He should have been accustom to death; no not death, it was much deeper than that, by now, but he wasn't. In silence he'd shake, biting his tongue from calling out for someone to hold his hand, a gentle and final touch for a life about to change. Regeneration is one of greatest abilities a Time Lord has, able to live over a thousand years, time and age are nearly meaningless. It's when he's talking to friends, listening to a joke, all those little moments in life he hates not having a true ending. Growing old with someone, perhaps even a family. Dying at 100 is a laughable concept to most on Galifrey, never to him.
As he feels the poison sweep through his body, feeling the regeneration process starting, Perri hurdled alone and scared unable to do anything. This time he doesn't hide the anguish as he screams out for that touch, that little piece of goodbye before the next life appears.