Pasteur’s Experiments

Scientists also observed the fact that the organic infusions kept in open vessel not only generate microorganisms but also undergo certain changes. In mid 19th century the scientists started to think that microorganisms bring about these changes or at least there is a relationship between them. Louis Pasteur, the Father of Microbiology, is the pioneer of this thought process. First he had not given much to the controversy between presence of microbes and spontaneous generation theory. But at last he turned his attention towards this grave problem. He published his work in 1861 as “Memoir on the Organized Bodies which Exist in the Atmosphere”. His work had revolutionized the world of microbiology.

Image from wikipedia.com

Spallanzani successfully proved the case against spontaneous generation theory. But the problem is that faulty experiments were still performed & as a result the controversy remained. Francois Apart in the beginning of 19th century made an interesting experiment. Instead of organic infusions he used food stuffs in the air tight bottle and heated it. Thus he was successful in storing or preserving food stuffs for long time which was earlier impossible. This was a practical application of Spallanzani’s experiment and known as canning or “Apertization” (on behalf of Apart) and used extensively to preserve food in that period.
Then another problem or controversy came in front regarding proving the presence of germs against the spontaneous theory. In late 18th century Oxygen was discovered by Priestley, Cavendish & Lavoisier and soon it was found that it is essential for the existence of living being. So many thought that due to the hermetic sealing used by Spallanzani or Apart; the oxygen supply was cut off & that was the reason of no microbial growth in the organic infusion; not the presence of germs in the air. This is really a big problem and is very difficult to deal with. Later it was proved that if germ free air is passed through the pre heated organic infusion then there will be no decomposition of the organic infusion even in the presence of oxygen.

But when more knowledge was gathered about living organisms, it became evident that this doctrine of Spontaneous Generation was not true. Earlier it was thought that maggots are formed in meat spontaneously. But Italian physician, Francesco Redi showed that the maggots are nothing but larval stages of the flies & will never appear if the meat is protected by placing it in vessel covered with fine gauze. In that case flies are not able to lay eggs on the meat. This experiment is of utmost importance as it gave a much needed proof against Spontaneous Generation theory. For technical reason it was very difficult to prove that microorganisms are growing inside the organic infusion not spontaneously but from their earlier life form already present in air or in the organic infusion. It was in the middle of nineteenth century that the cumulative evidence became sufficient to rule out this theory.
In the middle of 18th century Italian naturalist Lazzaro Spallanzani proved that heating can prevent the appearance of “animalcules” in infusions, although the duration of heating varies. He concluded that air is the carrier of animalcules in well heated infusions, he closed the flasks containing infusion hermetically (earlier others closed the vessel by mechanical plugging which is not sufficient to prevent the entry of air completely) and boiled the infusion. The boiled infusions are free of animalcules but if there is a tiny crack in the bottle the animalcules reappear. This strongly suggests air is the carrier of animalcules, & they are not generated spontaneously.

Origin of microbial world

I have already given you some facts about the discovery of the microbial world and the life of Leeuwenhoek. If you are interested about Leeuwenhoek’s life you will get to know about him in my nest post which will be about his life in short. So keep visiting my blog. I will also post an article on one of the most life threatening diseases of this planet – Malaria soon. But after the discovery of the “Microbial World” the nest thing that comes in mind is the origin of these microorganisms. So our next focus will be “The Origin of Microbial World”.
There are mainly two kinds of belief from the beginning regarding the origin of this wonder world. The first thought was about the belief that “animalcules” were formed spontaneously from nonliving materials. The second thought (Leeuwenhoek is one of the follower) told about formation of microbes from the “seeds” & “germs” of these animalcules, which were always present in the air.
The first thought was known as spontaneously generation or abiogenesis & this doctrine was accepted without question until the Renaissance.

Anton Van Leeuwenhoek Letter

In one letter he described for the first time the characteristic bacteria of the human mouth. He wrote:

I have several gentlewomen in my house, who were keen on seeing the little eels in vinegar; but some of them were so disgusted at the specticle, that they vowed they'd never use vinegar again. But what if one should till such people in the future that there are more animals living in the scum on the teeth in a man's mouth, than there are men in a whole kingdom?

But Leeuwenhoek’s death has ended this observation of microbial world, though everybody has marveled his discoveries. This was primarily because of the lack of skilled professionals for production of high quality simple microscope after Leeuwenhoek as simple microscope of high magnification is very difficult to make. There are compound microscopes available, but they suffer from serious optical defects. This is why ‘Robert Hooke’, a very capable & careful observer of Leeuwenhoek’s time, who was observing the microbial world with his compound microscope, could not see the intricate details seen by Leeuwenhoek simply because of the optical defects of his microscopes. So it took more than a century after Leeuwenhoek’s death (1820) to repeat his experiments with compound microscope after development of optical science. Meanwhile microbiology had also developed in another way i.e. the roles it plays in transformation of matter & causation of disease. Leeuwenhoek is considered the father of microscopy.

References: General Microbiology 5th edition.