D, D. JOEL AND E. P. CRONKITE 
893 
150 
10 
Lymph node, medulla 
Lymph node, cortex 
Thymus, cortex 
Red pulp 
1 
Dense \ I 
White pulp J 
Loose) 
Thoracic duct lymph 
Blood 
Spleen 
20 30 40 50 
Time after onset of ECIB (hr) 
60 
Figure 6. — Lymphocyte depletion in various areas of lymphoreticular organs, in the thoracic duct lymph and in 
the blood of the calf as a function of time after onset of continuous ECIB. (Reprinted from Ruchi et al., 
1970.) 
of thymic origin. It is of interest that recent 
studies provide evidence that, in the calf, the 
thymus issues into the blood a sufficient num- 
ber of lymphocytes to totally replace the easily 
mobilizable pool in less than 5 days.^^ It thus 
becomes quite evident that the vast majority of 
thymocytes in calves never enter the recirculat- 
ing pool. Large lymphocytes make up a small 
fraction of the mobilizable pool as evidenced by 
a decrease in these cells in the blood and tho- 
racic duct lymph during ECIB or ECIL. In con- 
trast to small lymphocytes recovery is relatively 
rapid. 
The size of the sessile pool of lymphocytes is 
difficult to measure for several reasons. (1) 
Estimates based on thoracic duct outputs during 
ECIL must take into account the input from 
formation of new cells and the contribution by 
afferent lymphatics. Neither of these are known. 
(2) The relative size of the sessile pool in 
lymphoreticular organs can be estimated by 
planimetry, however, this does not include 
lymphocytic infiltrates at sites other than the 
lymphoreticular organs. It seems probable that 
the sessile pool is considerably larger than the 
easily mobilizable pool particularly in lymph 
nodes. 
