INTER-RELATIONS OF LIVING CREATURES 



THE BALANCE OF NATURE THE WEIRD WAYS OF PARASITES 



MANY naturalists have had the vision of "the web of 

 life," but none so vividly as Darwin. It was central 

 in his picture of Animate Nature. By "the web of 

 life" we mean that no creature lives or dies to itself; that each 

 life is linked to other lives, often in obscure and unsuspected 

 ways. Everything, as the philosopher Locke put it, is a retainer 

 to other parts of the vast system of Nature. 



Balance of Nature 



We have seen that green plants feed on air, water, and 

 dissolved salts; that by utilising the energy of the sunlight they 

 are able in the laboratory of the leaf to build these up into com- 

 pounds ; and that on these products all animal life depends, either 

 directly in the case of vegetarian animals or indirectly in the 

 case of carnivores. There is a deep biological sense in which all 

 flesh is grass. This is one aspect of the Balance of Nature, that 

 there must be sufficient vegetable materials in an area to keep 

 the animals agoing. 



Another aspect of the Balance of Nature has to do with 

 oxygen and carbon dioxide. Few people realise that the bulk of 

 the oxygen in our atmosphere has been formed by green plants, 

 which in the daylight are always splitting up carbonic acid gas 

 and liberating oxygen into the air. This oxygen is used by ani- 

 mals, and by plants as well, for keeping up the oxidation or 

 combustion of carbon compounds which living always implies. 



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