“…The particular feature which makes the problem of exposure to chlorinated hydrocarbons interesting to the psychologist is that the major effect of this group of pesticides seems to take place at the level of the central nervous system (CNS) in both birds and mammals. Some of the symptomology which appears particularly indicative of CNS involvement are; long term alterations in cortical electroencephalograms (EEG) (Hoogendam, Versteeg, and DeVlieger, 19^3;Princi, 1957;Prior, 1963;Revzin, 1966;Speck and Maaske, 1958); a reduction in appetite (Conley,i960); hyper-irritability (Conley, 196O;Spiotta and "Winfield, 1952); apprehension, dizziness, and con fusion (Hayes, 1955); increased susceptibility to auditory seizure (Speck and Maaske, 1958); tremors and convulsions (Dale, Gaines, Hayes, and Pearce, 19^3;Hayes, 1955;Hoogendam et al, 1963;Princi, 1957;Eevzin, 1966;Speck and Maaske, 1958;Spiotta and Winfield, 1952); loss of consciousness and retrograde amnesia (Conley, 196O;Spiotta and Winfield, 1952); changes in classically conditioned responses including increased response latency, decreased differentiation, and accelerated extinction of the conditioned response (CE) (Medved, Spynu, and Kagàn, 1964); and defects in learning of a Visual discrimination (James and Davis, I965), Further, it has been suggested that the occurrence of clinical signs in dicative of DDT poisoning in rats is not highly correlated with the concentration of DDT in the body fat, but does seem to be directly correlated with the concentration of DDT in the brain (Dale et al,I963). In view of the above, it was de cided to investigate the effects of the chlorinated hydrocar bon Dieldrin on the retention of a conditioned avoidance re sponse (CAE) and the subsequent relearning of the response in sheep.…”