Bava Metzia 99 - Responsibility in Transit

If one was borrowing a cow and the lender sent it to him with his son, his slave, or his agent - or with the son, the slave, or the agent of the borrower - and the cow died naturally in transit, the borrower is not liable. Even the borrower's worker does not become an agent to assume responsibility for the cow, but only to transport it safely.

If, however, the borrower said to the lender, "Send me the cow with my son (my slave, my agent)" or "with your son (your slave, your agent)" and the cow died naturally in transit, the borrower is liable - not through the law of agency, but through the law of a guarantor: in consideration of the lender sending the cow on his say-so, the borrower assumes responsibility for any mishap that befalls the animal on the way.