Holmes on agency and contract 1891 3

Questions raised by the slaves acting ex persona domini principle: 

1. That slaves personify masters---is that pre-contractual, or a consequence of the contract made between master as slave-purchaser and slave-seller? (By pre-contractual, I mean does it result from something other than the contract; I don't mean to suggest it's already operative prior to the slave purchase, since no ownership would exist yet.)
2. The slave enjoys an advantage of directness (family-member-like, unlike strangers). Is this a species of the idea that a man is head of household, the "representative" of the woman and the children?
3. Slaves complicate the legal philosopher's task of inventorying the short list of legal concepts---let's include three to start with: the concept of the author of an action, the concept of property, and the concept of contract. Slaves muddy all of these.