116 Barbara E. Holmes 



By the use of tracer phosphate one can estimate the extent 

 of the new formation of deoxyribonucleic and can study at 

 the same time the turnover of phosphate in the ribonucleic 

 acid and the passage of phosphate through the cell membrane. 

 As measured by ^^P uptake, there is very little synthesis of 

 deoxyribonucleic in non-dividing tissue. 



Using the Jensen rat sarcoma as a dividing tissue and giving 

 an X-ray dose of 2,000 r. (which gives complete destruction 

 of over 50 per cent of the tumours) it w^as found that the up- 

 take of phosphate into the cell was not affected by this dose, 

 the turnover of phosphate in the ribonucleic acid was not 

 affected, but the deoxyribonucleic synthesis was reduced to 

 about half the normal rate. It should be stated here that 

 other agents may have a profound effect on phosphate uptake 

 and on ribonucleic acid turnover, but, of the systems we have 

 so far investigated, the synthesis of deoxyribonucleic is the 

 only one affected by this reasonable dose of X-rays. 



We are just beginning to make studies, histological and 

 metabolic together, of later stages after irradiation. In 

 one case, after two days, the deoxyribonucleic synthesis was 

 still proceeding at one half the normal rate, normal mitosis 

 was very hard to find, but many of the enlarged cells so com- 

 monly found after irradiation were present and it was tempt- 

 ing to suppose that some newly formed nucleic acid was 

 being laid down in these enlarging cells instead of forming 

 nucleic in new cells. There is no explanation as to why this 

 should happen, unless, perhaps, one can imagine that other 

 cell processes are proceeding at speed while the partial lack 

 of this one substance prevents the actual normal division 

 and that, thus, freaks may develop. 



To carry supposition further, it may be pictured that some 

 drugs and chemical compounds, having a more generalized 

 effect on the cell, might slow up cell division and many other 

 processes for a time and, when the drug was eventually 

 removed the inhibited cell might simply resume its normal 

 existence. In this case the cell would behave in a sense, like 

 an organism in which growth has been temporarily stopped 



