60 P. C. KOLLER AND S. M. A. DOAK 



and used as new marrow donors. In this manner five serial transplants were 

 made, assuming that the original iosgenic marrow persisted and functioned 

 in the secondary, tertiary and quaternary hosts. 



Analyses were made of the peripheral blood of 3-month-old untreated 

 C3H mice and of all marrow donors prior to their sacrifice. The peripheral 

 blood picture was also examined in the survivors of each group of 50 and 75 

 days post-irradiation. The number of erythrocytes/unit volume, together with 

 the haemoglobm index, and the number of leucocytes/unit volume were 

 determined. The relative proportions of mononuclears and polymorphs were 

 estimated from blood smears stamed with Giemsa. The non-polymorph 

 population of white blood cells in normal control mice is mainly small 

 lymphocytes; in the chimaeric mice, on the other hand, the cells are more 

 , generally monocytes and large lymphocytes and, occasionally, cells of the 

 early myeloid series may be identified. 



EXPERIMENTAL RESULTS 



PerijyJieral blood analysis before and after irradiation 

 Five C3H mice, 3 months old, were used to obtain an average peripheral 

 blood value as control. Two groups of 30 C3H mice were exposed to 650 r 

 total-body radiation; one received isogenic bone-marrow (5 x 10*^ cells) 

 intravenously within 4 hours of irradiation. Blood samples from each group 

 of mice were taken on 1, 3, 6, 9, 12, 15, 21 and 28 days post-irradiation. To 

 reduce the risk of altering the haematological picture by too frequent 

 sampling, the mice were batch bled in groups of 6 at intervals of not less than 

 10 days. The results together with the control data are presented in Fig. 1. 



There was no appreciable reduction in the number of circulatmg erythro- 

 cytes, nor a decrease in the amount of haemoglobin, until three days post- 

 irradiation. On the other hand, the number of mononuclears in the peripheral 

 blood dropped precipitously during the first few hours. By 3 days the poly- 

 morph population was also reduced in size, the total leucocyte count being 

 approxunately one-tenth of the control value. 



Irradiated mice given no further treatment did not live after 15 days. If 

 the mice received an injection of 5 x 10^ isogenic bone-marrow cells 24 hours 

 after the irradiation, the drop in the peripheral blood cells was arrested at 

 about the 5th day. On the 15th day there was evidence of an over-compensa- 

 tory hyperplasia of the leucocyte population. By 28 days the number of 

 erythrocytes and the haemoglobin level, together with the total leucocyte 

 count, were indistinguishable from the controls. However, the normal mono- 

 nuclear/polymorph ratio was not restored at 28 days, the recovery of the 

 leucocyte population being due mamly to granulopoiesis. 



