158 WATER, AND ITS IMPURITIES. 
speedily destroyed, and the whole fabric resolved into substances 
of more simple forms and constitution, as carbonic acid, car- 
bur etted hydrogen , a little ammonia , sometimes sulphuretted 
hydrogen, as well as probably, in some cases, other bodies of 
more subtle nature, the characters of which have not hitherto 
been determined. 
Dead Animal Impurities. — The dead animal organic im- 
purities present are the bodies of infusoria, annelidae, insects, 
fish, and animals, as well as the soluble proteine compounds, as 
albumen, gelatine, mucus, &c., derived from and dissolved out 
of these by the water. 
These several animal substances and compounds are likewise 
in a state of constant change ; their elements, obedient to the 
laws of chemical action, become re-arranged, and form com- 
binations more simple, as ammonia, nitric acid, cyanogen, sul- 
phuretted hydrogen, phosphur etted hydrogen, water, and many 
other bodies, some of which, like certain of those just enumerated, 
are probably of a highly deleterious nature. These changes, de- 
compositions, and re-combinations, are greatly facilitated and 
hastened by increased temperature, and therefore are effected 
more rapidly in summer. 
Living Organic Impurities. — The living organic im- 
purities are in direct dependence, as already remarked, upon 
the dead, from which they derive their nourishment and support, 
and, like them, are either vegetable or animal. 
Living Vegetable Impurities. — The living vegetable pro- 
ductions contained in impure water are algse, which are the 
fresh-water types of the plants commonly known as sea-weeds 
and water-plants. 
Living Animal Impurities. — The principal animal produc- 
tions contained in water are, fish, zoophytes, worms, larvae of 
insects, mollusca, and animalculae or infusoria. 
Circumstances which favour the Growth and determine the 
Kinds of Organic Life present in Water. 
Analysis has shewn that every vegetable is composed of oxy- 
gen, hydrogen, and carbon, with a variable but usually a small 
quantity of nitrogen. 
For the growth, therefore, of vegetables, it results as essen- 
tial conditions that they should be supplied with material con- 
taining the whole of these substances. 
Now, as one vegetable resembles in its general constitution 
another, it follows that decaying vegetable matters contain the 
whole of the materials necessary to the life of a plant, and thus 
