X-Rays and Cell Metabolism 117 



by starvation. The inhibition of mitosis by shock, which will 

 be mentioned later, seems to be a more generalized process, 

 which passes off altogether unless the shock is fatal. 



It was plain that the synthesis of protein, both cytoplasmic 

 and nuclear, in the dividing cells should next be considered, 

 and the effect of irradiation upon this should be determined. 



The protein fractions we found most easy to separate were 

 the histone from the sedimented nuclei, the ribonucleoprotein 

 (precipitated by calcium) remaining in the supernatant fluid, 

 and the heat coagulable protein remaining after the removal 

 of the ribonucleoprotein. Sulphur 35 was injected as sulphide 

 or as methionine into rats bearing the Jensen sarcoma, which 

 were killed 1^ hours later. Some of the tumours received 

 2,000 r. X-rays immediately after the injection and the uptake 

 of ^^S was measured in the different protein fractions of the 

 irradiated and control tumours. 



The histone fraction showed a variable uptake of radio- 

 active sulphur, but it was not possible, in this or either of the 

 other fractions, to show a constant effect of irradiation on 

 the protein turnover. If the histone is actually attached to the 

 deoxyribonucleic acid, the lack of correspondence in X-ray 

 effect on the two substances is remarkable. 



Some final experiments were carried out in which ^'^P and 

 methionine ^^S were injected simultaneously, in order that the 

 protein turnover and the nucleic acid formation could be 

 traced in the same animals. Table I gives the results and 

 shows the complete lack of any relation between the effects 

 of irradiation on the uptake of the two substances. These 

 results will be more fully discussed in a paper now in pre- 

 paration. 



So far, the work described suggests a somewhat specific 

 effect of irradiation. I should now like to describe the action 

 of very non-specific mitotic inhibiters, that is, the "shock" 

 substance or substances formed in a ligatured limb. 



In our earlier work we used to fix the animal for irradiation 

 partly by threads passing round the wrists and ankles ; these 

 were not tight but were sometimes pulled tight if the animal 



