STl'DIKS IN ANIMAL AGGREGATIONS. 



309 



the used substance it was necessary to add the same amount, one 

 drop of colloidal silver per 25 cc. to this suspension in order that 

 it might he as deeply colored as was a fresh suspension made up 

 with that amount of the colloidal silver. There was only sufficient 

 colloidal silver left in this twice used suspension to discolor the 

 liquid. Either the animals, or the aeration, or both, had removed 

 the greater part of the silver, and it can be readily demonstrated 

 that the effect was not wholly due to aeration. The water thus 

 treated was distinctly sirupy, and evidently held organic matter, 

 received from the two lots of Ophioderina which it had contained. 

 The effect of this twice reconditioned suspension was tested as 

 before. Comparison tests were run with newly prepared sus- 

 pensions, and the results are summarized in Table III. 



TABLE III. 



SHOWING RIGHTING TIME OF Ophioderma AFTER AN EXPOSURE OF 19 HOURS IN 

 TWICE RECONDITIONED AND IN FRESH SUSPENSIONS. 



Reconditioned Suspension. 



Bunch. 



Isolated. 



New Suspension. 



* One failed to give the righting reaction. 



There is no evidence here of the presence of an auto-protective 

 secretion in the sea water, protecting animals from the action of 

 the colloidal silver, nor is there evidence for the presence of an 

 active auto-destructive agent, which Drzewina and Bohn also 

 postulated to explain certain cases in which the greater mass of 

 animals exposed to KC1 die more rapidly than do the solitary 

 individuals. In the presence of an active auto-destructive secre- 

 tion one would expect the mass to die more rapidly than do the 

 isolated individuals, which is not the case. 



There is good evidence that the secretion of slime or other 

 organic matter into the suspension does remove the colloidal silver 

 and so render the solution less toxic. It is particularly significant 



