218 IDEAL HOME LIFE
and alligators become torpid and refuse to oat if the temperature goes down much below 70, and should always be kept at a hot-house temperature to make the best growth.
It is very important for all animals that the temperature should not vary suddenly, since in their natural environment they are not subjected to such rapid changes, and hence are not adapted to them. Fishes, especially the long-tailed varieties of goldfishes, may have the tissues of the fins injured by exposure to sudden changes in temperature, rendering them liable to the disease known as "tail-rot." Aquariums should, therefore, be kept out of cold draught in the winter time and water should be added only when it is at the same temperature as that of the aquarium.
For tropical fishes which require higher water temperature the year round, 75 to 80 degrees or more, various devices have been invented. Several of these are quite satisfactory, even with small tanks. When specially constructed tanks or other apparatus are required, it will be best to consult a dealer in aquarium supplies in regard to the matter.
It is possible to heat a tank by means of electric light bulbs placed near the tank, and a little careful experimentation with the aid of the thermometer will indicate how close the bulb should be placed. But the best appliances involve means of circulating the water so as to maintain nearly the same temperature in all parts of the aquarium.
Planting the Aquarium
This is an important proceeding, as upon the successful establishment of the plant growth depends the aeration of the standing aquarium, and consequently the health of the animals. Many kinds of aquatic plants, both wild and cultivated, will grow readily in the narrow limits of the aquarium.
Fine gravel or coarse sand, or a mixture of these, should first be placed in the bottom of the tank to the depth of one or two inches, depending upon the depth of the aquarium. For the best results the sand should not be evenly distributed over the bottom, but should slope toward the center, side, or