Louis Pasteur and Germ Theory

We're going to look now at one of the most significant turning points in medical understanding that there has ever been and this leads to a period of intense discovery and exciting progress in the second half of the 19th century really. So it begins with Louis Pasteur. He's this man, he is French and actually he's not a doctor to begin with, he's a university science professor and the story begins when the French Academy of Science challenges French scientists to look into the reasons why alcohol goes sour because this is something that's costing the French beer and wine industry a lot of money. Now Pasteur investigates and he realises or discovers that if you heat the alcohol very very quickly and let it cool down again then it doesn't go sour and it turns out that the same is also true of milk. It's much slower to go off when it's been treated in this way and it also cuts down on people getting a disease called tuberculosis from milk as well. So this is something that people start to do. It's named after Louis Pasteur, it's called pasteurisation. So if you've ever bought a bottle of pasteurised milk then you've brought milk that has been treated in a way that was invented by Louis Pasteur. So that's a pretty good discovery but what's even more exciting from a medical point of view is the ideas that Pasteur has developed around what is causing the alcohol to go sour. Now we know that people have been aware for a really long time that there are teeny tiny little living things all around us that are too small for the human eye to see. When Robert Hooke invents the microscope back in the 1600s he publishes a book called Micrographia which is full of pictures of the teeny tiny little living things that he has seen on various substances including on the plaque that has been scraped off people's teeth. And a little bit later on in 1677 another scientist called Antonie van Leeuwenhoek names these animalcules which I think is quite a cute name. So there is an understanding that there are little creatures living all around us and by the 18th and the 19th century people have started to link these with decay. One of the things that they've found is that decay seems to present more of these animalcules or what we might call microbes or microorganisms and they begin to come up with ideas about why there are so many of these teeny tiny little things present when there is decay. Now the most popular theory around this is called the spontaneous generation theory at the time and it suggests that where there is decay it leads to the creation and the spontaneous generation of these microorganisms and that they then go on and create miasma or miasmata. So remember that miasmata are the bad smells that were thought to carry disease into the body through the nose and this kind of makes sense because where you have things decaying it's very smelly and where people live near smelly decaying things they're more likely to get ill so it's kind of logical really. However in 1861 Pasteur publishes something that he calls his germ theory and this really turns the idea of spontaneous generation on its head because Pasteur first of all suggests that these microbes and microorganisms live in the air although they're not evenly distributed. Secondly that they can be destroyed by heat which is the principle behind pasteurization kills these little microorganisms and thirdly Pasteur suggests that instead of the decay creating these little microorganisms actually these little microorganisms are creating the decay and they're making the decay happen. So this is a big departure it really sort of takes spontaneous generation theory and turns it on its head. So Pasteur suggests that these microbes are actually causing the decay rather than being caused by it and he calls them germs which is short for germination based on the way that he's seen them reproduce under a microscope and he begins to wonder if this is the impact that these germs have on food and drink if it makes things decay then what impact are they having on the human body? Are they causing disease? Now in 1865 he's able to prove that germs are causing an epidemic that is killing silkworms and undermining the silkworm business. In 1880 he makes a discovery around chicken cholera it's actually an accident one of his assistants is supposed to inoculate a lot of chickens against cholera and he doesn't get the chance before the summer so he goes back and inoculates them after the summer and expects some of them to get cholera and die but none do. It was a happy chicken and Pasteur theorizes that this is because the germs became weaker over the summer and the chickens bodies learned to fight them off themselves. Now in this there is a really exciting link with the work of a previous doctor Edward Jenner. Remember Edward Jenner had realized that you could protect people from disease by vaccinating them with a lesser disease and he knew that it worked but he didn't understand how. So Pasteur may have found in this instance the link between his germ theory and the possibilities of vaccination. Incidentally Pasteur was very annoyed when it was suggested that he was lucky in this and he said chance only favours prepared minds. However his ideas aren't all that influential in Britain at first for a number of reasons. One is that British doctors and scientists are quite convinced by spontaneous generation theory. So there's somebody called Dr Henry Bastien for example whose name I'm going to write again but in blue so it matches spontaneous generation theory. Here we go Dr Henry Bastien who's very convinced by spontaneous generation theory and speaks up However there is a scientist called Joseph Lister and he is investigating in the 1860s and 70s ways in which to prevent infection in surgery patients and one of the things that he's realized is that carbolic acid will prevent infection and he is interested in germ theory and he's interested in applying germ theory. There's another scientist whose name is John Tyndall he's actually Irish and he's a physicist and he makes a speech in January 1870 where he links the work of Lister with the work of Pasteur and uses it to argue in favour of germ theory and in the possibility that germs are causing disease. However people aren't very convinced by this firstly because he's a physicist and not a doctor so what does he know and secondly because he doesn't have proof. So Pasteur has discovered more about the function of germs the race is now on really to find ways in which this applies to disease and ways in which this knowledge can be used to fight disease as well.