CHAP. II The Web of Life 21 



compensate both for their own breathing and for that of 

 animals. Thus the result within the globe need not be 

 suffocation, but harmonious prosperity. If the minute' 

 animals ate up all the plants, they would themselves die 

 for lack of oxygen before they had eaten up one another, 

 while if the plants smothered all the animals they would 

 also in turn die away. Some such contingency is apt to 

 spoil the experiment, the end of which may be a vessel of 

 putrid water tenanted for a long time by the very simple 

 colourless plants known as Bacteria, and at last not even 

 by them. Nevertheless the "vivarium" experiment is both 

 theoretically and practically possible. Now in nature there' 

 is, indeed, no closed vivarium, for there is no isolation and 

 there is open air, and it is an exaggeration to talk as if our 

 life were dependent on there being a proportionate number 

 of plants and animals in the neighbourhood. Yet the 

 " balance of nature " is a general fact of much importance, 

 though the economical relations of part to part over a wide 

 area are neither rigid nor precise. 



We have just mentioned the very simple plants called 

 Bacteria. Like moulds or fungi, they depend upon other 

 organisms for their food, being without the green colouring 

 stuff so important in the life of most plants. These very 

 minute Bacteria are almost omnipresent ; in weakly animals 

 — and sometimes in strong ones too — ^they thrive and 

 multiply and cause death. They are our deadliest foes, but 

 we should get rid of them more easily if we had greater love 

 of sunlight, for this is their most potent, as well as most, 

 economical antagonist. But it is not to point out the 

 obvious fact that a Bacterium may kill a king that we have 

 here spoken of this class of plants ; it is to acknowledge 

 their beneficence. They are the great cleansers of the 

 world. Animals die, and Bacteria convert their corpses 

 into simple substances, restoring to the soil what the plants, 

 on which the animals fed, originally absorbed through 

 their roots. Bacteria thus complete a wide circle ; they 

 unite dead animal and living plant. For thou^ many a 

 plant thrives quite independently of animals on the raw 

 materials of earth and air, others are demonstrably raising 



