Pasteur swan-necked flasks

Fig. 1.3 Pasteur s swan-necked flasks in the first flask, the unbroken neck hinders contamination if the neck is broken off as in the second flask, the sterile culture medium is invaded by microorganisms. After Pasteur (1862)...

In order to disprove this theory, Pasteur used swan-necked flasks unheated air could now enter the sterile culture solution. But in this case, the microorganisms in the air were deposited in the long S-shaped neck and did not enter the culture medium. If, however, the neck of a flask was broken off, they could enter the solution and multiply. 

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