DISCUSSION 265 



incorporated P^^ is about 5 times as efficient in inducing death after autogamy as 

 are Sr^^'^^Y^" solutions delivering the same beta-radiation dosage to the cell. 

 In our system the accumulation of phosphorus by the organism is a complicating 

 factor which reduces the calculated efficiency of P^^ to about 4 times that of the 

 Sr solutions. It should be noted that the Paramecium evidence concerns the 

 induction of changes in micronuclei which undergo a series of maturation di- 

 visions followed by the fusion of two gametic nuclei before the expression of the 

 effect. The phenomenon has, then, been detected in a system which is genetic 

 in the "gene-chromosome" sense. 



The experiments have been extended to radioactive hydrogen. Recent results 

 show that tritium is certainly no more efficient than one would expect on the 

 basis of dosage of ionizing radiation delivered to the cell by the beta particles 

 from the H^ atoms. It appears that the respective positions of P and H in the 

 structure of the nucleus are markedly different in importance. 



Solomon : 



In addition to the bond rupture around radioactive sulphur which Kamen 

 pointed out, it might also be possible to have the situation complicated by the 

 reacti\dty of the sulfur which is formed ; perhaps it can combine with the oxygen 

 atoms. In ovir laboratory we have found that sulfur produced from chlorine will 

 exchange with sulfur in the carbon disulfide molecule, which does not in the 

 ordinary way happen. 



Latarjet : 



What would be the efficiency of an ionization in Kamen's case as compared to 

 the one I obtained with soft x-ray * irradiation of intracellular T2? 



I am attempting at present to induce host range mutations in a bacteriophage 

 by ultraviolet irradiation of the intracellular phage during its growth process, f 

 I should like to ask Kamen whether he thinks that his technique would be 

 suitable for the same kind of experiment with ionizing radiation. 



Kamen : 



The effect could be studied. It might be possible to take mutants containing 

 P^^, cross them with members of a normal strain, and study the results of hy- 

 bridization. 



Latarjet : 



Is a the probabiUty of the efficiency of ionization? 



Kamen: 

 Yes. 



Latarjet : 



It is interesting that studies with x-rays on the same phage give -values of 

 approximately 0.12, which is in fair agreement with Kamen's value of 0.08. 



* J. Gen. Physiol, 31: 529, 1948. 

 t Compt. rend., 228: 1354, 1949. 



