306 W. C. ALLEE AND J. F. SCHUETT. 



One bunch of 5 animals with 5 cc. of sea water and 0.3 drops of 

 colloidal silver each, and with a surface exposure of 15.6 sq. cm. 

 per animal. 



Five isolated animals with 25 cc. of sea water and 1.5 drops of 

 colloidal silver each and with 78 sq. cm. surface exposure. 



A second set was exactly similar, except that the animals were 

 exposed to 2, 0.4, and 2 drops of colloidal silver per individual. 



The exposure in a typical experiment lasted 15.5 hours, after 

 which the animals were washed as usual and transferred to fresh 

 sea water for observation for the following 24 hours. At intervals 

 records of numbers righted after having been turned over, and 

 other evidences of activity, such as spontaneous motion of tube 

 feet, were recorded. 



All of the animals bunched in the 10 cm. fingerbowls recovered 

 sufficiently to right themselves within 24 hours, despite the fact 

 that four of the ten were much corroded by the action of silver that 

 had settled to the bottom of one of the fingerbowls. In both ex- 

 periments, the isolated animals fared next best, although they made 

 a much poorer showing than did the bunched individuals that were 

 exposed. to a much lower amount of colloidal silver per animal; 

 only six of this set of ten righted. The bunched animals, ex- 

 posed to the same volume and amount of colloidal silver as those 

 isolated, ranked a poor third, which may be due to the decreased 

 surface exposure, or to some of the better known ill effects of 

 crowding. 



These experiments indicate either that the decreased amount of 

 colloidal silver or the reduced volume of sea water present per 

 individual, or both, markedly favored the survival of the animals 

 bunched in the small amount of water present in the fingerbowls. 

 Drzewina and Bohn emphasize the latter factor, and accordingly 

 the following experiments were run to test out this point. 



Lots composed of four solitary Ophiodcrina and one bunch of 

 five were exposed in fingerbowls to 25, 50, 100, and 250 cc. of 

 sea water, each containing only two drops of the stock suspension 

 of colloidal silver. After 15 hours they were washed and tested 

 for activity as usual. Those in 250 cc. of sea water, where the 

 colloidal silver suspension had a value of one drop to 125 cc., 

 righted immediately whether they had been bunched or isolated. 



