CORRELATION BETWEEN THE POSSESSION OF A CHITINOUS CUTICLE AND SENSITIVITY TO DDT

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Abstract
The susceptibility of various species of Protozoa, Coelenterata, Platyhelminthes, Nema-toda, Rotifera, Gastrotricha, Bryozoa, Mollusca, Echino-dermata, Annelida, Crustacea, Insecta and fungi were tested using aqueous suspensions of DDT applied in the bathing medium. Maximum susceptibility is found only in those groups which possess a chitinous cuticle, namely certain Coelenterata and the Arthropoda. The Bryozoa, with a similar but somewhat different cuticle, show intermediate susceptibility. Numerous phyla appear to be immune to external application of this toxin. An hypothesis was developed that chitinous cuticles selectively concentrate DDT from the bathing medium and lead to building up a relatively high conc. inside animals with this type of cuticle. This is further supported by a direct demonstration of the adsorption of DDT by chitinous cuticles and purified chitin, and by the occurrence of a negative temp. coeff. of DDT action at lower concs. Evidence is presented and discussed showing that these data concern only the entry of DDT into the animals and the building up of a lethal conc. within the animals; the actual toxic action of DDT on protoplasm is clearly another problem.