300 N. I. GRASHCHENKOV 



after radiation. Not all sections, however, are equally damaged (the marked 

 changes in the higher vegetative centers of the hypothalamus are note- 

 worthy) , nor are all the structures which form part of a given section equally 

 involved. Portugalov (1957) attempted to account for this on the grounds 

 that those microstructures which were in an active condition at the moment 

 of irradiation suffered most damage. 



It has also been demonstrated that there are two stages in the development 

 of morphologic changes in the brain which occur during the first days of the 

 disease and at its climax. In the first period, the changes in the nervous 

 system are regarded as the result of direct action by radiation on the nerve 

 elements. As to the second period (late necroses), some authors are inclined 

 to regard these changes as the result of a hemodynamic disorder, while others 

 consider them the result of a metabolic disorder and a manifestation of 

 toxic elements. The latter hypothesis seems to be better founded, since 

 sometimes there are no hemodynamic disorders, while it has been demon- 

 strated that definite substances of lipoid origin, hemolysins, are present. They 

 are formed when tissues are subject to direct irradiation (Tarusov, 1957; 

 Benevolensky, 1 95 7 ) . 



The radiosensitivity of nerve elements in young animals and embryos is 

 not disputed, and there is a considerable amount of literature to attest to it 

 (Zavarzin et al., 1936; Emdin and Shefer, 1935; Olenev and Pushnitsyna, 

 1952; Manina, 1959; Aleksandrovskaya, 1959). 



It is possible to determine the morphologic changes which occur in the 

 peripheral nervous system during irradiation of the organism. Oleinikova 

 (1936) observed degenerative changes in the nerve trunks only 30-60 min- 

 utes after irradiation. These changes reached a peak at the height of the 

 radiation disease. The nerve fibers broke up into segments; some were in a 

 state of granular decay, and partial demyelination phenomena were observed. 

 Changes were also noted in the cells of the Auerbach and Meissner plexuses. 

 In 1953, Lebedev showed that Auerbach's plexus was involved and that 

 Meissner's plexus had great stability. He noted, however, reactive and de- 

 structive changes in the sensory cerebrospinal and craniocerebral (trigeminal 

 and vagal) ganglia and in the sympathetic ganglia. 



Anisimova and Aleksandrova (1959) consider the afferent nerve channels 

 and their terminal receptor apparatus to be the most sensitive. Kraevsky 

 (1957) also notes that of all the parts of the peripheral nervous system it 

 is the peripheral parts of the sympathetic nervous system which are most 

 susceptible. Gracheva (1959) is the only author who has not detected con- 

 vincing morphologic changes in the nerve cells of the vegetative and sensory 

 ganglia. Damage to the peripheral nervous system, accordingly, consists 

 primarily in disorders of the constituent parts of the vegetative nervous 

 system. 



