462 GENERAL DISCUSSION 



decent and not totally necrotic, a marked increase in the evoked response just 

 anterior to the lesion from a band of several millimeters, as compared to the 

 normal side. Relatively thin lesions may have an increase of activity to the evoked 

 response technique even within the lesion. The heavier lesions may have (in the 

 earlier phases at least, before the nerve fibers are all back) a considerable decrease 

 within the lamina, but still will have a hyperactive zone in front. 



Lal Harbans (University of Chicago): It was pointed out in various papers 

 that radiation produces changes in the blood-brain barrier, and an increase in the 

 mobility of the blood vessels can be produced. In studies on various effects on 

 nerve and other tissues, it is possible that the effects were altered by an animal 

 kept for observation which is eating toxic substances which reach the nerve cells 

 and other tissue in greater concentration because of the barrier changes. Thus, 

 we are exposing the tissue to greater toxicity. In one of the papers on the blood- 

 brain barrier, a dye was used, and it was only possible to show changes with a dose 

 of about 5,000 r in monkeys and only in those areas which already have soft 

 barriers, such as those close to the cerebrospinal fluid and around the hypophysis. 

 The sodium level was changed in doses as small as 15 r. When dyes are used as 

 indicators, they have a strong tendency to bind themselves with plasma proteins 

 which are large molecules. You should be able to make really big holes in the 

 blood vessels so that these proteins, along with the dyes, should be able to per- 

 meate and show on the slides. Using sodium and other smaller organic molecules, 

 as we use in labeled form, we keep in mind their various degrees of binding with 

 plasma proteins. If one can decrease the binding and let the molecule be small 

 enough to go back and forth by itself, one may be able to pick up smaller changes, 

 which will not be possible if you have not pushed up the plasma proteins through 

 the blood vessel to indicate the changes. 



Leo E. Lipetz (Ohio State University): In regard to the question Dr. Kruger 

 raised earlier about how a vascular change could cause such sharp destruction 

 of the neurons, I would like to do a little speculating in terms of the retina. 

 In the retina, every neuron is surrounded by glial cells, and apparently it 

 has to get all its nutrition via the glial cells. The glial cells are not large, so by 

 injuring them you could produce a localized destruction or interference in the 

 nutrition of a localized band of neurons. This might be a means of producing local 

 neuronal damage. I wonder whether this could apply to the rest of the central 

 nervous system. 



Orville Bailey (University of Illinois): I would not think that these lesions 

 could be well explained on neuroglial injury alone. Dr. Rose gave me the oppor- 

 tunity of spending some time on his preparations. The destruction of neuron 

 elements in the band is complete, and it is incredibly sharp. Along the edge of the 

 band one occasionally can see a cell body minus its apical dendrite in the more 

 acute phase. In the reparative phase, similar cells are so placed that it seems 

 necessary to conclude that the dendrite has grown back. From the standpoint of 

 general neuropathology, the evidence of true regeneration of neurons is of two 

 types. There are too many nerve fibers in the area. As a general pathologic phe- 

 nomenon, repair tissue ought not to be exactly in the expected normal proportions. 

 It is quite often too much, a criterion fulfilled admirably here. Second, the orienta- 



