CHAPTER II 



THE WEB OF LIFE 



I. Dependence upon surroundings 2. Interrelations of plants 

 and animals 3. Relation of animals to the eaith 4. Nutri- 

 tive relations 5. More complex interactions. 



IN the filmy web of the spider, threads delicate but firm 

 bind part to part, so that the whole system is made one. The 

 quivering fly entangled in a corner betrays itself through- 

 out the web ; often it is felt rather than seen by the lurking 

 spinner. So in the substantial fabric of the world part 

 is bound to part. In wind and weather, or in the business 

 of our life, we are daily made aware of results whose first 

 conditions are remote, and chains of influence not difficult 

 to demonstrate link man to beast, and flower to insect. 

 The more we know of our surroundings, the more we 

 realise the fact that nature is a vast system of linkages, 

 that isolation is impossible. 



1. Dependence upon Surroundings. Every living body 

 is built up of various arrangements of at least twelve 

 " elements," viz. Oxygen, Hydrogen, Carbon, Nitrogen, 

 Chlorine, Phosphorus, Sulphur, Magnesium, Calcium, 

 Potassium, Sodium, and Iron. All these elements are 

 spread throughout the whole world. By the magic touch 

 of life they are built up into substances of great complexity 

 and mutability, substances very sensitive to impulses 

 from, or changes in, their surroundings. Thus the 

 chemical substances known as proteids, which are abso- 

 lutely essential components of living matter, are intricate 

 compounds of Carbon, Hydrogen, Oxygen, and Nitrogen, 

 usually with small amounts of Sulphur. As the creature 

 lives, these and other complex substances are concerned 

 in intricate reactions. Many substances, e.g. the ex- 



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