NUCLEIC ACID IX RETROGRADE SARCOMATA 743 



injected 5 hours before the administration of a tracer dose of ^-P. The 

 results obtained are seen in Table 9. 



T.\BLE 9. — Effect of Administration of Ra- 

 diosodium of the formation of labelled 

 Desoxyribosenuci-eic Acid in the Liver in the 

 Course of 2 Hr. 



Specific Activity of Nucleic Acid P expressed in Percenta£<e of the Activity of 

 1 mgm inorganic P from 



In this experiment, as seen above, the radiation emitted by radioso- 

 dium was effective in diminishing the formation rate in the liver of the 

 desoxyribosenucleic acid. 



In experiments of short duration the replacement of Roentgen radia- 

 tion by radiation emitted by the injected radioactive substances has no 

 outstanding advantage. In experiments of long duration, however, the 

 last mentioned technique is often much to be ]>referred. 



Summary 



The percentage new formation of desoxyribonucleic acid phosphorus is only 

 slightly smaller in the spontaneously regressive Jensen sarcoma of the rat than 

 in the growing tumour. This fact indicates that the enzyme mechanism, respon- 

 sible for the incorporation of phosphate into the desoxyiibonucleic acid molecule, 

 is hardly disturbed in the regresssive sarcoma. 



Treatment of rats with colchicine influences the rate of formation of desoxy- 

 ribosenucleic acid phosphorus to a minor extent, 



A somewhat lower formation rate of desoxyribosenucleic acid phosphorus 

 is observed in grafted benzpyicne tumouis, than in Jensen saicoma. 



The rate of formation of labelled desoxyribosenucleic acid under uninterrupted 

 irradiaton during the whole experiment, previously reported to be very low, is 

 to be explained by a disturbance in the circulation of the rat, and not by a 

 correspondingly low rate of formation of labelled dosoxyribospnucleic acid. 



