POST-IRRADIATION AND BONE-MARROW COUNT 323 



that a faster regeneration of the precursors is accompanied by a reduction in 

 the number of reticular cells, which are transformed into the precursors 

 (Maisin, 1959). 



After 600 r (Table II) which is a LD^qq^^q^, the marrow of the sodium 

 ribonucleate-injected rats do not regenerate before the 6th day, neither the 

 white precursors nor the red. Thus yeast RNA is unable to induce any 

 regeneration in lethally irradiated rats within the 10th day. In fact, UNA is 

 'able to reduce the lesions in the white precursors, indeed the number of cells 

 in the RNA-injected rats are always significantly higher than in the control 

 irradiated, rats. There is no difference in the lesions in the red precursors. The 

 granulo-erythropoietic ratio confirms this discrepancy. The number of 

 reticular cells is the same in both the ribonucleate and control irradiated, 

 animals. 



In conclusion, we have arguments to support the view that the better 

 survival of the ribonucleate- or nucleotide-injected rats can be explained by 

 a general faster regeneration of the red and white marrow precursors but 

 particularly of the white. The regeneration of the red precursors is no longer 

 possible w^ith a LD^qq, it is thus limited by the size of the X-ray dose used; the 

 regeneration of the white precursors is reduced. It was not possible to show a 

 definite regeneration of the reticular cells, but even though it is not demon- 

 strable, the faster regeneration of the white and red precursors cannot be 

 explained without at least an easier transformation of the reticular cells 

 into white and red precursors. Considering the fact that yeast RNA was 

 protectmg, or treating, only medullary death (Maisin et al., 1960) these data 

 were very probable (Maisin et al., 1962) but now we have a clear and definite 

 answer. These experiments support the general concept of the action of RNA 

 and its nucleotides on marrow regeneration (Soska et al., 1958; Karpfel et al., 

 1959) and they specify and prove the action of yeast RNA. 



REFERENCES 



Detre, K. D., and Finch, S. C. (1958). Science 128, 656. 



Karpfel, Z., Soska, J., and Drasil, V. (1959). Nature, Lond. 183, 1600. 



Maisin, H. (1959). SjTidrome medullaire apres irradiation, Arscia, BruxeUes. 



Maisin, J., Dumont, P., and Dunjic, A. (1960). Nature, Lond. 186, 487. 



Maisin, J., Dunjic, A., and Dumont, P. (1962), to be published in Strahlenschutz in 



Forschung und Praxis, Band 2, Verlag Rombach, Freiburg im Breisgau. 

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