"Ye see what ye'd get, if ye try to run off.

These yer dogs has been raised to track niggers; and they'd jest as soon chaw one on ye up as eat their supper.
So, mind yerself! How now, Sambo!" he said, to a ragged fellow, without any brim to his hat, who was officious in his attentions.

"How have things been going ?" "Fust rate, Mas'r." "Quimbo," said Legree to another, who was making zealous demonstrations to attract his attention, "ye minded what I telled ye ?" "Guess I did, didn't I ?" These two colored men were the two principal hands on the plantation.
Legree had trained them in savageness and brutality as systematically as he had his bull-dogs; and, by long practice in hardness and cruelty, brought their whole nature to about the same range of capacities.

It is a common remark, and one that is thought to militate strongly against the character of the race, that the negro overseer is always more tyrannical and cruel than the white one.

This is simply saying that the negro mind has been more crushed and debased than the white.