STUDIES IN ANIMAL AGGREGATIONS. 



303 



TABLE I. 



SHOWING THE RESULTS OF EXPOSURE TO SUSPENSIONS OF COLLOIDAL SILVER 

 FOLLOWED BY TRANSFER TO WATER SIMILAR TO THAT TO 



WHICH THE ANIMALS WERE ACCUSTOMED. 

 All were run at room temperature. 



More cases with different concentrations could be given but 

 the result is the same in all. This agrees entirely with the expe- 

 rience of Drzewina and Bohn, who used a wide range of animals ; 

 and with that of Bresslau, using different toxic reagents with 

 ciliates. 



A priori one would expect exactly such a result since in each 

 case there is much less of the toxic substance present per indi- 

 vidual composing the larger groups, than when 1-3 animals are 

 placed in the same amount of the same concentration of toxic 

 substance (Pieron, 1921). Yet the possible menace of crowding, 

 so frequently given as the only result of confining many animals 

 within a small space, may easily be demonstrated even here. With 

 the Ophioderma, for example, if the glass fingerbowls were cov- 

 ered with glass plates during the exposure to colloidal silver, thus 

 stopping free gaseous exchange, the grouped animals were in 

 much worse condition than were their isolated fellows. 



CAUSE OF GROUP IMMUNITY. 



When one begins to inquire into the causes of the greater im- 

 munity of the grouped individuals, he immediately finds division 



RY 



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