"Similarly, though not to the same extent, the two aspects of the process of arabisation, namely, the spread of the Arabic language and the infiltration of Arab stock, differed both in range and in reach. There are physical and economic limits to the capacity of a country to admit and absorb migrations from the outside, even when, as happened with those waves of Arab colonisation, the process is carried through by superior force. The spread of the language was not circumscribed by those limitations. While Arabic went on advancing until it had completely enthroned itself, the tide of racial penetration found itself danmned within narrower confines."