Water in Relation to Health and Disease. 
739 
green mossy filaments, which form a broad sheet upon and be- 
neath the surface of the water. Others are much simpler in their 
organisation, and very minute, so much so that the entire plant 
may consist of a single cell only, of microscopic dimensions. Be- 
tween these two extremes of development there are intermediate 
forms of great variety. These plants Mr. Bennett classifies 
under the heads — 1. Blue-green algae. 2. Chloryphyll-green 
algos. Of the former he remarks : “ The amount of oxygen 
which they give off into the water is exceedingly small, and 
they can exercise no appreciable purifying influence ; while in 
their decay they frequently. give out noxious and foetid gases, 
and the presence in the water of any considerable quantity 
should be regarded as rendering it unfit for domestic purposes. 
Of the chlorophyll-green algae the family Conjugatce are 
extremely sensitive to organic impurities of a putrescent cha- 
racter ; they rapidly perish in water that is not well charged 
with oxygen, and when found in any quantity — or, at all events, 
if occurring in the reproductive condition — it may be taken as 
certain evidence that the water contains no considerable quantity 
of deleterious organic ingredients. They give off into the water 
an appreciable amount of oxygen, and thus contribute to purify 
it.” A striking illustration of the purifying influence of plant 
life on water arose, quite accidentally, some years ago in India, 
when all aquatic plants were removed from the water tanks. 
As a consequence of this the water, which before was good and 
wholesome, became unfit for use. Other species of algae, espe- 
cially “ blanket weed,” also give out a considerable amount of 
oxygen to the water in which they grow ; but when they exist 
in large amount, and undergo disintegration and decay, these 
alga? — harmless though they be during life — may prove a source 
of dangerous pollution after death. 
In the experience of Mr. Rafter 1 the freshwater alga, 
Volvox rjlobator , has “ on more than one occasion appeared in 
enormous quantities in the reservoirs which supply Rochester, 
in the State of New York, with water, imparting to it a fishy 
taste and odour, and apparently causing sickness and death 
among the cattle which drank it.” 
The Characece, commonly known as “ stoneworts” or “ brittle- 
worts,” from the fact of their becoming coated over with an 
earthy deposit, when existing in large quantity give off a 
foul odour of sulphuretted hydrogen, and impart to the wat^r 
deleterious properties. 
Water has been known to acquire a peculiar nauseous odour 
Transactions of the American Society of Civil Engineers. 
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