494 PAUL S. HENSHAW 



A point of departure has been the investigation of effects that follow pre- 

 natal exposure, when the nervous system is progenitive. As seen from re- 

 ports by Hicks and co-workers (see Hicks, 1954, 1958; Hicks et al., 1957), 

 Russell (1954), Rugh and Grupp (see Rugh, 1959a,b; Rugh and Grupp, 

 1959a-c, 1960), and others at this meeting, extensive changes are produced 

 in the developing morphology of the peripheral and central nervous system 

 by radiation dosages in this range. Along with these distinctive findings has 

 been the work since 1952 (Levinson, 1952; Tait et al, 1952; Furchtgott 

 and Echols, 1958a, b; Furchtgott et al, 1958; and Sikov et al, 1960) cor- 

 relating in utero exjx)sures with performance abilities in postnatal life. 

 Results indicate that a few hundred r have adverse effects on learning 

 ability, emotionality and locomotor coordination. In this session work will 

 be reported which deals with modifications in behavior stemming from 

 irradiation of adult organisms. 



There are reports by Eldredge and Trowbridge (1959), Arnold et al 

 (1954), Ross et al (1954), Lee et al (1955), and Gangloff and Haley 

 (1960) showing electroencephalographic changes within minutes, hours and 

 days following whole body exposures below the LD-50 range. Work by 

 Garcia and co-workers (see Garcia, 1960; Garcia et al, 1955, 1956a-c) 

 that conditioned aversion to saccharine can be established in rats by expo- 

 sure to a few hundred r of x-rays, and work by Lynn Brown and associates 

 (Brown et al, 1959, 1960; White and Brown, 1959; Overall and Brown, 

 1959) indicates that the effectiveness of peripheral cues in discrimination 

 learning tasks in monkeys is reduced by irradiation. 



Dosages from a few r to a few tens of r are in the range of threshold 

 levels of exposure, as far as presently measurable nervous system effects are 

 concerned. Rugh and Grupp (1960) reported certain brain anomalies in 

 mice exposed in utero to 5-25 r from 0.5 to 1.5 days after fertilization, 

 and foreign investigators, mostly Soviet (Lebedinsky, 1956; Lebedinsky et al, 

 1959; Krabbenhoft, 1955; Grigoryev, 1954, 1956; Kudritsky, 1955, 1957; 

 Nemenov, 1944; Livanov and Diryukov, 1959) have reported changes in 

 cognitive functions correlated with radiation exposures at 1 r and at 0.05 r 

 (Kudritsky). 



Except for the findings of Soviet investigators, exposures of 0.2 r, as far 

 as we know, are below the range found to have effects on nervous system 

 functions. It would be an important result of this conference to ascertain 

 if the specialized techniques and the work on the more complex nervous 

 functions in higher forms have enabled the lower dose findings. 



On our scale of exposures 0.02 r is in the range of permissible dose levels, 

 which is only a factor of 100 above the range of natural or background 

 radiations in which all life on the earth arose and evolved. 



