The Aquarium. 5699 



der it at all permanent, and which at the commencement of the expe- 

 riment had not been foreseen. The circumstances alluded to arose 

 from the natural decay of the leaves of the Vallisneria, the increase of 

 which rendered the water turbid, and caused a rapid growth of green 

 confervoid mucus on the surface of the water, and upon the sides of 

 the receiver; the fish also assumed a sickly appearance, and had this 

 been allowed to progress they must have speedily perished. The 

 removal of this decaying vegetation from the water as fast as it was 

 formed became, therefore, a point of paramount importance ; and to 

 effect this recourse was had to a very useful little scavenger (whose 

 highly important and beneficial functions throughout all nature have 

 been too much overlooked, and its indispensable uses in the economy 

 of animal life not well understood), the water snail, whose natural food 

 consists of decaying and confervoid vegetation. Five or six of these 

 little creatures, the Limuea stagnalis, were consequently introduced, 

 and by their extraordinary voracity and continued and rapid locomo- 

 tion soon removed the cause of interference, and restored the whole to 

 a healthy state. 



Thus, then, was established that wondrous and admirable balance 

 between the animal and vegetable kingdoms, and by a link so mean 

 and insignificant as almost to have escaped observation in its most 

 important functions. The principles which are here called into 

 action are, that the water, holding atmospheric air in solution, is a 

 healthy medium for the respiration of the fish, which thus converts 

 the oxygen constituent into carbonic acid. The plant, by its vital 

 functions, absorbs the carbonic acid, and, appropriating and solidify- 

 ing the carbon of the gaseous compound for the construction of its 

 proper tissues, eliminates the oxygen ready again to sustain the health 

 of the fish ; while the slimy snail, finding its proper nutriment in 

 the decomposing vegetation and confervoid mucus, by its voracity 

 prevents their accumulation, and by its vital powers converts that 

 which would otherwise act as a poisonous agent into a rich and fruit- 

 ful pabulum for the vegetable growth. Reasoning from analogy, it 

 was evident that the same balance should be capable of being perma- 

 nently maintained in sea water, and thus a vast and unexplored field 

 for investigation opened to the research of the naturalist ; and this 

 proved on trial to be the case. 



PRINCIPLES OF THE AQUARIUM I THE AIR CONTAINED DISSOLVED IN WATER. 



The ordinary atmospheric air is found to be composed of 79 vo- 

 lumes of nitrogen gas and 21 volumes of oxygen; and water has the 



