X-IRRADIATION AND DELAYED MYELOMALACIA 



243 



Fig. 6. Spinal cord of rat spine irradiated. Killed alter 7 months with no neuro- 

 logic signs, .\bout C 8-T 1. Early stage of small malacic focus about C 8-T 1 on 

 the left. Fatty marrow. Hematoxylin-eosin. X 16. 



Discussion 



A severe myelopathy, localized to the area of irradiation, can be produced 

 with some consistency in rats, at a dose le\el within the therapeutic range 

 used in man. and in which neuroparalytic accidents have occurred after 

 deliberate or accidental exposure of the spine. In rats, there is also the par- 

 allel of an unpredictable latent period, sometimes many months before the 

 onset of progressive neurologic signs. The e.xtent and localization of the 

 myelomalacia in the rats is thus responsible for the syndrome starting as 

 motor weakness of the hind legs and progressing to ataxia and paralysis. 

 The clinical pictiue is thus what is commonly called "posterior paralysis" 

 in animals, which bv itself means little. Neurologic examination of small 

 laboratory animals is restricted to obser\ations on a few cardinal objective 

 signs, and may be no indication of what is ultimately found after neuro- 

 pathologic studies. For example, in the course of this experimental work and 

 by virtue of extensive histologic work, we found pituitary chromophobe 

 adenoma in 3 rats, one spinal ependymoma, one sarcoma, and more recently 



