In order to find a standard cell system for a study of the effects of DDT, Lewis and Richards1 of the Wistar Institute, University of Pennsylvania, made numerous tests of the possible toxic action of DDT on in vitro tissue cultures. In their preliminary tests a small drop of saturated alcoholic or acetone solution of DDT was allowed to dry on a cover glass. Hanging drop cultures of heart, brain, intestine and spleen from seven to eight day chick embryos or one day rats were set up so as to include the dry DDT. During the seven day observation period the cell growth, migration and mitosis of fibroblasts, entoderm and macrophages were not appreciably different from those in control cultures without DDT. As they moved about in the cultures living fibroblasts often touched or even migrated over DDT crystals without appreciable injury.
This apparent nontoxicity was confirmed with several