228 THE CONTROL OF LIFE 



increase of animals and plants that are palatable, profit- 

 able, and pleasant. He has to do this yfith. scientific 

 caution both in removing and in adding. Let us briefly 

 illustrate some of the practical recommendations which 

 experience has brought into prominence. 



Realisation of the Web of Life. — If Man is to succeed 

 in the control of the realm of organisms, he must acquire 

 an increasing knowledge of the old-established, subtly 

 adjusted balance of nature or system of inter-relations, 

 a disturbance of which is often followed by portentous 

 results. The consequences of the careless introduction 

 of animals into a new habitat, where they multiply 

 unchecked, is familiar in connection with the rabbits 

 introduced into Australia and the sparrows introduced 

 into the United States. Contrariwise, the ruthless 

 killing off of birds and beasts of prey has been followed 

 by plagues of voles, and the destruction of white herons 

 has been followed by great losses in the rice-fields of 

 the East. Destroying squirrels may mean an over- 

 multipHcation of wood-pigeons, which are extremely 

 destructive to the crops. What is needed at every turn 

 is more science. 



Let us take a diagrammatic illustration. There was 

 some years ago a decrease in the yield of fish from 

 certain Australian rivers and estuaries. A hasty infer- 

 ence put the blame on cormorants, which are well 

 known to be greedy fish-eaters. So the edict went forth 

 for a massacre of cormorants, and the edict was obeyed. 

 But the extreme thinning of the cormorants did not 



