Section 55. Conversion of indorsement in blank into indorsement in full

55. Conversion of indorsement in blank into indorsement in full.— If a negotiable instrument, after having been indorsed in blank, is indorsed in full, the amount of it cannot be claimed from the indorser in full, except by the person to whom it has been indorsed in full, or by one who derives title through such person. 56 . Indorsement for part of sum due.— No writing on a negotiable instrument is valid for the purpose of negotiation if such writing purports to transfer only a part of the amount appearing to be due on the instrument; but where such amount has been partly paid, a note to that effect may be indorsed on the instrument, which may then be negotiated for the balance.