Medicine is about the best way to illustrate the progress. Essentially all medical practices from before 1800-s would now be considered actively harmful to patients. Simple surgeries are about the only surviving pieces of the pre-1800-s medical practices.
Consider this - germ theory of diseases has been developed only in late 1800-s! Before that doctors were using the crap like 'humour imbalance' theory, doing things like blood-letting to 'cure' weakness and infection!