aye. eee THE AUSTRALIAN NATURALIST. 
trouble was that the coral became discoloured, and of a dirty 
brown colour; when it got too bad he took it out and scrubbed 
it, but it always went back again, because it kept the water 
clear. 
Lloyd examined this piece of coral and found the diseoloxa- 
tion caused by a minute confervoid growth, which has since 
been found to be an excellent oxygen-producing medium. In 
fact, the lower forms of aquatic vegetation give off a far -greater 
quantity of oxygen than the higher forms do. ‘Therefore the 
coral did it after all; but why, he did not know. 
So this barber, without any. knowledge of science, actually 
kent the first self-supporting aquarium. : 
The supply of a sufficient quantity of oxygen is the secret of 
success in keeping fish in a globe or tank. So we shall dwell 
a little on this subject. 
All living creatures require oxygen to purify the blood. We 
ourselves, and life existing out of water, obtain it direct from the 
air by breathing and passing it through the lungs. 
A fish is continually taking in water by the mouth and pass- 
ing it out. through the gill-covers. This action is the breathing 
of a fish. The blood in its circulation through the body passes 
through the gills, the purification of the blood is effected here, 
where it becomes exposed to the oxygen dissolved in the water. 
The walls of the tubes forming the gills, while they hinder the 
water from mixing with the blood, are yet so delicate that the 
oxygen comes into contact with the blood, penetrating the thin 
' membranous coat, thus oxygenating the blood. 
For the requirements of land-dwellers there is any amount of 
oxygen, and so there is for fish in a stream or pond; but not so 
in the small vessel in which we keep our fish. Water absorbs 
oxygen direct from the air, but only to a very small extent; a 
sufficient amount of oxygen might be obtained in this manner 
were we to keep our fish in a shallow vessel with a large sur- 
face exposed to the air. Where the water is deeper, as in a fish- 
bowl, and a comparatively small surface exposed, we must find 
other means of introducing it. This can be done by constantly 
agitating the water or by frequent changes. But the. best 
means are to permit nature to do the work by the introduction 
_ of suitable plant life. Submerged plants must, of course, be 
selected. Roughly speaking, the plants absorb the carbonic acid 
gases from the water, converting these into oxygen. 
