PHYSIOLOGICAL EFFECTS 133 



bers greater survival in the occasional times of 

 stress brought on by a flood of fresh water at low 

 tide. 



Many other beneficial effects of crowding could 

 be given. Massed spermatozoa live longer and 

 retain their ability to fertilize eggs longer than 

 if they are relatively isolated. Bacteria, if present 

 in numbers, are frequently able to live and multi- 

 ply in the face of adverse conditions which kill off 

 isolated cells. Thus Bacillus coli of a strain 

 sensitive to gentian violet will grow in mass cul- 

 tures in the presence of the harmful dye. Inoc- 

 ulations of thirty cells will survive and flourish 

 under conditions which kill off single individuals or 

 smaller groups. The evidence shows that thirty 

 such bacteria living together are able to accom- 

 plish more work than can thirty similar, isolated 

 cells and this excess ability of the bacteria when 

 growing near each other has been attributed to 

 the communal activity of the bacteria. 



The facts presented in the present hasty survey 

 of some of the values that arise from aggregations 

 indicate that such groups of organisms have the 

 possibility of becoming what is commonly called 

 "social." To be sure, they must possess other 

 attributes. The mere existence of an aggrega- 

 tion implies that the collected animals have 

 tolerance for the presence of others in the same 



