m 



• id^ 



^^P- 



Fig 4 (Pollock). Colonies of Bad. coli mntahile orowing on the surface 

 of lactose-agar. 8 days' incubation. X 8. 



a. From Lac - inoculum (all Lac ' colonies). ^f t «p - and T ac + 



h From an inoculum containing a 50 : oO mixture of Lac and Lac 

 cells (showing 3 Lac + and 3 Lac - colonies). 



