The French bacteriologist Charles Chamberland improves the sterilising of medical equipment and develops filters for bacteria which lead to the discovery of viruses.

William Thomas, who will later become known as Lord Kelvin, puts forward the idea of the absolute zero of temperature.

It is discovered that sperm come from dividing cells, not from a type of fermentation as was originally thought.

The idea of valency is introduced in chemistry - the idea that each type of atom will combine with a particular number of others.

The Scottish physicist William Rankine introduces the idea of potential energy.

The French bacteriologist Pierre Roux discovers that diphtheria is caused by the toxin produced by a bacterium rather than by the bacterium directly.

The German chemist Robert Bunsen starts using a burner developed by his technician. This burner quickly becomes known as the Bunsen burner, although credit for its invention should really go to Michael Faraday.

The French biologist Claude Bernard introduces the idea of homeostasis and the importance of the idea of constant state in the body.

In Germany the first skeleton of Neanderthal people is found.

The French biologist Louis Pasteur discovers that fermentation is the result of the activity of microorganisms rather than simple chemical reactions.

Claude Bernard discovers glycogen, which he recognises as a way of storing glucose in the liver.

The British biologists Charles Darwin and Alfred Russell Wallace contact the Linnean Society with their ideas on evolution. No one takes much notice of them!

The Scottish chemist Archibald Scott Couper introduces the idea of bonds between atoms in chemistry. He is also the first person to recognise that carbon atoms form the backbone of organic compounds.

The element thallium is discovered as a bright green line in the spectrum of some selenium ore being analysed by the English chemist William Crookes. "Thallium" means "green twig".

In the same year Robert Bunsen discovers a bright red line in a spectrum. This represents another new element which is named rubidium after its colour.

The German chemist Johann Friedrick Wilhelm Adolf von Baeyer discovers the first barbiturate. Legend has it that it was named after his girlfriend, Barbara.

The English chemist John Alexander Newlands announces his 'law of octaves'. This is the first version of the Periodic Table - but the diagram does not come out when it is published, and Newlands is ridiculed and ignored.

The German chemist Friedrick August Kekulé has a dream in which snakes dance together, holding their tails. This reveals the structure of the benzene molecule to him. Unlikely as it sounds, Kekulé's ideas based on this dream are correct.

The German botanist Julius von Sachs discovers that chlorophyll is only found inside the chloroplasts in plant cells.

Ignaz Semmelweiss (b.1818) dies. A professor at the Universities of Pest and Vienna, Semmelwiess realised that childbed fever - which killed up to 1 in 3 new mothers giving birth in maternity hospitals during the 1840s - was caused by infection carried by doctors. He introduced the practice of hand washing before examining patients, reducing death rates to less than 1 per cent. Despite his success, Semmelweiss's findings were resisted for years by hospital and medical authorities.

Mendel publishes his work on heredity. It contains detailed descriptions of huge numbers of experiments which he subjects to statistical analysis. Despite its rigorous approach, Mendel's work is ignored for the next 34 years.

The clinical thermometer is developed. Earlier thermometers were very long, so it took about 20 minutes to take the patient's temperature - tedious for patients, doctors and nurses alike.

Helium is discovered from strange new line discovered in the sun's spectrum during an eclipse of the Sun. The name helium comes from the Greek word "helios" meaning "sun".

A scent and flavouring called coumain is developed by the English chemist William Henry Perkin. It will be used in foods for nearly 100 years, when it will be withdrawn because it is poisonous!

The Russian chemist Dmitri Ivanovich Mendeleev publishes his first version of the Periodic Table.

The German doctor Paul Langerhans dissects the pancreas really carefully and finds a small group of cells which become known as the Islets of Langerhans. It will later be discovered that these cells make the hormone insulin.

Charles Darwin publishes his book The Descent of Man and Selection in Relation to Sex in which he looks at evidence for the evolution of humans and sexual selection.

