298 N. I. GRASHCHENKOV 



and chiefly through the nervous system, in particular the vegetative nervous 

 system, and the blood and its principal morphologic elements. 



Owing to the special conditions under which physiology has been devel- 

 oping in the U.S.S.R. and the exceptional attention paid to the leading role 

 of the central nervous system in the physiologic functions and in the de- 

 velopment of disease pathogenesis in man, a great deal of research in the 

 U.S.S.R. has been devoted to the morphologic and structural changes which 

 represent the nervous system's response to ionizing radiation. 



This review does not cover all the published literature but merely gives 

 an idea of some of the main publications on this subject. 



Morphologic Changes in the Nervous System 

 Under the Effect of Ionizing Radiation 



Our ideas about the resistance of the nervous system to radiation are based 

 mainly on the negative morphologic picture observed after irradiation. A 

 definite discrepancy between the morphologic and the functional shifts has 

 come to light, providing evidence as to how the nervous system reacts to 

 radiation. A number of factors lie at the root of these apparent contradic- 

 tions. For one thing the methods in use today for studying the morphology 

 of the nervous system are fairly crude and not always adequate for the pur- 

 pose of estimating slight shifts occurring in the tissues. Progress in this field, 

 therefore, depends on the use of more precise methods of investigation, 

 particularly histochemical methods. Further, in cases of extremely serious 

 lesions, the death of the animal occurs quickly, and the morphologic changes 

 do not have a chance to develop over a long period. Finally, in recent years 

 fairly definite morphologic changes which account for shifts of a neuro- 

 dynamic character have been demonstrated. 



In the opinion of many Soviet investigators, the term radiosensitivity is 

 not a happy expression. It would be more correct to speak of radiore activity, 

 which would be described in terms of a change in some functional reaction 

 on the part of the nervous system, and of susceptibility to radiation damage, 

 which would be described in terms of morphologic symptoms. 



When animals are subjected to large doses of radiation which produce 

 the pattern of radiation disease, the following phenomena are seen in the 

 central nervous system: swelling of the cells, argentophilia, displacement of 

 the chromophil substance at the height of the disease, and hemorrhagic 

 diathesis, often in the thickness of the meninges. Degenerative necrotic 

 changes, such as vacuolation of the ganglionic cells, increased precipitation 

 of silver, distension of the cells, and changes in the processes (Kraevsky, 

 1957), are observed primarily in the zones of the higher vegetative subcorti- 

 cal centers. Some authors have not detected any reaction on the part of the 

 microglia (Kraevsky, 1957), while others found dystrophic changes (Alek- 

 sandrovskaya, 1959). 



