
CONDITIONS OF LIGHT, ETC. 
such conditions should be avoided. Frequent aeration will then also be 
necessary as the vitiating carbonaceous constituents combine with oxygen 
and form CQO,, the form in which the plants can best assimulate it, but 
which in excess is fatal to animal life. Oxygen is one of the best anticep- 
tics and for this reason some of the water should be dipped out and slowly 
poured back into the aquarium that it may absorb air. 
If the plants do not develop new shoots and leaves at all seasons, 
something is wrong with the water, if the light is sufficient but not excess- 
ive. When the roots are affected, indicated by their black appearance, 
the ease with which the plants are uprooted and the unsatisfactory general 
appearance of the leaves, the aquarium should be cleaned and refilled with 
-clean water. 
One very important consideration for success is the condition of the 
water when the fishes are transferred from an out-of-door to an aquarium 
existence. At this time many of the mishaps occur, and at no other period 
are the fishes more likely to contract fungus diseases. It is always better 
to fill the aquarium with the water in which the fishes have been kept, when 
this is in good condition, as they will not then be subjected to differences in 
temperature and composition of the water, will continue in the same con- 
ditions to which they have been accustomed, and not subjected to sudden 
changes, as they will be acclimated to household conditions in water 
which will gradually assume the temperature of the room. Experienced 
aquariists always employ this method of transfer. 
AERATION 
All animals require oxygen to maintain their existence, and have 
organs by which it is brought into the blood. In breathing, a part of 
this oxygen is taken from the air, distributed to every part of the organ- 
ism and consumed in the functions of life. In exhalation and surface 
expulsion CQO, or carbonic acid gas is given off, for which reason the 
air becomes poorer in oxygen and richer in carbon with every breath, as 
every 100 parts of inhaled air contains 20 parts of oxygen and approxi- 
mately .04 parts of carbon, and the exhaled air 16 parts of oxygen and 
4.38 parts of carbonic acid gas. This would indicate a consumption of 
one-fifth of the oxygen and an addition of one hundred times as much 
carbonic acid gas. Hence a constant breathing of normally constituted air 
is necessary or suffocation wil] result, not only from the consumption and 
consequent lack of oxygen but also from the poisonous effect of the ex- 
haled carbonic acid gas. 
Nature, however, has provided for the maintenance of an equilibrium 
by the breathing of plants which require the carbonic acid gas exhaled by 
177 
