One of the phrases that crop up in documentaries and history programmes is "changed the course of history". When this is said which is very often we greet it with a cheer. No such programme should be without it.
In the Mail today was an article about The Black Death and how it was spread. Experts now think that it was not just a matter of rats and fleas but from human to human as a result of lack of hygiene and airborne as well.
In the 19th Century when scientists were searching for the causes of diseases and especially epidemics with high fatality rates there was a fierce debate about how the bugs spread and what kind of bugs they were.
It became fashionable among some to deride the idea of airborne transmission for many complaints and the Victorian desire to prevent outside air to enter in many homes.
It took a long time and major technological and scientific developments to refine and identity the many ways that the bugs could get you.
Those of a certain age will recall the frantic propaganda Ministry of Information films threatening the nation with doom and disaster unless we followed the Health advice and behaved in the way we should.
There was a point to it all and not just economic. Before the new discoveries of drugs, notably antibiotics etc. a good many people died too soon and others were damaged for life.
In the meantime we have staved off, probably only temporarily, some of the potential bugs that have the potential to drastically reduce population levels.
But how long for?