632 ADVENTURES IN RADIOISOTOPE RESEARCH 



specific activity of the total iron present in the muscles as well and 

 found it, as to be expected increased under the effect of exposure, in 

 the third experiment from 0.714 to 0.810, in the fourth one from 

 0.687 to 1.04. 



DISCUSSION 



Hemoglobin is one of the comparatively few molecular constituents 

 of the adult organism that is formed in close connection with cell division. 

 The latter being very susceptible to the effect of ionising radiation, 

 exposure to radiation is bound to interfere with hemoglobin formation 

 as well. Furthermore, marrow cells are radiosensitive and exposure to 

 radiation may lead to destruction of marrow cells. Irradiation of rats 

 with 400 r was found to lead to a decrease in the total number of marrow 

 cells to almost one half of its normal value in the course of the first 

 day following exposure (Brecher(^^>) and the chemical composition of 

 the bone marrow was found markedly influenced. Lutwak-Mann^^'^ 

 found 3 hours only after total body exposure to a dose of 1500 r the 

 labile acid-soluble P of the bone marrow of rabbits to be reduced by 

 30o/o, that of DNA and RNA phosphorus by 20 and 16%. The total 

 nucleic acid P of the marrow of the to 500 r exposed rat amounted to 

 only half of that of controls. Manclel et al}^ report the bone-marrow 

 of rats exposed to 500 r to show after the lapse of 26 hours a by 50% 

 reduced PNA content, the DNA being reduced to 30% of that of the 

 controls after the lapse of 2 days. Thus radiation anemia is at least 

 partly due to the fact that hemoglobin is formed in close connection 

 with the cell division and also that it takes place in the radiosensitive 

 marrow cells. 



Altmann et al. (Richmond^^^^ Stokingek^^*^^) in their very extended 

 studies found incorporation of i^C into globin and hemin to be influenced 

 at a very different rate by irradiation. Incorporation of i*C into hemin 

 of the exposed animals was greatly depressed, whereas globin was 

 affected to a considerably smaller extent. From this finding it does not 

 necessarily follow that it is not the milieu of its formation, the bone 

 marrow, which is responsible for the radiation sensitivity of the formation 

 of hemoglobin. 



We found no interference with the formation of cytochrome b in the 

 liver of the strongly irradiated guinea-pig. In this case heme formation 

 is thus not radiosensitive. We found, however, interference with forma- 

 tion of myoglobin. 



