He talked about the physical properties of tiny things, including their relationship to gravity, here he mentioned J.B.S Haldane's 1928 essay On Being the Right Size. I was glad to find the text online, it's great.
Upstairs in Medicine Man there were some lovely Bonsai trees from Kew on display.
In Medicine Now there was a flea and talented small insect room curated by Pestival. Percy Smith's The Acrobatic Fly from 1910 was accompanied by a gentleman on the piano keyboard. There were 3 performances by a flea circus, which was very funny, I don't think that there were any fleas, but lots of flames and imaginative suggestion instead.
A little table top displayed some Mexican dressed fleas or Pulgas Vestidas, from the Natural History Museum. I've seen the little couple in Tring (below). What a thought-provoking evening.