306 N. I. GRASHCHENKOV 



Mushegyan and Abovyan showed in 1950 that radiation of the optic 

 thalamus in frogs leads to characteristic inhibition of the spinal reflexes. 



In 1957 Yanson established that, after rabbits had been exposed to 1,000 r 

 of x-radiation, a phase change began to occur in the condition of the labyrin- 

 thine and cervical tonic reflexes. This change intensified during the first 2 

 days but was unstable from the 3rd day on. During the first 3 days, a devel- 

 opment of the plastic tonus in the extremities was observed and maintained 

 for 7-10 days. 



Biryukov (1957) assumes that ionizing radiation acts on the reticular 

 formations of the brain stem, basing this view on the similarity between 

 certain physiologic effects produced by the action of aminazine and those 

 produced by ionizing radiation in birds. 



Livanov and co-workers (1959) regarded the diffuse character of the 

 EEG variations observed when the organism is exposed to ionizing radiation, 

 as grounds for assuming that the reticular system of the brain stem must be 

 included among the structures which condition the responses of the nervous 

 system to radiation. The EEG was similar to that of a desynchronization 

 response. Livshits, exposing the cerebellar region to directed x-rays, observed 

 sympathetic phenomena similar to the responses elicited by direct stimulation 

 of that organ. 



The influence of ionizing radiation on the function of spinal mechanisms 

 is widely known from the literature, but new discoveries have been made in 

 the last few years. Fedorova (1958) and Kudritsky (1957) have shown that 

 even small doses of radiation (10 r) lead to a change in the time taken by 

 the flexor reflexes of the posterior extremities of rabbits. When the rabbits 

 were exposed to daily radiation doses approaching the permissible limits 

 (0.1-0.5 r) for 14 days, the total activity (1.4-7.0 r) produced a lowering of 

 the flexor excitability. After 37 exposures, the flexor response threshold 

 ceased to alter, but its response was distorted when urethan was injected. 



Kudritsky (1957) showed that a change in the time taken by the flexor 

 reflexes of the knee occurs mainly as a result of variations in the activity of 

 the central apparatus and, to a lesser extent, of variations in the terminal 

 apparatus of the reflex arc. 



Godin and Gorshkov (1957) note that in rats fed with small doses of 

 radioactive sodium (0.5 [xc) the time of the defense reflex is slightly 

 reduced, and the spread in the variations of this reflex is increased. When 

 250 IXC were administered, the reflex time was first reduced and then began 

 to lengthen. When the dose exceeded 300 fxc, the unconditioned reflex 

 activity was immediately inhibited — an indication that the time taken to 

 effect the reflex had increased. 



In peripheral nerve, the functional variations following irradiation are 

 seen to follow a phaseal course. In 1934, Makarov noted parabiotic phe- 



