The performance of another person's obligation is clearly not required, so long as there is a probability that the obligor will perform it with reasonable promptness himself. It follows that one who seeks restitution for a benefit so conferred must show, ordinarily, that the defendant had notice or knowledge of the facts giving rise to his obligation and either refused to perform it or failed to perform it within a reasonable time.1 But if it appears that by reason of the urgency of the duty or the distance of the defendant, prompt performance by him was impossible, notice or knowledge of the facts need not be shown. Thus, a physician suing a father for services in attending a child, which services were not contracted for by the father, should be required to establish either that the father was notified of the child's illness and refused or failed to employ a physician, or that because of the extremity of the child's condition or the inaccessibility of the father, notice would have been of no avail.2