908 
GENETIC AND BIOLOGICAL EFFECTS OF RADIATION 
pated kill dates for these animals are also 
shown (Table III). However, actual kill dates 
may be changed depending upon clinical results 
observed. 
Results of clinical testing of animals in the 
study have indicated changes in only two of the 
parameters under observation. Both of these 
changes have occurred only in the large source 
dogs of Group I, i.e., 70X animals. Beginning 
about 2-3 months after implantation, total lym- 
phocyte counts were observed to decrease from 
the preimplantation normal of about 2,000 per 
cubic millimeter of blood. The decrease contin- 
ued over the next year until the lymphocyte 
count had fallen to approximately 50% of the 
control value, where it has remained since that 
time. Secondly, examination of semen collected 
beyond three months after implantation from 
the male 70X animals revealed a virtual absence 
of spermatozoa in the ejaculate. No consistent 
change from the normal has been observed in 
any of the other animals at this time. 
Of the forty-eight animals implanted to date 
only six have been killed. The six animals killed 
comprise half of Group I animals, i.e., two 70X 
animals (1 after three months and 1 at one year 
after implantation), two 15X animals (1 after 
four months and 1 at one year after implanta- 
tion), and two blanks (both at one year after 
implantation) . 
Post mortem examination of these animals 
was performed as outlined. One of the most 
striking lesions was seen in the lymphoid tissue. 
There were severe reductions in the lymphocyte 
populations of the white pulp of the spleen in 
the 70X animals. Similarly there were reduced 
populations of small and medium lymphocytes 
in the mesenteric lymph nodes of the two 70X 
animals and in the 15X dog killed after one 
year. In these animals there was an almost total 
ablation of the germinal centers of the lymph 
nodes. 
All four of the irradiated male dogs had gon- 
adal lesions. These consisted of altered cell pop- 
ulations within seminiferous tubules with mor- 
phologic evidence of reduction and qualitative 
change in spermatogenic sequences. In three 
dogs there appeared to be graded sub-normal 
levels of spermatogenesis while in one animal 
(a 70X dog killed after 1 year) there was a 
complete cessation of spermatogenesis. In addi- 
tion, an intratubular seminoma was found in 
the testes of one 15X dog. Since this lesion oc- 
curs quite frequently in the dog its presence 
cannot be interpreted as a radiation effect. 
In the two blank and two 15X animals, the 
implantation capsule was surrounded by a thin 
capsule of dense fibrous connective tissue 0.5 — 1 
mm thick with an incomplete inner lining of 
mesothelioid cells. On the outer surface of the 
fibrous capsules was a loose meshwork of areo- 
lar tissue which suspended the device between 
the muscle layers. Tissues immediately adjacent 
to the capsule seemed quite normal in all re- 
spects. The connective tissue layer surrounding 
the implantation capsule in the 70X dog killed 
after three months was intensely reactive ; this 
was interpreted as due to chronic infection 
since a fistula had developed in this dog shortly 
before it was terminated. 
The implantation site of the 70X dog killed 
after one year was also intensely reactive. The 
inferior aspect of the connective tissue capsule 
was distorted by a large spherical nodule (ap- 
proximately 5 cm in diameter) which proved 
histologically to be a mast cell sarcoma. The no- 
dule was intimately adherent to the capsule, but 
the overlying skin was not attached. In addition 
to the nodule, much of the tissue capsule was in- 
filtrated with nests of anaplastic mast cells, and 
a metastasis was present in the ipsilateral lum- 
bar lymph node. 
Technically satisfactory marrow specimens 
were available from the four dogs killed after 
one year. The 15X and 70X dogs showed an al- 
tered cell population characterized by a reduc- 
tion in megakaryocytes and erythropoietic ele- 
ments and an apparent predominance of large, 
relatively immature, and undifferentiated cells. 
These changes occurred in the marrow of bones 
immediately adjacent to the implantation cap- 
sule. 
DISCUSSION 
Assuming a mid-abdominal dose of roughly 
300 mrads/hr (extrapolated from Table II), 
the mesenteric lymph nodes and spleen probably 
received a dose of about 630 rads in three 
months which was sufficient to cause the de- 
