RIVER GARDENS; 
water. Sea shells, or corals, so often used for this 
purpose, have a very anomalous appearance, and de¬ 
stroy the natural character of the whole arrangement. 
The kind of water is not very material, if the 
balance of animal and vegetable life, after added, he 
nicely adjusted, and not introduced too profusely. 
A few cautions, however, are necessary. Water 
that has been boiled would not do; in fact, fish will 
live hut a very short time in boiled water, because 
in that operation the greater part of the oxygen has 
been expelled from it. The water of chalybeate 
springs is likewise unfit, as the salts contained in it 
are very injurious to vegetation. River water is 
best, hut pump or well water will answer very well, 
especially if well aerated, by pouring from one 
vessel to another before used. 
The water in the tank may he occasionally 
aerated, also, by means of a common pair of bellows 
with a piece of gutta-percha tubing attached to the 
end of the pipe. A contrivance of this sort is 
adapted for all the tanks at the Dublin Zoological 
Gardens, with branch pipes leading to each separate 
tank, so that one pair of bellows aerates the whole 
series. The action of the air, as it enters the vessels 
from these tubes, is said to produce a very pleasing 
effect, insomuch that Dr. Ball, when he described ,, 
16 
