Additional sentences

The period, if any, during which any prisoner has been unlawfully absent from prison, shall not be reckoned as part fulfilment of his sentence, but he shall be liable to undergo the full term of such original sentence, and every additional term of imprisonment, to which any prisoner, then 27 already undergoing imprisonment, may be sentenced shall commence from the period when such prisoner shall have actually undergone any previous sentence or sentences passed upon him. etc.