INTRODUCTION. 59 
We have already shown, that, as many of these little 
creatures live on dead animal matter, they are of immense 
service in keeping the waters pure by removing what would 
soon have rendered them loathsome and deadly. But they 
are not only useful in removing what is corrupt and cor- 
rupting, but they emit what contributes to the salubrious- 
ness of the waters. It is one of the remarkable discoveries 
of science that the functions of animal life are reversed in 
infusorial animalcules, and that, instead of evolving carbonic 
acid gas, as other animals, by breathing, do, they evolve 
pure oxygen. The air-bubbles given out by water, in 
which these living “minims” abound, contain such pure 
oxygen, that a small bit of deal matchwood, on which a 
flame has just been extinguished, will burst into a flame 
again on being immersed in these bubbles. The truth of 
this rests on no less authority than that of Liebig, the 
celebrated German chemist, who tells us that he had him- 
self ascertained it by experiment. 
Gosse, in speaking of coralline, says, “ Beyond its beauty, 
I know not that this little creature has any obvious claim 
on our consideration, except that, in common with other 
sea-plants, it gives out oxygen, and thus maintains water 
in which it grows in a state fit for the support of animal 
