114. General rule as to deductions.

Where the holder of an office or employment of profit is necessarily obliged to incur and defray out of the emoluments of the office or employment of profit expenses of travelling in the performance of the duties of that office or employment, or otherwise to expend money wholly, exclusively and necessarily in the performance of those duties, there may be deducted from the emoluments to be assessed the expenses so necessarily incurred and defrayed.