STUDIES IN ANIMAL AGGREGATIONS. 307 



Those in 100 cc., with the colloidal silver ratio of I drop to 

 50 cc. all righted; the bunched animals in from 15 to 30 seconds, 

 mean 27 seconds; the isolated in from 15 seconds to 8 minutes, 

 mean 161 seconds. 



The bunched animals in 50 cc., with the colloidal silver ratio of 

 one drop to 25 cc., all righted in from 10 to 220 seconds, mean 101 

 seconds. Two of the accompanying isolated animals righted, one 

 in 95 seconds and the other after an hour and a half. The others 

 did not right in the next two days. 



The bunch in 25 cc., with one drop to 12.5 cc. all righted in 

 from 3 hours, 38 minutes, to about six hours, with a mean of 4 

 hours, 41 minutes. One of the isolated individuals righted almost 

 immediately but none of the others did so. Contrary to the expe- 

 rience of Drzewina and Bohn (19210), the toxicity depends on 

 the concentration of the colloidal silver, rather than on the volume 

 to which the animals are exposed. 



It is worth noting that the protective action of the bunch appears 

 only in the more toxic suspensions, where apparently the toxic 

 strength per individual was more nearly reached even with the 

 bunched animals. Drzewina and Bohn apparently would inter- 

 pret such an observation as meaning that the auto-protective sub- 

 stance is secreted more rapidly in more toxic conditions. 



RECONDITIONED SOLUTIONS. 



The second and more convincing experiment used by Drzewina 

 and Bohn as evidence in favor of their view that the group pro- 

 tection is furnished by some sort of auto-protective secretion, 

 rather than by exhaustion of the toxic substance, is as follows 

 (19210) : 



; ' Nous decantons la solution out depuis 24 heures sejournent 

 une cinquantaine d'embryons (tadpoles of Rana fusca} et dont la 

 teinte revele la presence du collo'ide; nous y ajoutons le meme 

 nombre de gouttes que la veille, i par exemple, et nous y plagons 

 deux embryons neufs du meme age. Ceux-ci survivent, alors que 

 des individus temoins, places dans une solution neuve a I goutte de 

 collargol, succombent, comme c'est la regie pour les isoles. 11 

 semble ainsi que, attaquees par le colloide, les larves einettent, 



