28 THE DRIP-GLASS. 



lift out sucli animals as you wish to transfer, for 

 examination, or any other purpose, to another 

 vessel. As a general rule, however, they should 

 be disturbed as little as possible, and never 

 handled. 



Artificial Aeration. — Although living and 

 healthy plants will educe and throw off, under the 

 influence of light, oxygen, in sufficient quantity to 

 maintain in health a given number of animals, 

 yet the artificial admixture of atmospheric air 

 with the water may be employed as a valuable 

 auxiliary. I have used it with marked benefit ; 

 often having revived animals thereby, which, from 

 the exhaustion of the water, were apparently in a 

 dying state. Its utility as a means of maintaining 

 the purity of the water is still more obvious ; since 

 it is by the frequent and successive presentation of 

 the particles of water to the air, that the animal 

 excretions which they hold in suspension, become 

 chemically changed, and deprived of their putres- 

 cent qualities. This is what takes place in nature. 

 By the perpetual dashing of the waves against the 

 shore, and especially against the ragged rocks, an 

 immense quantity of air becomes entangled, in the 

 form of minute bubbles, which by the various cur- 

 rents are difiused through the sea, and even carried 

 to considerable depths, before they rise to the 

 surface and become dissipated. Thus the violent 

 agitation of the sea is a powerful agent in its puri- 

 fication. 



One of the simplest modes by which this object 

 can be eficcted, is the drip-glass. I have been 

 accustomed to suspend over the Aquarium, a per- 

 forated bell-glass (I think it is called a bee-glass) 

 of suitable size, into the orifice of which a bit of 



