1857.] on the Aquarium, 405 



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 indis- 

 pensable 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 limnea stagnalis, 

 were consequently introduced, and by their extraordinary voracity 

 and continued and rapid locomotion, soon removed the cause of 

 interference, and restored the wholb 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 solidifying the carbon of the gaseous compound for the con- 

 struction 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 fruitful pabulum for the vegetable growth. 

 Reasoning from analogy, it was evident that the same balance 

 should be capable of being permanently 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: the Air contained dissolved 

 in Water. — The ordinary atmospheric air is found to be composed 

 of 79 volumes of nitrogen gas and 21 volumes of oxygen ; and 

 water has the power of absorbing gaseous bodies in varying pro- 

 portions, thus: — 100 volumes of water, at a temperature of 60*^ 

 Fahr., and under ordinary barometric pressure, will absorb 



1 '56 volumes of nitrogen gas, 

 3-70 „ oxygen gas, 



100*00 „ carbonic acid gas, 



and hence we find that the air absorbed by water, and existent in 

 rivers to the extent of from 2 to 3 per cent., consists of about 29 of 

 oxygen and 71 of nitrogen. In fresh fallen rain and melted snow, 

 it ranges from 30 to 35 per cent, of oxygen, and in some spring 



