General Discussion 303 



Dr. Hollaender mentioned the very rapid irradiation effects pro- 

 duced by change in salt concentration of the surroundings. Perhaps 

 Dr. Hollaender is willing to give us some more details of how this 

 exciting experiment was carried out, and also to tell us if it is possible 

 and advisable to carry out experiments similar to those which 

 Anderson did in his laboratory with thymus tissue, with other types 

 of tissue, and if he expects to find marked differences. 



Hollaender: Dr. Gaulden, in previous studies, had demonstrated 

 that if she subjects the neuroblast to hypertonic culture medium, the 

 chromatin of cells in middle prophase takes the appearance of late 

 prophase and the chromatin of late prophase assumes the appear- 

 ance of very late prophase. These changes occurred in 15 to 30 

 seconds after the cells were placed in a medium hypertonic to them. 

 This apparent advancement of stages of mitosis was shown to be 

 accompanied by an accelerated mitotic rate. 



She then decided to set up some experiments to determine whether 

 the "reversing" action of X-rays on middle and late prophase prim- 

 arily responsible for mitotic inhibition at low doses could be prevented 

 by subjecting the neuroblast to a hypertonic medium which advances 

 these stages. The results indicated that this can be easily accomp- 

 lished. Whereas the mitotic rate of irradiated (3 r of X-rays) 

 neuroblast in isotonic medium was depressed down to about 25 per 

 cent of normal level, the mitotic rate of irradiated neuroblast in 

 hypertonic medium was depressed only down to about 75 per cent 

 of normal level. Thus, subjection to hypertonic medium immediately 

 following irradiation resulted in less radiation damage than if iso- 

 tonic solution is used. It was also found that if the cells were put in 

 a hypertonic medium more than a minute after irradiation had been 

 stopped, they responded to the irradiation in the same manner as 

 irradiated cells in isotonic solution. The most successful tests were 

 accomplished by irradiating these cells in a very slightly hypertonic 

 salt solution and then, immediately after irradiation, putting them 

 in a more definitely hypertonic medium. Under these conditions, one 

 could ehminate practically all the effect of mitotic inhibition pro- 

 duced by X-rays. It is not possible at this time to tell whether the 

 influence of hypertonic medium is due to removal of water from the 

 cell or to increased concentrations of certain inorganic salts or to both. 

 (See the forthcoming paper, " Prevention of X-ray induced mitotic in- 

 hibition in grasshopper neuroblasts by post-irradiation subjection to 

 hypertonic culture medium", which Dr. Gaulden is now preparing.) 

 I believe such an approach with hypertonic salt solution could be 

 used in connection with other radiation work. The important thing, 

 probably, is to get it into the cell very quickly after irradiation has 

 stopped so that the damage is still "reversible". 



