If a contract is entire, impossibility of performance of one of the material covenants operates as a discharge of the entire contract.1 A contract to furnish stenographic and clerical assistance from a certain date until the happening of a certain event in consideration of half of the net fees received by the employer during such period, is an entire contract in this sense;2 and if the employe is prevented by illness from rendering services for almost half of such period, he can not recover at the contract rate for the remaining period,3 but he is entitled only to reasonable compensation or for the value of the services rendered by him.4 An unconditional promise on the part of one of two or more joint promisors is not discharged by the fact that one of the joint promisors is an infant and that performance can not be enforced against the infant.5