BEGINNINGS OF CO-OPERATION 57 



grouped fish shared between them a dose easily fatal 

 for any one of them; the slime they secreted changed 

 much of the silver into a less toxic form. In the ex- 

 periment as set up the suspension was somewhat too 

 strong for any to survive; with a weaker suspension 

 some or all of the grouped animals would have lived; 

 as it was, the group gained for its members a longer 

 life. In nature, they could have had that many more 

 minutes for rain to have diluted the water or some 

 other disturbance to have cleared up the poison and 

 given the fish a chance for complete recovery. 



With other poisons, other mechanisms become 

 effective in supplying group protection. Grouped 

 Daphnia, (50) the active water fleas known to all 

 amateur fish culturists, survive longer in over-alka- 

 line solutions than daphnids isolated into the same 

 volume. The reason here is simple. The grouped 

 animals give off more carbon dioxide, and this neu- 

 tralizes the alkali. Long before the isolated individual 

 can accomplish this, it is dead; in the group those 

 on the outside may succumb, though if the num- 

 ber present is large enough even they may be able 

 to live until the environment is brought under tem- 

 porary control. 



Frequently the protective mechanism is much 

 more complex. With many aquatic animals, other 

 things being equal, isolated animals consume more 



