PROCEEDINGS OF SOCIETIES. 69 
ment, and render it at all permanent, and which at the com- 
mencement of the experiment had not been foreseen. 'The 
circumstances alluded to arose from the natural decay of the 
leaves of the Valisneria, the increase of which rendered the 
water turbid, and caused a rapid growth of green confervoid 
mucus on the surface of the water, and upon the sides of the 
receiver; the fish also assumed a sickly appearance, and had 
this been allowed to progress they must have speedily perished. 
The removal of this decaying vegetation from the water as 
fast as it was formed became, therefore, a point of paramount 
importance, and to effect this, recourse was had to a very use- 
ful little scavenger,—whose highly important and beneficial 
functions throughout all nature have been too much over- 
looked, and its indispensable uses in the economy of animal 
life not well understood,—the water snail, whose natural food 
consists of decaying and confervoid: vegetation. Five or six 
of these little creatures, the Limnea stagnalis, were conse- 
quently introduced, and by their extraordinary voracity and 
continued and rapid locomotion, soon removed the cause of 
interference, and restored the whole to a healthy state. 
Thus then was established that wondrous and admirable 
balance between the animal and vegetable kingdoms, and by 
a lmk so mean and insignificant as almost to have escaped 
observation, in its most important functions. The principles 
which are here called into action are, that the water, holding 
atmospheric air in solution, is a healthy medium for the 
respiration of the fish, which thus converts the oxygen con- 
stituent into carbonic acid. The plant, by its vital functions, 
absorbs the carbonic acid, and appropriating and solidifying 
the carbon of the gaseous compound for the construction of 
its proper tissues, eliminates the oxygen ready again to sus- 
tain the health of the fish. While the slimy snail, finding 
its proper nutriment in the decomposing vegetation and con- 
fervoid mucus, by its voracity prevents their accumulation, 
and by its vital powers converts that which would otherwise 
act as a poisonous agent into a rich and fruitful pabulum for 
the vegetable growth. Reasoning from analogy, it was 
evident that the same balance should be capable of being 
permanently maintained in sea water, and thus a vast and 
unexplored field for investigation opened to the research of 
the naturalist ; and this proved on trial to be the case. 
Principles of the Aquarium: the Air contained dissolved in 
Water.—The ordinary atmospheric air is found to be com- 
posed of 79 volumes of nitrogen gas and 21 volumes of 
oxygen ; and water has the power of absorbing gaseous bodies 
in varying proportions, thus: 100 volumes of water, at a 
