ON THE AIR AND WATER OF TOWNS. 27 
clear, gives after a time a brown flocculent deposit, entirely distinct from the 
mud deposit, which has been carefully removed beforehand. This flocculent 
posit contains many animals, large and gelatinous-looking; also below Chel- 
sea, and chiefly below Hungerford- market, little eels, Vi ibrio fluviatilis,” about 
J,th ofan inch long. The sideof the vessel in which the water stands is covered 
with another precipitate quite distinct, not flocculent but hard, of a light brown, 
nd chiefly towards that side of the vessel which is exposed to a moderate 
light. This precipitate is often mistaken for oxide of iron, which it strongly 
resembles, and to which it may probably owe its colour; but it may be known 
to differ from a simple oxide by the addition of muriatic acid, which gives 
_ ita beautiful green colour. When seen through the microscope, the colour 
‘will be found owing to the little dots of green which mark the polygas- 
ic character of these animalcules. These little creatures (chiefly I believe 
the “ Navicula fulva”) are covered with a crust of silica, and by boiling in 
Mmuriatic acid the silica may be separated from the other portions which are 
soluble. In this way phosphoric acid, lime and magnesia may be separated 
_ with ease ; and this will, I think, be found one of the best modes of collecting 
the phosphoric acid from water of this kind. The quantity of silica is very 
perce, as the number of these little loricated animalcules prove. Life of this 
kind may at once be considered as a proof of the presence of all those ele- 
_ ments essential to animal life generally, as these animalcules do not appear 
_ unless in the wreck of other animals or vegetables, whose requirements as to 
_ food are well known to be confined to certain elements. The abundance of 
silica is not from the upper part of the Thames, but no doubt from the sewers, 
proceeding from the decomposition of wheat, oats, &c., and may be viewed 
as a necessary consequence of the consumption of bread or any grasses 
used by cattle. 
__ There is then a great deal of matter in a state capable of being converted 
into living forms; this matter is not in suspension merely, but in solution 
also. A large quantity of organic matter is precipitated in contact with clay 
‘and mud in the Thames, but a great deal is also in clear solution. This 
‘Matter must be organized of course to some extent, and probably contains 
albumen; it seems to me that it is albumen which I have found in it, cer- 
ta inly a body much resembling it. The same may be obtained where many 
arge animalcules appear ; probably the quantity will be found the same 
Beeiher the animalcules be formed or not. The clear solution becomes a, 
“mass of growth very soon, if the matter contained in it be organisable. Or- 
“ganic matter may exist in a state in which, even under favourable circum- 
stances, animalcules are not formed, as I have found to be the case with 
some kept for some months in water. A similar thing may take place with 
Thames water at London ; if kept in close jars of earthenware no change 
roduced in the organic matter; as soon as removed into glass bottles, a 
aid change occurs, and a lively scene is produced of animals and vegeta- 
bles, Kept in the dark, the water dissolves much organic matter and be- 
f comes yellow; the water over the living matter is clear, or, in other words, 
the dead matter is to some extent soluble in water ; ; living matter is of course 
capable of having its parts broken up by mere water, and is insoluble. 
his growing of plants and animals is therefore a good mode of cleansing 
_ Water, when space and time are abundant, as in the larger operations of 
nature, but unfitted for waterworks, whera neither are very ample. The 
\ mode of cleansing used by water-companies is one employed by nature also, 
all the water which falls on the soil is filtered by passing through; that is 
to say, it first becomes exceedingly impure, being filled with matter from 
