Louis Pasteur (1822-1895) in 1886.

A certain Felix-Archimede Pouchet relaunches the debate on spontaneous generation.  This Rouen Naturalist, who had shown the ovulation cycle of mammals, transmits a communication to the Academie de medecine in December 1858, entitled Sur des proto-organismes vegetaux et animaux nes spontanement dans l’air artificiel et dans le gaz oxygene.  Pouchet observed some decoctions of hay which had been sterilized at 100 degrees Centigrade.  He sees diverse animacules produced in glass balloons where all organic germs had previously been destroyed.  Further, air only arrives inside after having been amply washed in concentrated sulphuric acid or having passed through the labyrinth of fragments of porcelain and asbestos brought to a red heat temperature.  Pouchet has just set off the greatest battle of this scientific war, a battle in which he will be one of the Generals, and which will destroy him in the end.  The fields of this battle will be the straw-matting in the laboratories and the amphitheatres of the Academie, the weapons will be test-tubes, retorts, alcohol lamps, microscopes…  and torrents of eloquence.  In the culture media, the formidable army of little organized beings is going to vibrionate and multiply, die and be born again to the rhythm of the experimentations put together by both camps during six years.  These six years which are going to revolutionize the History of Medicine.


Opposite Pouchet, Louis Pasteur, a fighter around forty years old, the Administrator and Director of Scientific Studies at the Ecole normale superieure.  Pasteur has already battled against the German Chemist Liebig over the apparition of yeasts in fermentation milieux, and he dreams of wringing the neck of the theory of spontaneous generation once and for all.  The scholar possesses in his home an old painting representing a standing man in a riding-coat, with a pointy, determined profile, placing a firm fist on a desk where there are a rudimentary microscope and some flasks.  It is the portrait of the Italian Abbot Spallanzani, the anti-heterogenist to whom Pasteur would like to be a worthy successor.  And Pasteur ironises before his pupils on Pouchet’s communication, himself giving both the questions and the answers:

“What do you want to object to Mr Pouchet?  Would you say to him:  ‘The oxygen that you have used contained germs?’

“He would reply to you:  ‘Of course not, for I made it come out of a chemical combination.’

“Would you say to him:  ‘The water that you used contained germs?’

“He would object:  ‘This water, which was exposed to the contact of air, was placed boiling into the recipient, thereby killing the germs.’

“You would say to him:  ‘It’s the hay.’

“He would retort:  ‘Of course not, the hay came out of a sterilizer heated to 100 degrees Centigrade.’

“But certain singular beings resist this temperature.  All right!  So he heats the hay to 200 degrees, to 300 degrees Centigrade.  At this moment, I admit, M. Pouchet’s experiment is irreproachable.  But…  but there is a cause for the error that M. Pouchet has not seen, and which renders his experiment illusionary:  I am going to show you, Messieurs, where the ‘mice’ dear to Van Helmont entered inside Mr Pouchet’s flasks.”

Pasteur explains that the germs entered this time via the mercury that Pouchet uses to isolate his milieux from the contact of air.  The mercury is covered in dust, and therefore in possible germs.  Pasteur adds a precaution as well. Before manipulating objects, they must first be cleaned of any pre-existing germs, “sterilize” them, as would be said later, to control the seeding action, a basic act which poses the foundations of scientific bacteriology.  The partisans of spontaneous generation reply that Pasteur, who heats the air in his flasks, could have changed its chemical properties and stopped the “spontaneous” germs from developing.

The conflict climbs to new heights.  On 21 September 1860, shepherds from Chamonix see a little caravan of a new kind passing by:  at its head walks a mule carrying a crate filled with thirty-three flasks containing a crystalline liquid, in fact yeast water, and an alcohol lamp for melting glass.  The animal is closely followed by a bearded man equipped from head to toe for the mountain, iron-tipped shoes, gaiters, woollen hat, who moves along the precipices supporting the crate to stop it from swaying.  No-one guesses that this hiker is on the point of penetrating one of Nature’s greatest secrets.  This alpinist is Louis Pasteur.

He knows, or guesses, that the higher you climb in altitude, far from human concentrations, the fewer micro-organisms there are in the air.  He puts together an experimental protocol:  after having introduced an easily alterable liquid into some glass balloons, beer yeast water, he submits it to boiling.  During this operation, he closes with the alcohol lamp the slim point in the glass, from which the vapour escapes, taking with it the air contained in the balloon.  Then he breaks the glass neck, as you would the end of a pharmaceutical ampoule, exposing it suddenly to air and dust in suspension, like a photographic plate that is exposed to light.  Finally, he melts the glass point again, hermetically sealing the balloon.  That day, on the summits, Pasteur “exposes” thirteen balloons and seals them by flame in an inn bedroom, open to the wind, where he passes the first night.  “Exposed” is the right word, for all of them will be altered afterwards.

The following day, the scientist climbs with a guide onto the Sea of Ice, that Empress Eugenie also visited, thereby launching the fashion for staying at Chamonix.  The twenty remaining glass balloons, heated and sealed, are opened to the mountain air, then closed.  Here is Pasteur’s description of this trip:

“We slept at Montanvert, the night is admirable.  At sunrise, a sharp, whistling wind, an obviously favourable circumstance.  I went to open the rest of my balloons, whose points I had previously heated.  I held them above my head and with iron tongs passed in the flames a few minutes beforehand, I broke the points offering them to the direction of the wind.”

In fact, Pasteur, leaving from Arbois, had already seeded forty of these balloons along the road before arriving at Chamonix:  twenty balloons were opened on the way to Dole, not far from the paternal tannery, then at Salins he had climbed Mount Poupet, which rises eight hundred and fifty metres above sea-level, and had opened twenty other balloons.  Only five of these were altered.  The liquid of nineteen sealed glass balloons brought back from the Sea of Ice by the scholar remain limpid and exempt from animalcules and other infusionaries.  The liquid of only one is troubled.  These little balloons of two hundred and fifty cubic centimetres ending in a narrow point, sealed by the flame of an alcohol lamp at an altitude of two thousand metres, will remain famous forever in the world of experimenters.

To be continued.