PROTECTION FROM TOXIC REAGENTS 207 



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 interpret 

 such an observation as meaning that the autoprotective substance 

 is secreted more rapidly under 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 autoprotective secretion, rather 

 than by exhaustion of the toxic substance, is as follows (1921(1): 



"Nous decantons la solution oil depuis 24 heures sejournent une 

 cinquantaine d'embryons (tadpoles of Rana fusca) et dont la teinte 

 revele la presence du colloide; nous y ajoutons le meme nombre de 

 gouttes que la veille, i par exemple, et nous y plagons deux em- 

 bryons neufs du meme age. Ceux-ci survivent, alors que des in- 

 dividus temoins, places dans une solution neuve a i goutte de 

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

 ainsi que, attaquees par le colloide, les larves emettent, rapidement, 

 une substance (ou des substances) qui a pour effet de les proteger." 



Wholly similar experiments were run with the brittle starfish, 

 Opiiiodcrma, to test for the presence of the postulated autopro- 

 tective secretion. Colloidal suspensions in which Ophioderma had 

 been exposed were reconditioned by 3 hours aeration with room 

 air in order that the new lot might not suffer from low oxygen 

 tension, and were filled to the original volume with distilled water. 

 The original suspension had been made with i drop of colloidal 

 silver for each 25 cc, and the same amount was added to this re- 

 conditioned water. Tests showed that the aeration of freshly pre- 

 pared suspensions for this length of time caused a color change 

 but did not markedly affect the toxicity. 



Three lots, each consisting of one group of 5 bunched animals and 

 4 isolated individuals, were placed severally in 50 cc. of such a re- 

 conditioned suspension, 9 hours after the previous experiment had 

 closed. These were run simultaneously with three similar lots in 



