User blog comment:Xilinoc/Ch. 639 - BABY,HOLD YOUR HAND 2/@comment-24479616-20150820182246

I thought the thing with the arms being 'stopping' and 'andvancing' could also refer to what they do. Like, Mimihagi as the right arm did 'stop' Ukitake's sickness from progressing any more and kind of kept him in a state where he could (barely) manage to live on, with his condition neither getting better or worse but his body simply 'staying' the way it was as long as Mimihagi was possessing Ukitake. And with Pernida on the other hand making things 'advance' or 'progress', like his finger developing an eye of its own or parts of it evolving into full hands and arms. Not entirely sure about it but this could explain why Mayuri brought it up^^