890 
GENETIC AND BIOLOGICAL EFFECTS OF RADIATION 
cytes (Figure 2b) as compared to large lympho- 
cytes. Direct verification of this effect was estab- 
lished in size distribution studies on suspensions 
of thoracic duct lymphocytes. In untreated 
calves the volume distribution of thoracic duct 
lymphocytes is a continuum between 120 and 
1,200 /i3 with a mode between 240 and 288 /a^ 
(Figure 3). These data, when plotted on loga- 
rithjonic probability paper, indicated the pres- 
ence of two populations of lymphocytes: (1) a 
small population with a median cell volume of 
250 ]j? and constituting 90-95% of the total, 
and (2) a large population with a median cell 
volume of 648 ju,^. Lymphocytopenia induced by 
either ECIB or ECIL markedly alters the size 
distribution (Figure 3) due principally to a loss 
of cells within the small lymphocyte category. 
Continuous ECIL also results in a marked de- 
crease in the blood lymphocyte count and cellu- 
lar output in the thoracic duct as illustrated 
in Figure 4, where large and small lymphocytes 
are plotted separately. Lymphocyte depletion of 
both blood and lymph did not occur according to 
a single exponential function but rather fol- 
lowed a curve with at least two components. 
This is shown in Figure 5 for the thoracic duct 
DISTRIBUTION OF THORACIC DUCT LYMPHOCYTES 
LU 
tr 
40 
35 
30 
25 
20 
I 5 
10 
REPRESENTS RANGE OVER 
48 HOUR PERIOD (NO ECIL) 
° AFTER 23 DAYS OF ECIL 
Figure 3.— Distribution curve of thoracic duct lymphocytes from calves vsrhich received no treatment ( ) and 
from a calf which had 23 days of continuous extracorporeal irradiation of lymph (ECIL) (O O). 
