CHAIRMAN'S SUMMATION 



Webb Haymaker: We have heard a good deal about the cerebellum. One of 

 the interesting observations pointed out by Dr. Vogel was with reference to the 

 cerebellar cells in his tissue culture. Granular cells underwent significant changes 

 in response to radiation, but the inner cells of the cultures apparently were un- 

 affected. This must mean that granule cells are more radiovulnerable than other 

 cerebellar cells, as we already know. The point of Dr. Vogel's observations is that 

 nuclear pyknosis and early enlargement of the cytoplasm, pointed out also by 

 Dr. Schummelfeder, took place without the benefit of circulatory disturbance. 

 In his presentation on the cerebellum of the mouse. Dr. Schummelfeder considered 

 the effect of circulatory disturbances on granule cell changes, and at all doses 

 between 60,000 r to 2,000 r granule cells were always altered first. Then after a 

 latent period, the vessels underwent morphologic changes. To him, and apparently 

 to the two Drs. Bailey, quite definitely the ultimate pathologic picture when the 

 latent period has passed is apparently the outcome of the combination of direct 

 effects and the effects of vascular origin. The paper by Drs. Hager, Hirschberger, 

 and Breit aroused particular interest because it dealt with observations under 

 electron microscopy. They too, found that the granule cells of the cerebellum were 

 particularly radiovulnerable, but they dealt also with the broader aspects of the 

 problem of pathogenesis. This area of pathogenesis is a kind of twilight zone 

 without a horizon, where observation still blends too much with opinion. Dr. 

 Hager and associates, using high doses of 40 kv x-rays, provided the following 

 timetable according to electron microscopy as seen in the brain of the Syrian 

 hamster: First, there was increased vascular permeability as manifested by swelling 

 of cells which they called astrocytes, by plasma exudation, and by erythrodiaped- 

 esis. Their observations showed that at these dose levels the first stage seen in the 

 electron microscope was vascular disturbance. Dr. Hager and his associates feel 

 that the loosening of tissue and the fine sponginess seen after radiation is merely 

 a reflection of the accumulation of fluid in the astrocyte, or what has been called 

 the astrocyte, and that gross sponginess is attributed to astrocytic and other mem- 

 branes either in vivo or during tissue processing or both. These cells called 

 astrocytes become watery. At the same time that the astrocytic change occurs, they 

 said, the capillary endothelium shows suggestive swelling, and about this time a 

 structureless material considered to be plasma exudate is seen in the perivascular 

 space. Only later are nerve cell changes seen, and still later changes are seen in 

 the large blood vessels. Dr. O. T. Bailey emphasized the relative radiovulner- 

 ability of the astrocyte. Professor Scholz and his associates demonstrated with 

 high dose x-rays that astrocytic processes break down at an early stage, at a time 

 when only minor changes are visible in nerve cells. I think we are now at the stage 

 of knowledge at which we can generalize and say that when radiation upsets the 

 transport in the metabolic mechanism of the astrocyte, nerve cells are bound to 

 suffer as a consequence. Dr. Innes and Dr. Carsten showed us the later stages of 



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