742 



ADVENTURES IX RADIOISOTOPE RESEARCH 



of the results obtained by Levine/^^ who found a combination of X-ray 

 and colchicine treatment of roottips to be very effective in retarding the 

 growth of ^/ZmmCepa, a more detailed investigation of such a combined 

 effect on the nucleic acid turnover in animal tissues may be of interest. 



Table 8. — Percentage New Formation of 



Desoxyribosenxjcleic Acid in Colchicine 



Treated and Irradiated Rats 



Replacement of Irradiation with Roentgen Rays by Radiation Emitted 



by Injected Radio-Elements 



By injecting very substantial amounts of ^^P we can expect to find 

 a reduced formation of labelled desoxyribosenucleic acid. 1 microcurie 

 per gm tissue produces in the course of 2 hours an ionisation corresponding 

 to 3.5 r units(2).To produce 175 r units in the course of 2 hours we have to 

 administer about 50 microcuries per gm, or 7.5 millicuries, to a rat weigh- 

 ing 150 gm. In this calculation the excretion of some of ^^P administered 

 during the experiment taking 2 hours is disregarded. 



We have not at our disposal sufficiently strong radioactive prepara- 

 tions to carry out such an experiment. In one experiment, however, 

 we injected 3.9 millicuries of radiosodium 5 hours before administering 

 a tracer dose of ^^P. The mean radiosodium activity per gm tissue of the 

 rat weighing 190 gm was in this experiment 20.5 microcurie. The /j-rays 

 of the radiosodium acted upon the tissue for 5 + 2 = 7 hours producing 

 an ionisation corresponding to 250 r units. Radiosodium emits, l)eside 

 /5-rays, also y-rays, which are only partly absorbed into the rat's body. 

 The ionisation produced by these rays in the rat can be estimated as 

 corresponding roughly to a total dose of about 60 r in the course of 7 

 hours, bringing the total dose up to about 310 r. 



The radiosodium was administered by subcutaneous injection in tlie 

 form of 1.2 ml physiological sodiumchloride solution. In the control 

 experiment the same volume of non radioactive sodiumchloride was 



^'i>M. Levine, Cancer Res. 3, 107 (1943). 



^2) L. D. Marinelli, Amer. J. Roentgenol. 47, 210 (1942). 



