64 Professor J. Arthur Thomson on 



we cannot give an account of either eddy or trout apart from the 

 stream. All the energies of organisms come from their environment 

 and from the sun in the long run. We ourselves depend for food 

 on plants and animals, and through these animals on plants 

 ultimately ; the plants feed on air, water, and salts, which, with the 

 aid of the sunlight, they build into organic compounds ; but the 

 sunlight must shine through the screen of green chlorophyll in 

 the leaves, and there cannot be chlorophyll without iron ; therefore 

 our whole social framework is founded on Iron. 



We have ceased to wonder at the circulation of blood in our 

 body ; have we begun to wonder at the ceaseless circulation of 

 matter in the system of Nature? Nutritive chains, often quaintly 

 suggestive of ''The House that Jack Built" and similar old 

 rhymes, bind gull to fish, fish to fish, fish to crustacean, crustacean 

 to infusorian and diatom. The plant lives on the inorganic, — air, 

 water, and salts. The animal eats the plant and a new incarnation 

 begins. The animal eats another animal and re-incarnation con- 

 tinues. The animal dies and the Bacteria of decay break down 

 the dead, so that there is a return to air and water and salts. 



Mud. and manure placed in boxes round a fish pond form a 

 basis of operations for Bacteria. These provide food for or are 

 themselves eaten by Infusorians which fall in a living cataract into 

 the water. The Infusorians form the food of minute crustaceans 

 or water-fleas, which again are devoured by fishes, and some of 

 these again are eaten by man. As fish-flesh is said to be good for 

 the brain, we discover a nexus between mud and clear thinking. 

 It has been shown in a most circumstantial way that the quantity 

 of mackerel brought into Billingsgate is correlated with the amount 

 of sunshine in Spring. The more sunshine there is, the greater 

 the multiplication of diatoms and Peridinid infusorians. The more 

 of this microscopic plankton there is — the "stock" of the "sea- 

 soup" — the greater the abundance of Copepods, but it is on 

 Copepods that the mackerel largely depend. Just as there is a 

 sense in which all flesh is grass, so all fish is diatom and detritus, 

 infusorian and water-flea. 



From 'Nutritive chains' we pass to instances of the depend- 



