One of the most important things Pasteur able to do was to demonstrate that air does contain microscopically observable “organized bodies”. What he did was to pass air through a tube plugged with guncotton (served as a filter). He then removed the guncotton & dipped in alcohol and ether mixture. The sediment thus obtained was examined under microscope. It was found that the mixture contains many small, round bodies besides organic matter. These bodies were believed to be the microorganisms everybody was talking about. He then performed two additional experiments which fully proof the fact that of the presence of microorganisms in air. First he passed heated air through preheated organic infusion to find that there is no growth. And 2^nd he placed a piece of germ-laden guncotton a well heated airtight organic infusion to find that growth is appearing through these is as air supply. Thus he proved successfully the presence of microbes in air.