STUDIES IN ANIMAL AGGREGATIONS. 311 



principal element in the -protective action. The results of typical 

 experiments are summarized in Tables IV and V. 



TABLE IV. 



SHOWING THE NOX-SPECIFICITY OF THE PROTECTION AGAINST COLLOIDAL SILVER. 



TABLE V. 



SHOWING COMMUNITY PROTECTION AGAINST THE ACTION OF COLLOIDAL SILVER. 

 Two drops of colloidal silver in 5 cc. pond water; exposure 13 hour';, then 

 washed and placed in pond water. Temperature 21. 



As these tables show, such diverse organisms as Cladocera, 

 Asellus, pond snails, pond leeches, Dendroccelum, and even pond 

 moss, if present in quantity, markedly protect planarians from the 

 toxic action of colloidal silver. Even the actual presence of living 

 organisms is unnecessary; snail slime without ihe snails protects 

 efficiently apparently by adsorbing the colloidal silver. The slime 

 becomes densely colored as the water becomes lighter in color. 

 Suspensions in water of desiccated parotid glands of sheep ex- 

 hibit similar adsorptive phenomena and have similar protective 

 value. 



