Abstract
Experiments were carried out for testing selection effects against the "A"-inagglutinable red cells. Three birds picked at random and not exposed to x-irradiation showed decreases in the number of inagglutinable cells in a Cr51-labeled cell population at 7 days. Two of these decreases were quite large, being >5-fold, and the three averaged an ICF change of -3.57-fold. The substantial reduction in survival of the "A"-inagglutinable cells was attested by the lowered inagglutinable cell frequency at 7 days postinfusion.
Seven birds uniform in titer and in their negative response to previous irradiation (360 r) averaged a 3.75-fold decrease in ICF at 8 days postinfusion. Four birds of a similar group but which had been very responsive to previous irradiation were treated in identical fashion. At 8 days postinfusion the average change in ICF was +0.80. This change is not significant, being within the experimental error of ±1.5-fold.
The marked difference in results between the "low-response" group (-3.75 ±0.56) and the "high-response" group (+0.80 ±0.88) was interpreted to be due to negative selection operating strongly in the former group.
