I doubt that any of the chemists working with Arsenic in the 18th and 19th Centuries lived to a ripe old age: certainly, Marsh did not.

All of them worked over open benches with equipment that leaked arsenous vavours - or did not 'leak', there being no barrier to air at all - and none of them used impermeable gloves.

Given that they knew arsenic was a cumulative poison, their insouciance is remarkable: but it's a common theme in all scientific endeavours of that age.