60 THE AQUARIUM. 
action takes place only under the influence of light, 
as during the night the contrary occurs, the leaves 
giving out carbon and absorbing oxygen, although in 
very small quantities compared with what is emitted 
during the daytime. 
If a bunch of leaves be introduced into a jar of 
air which has been deprived of its vitality by means 
of animal respiration, and the jar exposed to the rays 
of the sun, the air will, in a few hours, again become 
pure and wholesome. 
The same principle holds good in aquatic plants, 
many of them having the power of keeping the water 
in which they grow from becoming impure or foul. 
In ponds where there is no regular supply of fresh 
water from running streams, it has been noticed that, 
during the winter, when the plants are dead, the fish 
frequently come to the surface to breathe, while in 
the summer, when the plants are growing, the vitality 
of the water is preserved. 
It is upon this wonderful law of Nature that the 
aquarium, that endless source of amusement and in- 
struction, is based; and although it is as much 
intended to illustrate the functions of animal as of 
vegetable life, perhaps the following account, taken 
from a beautiful work, entitled “Ocean and River 
Gardens,” descriptive of the principles upon which 
it is conducted, may be interesting to the reader. 
“The successful treatment of aquatic plants and 
animals, in the confined space of a glass aquarium, 
depends entirely upon the discovery that there exists 
in Nature a self-adjusting balance between the supply 
DAs silt Laide dae SD 
