"When the cell digested lactose, it reduced the amount of lactose in the
cell. When the amount of lactose was too small to inactivate the repressor, the 
repressor bound to the operator and switched it off. The transcription of the 
genes stopped, and the cell stopped making digestive enzymes, which was good, 
since the enzymes weren’t needed. If you were to dump one of these Escherichia
things into a vat of lactose..."