Methods

Spraguc-Dawlcy male rats were given intraperitoneal or intravenous injections of H3-thymidine (TTH) with a specific activity of 1.9 c/mM. The thoracic duct lymph (TDL) was collected via a Reinhardt (19) or a Bollman type fistula (20) as modified by GOWANS (11). The animals with the Bollman fistula were kept in restraining cages (21) and were given one injection of a solution (5 ml.) containing 5% dextrose and 0.45% NaCl after the operation to promote a good initial flow of lymph and to eliminate the need for anticoagulants. Smears were made of the TDL and radioautographed, employing NTB3 liquid emulsion, as previously described (6). The slides were exposed for 8 weeks, developed in the conventional way (8), stained for 4 minutes with tetrachrome stain (22) and dcstained in Sorensen’s phosphate buffer (pH 6.4). The percentage of labeled small lymphocytes in the TDL was calculated by counting 1,000 small cells. The cells interpreted as small were those having a nuclear diameter of 7//or less and comprising approximately 90% of the cells in the TDL.