GENERAL DISCUSSION 



Jerzy Rose (Johns Hopkins University, School of Medicine): Many papers 

 were concerned with the dose of heavy ionizmg radiation, the consideration of 

 species differences, individual differences, differences in different portions of the 

 brain, differences in time of appHcation and examination of the tissue, and more 

 sensitive methods to detect radiation damage before pathologic changes are 

 apparent. Perhaps we need to define a little better what we mean by "minimal 

 radiation dose," "lethal dose," and other terms. 



F. A. Mettler (New York, New York): Dr. Malis showed a section in which 

 there was irradiation of the Bragg peak and elimination of fibers. Later, on a 

 subsequent slide, we saw fibers present in excess. There are three possibilities that 

 might explain this. Some of them are rather significant in terms of a possible 

 explanation with regard to physiologic experiments in general. The first possibility 

 is perhaps trivial, but Dr. Zeman showed a picture in which there was passage of 

 the beam and no fibers degenerated. So, the first possibility would be that these 

 fibers were not degenerated at all. If one considers the paper by Drs. Janssen, 

 Tobias, and Haymaker and several other papers in which there was considerable 

 damage in the capillaries in the level of the Bragg peak, the second possibility 

 would be that the fibers seen in the second slide of Dr. Malis were really not nerve 

 fibers, but were fibers of connective tissue, perhaps fibers of glia. The third pos- 

 sibility would be that the fibers seen in the second slide were nerve fibers. If so, 

 where did they come from? They could come from two places. There was a paper 

 presented earlier which was of remarkable importance to the question of regenera- 

 tion of the nervous system. There was transection of the cord with no interference 

 with the external meninges, an ideal situation for determination of regeneration in 

 the cord. So, these fibers might be regenerative. If this were an area of peripheral 

 degeneration or denervation, it would be possible to conceive of another possibility, 

 for we know that in peripheral areas of denervation other fibers have a tendency 

 to invade. So, if regeneration occurred, it could occur as regeneration from a nerve 

 fiber, or it could occur from the invasion of other fibers in the vicinity. Such a 

 situation has never been implied in the central nervous system. It it does exist, 

 it is of considerable importance in the interpretation of chronic neurologic prep- 

 arations. I would like to ask the chairman his opinion. 



Jerzy Rose: We did not present the material completely, because giving evi- 

 dence required many slides and there simply was not enough time, so we presented 

 only a few slides which illustrated that damage was done. There is no question 

 that these are nerve fibers. I think we have rather large material on this aspect. 

 If we skip the unessential modification, we have done a sufficient number of a variety 

 of these things, and as long as we are going to believe that a silver stain or any 

 other accepted classic neurologic stain means a nerve fiber, it is a nerve fiber. Not 

 only that, but it is easy to demonstrate in the older lesion that apical dendrites 



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