If the hawkers of even the meanest forms of service seem to us to have put forth unusual effort, we give them something besides what we have agreed upon; we dispense gratuities to a pilot, to a man who works with the commonest material, and to one who hires out his services by the day. Surely, in the case of the noblest professions that either maintain or beautify life, a man is ungrateful if he thinks that he owes no more than he bargained for. Add, too, that in the transmission of such knowledge mind is fused with mind; therefore, when this happens, to the teacher, and to the physician as well, is paid the price of his service, but the price of his mind is still owed.