2 



THE MARINE 



animals alone in sea-water, however pure it may 

 have been at first, it speedily becomes offensively 

 fetid, the creatures look sickly, and rapidly die off, 

 and we are glad to throw away the whole mass of 

 corruption. 



Why is this? Why should they die in our 

 vessels, when they live so healthily in the little 

 pools and basins of the rock, that are no larger ? 

 For the very same reason that we should quickly 

 die in a room perfectly air-tight. The blood of all 

 animals requires to be perpetually renewed by the 

 addition to it of the element called oxygen ; and 

 when it cannot obtain this it becomes unfit for the 

 support of life. Terrestrial animals obtain this 

 gaseous element from the air; aquatic animals (that 

 is, those which are strictly such) obtain it from the 

 water. But in either case it is principally produced 

 by living plants while under the action of light. If, 

 then, we can furnish our captives with a perpetual 

 manufactory of oxygen, the main cause of their 

 sudden death is removed. Of course they have 

 other requirements, but this is the most urgent, the 

 indispensable. 



In a state of nature, the rocks, the crannies, the 

 pools, the sea-bottom are studded with various 

 living plants, which we call sea-weeds ; and these, 

 under the daily stimulus of sunlight, direct or 

 indirect, produce and throw off a vast quantity of 

 oxygen, which, by the action of the waves and 

 currents, is diffused through all parts of the habi- 

 table sea, and maintains the health of its countless 

 swarms of animals. 



In an Aquarium we seek to imitate this chemistry 

 of nature. We collect the plants as well as the 

 animals ; and, a little observation teaching us how 



