Any person performing labor or furnishing materials for a subcontractor, in order to perfect the lien given him by § 43-3, shall comply with the provisions of § 43-4, and in addition thereto give notice in writing to the owner of the property, or his agent, and to the general contractor, or his agent, of the amount and character of his claim. But the amount for which a lien may be perfected by such person shall not exceed the amount for which such subcontractor could himself claim a lien under § 43-7.