10 ANIMAL LIFE AND SOCIAL GROWTH 



lake; and it has an especial advantage, since, 

 when the animal food becomes scarce, it may grow 

 roots and live as do other plants. Here again we 

 find good evidence that plants cannot be excluded 

 from the community life which we are describing. 



When poisonous materials, such as come from 

 many factories, find their way into a lake, the 

 greater the volume of animal and plant life, the 

 greater the chance of survival of each individual. 

 If the poison is not too great in amount, or too 

 deadly, the myriads of animals either directly or 

 through their secretions and waste products, 

 absorb or otherwise fix the toxic materials so as 

 to cleanse the water. At the worst, if there are 

 many, each receives a smaller dose of the poison 

 than if there were but few, and many will be able 

 to survive the lighter dosage that would perish 

 if exposed in small numbers to the full strength of 

 the poisonous materials. In such cleansing of 

 the waters, conducted in an entirely subconscious 

 manner, all the animals and plants are associated. 

 In this the black bass aids the fishes which to- 

 morrow it will take as food, just as the latter 

 help prevent their arch enemy from being poi- 

 soned by automatically fixing a part of the poison 

 themselves. 



A different phase of the story is shown by the 

 history of life in prairie lakes which are appendages 



