168 ORVILLE T. BAILEY 



monkeys posterior to the motor strip, an area of necrosis is produced (Fig. 

 1 ) . Observation of such animals gives some indication of progression in the 

 lesions. Hemiparesis which developed in 6 of 21 monkeys did not appear 

 until 3 weeks to 20 months after radiation, the animals previously being 

 neurologically normal (Bailey ct al., 1958). 



Electroencephalograms a few days after radiation showed decreased voltage 

 and some slow waves on the radiated side, while on the opposite side there 

 was a predominant frecjuency faster than the one before radiation. This 

 condition remained and was most prominent 6 to 8 weeks after radiation. 

 The EEG pattern then reverted almost to normal. At longer intervals, slow 

 waves again appeared on the radiated side, and many records demonstrated 

 voltage asymmetry with decreased voltage on that side. Two years after 

 radiation, 2 animals developed runs of spikes and fast activity localized to 

 the region of radiation. One of these developed generalized clonic and tonic 

 seizures 30 months after completion of radiation (Bailey et al., 1958). There 

 was thus some EEG evidence of progression. These results are in fair agree- 

 ment with those of Ross ct al. ( 1954), though the conditions of radiation are 

 so different that direct comparison is difficult. 



The histologic changes in these animals became more striking as the 

 interval between radiation and sacrifice was lengthened. There was more 

 evidence of irregular streaks of injury extending out from the necrotic region 

 in which the Ta^^- wire had originally been placed (Fig. 1 ) . 



Studies of radiation efTects in the spinal cord of experimental animals 

 have not been numerous (Cairns and Fulton, 1930; DavidofF ct al., 1938; 

 McLaurin ct al, 1955; Pendergrass ct al, 1922; Peyton, 1934; Sicard and 

 Bauer, 1907). However, the spinal cord has pro\ed a \ery favorable area 

 for the study of radiation efTects. 



In personal studies, clinical observations ot monkeys gave .some evidence 

 of the time factor as an important consideration. With Ta^""- radiation of 18 

 monkeys, 2 developed transitory paraplegia with complete recovery, 6 perma- 

 nent paraplegia, and 1 early paraplegia, then recovery followed by permanent 

 paraplegia after 6 weeks. When roentgen radiation was used, 6 of 1 7 animals 

 developed paraplegia. In some monkeys dying with complete paraplegia 

 within a few days after either form of radiation, there were no histologic 

 changes or only scattered vacuolation of myelin in white fiber tracts. In view 

 of the striking alterations described in monkeys surviving for long periods 

 after radiation, there is good evidence that the histologic changes become 

 progressively more obvious, at least to light microscopy, as the inter\al be- 

 tween completion of radiation and sacrifice is lengthened. 



The time factor thus becomes a dominant consideration in defining dosage 

 effective in causing histologic change and especially in determining the ulti- 

 mate effect on a living organism subjected to ionizing radiation. 



