Meet Spallanzani, Who Showed the Truth About Spontaneous Generation

The first Microbe Hunter, Leeuwenhoek, died in 1723, but his legacy inspired a new generation of truth-searchers, of which Lazzaro Spallanzani, born in 1729 in the North of Italy.

Where did Spallanzani come from, and the importance of a mentor

Spallanzani’s father, a lawyer, wanted his son to follow in his footprints. The boy was fascinated by many things, from the stars to fireworks, volcanoes, skipping stones on still water, or what makes fountains work… Law was not quite so exciting to him, but his father insisted.

The famous scientist Vallisnieri saw the student’s craving for answers and told Spallanzani’s father: “Your boy is going to be a searcher, he will honor Scandiano (their town) and make it famous — he is like Galileo!” Suddenly, the youngster was released and went to the University of Reggio with his father’s blessing.

At 25 years old, well-instructed Spallanzani translated Homer, studied mathematics, and wrote a theory of the mechanics of skipping stones. To cover up his contempt for dogmas, he even became a Priest of the Catholic Church, cunningly gaining the good graces of authority.

By 30, Spallanzani was a Professor at the University of Reggio, where he started to experiment on the animalcules that Leeuwenhoek has discovered — saving them from oblivion.

Do they have parents?

The tough question of his time was “Can living things, including these minuscule animalcules, arise spontaneously, or do they have to have parents?”

It was generally accepted that flies arose spontaneously from rotten flesh and cow dung. A recipe to create bees was: “Take a young bullock, kill him with a knock on the head, bury him under the ground in a standing position with his horns sticking out. Leave him there for a month, then saw off his horns — and out will fly your swarm of bees.” The naturalist Ross assured that “to question that beetles and wasps were generated in cow dung is to question reason, sense, and experience.” Yet, Spallanzani was not convinced.

One night, Spallanzani was reading a book by Redi. The author wrote how the most intelligent people were convinced that maggots and flies arose naturally from putrid meat. So, he made a simple experiment. He took two jars and put a piece of meat in each one. He left one jar open and sealed a light veil over the other — and watched. He saw flies get in the meat in the open jar, and sure enough, after a while, maggots grew there. In the other jar, not even one. Aha!

What about animalcules? Needham and Spallanzani’s experiments

The next day, Spallanzani wanted to create a similar experiment with the microscopic animals. He started, with patience and persistence, by learning to grow, observe and distinguish the tiny shapes.

While Spallanzani was getting acquainted with the art of microbiology, a Catholic Priest, Needham, declared that the microscopic animals, like bees in horns, were generated beautifully in mutton gravy. He’d taken gravy hot from the fire, put it in a bottle, and plugged the bottle with a cork, to impede animalcules from air getting in. When he opened the bottle a few days later, it was swarming with microscopic life. He said soups made from seeds or almonds worked just as well.

The Royal Society was impressed. Spallanzani frowned and said he’d find the loophole. He thought “Needham didn’t heat the bottles long enough, and didn’t plug them tight enough!”

So Spallanzani set to work. He cleaned his glassware and added seeds in some, peas and almonds in others, and water on top. He sealed the flasks by melting the bottleneck in a hot flame — sometimes burning his fingers, dropping the flask, making a mess, and starting all over again — and capped others with corks. He heated some of the soups for a short time and boiled others for an hour. Then he went about his life, taught his students, went hunting and fishing… and came back to his flasks with anxious expectations.

He first cracked the neck of the flasks sealed by the melted glass and boiled for an hour. Calmly, he observed drop by drop under the microscope. His long squinting was rewarded by… nothing.

He turned to the flasks that were heated for a few minutes and observed. He jumped. There was an animalcule, smaller than those he had seen before, but surely playing and moving around, alive. “These flasks were sealed, nothing could get into them from the outside, yet here are little beings that have stood a heat of boiling water for several minutes!”

Turning to the flasks plugged with cork, low-boil and hard-boil, he found them all swarming with animalcules.

Spallanzani, excited, told his siblings about his pretty experiment. He taught his students that “life only comes from life; every living thing has to have a parent”. Finally, he threw his results at Needham in a brilliant, sarcastic article, and thrust the world of science into turmoil.

“He had rescued the baby science of microbe hunting from a fantastic myth that would have made all scientists of other kinds hold their noses at the very mention of microbe hunting as a sound branch of knowledge.”

