Negroes played an increasingly important part in the life of Marlborough, particularly after the manor house was built. Between 1731 and 1750 Mercer purchased 89 Negroes. Most of these are listed by name in the ledger accounts. Forty-six died in this period, while 25 were born, leaving a total of 66 Negroes on his staff in 1750. In 1746 he bought 6 men and 14 women at £21 10s. from Harmer & King in Williamsburg. The new house and the expanded needs for service were perhaps the reasons for this largest single purchase of slaves.
There is no indication that Mercer treated his slaves other than well, or that they caused him any serious difficulties. On the other hand, his frequent reference to them by name, the recording of their children's names and birth dates in his ledger, and the mention in his journal of new births among his slave population all attest to an essentially paternalistic attitude that was characteristic of most Virginia planters during the 18th century. Good physical care of the Negroes was motivated perhaps as much by self-interest in protecting an investment as by humane considerations, but, nonetheless, we find such items in the ledger as "To Cash p^d Doctor Lynn for delivering Deborah."
That discipline served for the Negroes as it usually did for all colonials, whether the lawbreaker were slave, bondsman, or free citizen, is indicated by an entry in the Dick account: "2 thongs w^{ th} Silk lashes 1/3." One must bear in mind that corporal punishment was accepted universally in the 18th century. Its application to slaves, however, usually was left to the discretion of the slave owner, so that the restraint with which it was administered depended largely upon the humanity and wisdom of the master.
The use of the lash was more often than not delegated to the overseer, who was hired to run, or help run, the plantation. It was the overseer who had a direct interest in eliciting production from the field hands; a sadistic overseer, therefore, might create a hell for the slaves under him. It is clear from Mercer's records that some of his overseers caused problems for him and that at least one was a brutal man. For October 1747 a chilling entry appears in the account of William Graham, an overseer at Bull Run Quarters: "To Negroes for one you made hang himself. £35." Entered in the "Negroes" account, it reappears, somewhat differently: "To William Graham for Frank (Hanged) £35 Sterling. £50. 15." This is one of several instances on record of Negroes driven to suicide as the only alternative to enduring cruelties.[103] In this case, Graham was fined 50 shillings and 1293 pounds of tobacco.