THE AQUARIUM. 17 



in globes ; but such a tiling is against all rules of nature, 

 and, therefore, impossible. If we keep gold-fish, or, indeed, 

 any other kind of fish, in a globe of water, they sooner 

 or later die, and if we do not change the water often, 

 that catastrophe will the more speedily occur. Bat let us 

 procure a handful of any submerged aquatic plant, that is 

 to Bay, a plant that grows beneath the surface of fresh- 

 water, and, having washed it well, throw it into our fish 

 globe, and we will, if the vessel does not contain too 

 many fish, find we shall not have to change the water 

 for days, nor, perhaps, weeks. It is on this principle of 

 the action that the plants exert in keeping the water fit 

 for the inhabitancc of fish, that the Aquarium is con- 

 structed. 



It has been found by experiment that animals take into 

 their lungs the gas, oxygen or vital air as it is also 

 called, one of the components of the atmosphere, and give 

 out this gas, combined with another substance, carbon or 

 charcoal, which is one of the constituents of all organized 

 or living matter, be it animal or vegetable. Now, when 

 carbon (a perfectly harmless substance) is combined with 

 oxygen (a life-giving body), there is formed a very poisonous 

 compound, termed carbonic-acid gas, being the same body 

 that collects in wells, in some of our mines, and which is 

 also given off from stoves, often causing disease and death. 



Who does not know the dreadful tale of the suflerings of 

 hundreds of persons, shut up at night in a prison called 

 " the black hole," at Calcutta, to which there were but two 

 openings, the door, that was locked, and a small window, 

 placed near the ceiling? Now, as carbonic-acid gas, which 



