Sentence:  As to the argument about the possibility of the <WSD>reversionist</WSD> not being capable of discharging his duties, that would equally apply to the granting a place for one life, as then the holder might live so long, or become so infirm as to be unable to fulfil all the duties of his situation. 
Meaning of the word marked with <WSD> tags:  The person to whom a property reverts when a freehold expires.