16 
more slowly and Is able to grow back five orders of magnitude after 100 
hours of starvation in DAP-less media (Curtiss ejt al_ . , Figure 10). The 
possibility that these survivors are in fact genotypic revertants to the 
phenotype of DAP-less death was not ruled out. In addition, it seems that 
the parents to x!8?6, XL846 and Xl849, die faster than X1876 and lack the 
resistant population present in X1876 cultures (Curtiss et al. , Figure 11). 
c) When DAP-less death of XL876 is observed in the presence of the 
. parent x289, X1876 initially dies and then stops dying by 4 to 9 hours 
"as though being crossfed or protected by x289" (Curtiss et^ al _ . , p.17. 
Figure 16). Curtiss _et_ a_l. then conclude, on the basis of a single 
datum-point at a late time (24 hours), that xl^76 dies rapidly after 9 
hours. These data are in seeming contradiction to findings presented later, 
which demonstrate that XL876 can conjugate with recipients under similar 
conditions for much longer times than it is supposedly alive. 
It is not at all clear whether x!876 exhibits its DAP-less death 
phenotype when other cells are present to the extent claimed by Curtiss j^t al . 
d) The "rfb-2" phenotype is completely masked by the DAP-less 
death phenotype, since the additional presence of bile salts or detergents 
when a culture is undergoing DAP-less death does not increase the death rate 
of the culture appreciably. 
59. Thymineless death: 
a) Thymineless death is not complete, and prolonged starvation 
leads to regrowth of cells which are genotypically resistant ( d coB , deoC ) 
to thymineless death (curtiss et^ a^. , Figure 19) . 
b) It is also not clear whether rescue after thymineless death 
is due to regrowth of resistant cells or to the addition of thymine, since 
[Appendix C — 204] 
