26 H. MAISIN 



DISCUSSION 



ALEXANDER: Did you do a sham irradiation, Dr. Maisin? Is it possible that you could get 



such a result if you just put the animals under the X-ray machine but did not switch it on? 



Could it be a stress phenomenon? 



MAISIN: We didn't always do a sham irradiation, but we sometimes did, and we never got 



any increase in the total number of cells, or in erythropoiesis. 



LAMERTON: Did you say that you got about the same extent of stimulation if 3^011 used 



50 r? If so, then 3'ou have something which is apparently invariant over a wide range of 



dose. 



MAISIN: I would not say that with different doses we got a stimulation which was greater 



after 1 r than after 50 r. 100 r is too much, but 50 r can cause an increase. On the other 



hand the stimulation lasts longer after 1 r. 



LAMERTON: But we also know that after 50 r there is a decrease in the radioactive-iron 



uptake very soon after irradiation. 



MAISIN: Yes, very soon after. We didn't repeat your experiment this time, but formerly 



we did and we got the same results. I know, too, that you did an experiment showing that 



even with 25 r or 5 r there is a decrease. I have the feeling that later the animals react in 



another way. 



BRiNKMAN: In some irradiation rooms you can smell ozone and we have often been 



troubled by getting results which were due to the presence of ozone and not to the 



irradiation itself. Could there be something like this in j^our experiments? 



MAISIN: I don't think so because with modern machines the ozonization of the room is 



not large. Moreover, the sham-irradiated animals were kept in the same room. 



BACQ: There is one thing which troubles me. If you had more red-ceU precursors in the 



marrow; if you had more reticulocytes in the circulatmg blood for a long time, then, over 



a long period, you must get polycythaemia unless the mean life-span of the cells is 



decreased after this type of irradiation. Have you measured the mean life-span of these 



red cells? 



MAISIN: Not yet. 



rotblat: I notice that there was a gradual decrease in mortality after the additional 500 r. 



MAISIN: If you look at the Figure you can see that certain rats receivuig 1 r or 0-1 r have 



a decreased mortality, but you see the same phenomenon in the controls. In fact it 



happens in all the groups ^\■hich we fed on purina chow. Thus you cannot speak of a 



gradual decrease in mortality. The rats which did not receive purina chow were more 



sensitive. We thuik that it is a question of nutrition. 



mole: I think these results are quite startling. One of my colleagues ran into trouble over 



the estimation of peroxide in irradiated animals because he found that just picking the 



animals up made a difference. It is very important if the effect of a very small dose of 



irradiation like this can be revealed, so I do hope you wUl do the experiment in what is 



called a "double blind trial", where the people who examine the animals don't know which 



have been irradiated. I think that, to be really convincing, this is what you will have to do. 



MAISIN: We have got systematic results. Most of the experiments were repeated, not all of 



them but some of them, but we agree that the double blind method can be applied. 



UPTON: How many replicate experiments do the data represent? Was it the same number 



each time? 



MAISIN: Each time we counted 6 animals for each dose, always with controls and always 



for the irradiated animals. We repeated this at least two or three times for all the results 



which were statistically different. At first I was sceptical myself. 



