NEUTRON EFFECTS ON ANIMALS 153 



Changes in Number of White Blood Cells after Neutron Irradiation. Three 

 groups of 20 male rats, each rat weighing approximately 200 grams, were 

 irradiated (Enns et al. (14)) in Box No. 7 with 11.3, 56.4 and 113 n respec- 

 tively. The rate of administration of the doses was approximately 1 n 

 per minute. Th? dose of 113 n was given in equal parts on two successive 

 days. 



Blood was taken from the tail. Pre-irradiation counts were made on 

 all animals. After irradiation, counts were made daily at the same hour 

 until recover}' was practically complete, then t'snce weekly. 



11.3 n: Twenty-seven hours after completion of irradiation there was 

 a marked decrease in the total white blood cell count. The minimum 

 value was reached between the 4th and 7th da\^s after irradiation. The 

 return to normal was rapid and full recovery had occurred by the 22nd 

 day (Fig. lA). 



A temporary lymphopenia reached a maximum on the 2nd day after 

 completion of irradiation (Fig. IB). Return t ; the pre-irradiation value 

 was rapid and was reached approximately on the 7th day. The reduction 

 in the absolute number of lymphocytes reached its maximum on the 2nd 

 da}'. This dep.ession occurred 2 to 5 days sooner than the maximum 

 leukopenia or the maximum absolute reduction of neutrophils. However, 

 return to normal of the absolute Ij^mphocyte count paralleled that of the 

 leukocyte count. 



The relative neutrophils increased imtil the second day (Fig. IB) but, 

 the absolute neutrophil count was depressed (Fig. lA) until the 7th day 

 and then returned to the pre-irradiation level about the 9th daj^ 



56.4 n: There was a profound drop in the total white blood cell count 

 in the first 24 hours after irradiation. The maximum depression was 

 reached on the 3rd day (Fig. IC). After this there was a rise in the total 

 white blood cell count so that about the 32nd day the count approximated 

 the pre-irradiation level. The changing values for the relative number of 

 lymphocytes and neutrophils are shown in Fig. ID. The gi'eatc st reduction 

 in the relative number of honphocytes and the greatest increase in the 

 relative number of neutrophils were reached on the 2nd day. The differ- 

 ential count had almost reached the pre-irradiation values 8 days after 

 irradiation and fully reached them by the 32nd day. The absolute num- 

 ber of Ijinphocytes reached its maximum depression at approximately^ the 

 same time as that of the total number of leukocytes and a short time before 

 the maximum depression of the absolute number of neutrophils. Return to 

 l)re-irradiation values of the lymphocyte count paralleled that of the total 

 white blood cell count. The relative neutrophilia had returned to j^re- 

 irradiation values on the 5th day (Fig. IC), but the absolute neutropenia 



