136 S. R. Pelc 



doses will be one twentieth of the calculated values. Also 

 the dose will in general be lower for gradual uptake and 

 subsequent excretion. These calculated values can therefore 

 be taken as maximum values, unless the factors k and f be 

 very unfavourable. 



REFERENCES 



Berriman, R. W., Herz, R. H., and Stevens, G. W. W. (1950). Brit. 



J. Radiol., 23, 474. 

 Howard, A., and Pelc, S. R. (1950). Brit. J. Radiol., 23, 634. 

 Lamerton, L. F. (1950). Private communication of preliminary 



results. 

 Marinelli, L. D. (1949). J. din. Invest., 28, 1271. 

 Morgan, K. F. (1947). J. phys. colloid Chem., 51, 984. 

 Pelc, S. R., and Spear, F. G. (1950a). Unpublished. 

 Pelc, S. R., and Spear, F. G. (19506). Brit. J. Radiol., 23, 287. 



DISCUSSION 



Lamerton: I would like to ask Dr. Pelc how he calculated the value 

 2-5 roentgens for the dose given to the thyroid — whether he did in 

 fact assume a uniform distribution of iodine? 



Pelc: That figure was based on actual experiments. We gave the 

 rats varying amounts of radioactive iodine and found the smallest 

 amount which will still give an autoradiograph. One lobe was taken 

 out, the total amount of iodine in this lobe was determined and the 

 radiation dose calculated, assuming that the radioactive material is 

 evenly distributed throughout the thjToid. 



Lamerton: Isn't there a fairl^'- considerable error there, particularly 

 with the variation in concentration you get in the thyroid? 



Pelc: It depends on the time of removal. In the beginning you have 

 a fair amount of iodine present, and therefore the difference will not 

 be large. Later on, 24 or 48 hours, the difference might be appreciable. 

 It is unlikely to be tremendous, however. 



Gray: I think it is a matter of the greatest importance to radio- 

 biological research that it should be possible, as Dr. Pelc has demon- 

 strated, to prepare autoradiographs showing the localization of isotopes 

 such as 3 2p and ^^S in living cells without appreciable damage being 

 caused to those cells by the radiation emitted from the isotope. 



It is characteristic of certain aspects of the damage induced by ionizing 

 radiation that it appears only in a proportion of the cells. One cell may 

 be heavily damaged and its neighbour apparently unaffected. Bio- 

 chemical analysis of tissues is too coarse for the study of such phenomena, 

 because the results obtained represent the average response of a cell 

 population in which the proportion of damaged cells may be very small. 

 Cell-autoradiography, on the other hand, reveals the metabolic condition 



