28 NEUTRON EFFECTS ON ANIMALS 



entirely of neutrons. Furthermore, one very important phase of the 

 problem Avhich has not previously been reported is that of the effect of 

 repeated exposure to relatively low doses of neutrons. A knowledge of the 

 effects of repeated exposures to low neutron doses is of importance to those 

 working with neutrons in order that protective measures ma}' be instituted 

 where necessary. The experimental work described in this paper shows 

 the general effects of short exposures to relatively heavy doses of neutrons 

 as well as those of repeated exposures to low doses. 



EXPERIMENTAL DATA 



General Experimental Data. All experiments described in this paper 

 were carried out on white rats of the Brooklyn Strain from the laboratory 

 colony. Adult rats weighing from 150 to 220 grams were chosen for this 

 work since it is planned to use animals of this size in future detailed investi- 

 gations of the mechanism of action of neutron rays. Prior to exposure to 

 irradiation the rats were kept under observation for at least two weeks 

 during which time repeated checks of body weight and white blood cell 

 counts were made and also in some instances red blood cell counts and 

 blood hemoglobin determinations. This latter determination was carried 

 out by the acid-hematin method on .01 ml. of blood using a Klett-Sum- 

 merson photoelectric colorimeter with a No.*42 filter. Control groups of 

 rats of comparable weight were also studied along with the irradiated 

 groups. Identification of tumors and histological studies were made by 

 Dr. Douglas M. Gay of this Laboratory. 



All animals were irradiated by the cyclotron of the Biochemical Research 

 Foundation under the supervision of the Physics Department. The de- 

 tails of this cyclotron, of the methods and conditions of irradiation, and 

 of the characteristics of the neutron beam have been described by Enns 

 et at. (7). All neutron doses have been reported in terms of n units, meas- 

 ured on the 100 r Victoreen chamber. A summary of the radiation data 

 for all experiments is given in Table I. 



In subsequent sections of this paper, the experimental data have been 

 divided into three groups for discussion purposes as follows: 



1. Neutron doses of 17.5 to 240 n. 



2. Neutron dose of 10 n repeated twelve times — Accumulated dose of 



120 n given over a period of 14 days with no irradiation on the 

 third and fourth days. 



3. Neutron doses of 1.8 n repeated — Given daily, except Sundays, for 



a total of 251 doses (total elapsed time of 299 days) in one experi- 

 ment and for a total of 172 doses (total elapsed time of 203 days) 

 in two additional experiments. 

 Neutron Doses of 17.5 n to 240 n. The purpose of this phase of the ex- 



