ABSTRACT
The presence of micro-organisms in air was first demonstrated by Pasteur who filtered a large volume of air through a guncotton plug. When the guncotton was dissolved in alcohol and ether the residue contained small bodies identical to micro-organisms. Subsequently Pasteur demonstrated that guncotton containing large numbers of micro-organisms as a consequence of filtration was able to induce growth in previously sterile infusions. As a result of these experiments Pasteur undertook further studies using swannecked flasks (see Fig. 1.2) for which he remains famous. Infusions sterilized in these flasks remain uncontaminated despite contact with air through the neck. Although the micro-organisms could travel along the descending limb of the neck they were unable to pass through the ascending part and were thus prevented from contaminating the infusion. If, however, the neck of the flask was broken or the flask tilted so that the infusion was allowed to enter the neck and then returned, contamination occurred. Although not the first to propose that fermentation was a microbial process Pasteur finally persuaded the scientific community of this fact with the aid of experimental evidence. He also identified microbial growth in the absence of oxygen
which he termed anaerobic to distinguish it from growth in the presence of oxygen which he called aerobic.
