64 



CHLOROSPERMS. 



If even one or two fish, crabs, or indeed any 

 living animals, be placed in a jar of sea-water^ 

 they speedily exhaust the free oxygen of the 

 water, and, as the water cannot absorb fresh 

 oxygen from the atmosphere so rapidly as the 

 animals consume it, the water soon becomes 

 unfit to support animal life, and its inhabitants 

 die as surely as a man would who was enclosed 

 in an air-tight box. It is possible to renew the 

 oxygen by dashing water into the jar from a 

 height, or even by pumping fresh air into it; 

 but such a process would be very fatiguing, as 

 it must be continually carried on day and night. 

 But it is found that plants have the property 

 of pouring out oxygen when they are in a healthy 

 state and acted on by light. So, if we can 

 procure plants that will thrive in a confined 

 space, and keep them in a light room, we shall 

 find that each plant acts as a natural pump, and 

 not only supplies continually fresh oxygen, but 

 consumes the carbonic acid gas that loads the 

 water with its stifling influence. The Chlo- 

 rosperms are peculiarly useful for this purpose, 

 as many of them will live for an unlimited time 

 in confinement, continually regenerating the 

 water in which they are placed. I have now an 

 aquarium containing water that I brought from 



