ii THE WEB OF LIFE 21 



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 economic 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 colour- 

 ing 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 though many a plant thrives quite in- 

 dependently of- animals on the raw materials of earth 

 and air, others are demonstrably raising the ashes of 



