320 H. MAISIN 



EXPEEIMENTAL CONDITIONS 



We used homogeneous albino rats of our L strain. They were 4-month-old 

 males weighing from 130 to 145 g. The rats were irradiated with a Genreal 

 Electric Maxitron 250 X-ray at 250 kV 25 mA filter, 0-25 mm Cu + 1 mm Al, 

 distance: 80 cm, output in air with a Victoreen Radocon was 47 r/min. The 

 animals were irradiated four at a time on a turntable and fasted for 24 hours 

 before, and after, exposure. The X-ray doses were 600 r-LDjoQ^Q) and 

 500 r-LD-Q(gQ). After ii-radiation, daily records were kept of the rats. 



We irradiated two groups of 24 rats at 600 r and 500 r. After each X-ray 

 dose, 12 of the rats were kept for controls. Fifteen minutes after the 600 r, the 

 other 12 rats were injected intrapetitoneaUy with 2 ml of saline containing 

 100 mg of sodium ribonucleic acid (Merck). After 500 r, 12 rats also were 

 injected intraperitoneally with nucleotides obtained from 100 mg of the 

 sodium ribonucleic acid by controlled alkaline hydrolysis (Maisin et al., 1960). 



After 600 r, 4 rats of each group were sacrified at 2-, 4- and 6-day intervals, 

 after 500 r, the same number of rats were killed at 2-, 3- and 6-day intervals. 



From each rat, we removed one femur for counting the number of bone- 

 marrow nucleated cells per mg marrow following a method published by 

 Maisin (1959), and one tibia for marrow air-dried smear. The marrow smear 

 was stained by the May-Griinwald-Giemsa method. The results of the number 

 of the bone-marrow nucleated cells per mg of marrow were combined with 

 differential counts of the marrow smears and the absolute number of each 

 type of cell per mg of marrow obtained. We just mention here the total 

 number of white and red precursors and of reticular cells. We also examined 

 under the same conditions marrow of 4 normal, non-irradiated, rats of the 

 same age and same weight. 



RESULTS AND DISCUSSION 



After 500 r (Table I), in contrast to the irradiated controls, the total 

 number of marrow cells started to increase from the 3rd day in the rats 

 injected with nucleotides. If we look at the number of red and white precur- 

 sors, we see that the white precursors in the nucleotide-injected rats are 

 regenerating first, the difference from the white precursors of the controls 

 being statistically significant. At the 6th day after irradiation, the red cell 

 precursors are regenerating both in the controls and in the nucleotide-injected 

 rats but the red precursors of the nucleotide-injected rats are regenerating 

 faster, the difference also being highly significant. In other words, the yeast 

 nucleotides influence first the white precursors. Curiously the total number of 

 reticular cells of both controls and nucleotide-injected rats do not differ 

 except perhaps on the 3rd day. However, following previous work, we feel 



