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 COg, 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 i/i 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 CO2 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 will 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 equihbrium 

 by the breathing of plants which require the carbonic acid gas exhaled by 



177 