Europe in a boil behind the Vegetative Force

Soon, the fancy salons were debating spontaneous generation. Needham had gone to Paris to tell the world about his mutton gravy and there he met the famous Buffon, who loved to write about science, but was “rather too well dressed to do experiments”. Together, the two men invented a theory about how life arises, that was satisfying both to Christians and atheists. They called the Force of Life in mutton gravy the “Vegetative Force”.

The Royal Society elected Needham a Fellow, and the Paris Academy of Sciences made him an Associate. The Italian was raging.

“The heat weakens the Vegetative Force”

Finally, Needham made an objection to Spallanzani’s demonstration: “Your experiment does not hold, because you have heated your flasks for an hour, and that fierce heat weakens and so damages the Vegetative Force that it can no longer make little animals.”

Spallanzani rolled up his sleeves and got back to the laboratory. He brewed soups of all kinds and filled the room with flasks, to test different boiling times. If Needham was correct, the flasks boiled least should have the most animals. Spallanzani plugged the first round of soup bottles with cork and sealed the second with melted glass. 

And then, he waited.

After a few days, he pulled the corks and looked at the soup drops in the microscope. He burst out with delight when he saw that the bottles that had been boiled for two hours had even more animalcules than those boiled for a few minutes. This settled that the heat had not killed the Vegetative Force: the animals came in after the soup had cooled down.

Spallanzani proclaimed to Europe that the so-called Vegetative Force was a myth, and Europe began to listen.

“The boiling hurts the elasticity of the air”

However, Needham still wasn’t convinced: “But there is a Vegetative Force, a mysterious something that can make life arise out of gravy or soup or out of nothing at all, perhaps. What it needs particularly is a very elastic air. And when Spallanzani boils his flasks for an hour, he hurts the elasticity of the air inside the flasks!”

Once more, Spallanzani rolled up his sleeves and thought hard about how to leave its elasticity to the air. This was more of a head-scratcher. Indeed, when he cracked the neck of his bottles, he could hear the hiss of air, and holding a candle before the bottle’s neck confirmed the air was going in. “The air in the bottle is less elastic than the air outside” he thought, “maybe Needham is right.”

He tried closing the flasks differently. He sealed the bottles in two phases — leaving a tiny needle-sized opening first, letting the liquid cool down with air exchange, and then sealing off the tiny hole without expelling any of the air that was inside. After which, he boiled the flask for an hour, and let it rest for a few days. When he opened it, there was a hiss again — but the candle flame showed it was in the other direction, away from the flask! It was not the boiling that made the air less elastic. The air was now super-elastic but drop by drop under the lens revealed no life. He repeated the experiment many times, always with the same result.

Spallanzani triumphantly revealed his results to Europe, and this time Needham and Buffon had nothing to answer.

Spallanzani’s triumph

Spallanzani’s name appeared in gold in the universities of Europe, and almost 2 centuries later, was given to the Spallanzani Hospital of Infectious Diseases in Rome.

“Spallanzani was sure now that even the littlest beasts had to come — always — from beasts that had lived before. He was certain too, that a wee microbe always remained of the same kind that its parents had been, just as a zebra doesn’t turn into a giraffe, but always stays a zebra- and has zebra babies.”

De Saussure “the joys of marriage are unknown to them”

The next discovery on microbes’ reproduction came from de Saussure, who observed the animals long enough to affirm that “when you see two of the small beasts stuck together, they haven’t come together to breed. On the contrary — marvelous to say — these coupled beasts are nothing more nor less than an old animalcule which is dividing into two parts, into two new little animals!” De Saussure said, “the joys of marriage were unknown to them!”

Spallanzani then attached himself to other mysteries of his time. He experimented on his own body to understand human digestion. He investigated, in his attic, bats and their perfect orientation. He famously asked why the toad holds the female so violently and persistently. His curiosity made him do cruel tests on animals, and on himself. He gave lectures about everything and conducted expeditions up to dangerous mountains, from where he collected incredible specimens that be brought back to the museum.

He died before the turn of the century, in 1799. Knowing his bladder was diseased, he suggested having it out after he’d pass — “maybe you’ll find an astonishing new fact about diseased bladders.”

Acknowledgement

The details and quotes are from the 1926 book Microbe Hunters, by Paul De Kruif, who retraces the discoveries and characters that made the beginnings of Microbiology. De Kruif is a fantastic storyteller who learned the intimacy of those early scientists — if you like this chronicle, I recommend you read the whole book! Or hit the bell on my profile to follow me and see more stories about Microbes.