.e. f 
capable of secreting chlorophyll, was abundant. Water- 
weeds grew in the stream, and reeds and sedges flourished 
at its margin. Near, and especially within the town, these 
organisms disappeared. The fishes avoided, or perished in 
this part of the river, and in place of the green plants that 
inhabited the purer waters, growths devoid of chlorophyll 
made their appearance, among which figured the true 
“ sewage-fungus.” Relow the town, as the quality of the 
water again improved and the percentage of dissolved free 
oxygen rose, the higher forms both of animal and vegetable 
life reappeared. 
If the observations thus made are generally confirmed, 
two conclusions not without importance may fairly be 
drawn : — That the proportion of oxygen in the water of a 
river is causally and very simply related with the presence 
of the higher forms of animal and vegetable life; and that 
from inspection of such organism a tolerable approximate 
notion may be formed as regards the purity and the impurity 
of a stream. It has, indeed, been repeatedly asserted in 
French scientific journals, that water-cress can only grow in 
fairly good water. This assertion struck me as being little 
in harmony with my own observations and those of my 
friends. Mr. C. Cresswell, of Isleworth, a gentleman well- 
known for his zeal for sanitary reform, came upon a ditch 
which received the entire sewage and household refuse in 
general of a row of about a dozen cottages. Yet it was filled 
with the most luxuriant water-cress, which, sad to say, ap- 
peared to be regularly cut for sale. To decide the matter I 
carried on a somewhat extensive series of experiments at 
Aylesbury in the summer and autumn of the year 1878. 
Earth was placed at the bottom of four small movable 
tanks, and in each were planted healthy roots of water-cress. 
The tanks w 7 ere then filled respectively with town sewage, 
undiluted and taken direCtly from the sewer-mouth; with 
water from a branch of the river Thame which flows past 
the town, receiving the drainage of manured and cultivated 
lands, and I believe sewage from scattered cottages in the 
upper part of its course; with sewage after treatment by the 
“ABC process,” i.e., precipitation with sulphate of alumina, 
clay and carbon ; and lastly, with potable water. The loss 
by evaporation or leakage in each tank was made up by the 
regular addition of the same kind of water as had been taken 
L 2 
