166 ORVILLE T. BAILEY 



208 r to 55,000 r, measured at the center of the cord. Survival times were 

 from 1 day to 36 months. 



The third series was concerned with the eflfects of roentgen radiation in 

 17 Macaca mulatta monkeys receiving 138 r per minute to the lower dorsal 

 region while under Pentothal or Nembutal anesthesia. Dosages varied from 

 4,000 to 54,500 r, and survival times from 5 days to 18 weeks. In one addi- 

 tional monkey, both Ta'^- and roentgen radiation were used. 



Time Factor in Tissue Responses 



The influence of time on the appearance, extent, and character of the 

 histologic lesions produced by roentgen radiation has been recognized for 

 over 50 years, the early studies being based on the skin of those engaged in 

 therapeutic use of this agent (Wolbach, 1909). Using dogs Nemenow 

 (1934a, b) studied physiologically in regard to conditioned reflexes, Lyman 

 et al. (1933) have demonstrated the increase in the intensity of histologic 

 lesions in the brain caused by roentgen radiation as the interval between the 

 end of radiation and sacrifice is increased. This paper also contains a thor- 

 ough review of the literature to 1933, as does tliat of Warren ( 1943). 



The eflfects of radiation in experimental animals has been turther consid- 

 ered by Scholz ( 1934, 1935). In fully grown animals, the immediate reaction 

 is not detectable microscopically, but if the animals survive from 4/2 weeks 

 to 1 year alter ladiation, histologic lesions are stiiking. In a study of delayed 

 lesions of brain and spinal cord in the dog, Davidoff ct al. (1938) pointed 

 out that the rapidity with which clinical exidence of spinal cord injury ap- 

 peared is proportional to the dosage and that disabilities in the monkeys tend 

 to be progressive. The importance of time as a crucial factor in the appearance 

 and interpretation of cerebral changes induced by roentgen radiation was 

 carefully studied by Russell it al. ( 1949). They ha\e shown that with dosages 

 of 2,850 r in rabbits no histologic changes were found before 82 days, but 

 were present after that in all but one animal (of 7). Behavioral changes and 

 abnormal neurologic signs did not appear until about 100 days after radia- 

 tion, yet three rabbits killed before these changes appeared (82, 85, and 90 

 days) showed well defined lesions. The brains of rabbits killed earlier than 

 82 days after radiation showed no changes detectable by light microscopy. 

 They also found that reducing the dose of radiation lengthened the latent 

 interval. 



These and other substantial contributions have clearly established that the 

 intensity of the histologic changes induced by roentgen radiation increase 

 with time interval between radiation and sacrifice or death of the experi- 

 mental animal. There are indications that the character of the lesions also 

 alters with time. 



