2000 BC  -  Here, eat this root.

1000 AD  -  That root is heathen.   Here, say this prayer.

1850  -   That prayer is superstitious.  Here, drink this potion.

1920   -  That potion is snake oil.   Here, swallow this pill.

1945   -  That pill is ineffective.   Here, take this penicillin.

1955  – Ooops.  Bugs mutated.  Here, take this tetracycline.

1960-1999 -  39 more “Ooops”.  Here, take this more powerful drug.

2000  – The bugs have won.  Here, eat this root.

Source:   British Medical Journal  (author unknown)