KEMPNER AND POLLARD 



129 



1000 



300 



100 



UJ 



^ 30 

 \ 



3 

 O 



° 10 



Whole Cell 



TCA 

 Insoluble 



JL 



_L 



0.2 0.4 0.6 0.8 



DOSE (ROENTGENS) 



1.0 



1.2x10 



Fig. 4. Survival of methionine incorporation with Y-ray dose. The ordinate is on a 

 logarithmic scale. Pool fraction shows similar survival. 



the second column. The last column, the "equivalent spherical radius," is the 

 value calculated assuming that the sensitive volume is the shape of a sphere; 

 it is listed for comparative purposes only. 



Cyclotron irradiations produced similar effects. The data scatter even more, 

 probably owing to the difficulty in securing irradiations involving the same 

 time of exposure on the Millipore filter. There is quite clear evidence of a 

 reduction in activity, as can be seen from figure 5, where the uptake of methi- 

 onine is shown for control and two irradiated points. Uptake curves of the 

 sulfur-labeled amino acids do not extrapolate to zero counts per minute at zero 

 time, owing to adsorption of the label, and this correction is deducted in plot- 

 ting survival curves. Figure 6 shows analogous curves for proline incorpora- 

 tion, also after deuteron irradiation. These experiments were performed with- 

 out added aluminum absorber in the cyclotron beam. 



Similar studies were carried out with various absorbing foils, and, from the 

 uptake curves, curves relating the per cent uptake remaining to the number of 

 deuterons per square centimeter used to irradiate were drawn for each foil 

 thickness. In each case, the 37 per cent dose (in deuterons per square centi- 



