"What were his reflections concerning the last member of this series and late occupant of the bed?
Reflections on his vigour (a bounder), corporal proportion (a billsticker), commercial ability (a bester), impressionability (a boaster).

Why for the observer impressionability in addition to vigour, corporal proportion and commercial ability?
Because he had observed with augmenting frequency in the preceding members of the same series the same concupiscence, inflammably transmitted, first with alarm, then with understanding, then with desire, finally with fatigue, with alternating symptoms of epicene comprehension and apprehension." (U17.2143)