STUDIES IN ANIMAL AGGREGATIONS: THE RELATION BETWEEN MASS OF ANIMALS AND RESISTANCE TO COLLOIDAL SILVER

Abstract

The findings of Drzewina and Bohn that, when exposed to suspensions of colloidal silver, other things being equal, there is greater protection the greater the mass of the animals in proportion to the volume of the toxic substance, are confirmed, when the mass of animals in a limited volume of water is not too large. With plana-rians and with the ophiurid, Ophioderma, at least a large part of the protective action of the mass is due to the adsorption of the colloidal silver either by slime or directly on the surfaces of the exposed animals. The protective action is not specific for undercontrolled conditions; planarians are protected by the presence of numbers of carefully washed individuals of Dendrocoelum, Cladocera, pond snails or their slime, pond leeches, Asellus alive or dead, and even by pond mosses or suspensions of desiccated mammalian parotid glands. The protection has been reciprocal whenever tested. These observations verify conclusions gained by other means that aggregations of animals may have survival value for their members, and throw new light on the possible survival value of communities of taxo-nomically unrelated organisms of dissimilar habits. They suggest the presence of an integrating factor in animal communities more subtle than those demonstrated hitherto for simpler organisms.