120 ANIMAL LIFE AND SOCIAL GROWTH 



Grouped fishes in the presence of a poisonous 

 material such as colloidal silver are able to remove 

 the toxic silver from the suspension and survive, 

 when isolated fishes are unable to do so, and perish. 

 Chemical analyses show that the grouped fishes 

 protect themselves because of the adsorption of 

 the silver on the slime which they secrete. Such 

 group survival is most clearly shown when the 

 volume and the concentration of the harmful 

 colloidal silver is the same for the grouped that 

 it is for each of the isolated fishes. Under these 

 conditions the group gives off more slime than can 

 a single isolated fish, hence more of the toxic 

 substance can be removed. 



Animals in nature may be called upon to en- 

 counter exactly such a set up. In a given pond, 

 the entire fish population whether it consists of 

 one or of many would be exposed to the same 

 total amount of toxic material if any were present. 

 In the presence of many fishes, each one would 

 receive a dosage of the poison which might be 

 insufficient to cause its death, while if only one 

 were exposed to the whole amount of poison, 

 death might certainly result. A similar clearing 

 up of poisons by groups of animals has been 

 demonstrated for many other kinds of animals and 

 appears to be a widespread phenomenon in 

 nature. 



