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 tluis maintains water 

 in which it grows in a state fit for the support of animal 