Dmitri Mendeleev stirs interest in his Periodic Table by saying that the gaps represent undiscovered elements, and predicting their properties. They will be found in 1875, 1879 and 1885 with the properties predicted by Mendeleev. As a result he will become famous and his Periodic Table will become universally accepted.

Louis Pasteur discovers anaerobic organisms in beer that send it bad and which cannot live in oxygen.

The term "enzyme" is used for the first time after trypsin is discovered in pancreatic juice.

The term "cathode ray" is coined to describe the radiation which arises at the negatively charged electrode in a vacuum tube carrying a current.

A young Spanish girl called Maria Sautuola is the first person to see Cro-Magnon cave paintings for 10,000 years. While exploring some caves with her father, she can stand where he has to crawl - so she can see the ceiling!

Louis Pasteur accidentally discovers that weakened cholera bacteria do not cause cholera in chickens, and that these infected chickens are then immune to the disease. This is the principle by which vaccines for many more diseases will be developed.

The German bacteriologist Robert Koch starts using solid cultures - gelatin - to grow bacteria.

Louis Pasteur develops his germ theory of disease.

Louis Pasteur develops the first artificially produced vaccine against anthrax and shows that it works on sheep in a public demonstration.

The German physicist Hermann Ludwig von Helmholtz shows that there is a smallest unit of electric charge that can exist.

Women begin to be admitted to the Cavendish Laboratory in Cambridge on same terms as men.

Robert Koch discovers the bacterium that causes tuberculosis - the first time that a microorganism has been associated with a specific human disease.

The prime meridian is set through Greenwich, England.

The first steam turbine generator for making electricity is developed.

The English geologist Arthur Holmes uses radioactivity to date the Earth from rocks. He finds it is 4.6 billion years old.

In Germany, Emil von Behring develops a vaccine against tetanus and diphtheria.

William Halsted, an American surgeon, introduces the practice of wearing rubber gloves during surgery.

Viruses are hypothesised as the cause of tobacco mosaic virus.

In America, William Burroughs produces an adding-subtracting machine with a printer.

Grace Chisholm Young receives a doctorate in mathematics in Germany - the first woman to get a doctorate by regular examination processes.

Helium is discovered on Earth - it was previously thought only to exist in the Sun.

In Germany, Wilhelm Konrad Roentgen discovers X-rays.

Swedish chemist Svante Arrhenius links the level of carbon dioxide in the atmosphere with global temperatures and suggests that the ice ages were the result of low carbon dioxide levels.

In France, Antoine-Henri Becquerel discovers rays produced by uranium affect photographic plates - the first scientific observation of natural radioactivity.

X-rays are used in medicine to help set broken bones.

A cell-free yeast extract is found to convert sugar into alcohol. This contains the enzyme zymase, and shows that life processes can take place outside the cell.

The Russian physicist Alexander Popov uses an antenna to transmit radio waves over a distance of 5km.

The electron is discovered by English physicist Joseph John Thomson.

The tobacco mosaic virus is identified.

In France, Pierre and Marie Curie discover the radioactive elements polonium and radium.

Working in Bombay, Paul-Louis Simond realises that the fleas on rats transmit bubonic plague to humans.

In Cambridge, England, Ernest Rutherford discovers that the radiation from uranium has at least two different forms which he calls alpha and beta particles.

J J Thomson measures the charge on the electron, and proves that it carries the same amount of charge as the hydrogen ions in electrolysis.

Working completely independently, Hugo Marie De Vries, Karl Franz Joseph Correns and Erich Tschermak von Seysenegg rediscover Gregor Mendel's work on genetics, which has been ignored for 34 years. They each rediscover his laws for themselves, search the literature, and when they find Mendel's work they each give Mendel the credit, in an astonishingly unselfish gesture.

Paul Karl Ludwig Drude shows that moving electrons conduct electricity in metals.

In France, Paul Ulrich Villard is the first person to observe gamma radiation.