24 



MUTATIONS 



was normal, so we concluded that if such cells had been produced, 

 they would have persisted. 



We had two opportunities to study these. The first one was a test 

 for A to B, consisting of cleaning out all the A cells with anti-A and 

 then starting with anti-B and seeing whether any further cells were 

 removed with anti-B and B carrier, and finally putting some Ulex in, 

 to be sure that the cells remaining were actually 0. 



This experiment (Fig. 5) was done by Takashi Ito in some very care- 



10" 



-I 



o 



111 

 m 



< 



° 10-2 



K 

 O 



a. 

 o 

 o: 



0. 



<9 



< 

 Z 



o: 10' 



,-3 



10' 



STAGE 



Figure 5. Isotope dilution curve for an agamma- 

 globulinemic, group A, probable heterozygote. Anti-A, 

 anti-B, and Ulex in sequence. Absence of B cells is 

 suggested by minimal effect of anti-B. The curve is 

 broken at this point to indicate the size of the possible 

 B cell population, but its reality is questionable. 



