464 GENERAL DISCUSSION 



in various parts of the brain with regard to accessibility. The Swedish investigators, 

 particularly Dr. Anderson, have for many years been studying the hypothalamus 

 with electrodes which reach in the same direction. And the Russian investigators, 

 in total brain irradiation studies, have for some time been realizing the inacces- 

 sibility of the hypothalamus which follows irradiation. 



Jerzy Rose: It seems to me that as far as protons, alpha particles, and neutrons 

 are concerned there seems to be agreement among all hands as to the minimal 

 dose, properly defined, with a proper relationship of latent periods and without 

 fluorescein. Minimum lethal dose seems to be about 50,000 rad. The total destruc- 

 tive dose is around 75,000, an unsatisfactory figure in detail, but of the proper order. 

 Perhaps our Swedish guests would comment on whether they agree with this con- 

 clusion and Professor Grashchenkov would comment on what the investigators in 

 the Soviet Union found. 



N. I. Grashchenkov (U. S. S. R.): We have some figures which indicate that 

 part of the brain connection with the hypothalamic region was damaged by a 

 small dose of irradiation. At the same time we have some investigations — mor- 

 phologic as well as postphysiologic — which indicates the role that the brain played. 

 In our country, Professor Stamm and his large school with many collaborators 

 have dealt with this problem. In this last period, his studies indicated that this 

 formulation played an important part in the mechanism of hyalinization. 



Patrick Sourander (University of Gothenburg, Goteborg, Sweden): When the 

 spinal cord was irradiated with the 1.5 mm beam, there was little vascular damage 

 seen. Of course, there was irradiation of red blood corpuscles in the capillaries, 

 but no damage of the bigger cortexes. If a broader beam was of 10 mm, after a 

 few days considerable damage of blood vessels was seen with massive hemorrhages. 

 One explanation would be that with the 1.5 mm beam only a relatively small 

 volume of capillaries are destroyed, and there might be compensatory mechanisms 

 in the circulation. When a bigger volume is destroyed, this compensatory mech- 

 anism fails. I do not know if this is the right explanation, and I would like to 

 ask the specialists what they think about such an explanation. The other phenom- 

 enon observed, both in the thin beam and the broad beam, was that some fibers 

 were always affected. One possible explanation would be that the situation as to 

 the blood supply might be better for the periphery or the spinal cord than the 

 central parts. Concerning changes in the nerve cells, I would like to mention a 

 general point of view. I doubt the reliability of the methods used for studying the 

 nuclear proteins and nucleic acids in nerve cells after irradiation, whether used in 

 fluorescein stains or aniline stains at a certain pH. Certainly, there are more 

 reliable methods, such as the ultraviolet absorptions at 2,600 Angstrom, both 

 before and after digesting with ribonuclease or desoxyribonuclease. There are 

 recently published methods from Goteborg concerning nucleic acids seen in the 

 glial cells. They were studied by means of electrophoresis on a micro scale with 

 single cells. It is by no means clear that there should be initially a depletion or 

 reduction of nucleic acids in degenerating neurons. As was recently shown by 

 Ingstrom, after the axon is cut, there is an increase of nucleic acids and later a 

 decrease of nucleic acids. I think these newer methods should be used when 

 studying the effects of irradiation on nerve cells. 



Herbert Locksley (Iowa City, Iowa): I have been appreciative of the progress 



